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Thome C, Janssen JM, Karabulut S, Acuna C, D’Este E, Soyka SJ, Baum K, Bock M, Lehmann N, Roos J, Stevens NA, Hasegawa M, Ganea DA, Benoit CM, Gründemann J, Min L, Bird KM, Schultz C, Bennett V, Jenkins PM, Engelhardt M. Live imaging of excitable axonal microdomains in ankyrin-G-GFP mice. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.02.01.525891. [PMID: 38948770 PMCID: PMC11212890 DOI: 10.1101/2023.02.01.525891] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/02/2024]
Abstract
The axon initial segment (AIS) constitutes not only the site of action potential initiation, but also a hub for activity-dependent modulation of output generation. Recent studies shedding light on AIS function used predominantly post-hoc approaches since no robust murine in vivo live reporters exist. Here, we introduce a reporter line in which the AIS is intrinsically labeled by an ankyrin-G-GFP fusion protein activated by Cre recombinase, tagging the native Ank3 gene. Using confocal, superresolution, and two-photon microscopy as well as whole-cell patch-clamp recordings in vitro, ex vivo, and in vivo, we confirm that the subcellular scaffold of the AIS and electrophysiological parameters of labeled cells remain unchanged. We further uncover rapid AIS remodeling following increased network activity in this model system, as well as highly reproducible in vivo labeling of AIS over weeks. This novel reporter line allows longitudinal studies of AIS modulation and plasticity in vivo in real-time and thus provides a unique approach to study subcellular plasticity in a broad range of applications.
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Affiliation(s)
- Christian Thome
- Institute of Anatomy and Cell Biology, Johannes Kepler University, 4020 Linz, Austria
- Clinical Research Institute of Neuroscience, Johannes Kepler University, 4020 Linz, Austria
- Institute of Physiology and Pathophysiology, Heidelberg University, 69120 Heidelberg, Germany
| | - Jan Maximilian Janssen
- Institute of Anatomy and Cell Biology, Johannes Kepler University, 4020 Linz, Austria
- Clinical Research Institute of Neuroscience, Johannes Kepler University, 4020 Linz, Austria
- Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
| | - Seda Karabulut
- Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
| | - Claudio Acuna
- Chica and Heinz Schaller Research Group, Institute of Anatomy and Cell Biology, Heidelberg University, 69120 Heidelberg, Germany
| | - Elisa D’Este
- Optical Microscopy Facility, Max Planck Institute for Medical Research, 69120 Heidelberg, Germany
| | - Stella J. Soyka
- Institute of Anatomy and Cell Biology, Dept. of Functional Neuroanatomy, Heidelberg University, 69120 Heidelberg, Germany
| | - Konrad Baum
- Institute of Anatomy and Cell Biology, Johannes Kepler University, 4020 Linz, Austria
- Clinical Research Institute of Neuroscience, Johannes Kepler University, 4020 Linz, Austria
| | - Michael Bock
- Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
| | - Nadja Lehmann
- Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
| | - Johannes Roos
- Institute of Anatomy and Cell Biology, Johannes Kepler University, 4020 Linz, Austria
- Clinical Research Institute of Neuroscience, Johannes Kepler University, 4020 Linz, Austria
- Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
| | - Nikolas A. Stevens
- Institute of Physiology and Pathophysiology, Heidelberg University, 69120 Heidelberg, Germany
| | - Masashi Hasegawa
- German Center for Neurodegenerative Disease (DZNE), Neural Circuit Computations, 53127 Bonn, Germany
| | - Dan A. Ganea
- University of Basel, Department of Biomedicine, 4031 Basel, Switzerland
| | - Chloé M. Benoit
- German Center for Neurodegenerative Disease (DZNE), Neural Circuit Computations, 53127 Bonn, Germany
- University of Basel, Department of Biomedicine, 4031 Basel, Switzerland
| | - Jan Gründemann
- German Center for Neurodegenerative Disease (DZNE), Neural Circuit Computations, 53127 Bonn, Germany
- University of Basel, Department of Biomedicine, 4031 Basel, Switzerland
| | - Lia Min
- Departments of Pharmacology and Psychiatry, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Kalynn M. Bird
- Departments of Pharmacology and Psychiatry, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Christian Schultz
- Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
| | - Vann Bennett
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
| | - Paul M. Jenkins
- Departments of Pharmacology and Psychiatry, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Maren Engelhardt
- Institute of Anatomy and Cell Biology, Johannes Kepler University, 4020 Linz, Austria
- Clinical Research Institute of Neuroscience, Johannes Kepler University, 4020 Linz, Austria
- Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
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Zhao R, Ren B, Xiao Y, Tian J, Zou Y, Wei J, Qi Y, Hu A, Xie X, Huang ZJ, Shu Y, He M, Lu J, Tai Y. Axo-axonic synaptic input drives homeostatic plasticity by tuning the axon initial segment structurally and functionally. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.11.589005. [PMID: 38659885 PMCID: PMC11042219 DOI: 10.1101/2024.04.11.589005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/26/2024]
Abstract
The stability of functional brain network is maintained by homeostatic plasticity, which restores equilibrium following perturbation. As the initiation site of action potentials, the axon initial segment (AIS) of glutamatergic projection neurons (PyNs) undergoes dynamic adjustment that exerts powerful control over neuronal firing properties in response to changes in network states. Although AIS plasticity has been reported to be coupled with the changes of network activity, it is poorly understood whether it involves direct synaptic input to the AIS. Here we show that changes of GABAergic synaptic input to the AIS of cortical PyNs, specifically from chandelier cells (ChCs), are sufficient to drive homeostatic tuning of the AIS within 1-2 weeks, while those from parvalbumin-positive basket cells do not. This tuning is reflected in the morphology of the AIS, the expression level of voltage-gated sodium channels, and the intrinsic neuronal excitability of PyNs. Interestingly, the timing of AIS tuning in PyNs of the prefrontal cortex corresponds to the recovery of changes in social behavior caused by alterations of ChC synaptic transmission. Thus, homeostatic plasticity of the AIS at postsynaptic PyNs may counteract deficits elicited by imbalanced ChC presynaptic input. Teaser Axon initial segment dynamically responds to changes in local input from chandelier cells to prevent abnormal neuronal functions.
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Wang Y, Chen Y, Chen L, Herron BJ, Chen XY, Wolpaw JR. Motor learning changes the axon initial segment of the spinal motoneuron. J Physiol 2024; 602:2107-2126. [PMID: 38568869 PMCID: PMC11196014 DOI: 10.1113/jp283875] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2023] [Accepted: 03/12/2024] [Indexed: 04/05/2024] Open
Abstract
We are studying the mechanisms of H-reflex operant conditioning, a simple form of learning. Modelling studies in the literature and our previous data suggested that changes in the axon initial segment (AIS) might contribute. To explore this, we used blinded quantitative histological and immunohistochemical methods to study in adult rats the impact of H-reflex conditioning on the AIS of the spinal motoneuron that produces the reflex. Successful, but not unsuccessful, H-reflex up-conditioning was associated with greater AIS length and distance from soma; greater length correlated with greater H-reflex increase. Modelling studies in the literature suggest that these increases may increase motoneuron excitability, supporting the hypothesis that they may contribute to H-reflex increase. Up-conditioning did not affect AIS ankyrin G (AnkG) immunoreactivity (IR), p-p38 protein kinase IR, or GABAergic terminals. Successful, but not unsuccessful, H-reflex down-conditioning was associated with more GABAergic terminals on the AIS, weaker AnkG-IR, and stronger p-p38-IR. More GABAergic terminals and weaker AnkG-IR correlated with greater H-reflex decrease. These changes might potentially contribute to the positive shift in motoneuron firing threshold underlying H-reflex decrease; they are consistent with modelling suggesting that sodium channel change may be responsible. H-reflex down-conditioning did not affect AIS dimensions. This evidence that AIS plasticity is associated with and might contribute to H-reflex conditioning adds to evidence that motor learning involves both spinal and brain plasticity, and both neuronal and synaptic plasticity. AIS properties of spinal motoneurons are likely to reflect the combined influence of all the motor skills that share these motoneurons. KEY POINTS: Neuronal action potentials normally begin in the axon initial segment (AIS). AIS plasticity affects neuronal excitability in development and disease. Whether it does so in learning is unknown. Operant conditioning of a spinal reflex, a simple learning model, changes the rat spinal motoneuron AIS. Successful, but not unsuccessful, H-reflex up-conditioning is associated with greater AIS length and distance from soma. Successful, but not unsuccessful, down-conditioning is associated with more AIS GABAergic terminals, less ankyrin G, and more p-p38 protein kinase. The associations between AIS plasticity and successful H-reflex conditioning are consistent with those between AIS plasticity and functional changes in development and disease, and with those predicted by modelling studies in the literature. Motor learning changes neurons and synapses in spinal cord and brain. Because spinal motoneurons are the final common pathway for behaviour, their AIS properties probably reflect the combined impact of all the behaviours that use these motoneurons.
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Affiliation(s)
- Yu Wang
- National Center for Adaptive Neurotechnologies, Albany Stratton VA Medical Center, 113 Holland Ave, Albany, NY 12208
| | - Yi Chen
- National Center for Adaptive Neurotechnologies, Albany Stratton VA Medical Center, 113 Holland Ave, Albany, NY 12208
| | - Lu Chen
- National Center for Adaptive Neurotechnologies, Albany Stratton VA Medical Center, 113 Holland Ave, Albany, NY 12208
| | - Bruce J. Herron
- Wadsworth Center, New York State Department of Health, 150 New Scotland Ave, Albany, NY 12208
- Department of Biomedical Sciences, School of Public Health, State University of New York, Albany, New York
| | - Xiang Yang Chen
- National Center for Adaptive Neurotechnologies, Albany Stratton VA Medical Center, 113 Holland Ave, Albany, NY 12208
- Department of Biomedical Sciences, School of Public Health, State University of New York, Albany, New York
| | - Jonathan R. Wolpaw
- National Center for Adaptive Neurotechnologies, Albany Stratton VA Medical Center, 113 Holland Ave, Albany, NY 12208
- Department of Biomedical Sciences, School of Public Health, State University of New York, Albany, New York
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Theyel BB, Stevenson RJ, Connors BW. Activity-Dependent Ectopic Spiking in Parvalbumin-Expressing Interneurons of the Neocortex. eNeuro 2024; 11:ENEURO.0314-23.2024. [PMID: 38637152 PMCID: PMC11069434 DOI: 10.1523/eneuro.0314-23.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Revised: 03/12/2024] [Accepted: 03/17/2024] [Indexed: 04/20/2024] Open
Abstract
Canonically, action potentials of most mammalian neurons initiate at the axon initial segment (AIS) and propagate bidirectionally: orthodromically along the distal axon and retrogradely into the soma and dendrites. Under some circumstances, action potentials may initiate ectopically, at sites distal to the AIS, and propagate antidromically along the axon. These "ectopic action potentials" (EAPs) have been observed in experimental models of seizures and chronic pain, and more rarely in nonpathological forebrain neurons. Here we report that a large majority of parvalbumin-expressing (PV+) interneurons in the upper layers of mouse neocortex, from both orbitofrontal and primary somatosensory areas, fire EAPs after sufficient activation of their somata. Somatostatin-expressing interneurons also fire EAPs, though less robustly. Ectopic firing in PV+ cells occurs in varying temporal patterns and can persist for several seconds. PV+ cells evoke strong synaptic inhibition in pyramidal neurons and interneurons and play critical roles in cortical function. Our results suggest that ectopic spiking of PV+ interneurons is common and may contribute to both normal and pathological network functions of the neocortex.
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Affiliation(s)
- Brian B Theyel
- Department of Psychiatry and Human Behavior, Warren Alpert Medical School, Brown University, Providence, Rhode Island 02912
- Department of Neuroscience, Brown University, Providence, Rhode Island 02912
- Care New England Medical Group, Providence, Rhode Island 02906
| | - Rachel J Stevenson
- Department of Neuroscience, Brown University, Providence, Rhode Island 02912
| | - Barry W Connors
- Department of Neuroscience, Brown University, Providence, Rhode Island 02912
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5
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Nelson AD, Catalfio AM, Gupta JP, Min L, Caballero-Florán RN, Dean KP, Elvira CC, Derderian KD, Kyoung H, Sahagun A, Sanders SJ, Bender KJ, Jenkins PM. Physical and functional convergence of the autism risk genes Scn2a and Ank2 in neocortical pyramidal cell dendrites. Neuron 2024; 112:1133-1149.e6. [PMID: 38290518 PMCID: PMC11097922 DOI: 10.1016/j.neuron.2024.01.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 04/26/2023] [Accepted: 01/03/2024] [Indexed: 02/01/2024]
Abstract
Dysfunction in sodium channels and their ankyrin scaffolding partners have both been implicated in neurodevelopmental disorders, including autism spectrum disorder (ASD). In particular, the genes SCN2A, which encodes the sodium channel NaV1.2, and ANK2, which encodes ankyrin-B, have strong ASD association. Recent studies indicate that ASD-associated haploinsufficiency in Scn2a impairs dendritic excitability and synaptic function in neocortical pyramidal cells, but how NaV1.2 is anchored within dendritic regions is unknown. Here, we show that ankyrin-B is essential for scaffolding NaV1.2 to the dendritic membrane of mouse neocortical neurons and that haploinsufficiency of Ank2 phenocopies intrinsic dendritic excitability and synaptic deficits observed in Scn2a+/- conditions. These results establish a direct, convergent link between two major ASD risk genes and reinforce an emerging framework suggesting that neocortical pyramidal cell dendritic dysfunction can contribute to neurodevelopmental disorder pathophysiology.
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Affiliation(s)
- Andrew D Nelson
- Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, USA; Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
| | - Amanda M Catalfio
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Julie P Gupta
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Lia Min
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, USA
| | | | - Kendall P Dean
- Cellular and Molecular Biology Program, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Carina C Elvira
- Cellular and Molecular Biology Program, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Kimberly D Derderian
- Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, USA; Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
| | - Henry Kyoung
- Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, USA; Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
| | - Atehsa Sahagun
- Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, USA; Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
| | - Stephan J Sanders
- Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, USA; Department of Psychiatry, University of California, San Francisco, San Francisco, CA, USA
| | - Kevin J Bender
- Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, USA; Department of Neurology, University of California, San Francisco, San Francisco, CA, USA.
| | - Paul M Jenkins
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, USA; Department of Psychiatry, University of Michigan Medical School, Ann Arbor, MI, USA.
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6
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Stevens NA, Lankisch K, Draguhn A, Engelhardt M, Both M, Thome C. Increased Interhemispheric Connectivity of a Distinct Type of Hippocampal Pyramidal Cells. J Neurosci 2024; 44:e0440232023. [PMID: 38123997 PMCID: PMC10869156 DOI: 10.1523/jneurosci.0440-23.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Revised: 11/02/2023] [Accepted: 11/19/2023] [Indexed: 12/23/2023] Open
Abstract
Neurons typically generate action potentials at their axon initial segment based on the integration of synaptic inputs. In many neurons, the axon extends from the soma, equally weighting dendritic inputs. A notable exception is found in a subset of hippocampal pyramidal cells where the axon emerges from a basal dendrite. This structure allows these axon-carrying dendrites (AcDs) a privileged input route. We found that in male mice, such cells in the CA1 region receive stronger excitatory input from the contralateral CA3, compared with those with somatic axon origins. This is supported by a higher count of putative synapses from contralateral CA3 on the AcD. These findings, combined with prior observations of their distinct role in sharp-wave ripple firing, suggest a key role of this neuron subset in coordinating bi-hemispheric hippocampal activity during memory-centric oscillations.
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Affiliation(s)
- Nikolas Andreas Stevens
- Institute of Physiology and Pathophysiology, Heidelberg University, 69120 Heidelberg, Germany
| | - Katja Lankisch
- Institute of Physiology and Pathophysiology, Heidelberg University, 69120 Heidelberg, Germany
| | - Andreas Draguhn
- Institute of Physiology and Pathophysiology, Heidelberg University, 69120 Heidelberg, Germany
| | - Maren Engelhardt
- Institute of Anatomy and Cell Biology, Medical Faculty, Johannes Kepler University Linz, 4020 Linz, Austria
| | - Martin Both
- Institute of Physiology and Pathophysiology, Heidelberg University, 69120 Heidelberg, Germany
| | - Christian Thome
- Institute of Physiology and Pathophysiology, Heidelberg University, 69120 Heidelberg, Germany
- Institute of Anatomy and Cell Biology, Medical Faculty, Johannes Kepler University Linz, 4020 Linz, Austria
- Institute of Stem Cell Biology and Regenerative Medicine, Stanford University, Stanford, California 94305
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Brown CO, Uy JA, Murtaza N, Rosa E, Alfonso A, Dave BM, Kilpatrick S, Cheng AA, White SH, Scherer SW, Singh KK. Disruption of the autism-associated gene SCN2A alters synaptic development and neuronal signaling in patient iPSC-glutamatergic neurons. Front Cell Neurosci 2024; 17:1239069. [PMID: 38293651 PMCID: PMC10824931 DOI: 10.3389/fncel.2023.1239069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Accepted: 12/14/2023] [Indexed: 02/01/2024] Open
Abstract
SCN2A is an autism spectrum disorder (ASD) risk gene and encodes a voltage-gated sodium channel. However, the impact of ASD-associated SCN2A de novo variants on human neuron development is unknown. We studied SCN2A using isogenic SCN2A-/- induced pluripotent stem cells (iPSCs), and patient-derived iPSCs harboring a de novo R607* truncating variant. We used Neurogenin2 to generate excitatory (glutamatergic) neurons and found that SCN2A+/R607* and SCN2A-/- neurons displayed a reduction in synapse formation and excitatory synaptic activity. We found differential impact on actional potential dynamics and neuronal excitability that reveals a loss-of-function effect of the R607* variant. Our study reveals that a de novo truncating SCN2A variant impairs the development of human neuronal function.
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Affiliation(s)
- Chad O. Brown
- Department of Biochemistry and Biomedical Sciences, Faculty of Health Sciences, McMaster University, Hamilton, ON, Canada
- Krembil Research Institute, University Health Network, Toronto, ON, Canada
| | - Jarryll A. Uy
- Krembil Research Institute, University Health Network, Toronto, ON, Canada
- Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, ON, Canada
| | - Nadeem Murtaza
- Department of Biochemistry and Biomedical Sciences, Faculty of Health Sciences, McMaster University, Hamilton, ON, Canada
- Krembil Research Institute, University Health Network, Toronto, ON, Canada
| | - Elyse Rosa
- Department of Biochemistry and Biomedical Sciences, Faculty of Health Sciences, McMaster University, Hamilton, ON, Canada
| | - Alexandria Alfonso
- Department of Biochemistry and Biomedical Sciences, Faculty of Health Sciences, McMaster University, Hamilton, ON, Canada
| | - Biren M. Dave
- Department of Molecular Genetics, Faculty of Medicine, University of Toronto, Toronto, ON, Canada
- SickKids Research Institute, The Hospital for Sick Children, Toronto, ON, Canada
| | - Savannah Kilpatrick
- Department of Biochemistry and Biomedical Sciences, Faculty of Health Sciences, McMaster University, Hamilton, ON, Canada
- Krembil Research Institute, University Health Network, Toronto, ON, Canada
| | - Annie A. Cheng
- Krembil Research Institute, University Health Network, Toronto, ON, Canada
| | - Sean H. White
- Department of Biochemistry and Biomedical Sciences, Faculty of Health Sciences, McMaster University, Hamilton, ON, Canada
| | - Stephen W. Scherer
- Department of Molecular Genetics, Faculty of Medicine, University of Toronto, Toronto, ON, Canada
- SickKids Research Institute, The Hospital for Sick Children, Toronto, ON, Canada
| | - Karun K. Singh
- Department of Biochemistry and Biomedical Sciences, Faculty of Health Sciences, McMaster University, Hamilton, ON, Canada
- Krembil Research Institute, University Health Network, Toronto, ON, Canada
- Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, ON, Canada
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8
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Zhang W, Fu Y, Peng L, Ogawa Y, Ding X, Rasband A, Zhou X, Shelly M, Rasband MN, Zou P. Immunoproximity biotinylation reveals the axon initial segment proteome. Nat Commun 2023; 14:8201. [PMID: 38081810 PMCID: PMC10713531 DOI: 10.1038/s41467-023-44015-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Accepted: 11/27/2023] [Indexed: 12/18/2023] Open
Abstract
The axon initial segment (AIS) is a specialized neuronal compartment required for action potential generation and neuronal polarity. However, understanding the mechanisms regulating AIS structure and function has been hindered by an incomplete knowledge of its molecular composition. Here, using immuno-proximity biotinylation we further define the AIS proteome and its dynamic changes during neuronal maturation. Among the many AIS proteins identified, we show that SCRIB is highly enriched in the AIS both in vitro and in vivo, and exhibits a periodic architecture like the axonal spectrin-based cytoskeleton. We find that ankyrinG interacts with and recruits SCRIB to the AIS. However, loss of SCRIB has no effect on ankyrinG. This powerful and flexible approach further defines the AIS proteome and provides a rich resource to elucidate the mechanisms regulating AIS structure and function.
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Affiliation(s)
- Wei Zhang
- College of Chemistry and Molecular Engineering, Synthetic and Functional Biomolecules Center, Beijing National Laboratory for Molecular Sciences, Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, Peking University, Beijing, 100871, China
- Academy for Advanced Interdisciplinary Studies, PKU-Tsinghua Center for Life Science, Peking University, Beijing, 100871, China
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA
| | - Yu Fu
- College of Chemistry and Molecular Engineering, Synthetic and Functional Biomolecules Center, Beijing National Laboratory for Molecular Sciences, Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, Peking University, Beijing, 100871, China
| | - Luxin Peng
- College of Chemistry and Molecular Engineering, Synthetic and Functional Biomolecules Center, Beijing National Laboratory for Molecular Sciences, Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, Peking University, Beijing, 100871, China
| | - Yuki Ogawa
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA
| | - Xiaoyun Ding
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA
| | - Anne Rasband
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA
| | - Xinyue Zhou
- Academy for Advanced Interdisciplinary Studies, PKU-Tsinghua Center for Life Science, Peking University, Beijing, 100871, China
| | - Maya Shelly
- Department of Neurobiology and Behavior, Stony Brook University, New York, NY, USA
| | - Matthew N Rasband
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA.
| | - Peng Zou
- College of Chemistry and Molecular Engineering, Synthetic and Functional Biomolecules Center, Beijing National Laboratory for Molecular Sciences, Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, Peking University, Beijing, 100871, China.
- Academy for Advanced Interdisciplinary Studies, PKU-Tsinghua Center for Life Science, Peking University, Beijing, 100871, China.
- PKU-IDG/McGovern Institute for Brain Research, Peking University, Beijing, 100871, China.
- Chinese Institute for Brain Research (CIBR), Beijing, 102206, China.
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9
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Schamiloglu S, Wu H, Zhou M, Kwan AC, Bender KJ. Dynamic Foraging Behavior Performance Is Not Affected by Scn2a Haploinsufficiency. eNeuro 2023; 10:ENEURO.0367-23.2023. [PMID: 38151324 PMCID: PMC10755640 DOI: 10.1523/eneuro.0367-23.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2023] [Revised: 10/23/2023] [Accepted: 11/14/2023] [Indexed: 12/29/2023] Open
Abstract
Dysfunction in the gene SCN2A, which encodes the voltage-gated sodium channel Nav1.2, is strongly associated with neurodevelopmental disorders including autism spectrum disorder and intellectual disability (ASD/ID). This dysfunction typically manifests in these disorders as a haploinsufficiency, where loss of one copy of a gene cannot be compensated for by the other allele. Scn2a haploinsufficiency affects a range of cells and circuits across the brain, including associative neocortical circuits that are important for cognitive flexibility and decision-making behaviors. Here, we tested whether Scn2a haploinsufficiency has any effect on a dynamic foraging task that engages such circuits. Scn2a +/- mice and wild-type (WT) littermates were trained on a choice behavior where the probability of reward between two options varied dynamically across trials and where the location of the high reward underwent uncued reversals. Despite impairments in Scn2a-related neuronal excitability, we found that both male and female Scn2a +/- mice performed these tasks as well as wild-type littermates, with no behavioral difference across genotypes in learning or performance parameters. Varying the number of trials between reversals or probabilities of receiving reward did not result in an observable behavioral difference, either. These data suggest that, despite heterozygous loss of Scn2a, mice can perform relatively complex foraging tasks that make use of higher-order neuronal circuits.
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Affiliation(s)
- Selin Schamiloglu
- Neuroscience Graduate Program, University of California, San Francisco, CA 94158
- Center for Integrative Neuroscience, Department of Neurology, University of California, San Francisco, CA 94158
| | - Hao Wu
- Interdepartmental Neuroscience Program, Yale University School of Medicine, New Haven, CT 06511
| | - Mingkang Zhou
- Neuroscience Graduate Program, University of California, San Francisco, CA 94158
- Center for Integrative Neuroscience, Department of Neurology, University of California, San Francisco, CA 94158
| | - Alex C Kwan
- Interdepartmental Neuroscience Program, Yale University School of Medicine, New Haven, CT 06511
- Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY 14853
| | - Kevin J Bender
- Center for Integrative Neuroscience, Department of Neurology, University of California, San Francisco, CA 94158
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10
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Iwahashi M, Yoshimura T, Harigai W, Takuma K, Hashimoto H, Katayama T, Hayata-Takano A. Pituitary adenylate cyclase-activating polypeptide deficient mice show length abnormalities of the axon initial segment. J Pharmacol Sci 2023; 153:175-182. [PMID: 37770159 DOI: 10.1016/j.jphs.2023.08.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2023] [Revised: 08/08/2023] [Accepted: 08/25/2023] [Indexed: 10/03/2023] Open
Abstract
We previously found that pituitary adenylate cyclase-activating polypeptide (PACAP)-deficient (PACAP-/-) mice exhibit dendritic spine morphology impairment and neurodevelopmental disorder (NDD)-like behaviors such as hyperactivity, increased novelty-seeking behavior, and deficient pre-pulse inhibition. Recent studies have indicated that rodent models of NDDs (e.g., attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorder) show abnormalities in the axon initial segment (AIS). Here, we revealed that PACAP-/- mice exhibited a longer AIS length in layer 2/3 pyramidal neurons of the primary somatosensory barrel field compared with wild-type control mice. Further, we previously showed that a single injection of atomoxetine, an ADHD drug, improved hyperactivity in PACAP-/- mice. In this study, we found that repeated treatments of atomoxetine significantly improved AIS abnormality along with hyperactivity in PACAP-/- mice. These results suggest that AIS abnormalities are associated with NDDs-like behaviors in PACAP-/- mice. Thus, improvement in AIS abnormalities will be a novel drug therapy for NDDs.
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Affiliation(s)
- Misaki Iwahashi
- Department of Child Development and Molecular Brain Science, United Graduate School of Child Development, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Takeshi Yoshimura
- Department of Child Development and Molecular Brain Science, United Graduate School of Child Development, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
| | - Wakana Harigai
- Department of Child Development and Molecular Brain Science, United Graduate School of Child Development, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Kazuhiro Takuma
- Department of Pharmacology, Graduate School of Dentistry, Osaka University, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan; Molecular Research Center for Children's Mental Development, United Graduate School of Child Development, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Hitoshi Hashimoto
- Molecular Research Center for Children's Mental Development, United Graduate School of Child Development, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan; Laboratory of Molecular Neuropharmacology, Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871, Japan; Transdimensional Life Imaging Division, Institute for Open and Transdisciplinary Research Initiatives, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan; Division of Bioscience, Institute for Datability Science, Osaka University, 2-8 Yamadaoka, Suita, Osaka, 565-0871, Japan; Department of Molecular Pharmaceutical Science, Graduate School of Medicine, Osaka University, 2-2 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Taiichi Katayama
- Department of Child Development and Molecular Brain Science, United Graduate School of Child Development, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Atsuko Hayata-Takano
- Department of Pharmacology, Graduate School of Dentistry, Osaka University, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan; Molecular Research Center for Children's Mental Development, United Graduate School of Child Development, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan; Laboratory of Molecular Neuropharmacology, Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871, Japan.
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11
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Lipkin AM, Bender KJ. Axon Initial Segment GABA Inhibits Action Potential Generation throughout Periadolescent Development. J Neurosci 2023; 43:6357-6368. [PMID: 37596053 PMCID: PMC10500977 DOI: 10.1523/jneurosci.0605-23.2023] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2023] [Revised: 07/04/2023] [Accepted: 08/01/2023] [Indexed: 08/20/2023] Open
Abstract
Neurons are remarkably polarized structures: dendrites spread and branch to receive synaptic inputs while a single axon extends and transmits action potentials (APs) to downstream targets. Neuronal polarity is maintained by the axon initial segment (AIS), a region between the soma and axon proper that is also the site of action potential (AP) generation. This polarization between dendrites and axons extends to inhibitory neurotransmission. In adulthood, the neurotransmitter GABA hyperpolarizes dendrites but instead depolarizes axons. These differences in function collide at the AIS. Multiple studies have shown that GABAergic signaling in this region can share properties of either the mature axon or mature dendrite, and that these properties evolve over a protracted period encompassing periadolescent development. Here, we explored how developmental changes in GABAergic signaling affect AP initiation. We show that GABA at the axon initial segment inhibits action potential initiation in layer (L)2/3 pyramidal neurons in prefrontal cortex from mice of either sex across GABA reversal potentials observed in periadolescence. These actions occur largely through current shunts generated by GABAA receptors and changes in voltage-gated channel properties that affected the number of channels that could be recruited for AP electrogenesis. These results suggest that GABAergic neurons targeting the axon initial segment provide an inhibitory "veto" across the range of GABA polarity observed in normal adolescent development, regardless of GABAergic synapse reversal potential.Significance Statement GABA receptors are a major class of neurotransmitter receptors in the brain. Typically, GABA receptors inhibit neurons by allowing influx of negatively charged chloride ions into the cell. However, there are cases where local chloride concentrations promote chloride efflux through GABA receptors. Such conditions exist early in development in neocortical pyramidal cell axon initial segments (AISs), where action potentials (APs) initiate. Here, we examined how chloride efflux in early development interacts with mechanisms that support action potential initiation. We find that this efflux, despite moving membrane potential closer to action potential threshold, is nevertheless inhibitory. Thus, GABA at the axon initial segment is likely to be inhibitory for action potential initiation independent of whether chloride flows out or into neurons via these receptors.
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Affiliation(s)
- Anna M Lipkin
- Neuroscience Graduate Program
- Center for Integrative Neuroscience Department of Neurology, University of California, San Francisco 94158, California
| | - Kevin J Bender
- Center for Integrative Neuroscience Department of Neurology, University of California, San Francisco 94158, California
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12
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Yang S, Park JH, Lu HC. Axonal energy metabolism, and the effects in aging and neurodegenerative diseases. Mol Neurodegener 2023; 18:49. [PMID: 37475056 PMCID: PMC10357692 DOI: 10.1186/s13024-023-00634-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Accepted: 06/08/2023] [Indexed: 07/22/2023] Open
Abstract
Human studies consistently identify bioenergetic maladaptations in brains upon aging and neurodegenerative disorders of aging (NDAs), such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and Amyotrophic lateral sclerosis. Glucose is the major brain fuel and glucose hypometabolism has been observed in brain regions vulnerable to aging and NDAs. Many neurodegenerative susceptible regions are in the topological central hub of the brain connectome, linked by densely interconnected long-range axons. Axons, key components of the connectome, have high metabolic needs to support neurotransmission and other essential activities. Long-range axons are particularly vulnerable to injury, neurotoxin exposure, protein stress, lysosomal dysfunction, etc. Axonopathy is often an early sign of neurodegeneration. Recent studies ascribe axonal maintenance failures to local bioenergetic dysregulation. With this review, we aim to stimulate research in exploring metabolically oriented neuroprotection strategies to enhance or normalize bioenergetics in NDA models. Here we start by summarizing evidence from human patients and animal models to reveal the correlation between glucose hypometabolism and connectomic disintegration upon aging/NDAs. To encourage mechanistic investigations on how axonal bioenergetic dysregulation occurs during aging/NDAs, we first review the current literature on axonal bioenergetics in distinct axonal subdomains: axon initial segments, myelinated axonal segments, and axonal arbors harboring pre-synaptic boutons. In each subdomain, we focus on the organization, activity-dependent regulation of the bioenergetic system, and external glial support. Second, we review the mechanisms regulating axonal nicotinamide adenine dinucleotide (NAD+) homeostasis, an essential molecule for energy metabolism processes, including NAD+ biosynthetic, recycling, and consuming pathways. Third, we highlight the innate metabolic vulnerability of the brain connectome and discuss its perturbation during aging and NDAs. As axonal bioenergetic deficits are developing into NDAs, especially in asymptomatic phase, they are likely exaggerated further by impaired NAD+ homeostasis, the high energetic cost of neural network hyperactivity, and glial pathology. Future research in interrogating the causal relationship between metabolic vulnerability, axonopathy, amyloid/tau pathology, and cognitive decline will provide fundamental knowledge for developing therapeutic interventions.
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Affiliation(s)
- Sen Yang
- The Linda and Jack Gill Center for Biomolecular Sciences, Indiana University, Bloomington, IN, 47405, USA
- Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, 47405, USA
- Program in Neuroscience, Indiana University, Bloomington, IN, 47405, USA
| | - Jung Hyun Park
- The Linda and Jack Gill Center for Biomolecular Sciences, Indiana University, Bloomington, IN, 47405, USA
- Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, 47405, USA
- Program in Neuroscience, Indiana University, Bloomington, IN, 47405, USA
| | - Hui-Chen Lu
- The Linda and Jack Gill Center for Biomolecular Sciences, Indiana University, Bloomington, IN, 47405, USA.
- Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, 47405, USA.
- Program in Neuroscience, Indiana University, Bloomington, IN, 47405, USA.
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13
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Spirou GA, Kersting M, Carr S, Razzaq B, Yamamoto Alves Pinto C, Dawson M, Ellisman MH, Manis PB. High-resolution volumetric imaging constrains compartmental models to explore synaptic integration and temporal processing by cochlear nucleus globular bushy cells. eLife 2023; 12:e83393. [PMID: 37288824 PMCID: PMC10435236 DOI: 10.7554/elife.83393] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Accepted: 06/07/2023] [Indexed: 06/09/2023] Open
Abstract
Globular bushy cells (GBCs) of the cochlear nucleus play central roles in the temporal processing of sound. Despite investigation over many decades, fundamental questions remain about their dendrite structure, afferent innervation, and integration of synaptic inputs. Here, we use volume electron microscopy (EM) of the mouse cochlear nucleus to construct synaptic maps that precisely specify convergence ratios and synaptic weights for auditory nerve innervation and accurate surface areas of all postsynaptic compartments. Detailed biophysically based compartmental models can help develop hypotheses regarding how GBCs integrate inputs to yield their recorded responses to sound. We established a pipeline to export a precise reconstruction of auditory nerve axons and their endbulb terminals together with high-resolution dendrite, soma, and axon reconstructions into biophysically detailed compartmental models that could be activated by a standard cochlear transduction model. With these constraints, the models predict auditory nerve input profiles whereby all endbulbs onto a GBC are subthreshold (coincidence detection mode), or one or two inputs are suprathreshold (mixed mode). The models also predict the relative importance of dendrite geometry, soma size, and axon initial segment length in setting action potential threshold and generating heterogeneity in sound-evoked responses, and thereby propose mechanisms by which GBCs may homeostatically adjust their excitability. Volume EM also reveals new dendritic structures and dendrites that lack innervation. This framework defines a pathway from subcellular morphology to synaptic connectivity, and facilitates investigation into the roles of specific cellular features in sound encoding. We also clarify the need for new experimental measurements to provide missing cellular parameters, and predict responses to sound for further in vivo studies, thereby serving as a template for investigation of other neuron classes.
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Affiliation(s)
- George A Spirou
- Department of Medical Engineering, University of South FloridaTampaUnited States
| | - Matthew Kersting
- Department of Medical Engineering, University of South FloridaTampaUnited States
| | - Sean Carr
- Department of Medical Engineering, University of South FloridaTampaUnited States
| | - Bayan Razzaq
- Department of Otolaryngology, Head and Neck Surgery, West Virginia UniversityMorgantownUnited States
| | | | - Mariah Dawson
- Department of Otolaryngology, Head and Neck Surgery, West Virginia UniversityMorgantownUnited States
| | - Mark H Ellisman
- Department of Neurosciences, University of California, San DiegoSan DiegoUnited States
- National Center for Microscopy and Imaging Research,University of California, San DiegoSan DiegoUnited States
| | - Paul B Manis
- Department of Otolaryngology/Head and Neck Surgery, University of North Carolina at Chapel HillChapel HillUnited States
- Department of Cell Biology and Physiology, University of North CarolinaChapel HillUnited States
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14
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Caspi Y, Mazar M, Kushnir Y, Mazor Y, Katz B, Lev S, Binshtok AM. Structural plasticity of axon initial segment in spinal cord neurons underlies inflammatory pain. Pain 2023; 164:1388-1401. [PMID: 36645177 DOI: 10.1097/j.pain.0000000000002829] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Accepted: 10/19/2022] [Indexed: 01/17/2023]
Abstract
ABSTRACT Physiological or pathology-mediated changes in neuronal activity trigger structural plasticity of the action potential generation site-the axon initial segment (AIS). These changes affect intrinsic neuronal excitability, thus tuning neuronal and overall network output. Using behavioral, immunohistochemical, electrophysiological, and computational approaches, we characterized inflammation-related AIS plasticity in rat's superficial (lamina II) spinal cord dorsal horn (SDH) neurons and established how AIS plasticity regulates the activity of SDH neurons, thus contributing to pain hypersensitivity. We show that in naive conditions, AIS in SDH inhibitory neurons is located closer to the soma than in excitatory neurons. Shortly after inducing inflammation, when the inflammatory hyperalgesia is at its peak, AIS in inhibitory neurons is shifted distally away from the soma. The shift in AIS location is accompanied by the decrease in excitability of SDH inhibitory neurons. These AIS location and excitability changes are selective for inhibitory neurons and reversible. We show that AIS shift back close to the soma, and SDH inhibitory neurons' excitability increases to baseline levels following recovery from inflammatory hyperalgesia. The computational model of SDH inhibitory neurons predicts that the distal shift of AIS is sufficient to decrease the intrinsic excitability of these neurons. Our results provide evidence of inflammatory pain-mediated AIS plasticity in the central nervous system, which differentially affects the excitability of inhibitory SDH neurons and contributes to inflammatory hyperalgesia.
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Affiliation(s)
- Yaki Caspi
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah School of Medicine, Jerusalem, Israel
- The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Michael Mazar
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah School of Medicine, Jerusalem, Israel
- The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Yishai Kushnir
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah School of Medicine, Jerusalem, Israel
- The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Yoav Mazor
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah School of Medicine, Jerusalem, Israel
- The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
- Department of Gastroenterology, Rambam Health Care Campus, Haifa, Israel
| | - Ben Katz
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah School of Medicine, Jerusalem, Israel
- The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Shaya Lev
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah School of Medicine, Jerusalem, Israel
- The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Alexander M Binshtok
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah School of Medicine, Jerusalem, Israel
- The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
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15
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Garrido JJ. Contribution of Axon Initial Segment Structure and Channels to Brain Pathology. Cells 2023; 12:cells12081210. [PMID: 37190119 DOI: 10.3390/cells12081210] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2023] [Revised: 04/17/2023] [Accepted: 04/20/2023] [Indexed: 05/17/2023] Open
Abstract
Brain channelopathies are a group of neurological disorders that result from genetic mutations affecting ion channels in the brain. Ion channels are specialized proteins that play a crucial role in the electrical activity of nerve cells by controlling the flow of ions such as sodium, potassium, and calcium. When these channels are not functioning properly, they can cause a wide range of neurological symptoms such as seizures, movement disorders, and cognitive impairment. In this context, the axon initial segment (AIS) is the site of action potential initiation in most neurons. This region is characterized by a high density of voltage-gated sodium channels (VGSCs), which are responsible for the rapid depolarization that occurs when the neuron is stimulated. The AIS is also enriched in other ion channels, such as potassium channels, that play a role in shaping the action potential waveform and determining the firing frequency of the neuron. In addition to ion channels, the AIS contains a complex cytoskeletal structure that helps to anchor the channels in place and regulate their function. Therefore, alterations in this complex structure of ion channels, scaffold proteins, and specialized cytoskeleton may also cause brain channelopathies not necessarily associated with ion channel mutations. This review will focus on how the AISs structure, plasticity, and composition alterations may generate changes in action potentials and neuronal dysfunction leading to brain diseases. AIS function alterations may be the consequence of voltage-gated ion channel mutations, but also may be due to ligand-activated channels and receptors and AIS structural and membrane proteins that support the function of voltage-gated ion channels.
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Affiliation(s)
- Juan José Garrido
- Instituto Cajal, CSIC, 28002 Madrid, Spain
- Alzheimer's Disease and Other Degenerative Dementias, Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED), 28002 Madrid, Spain
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16
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Jungenitz T, Bird A, Engelhardt M, Jedlicka P, Schwarzacher SW, Deller T. Structural plasticity of the axon initial segment in rat hippocampal granule cells following high frequency stimulation and LTP induction. Front Neuroanat 2023; 17:1125623. [PMID: 37090138 PMCID: PMC10113456 DOI: 10.3389/fnana.2023.1125623] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Accepted: 03/20/2023] [Indexed: 04/25/2023] Open
Abstract
The axon initial segment (AIS) is the site of action potential initiation and important for the integration of synaptic input. Length and localization of the AIS are dynamic, modulated by afferent activity and contribute to the homeostatic control of neuronal excitability. Synaptopodin is a plasticity-related protein expressed by the majority of telencephalic neurons. It is required for the formation of cisternal organelles within the AIS and an excellent marker to identify these enigmatic organelles at the light microscopic level. Here we applied 2 h of high frequency stimulation of the medial perforant path in rats in vivo to induce a strong long-term potentiation of dentate gyrus granule cells. Immunolabeling for βIV-spectrin and synaptopodin were performed to study structural changes of the AIS and its cisternal organelles. Three-dimensional analysis of the AIS revealed a shortening of the AIS and a corresponding reduction of the number of synaptopodin clusters. These data demonstrate a rapid structural plasticity of the AIS and its cisternal organelles to strong stimulation, indicating a homeostatic response of the entire AIS compartment.
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Affiliation(s)
- Tassilo Jungenitz
- Institute of Clinical Neuroanatomy, Goethe University Frankfurt, Frankfurt am Main, Germany
- *Correspondence: Tassilo Jungenitz,
| | - Alexander Bird
- Interdisciplinary Centre for 3Rs in Animal Research, Justus Liebig University Giessen, Giessen, Germany
| | - Maren Engelhardt
- Institute of Anatomy and Cell Biology, Johannes Kepler University Linz, Linz, Austria
| | - Peter Jedlicka
- Institute of Clinical Neuroanatomy, Goethe University Frankfurt, Frankfurt am Main, Germany
- Interdisciplinary Centre for 3Rs in Animal Research, Justus Liebig University Giessen, Giessen, Germany
| | | | - Thomas Deller
- Institute of Clinical Neuroanatomy, Goethe University Frankfurt, Frankfurt am Main, Germany
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17
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Masoli S, Rizza MF, Tognolina M, Prestori F, D’Angelo E. Computational models of neurotransmission at cerebellar synapses unveil the impact on network computation. Front Comput Neurosci 2022; 16:1006989. [PMID: 36387305 PMCID: PMC9649760 DOI: 10.3389/fncom.2022.1006989] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Accepted: 10/10/2022] [Indexed: 11/25/2022] Open
Abstract
The neuroscientific field benefits from the conjoint evolution of experimental and computational techniques, allowing for the reconstruction and simulation of complex models of neurons and synapses. Chemical synapses are characterized by presynaptic vesicle cycling, neurotransmitter diffusion, and postsynaptic receptor activation, which eventually lead to postsynaptic currents and subsequent membrane potential changes. These mechanisms have been accurately modeled for different synapses and receptor types (AMPA, NMDA, and GABA) of the cerebellar cortical network, allowing simulation of their impact on computation. Of special relevance is short-term synaptic plasticity, which generates spatiotemporal filtering in local microcircuits and controls burst transmission and information flow through the network. Here, we present how data-driven computational models recapitulate the properties of neurotransmission at cerebellar synapses. The simulation of microcircuit models is starting to reveal how diverse synaptic mechanisms shape the spatiotemporal profiles of circuit activity and computation.
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Affiliation(s)
- Stefano Masoli
- Department of Brain and Behavioral Sciences, University of Pavia, Pavia, Italy
| | | | | | - Francesca Prestori
- Department of Brain and Behavioral Sciences, University of Pavia, Pavia, Italy
- *Correspondence: Francesca Prestori,
| | - Egidio D’Angelo
- Department of Brain and Behavioral Sciences, University of Pavia, Pavia, Italy
- IRCCS Mondino Foundation, Brain Connectivity Center, Pavia, Italy
- Egidio D’Angelo,
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18
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Ostos S, Aparicio G, Fernaud-Espinosa I, DeFelipe J, Muñoz A. Quantitative analysis of the GABAergic innervation of the soma and axon initial segment of pyramidal cells in the human and mouse neocortex. Cereb Cortex 2022; 33:3882-3909. [PMID: 36058205 DOI: 10.1093/cercor/bhac314] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 07/16/2022] [Accepted: 07/17/2022] [Indexed: 11/13/2022] Open
Abstract
Perisomatic GABAergic innervation in the cerebral cortex is carried out mostly by basket and chandelier cells, which differentially participate in the control of pyramidal cell action potential output and synchronization. These cells establish multiple synapses with the cell body (and proximal dendrites) and the axon initial segment (AIS) of pyramidal neurons, respectively. Using multiple immunofluorescence, confocal microscopy and 3D quantification techniques, we have estimated the number and density of GABAergic boutons on the cell body and AIS of pyramidal neurons located through cortical layers of the human and mouse neocortex. The results revealed, in both species, that there is clear variability across layers regarding the density and number of perisomatic GABAergic boutons. We found a positive linear correlation between the surface area of the soma, or the AIS, and the number of GABAergic terminals in apposition to these 2 neuronal domains. Furthermore, the density of perisomatic GABAergic boutons was higher in the human cortex than in the mouse. These results suggest a selectivity for the GABAergic innervation of the cell body and AIS that might be related to the different functional attributes of the microcircuits in which neurons from different layers are involved in both human and mouse.
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Affiliation(s)
- Sandra Ostos
- Departamento de Neurobiología Funcional y de Sistemas, Instituto Cajal (CSIC), Avenida Doctor Arce 37, 28002, Madrid, Spain.,Laboratorio Cajal de Circuitos Corticales (CTB), Universidad Politécnica de Madrid, Campus de Montegancedo, 28223, Pozuelo de Alarcón, Madrid, Spain
| | - Guillermo Aparicio
- Departamento de Neurobiología Funcional y de Sistemas, Instituto Cajal (CSIC), Avenida Doctor Arce 37, 28002, Madrid, Spain.,Laboratorio Cajal de Circuitos Corticales (CTB), Universidad Politécnica de Madrid, Campus de Montegancedo, 28223, Pozuelo de Alarcón, Madrid, Spain
| | - Isabel Fernaud-Espinosa
- Departamento de Neurobiología Funcional y de Sistemas, Instituto Cajal (CSIC), Avenida Doctor Arce 37, 28002, Madrid, Spain.,Laboratorio Cajal de Circuitos Corticales (CTB), Universidad Politécnica de Madrid, Campus de Montegancedo, 28223, Pozuelo de Alarcón, Madrid, Spain
| | - Javier DeFelipe
- Departamento de Neurobiología Funcional y de Sistemas, Instituto Cajal (CSIC), Avenida Doctor Arce 37, 28002, Madrid, Spain.,Laboratorio Cajal de Circuitos Corticales (CTB), Universidad Politécnica de Madrid, Campus de Montegancedo, 28223, Pozuelo de Alarcón, Madrid, Spain.,CIBERNED, Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas, Avenida Monforte de Lemos, 3-5, 28029 Madrid, Spain
| | - Alberto Muñoz
- Departamento de Neurobiología Funcional y de Sistemas, Instituto Cajal (CSIC), Avenida Doctor Arce 37, 28002, Madrid, Spain.,Laboratorio Cajal de Circuitos Corticales (CTB), Universidad Politécnica de Madrid, Campus de Montegancedo, 28223, Pozuelo de Alarcón, Madrid, Spain.,Departamento de Biología Celular, Universidad Complutense, José Antonio Novais 12, 28040 Madrid, Spain
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19
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Wienbar S, Schwartz GW. Differences in spike generation instead of synaptic inputs determine the feature selectivity of two retinal cell types. Neuron 2022; 110:2110-2123.e4. [PMID: 35508174 DOI: 10.1016/j.neuron.2022.04.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Revised: 03/21/2022] [Accepted: 04/11/2022] [Indexed: 12/19/2022]
Abstract
Retinal ganglion cells (RGCs) are the spiking projection neurons of the eye that encode different features of the visual environment. The circuits providing synaptic input to different RGC types to drive feature selectivity have been studied extensively, but there has been less research aimed at understanding the intrinsic properties and how they impact feature selectivity. We introduce an RGC type in the mouse, the Bursty Suppressed-by-Contrast (bSbC) RGC, and compared it to the OFF sustained alpha (OFFsA). Differences in their contrast response functions arose from differences not in synaptic inputs but in their intrinsic properties. Spike generation was the key intrinsic property behind this functional difference; the bSbC RGC undergoes depolarization block while the OFFsA RGC maintains a high spike rate. Our results demonstrate that differences in intrinsic properties allow these two RGC types to detect and relay distinct features of an identical visual stimulus to the brain.
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Affiliation(s)
- Sophia Wienbar
- Department of Ophthalmology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA; Northwestern University Interdepartmental Neuroscience Program, Northwestern University, Evanston, IL 60208, USA
| | - Gregory William Schwartz
- Department of Ophthalmology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA; Department of Neuroscience, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA; Department of Neurobiology, Weinberg College of Arts and Sciences, Northwestern University, Evanston, IL 60208, USA.
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20
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Kaneko K, Currin CB, Goff KM, Wengert ER, Somarowthu A, Vogels TP, Goldberg EM. Developmentally regulated impairment of parvalbumin interneuron synaptic transmission in an experimental model of Dravet syndrome. Cell Rep 2022; 38:110580. [PMID: 35354025 PMCID: PMC9003081 DOI: 10.1016/j.celrep.2022.110580] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Revised: 01/09/2022] [Accepted: 03/06/2022] [Indexed: 11/25/2022] Open
Abstract
Dravet syndrome is a neurodevelopmental disorder characterized by epilepsy, intellectual disability, and sudden death due to pathogenic variants in SCN1A with loss of function of the sodium channel subunit Nav1.1. Nav1.1-expressing parvalbumin GABAergic interneurons (PV-INs) from young Scn1a+/− mice show impaired action potential generation. An approach assessing PV-IN function in the same mice at two time points shows impaired spike generation in all Scn1a+/− mice at postnatal days (P) 16–21, whether deceased prior or surviving to P35, with normalization by P35 in surviving mice. However, PV-IN synaptic transmission is dysfunctional in young Scn1a+/− mice that did not survive and in Scn1a+/− mice ≥ P35. Modeling confirms that PV-IN axonal propagation is more sensitive to decreased sodium conductance than spike generation. These results demonstrate dynamic dysfunction in Dravet syndrome: combined abnormalities of PV-IN spike generation and propagation drives early disease severity, while ongoing dysfunction of synaptic transmission contributes to chronic pathology. Dravet syndrome is caused by variants in SCN1A with loss of function of Nav1.1 sodium channels. Kaneko et al. use the “mini-slice” to record at two developmental time points. Impaired spike generation of Nav1.1-expressing PV interneurons in Scn1a+/− mice is transient, while abnormalities of PV interneuron synaptic transmission persist.
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Affiliation(s)
- Keisuke Kaneko
- Division of Neurology, Department of Pediatrics, The Children's Hospital of Philadelphia, Abramson Research Center, Philadelphia, PA 19104, USA
| | - Christopher B Currin
- The Institute of Science and Technology Austria, Am Campus 1, Klosterneuburg, Austria
| | - Kevin M Goff
- Medical Scientist Training Program (MSTP), The University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA; Neuroscience Graduate Group, The University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA
| | - Eric R Wengert
- Division of Neurology, Department of Pediatrics, The Children's Hospital of Philadelphia, Abramson Research Center, Philadelphia, PA 19104, USA
| | - Ala Somarowthu
- Division of Neurology, Department of Pediatrics, The Children's Hospital of Philadelphia, Abramson Research Center, Philadelphia, PA 19104, USA
| | - Tim P Vogels
- The Institute of Science and Technology Austria, Am Campus 1, Klosterneuburg, Austria
| | - Ethan M Goldberg
- Division of Neurology, Department of Pediatrics, The Children's Hospital of Philadelphia, Abramson Research Center, Philadelphia, PA 19104, USA; Neuroscience Graduate Group, The University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA; Department of Neurology, The University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA; Department of Neuroscience, The University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA.
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21
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Radulovic J, Ivkovic S, Adzic M. From chronic stress and anxiety to neurodegeneration: Focus on neuromodulation of the axon initial segment. HANDBOOK OF CLINICAL NEUROLOGY 2022; 184:481-495. [PMID: 35034756 DOI: 10.1016/b978-0-12-819410-2.00025-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
To adapt to the sustained demands of chronic stress, discrete brain circuits undergo structural and functional changes often resulting in anxiety disorders. In some individuals, anxiety disorders precede the development of motor symptoms of Parkinson's disease (PD) caused by degeneration of neurons in the substantia nigra (SN). Here, we present a circuit framework for probing a causal link between chronic stress, anxiety, and PD, which postulates a central role of abnormal neuromodulation of the SN's axon initial segment by brainstem inputs. It is grounded in findings demonstrating that the earliest PD pathologies occur in the stress-responsive, emotion regulation network of the brainstem, which provides the SN with dense aminergic and cholinergic innervation. SN's axon initial segment (AIS) has unique features that support the sustained and bidirectional propagation of activity in response to synaptic inputs. It is therefore, especially sensitive to circuit-mediated stress-induced imbalance of neuromodulation, and thus a plausible initiating site of neurodegeneration. This could explain why, although secondary to pathophysiologies in other brainstem nuclei, SN degeneration is the most extensive. Consequently, the cardinal symptom of PD, severe motor deficits, arise from degeneration of the nigrostriatal pathway rather than other brainstem nuclei. Understanding when and how circuit dysfunctions underlying anxiety can progress to neurodegeneration, raises the prospect of timed interventions for reversing, or at least impeding, the early pathophysiologies that lead to PD and possibly other neurodegenerative disorders.
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Affiliation(s)
- Jelena Radulovic
- Department of Neuroscience, Albert Einstein Medical College, Bronx, NY, United States; Department of Psychiatry and Behavioral Sciences, Albert Einstein Medical College, Bronx, NY, United States.
| | - Sanja Ivkovic
- Department of Molecular Biology and Endocrinology, Vinca Institute of Nuclear Sciences, National Institute of the Republic of Serbia, University of Belgrade, Belgrade, Serbia
| | - Miroslav Adzic
- Department of Molecular Biology and Endocrinology, Vinca Institute of Nuclear Sciences, National Institute of the Republic of Serbia, University of Belgrade, Belgrade, Serbia
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22
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Usui N, Tian X, Harigai W, Togawa S, Utsunomiya R, Doi T, Miyoshi K, Shinoda K, Tanaka J, Shimada S, Katayama T, Yoshimura T. Length impairments of the axon initial segment in rodent models of attention-deficit hyperactivity disorder and autism spectrum disorder. Neurochem Int 2021; 153:105273. [PMID: 34971749 DOI: 10.1016/j.neuint.2021.105273] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Revised: 12/22/2021] [Accepted: 12/24/2021] [Indexed: 11/25/2022]
Abstract
The axon initial segment (AIS) is a structural neuronal compartment of the proximal axon that plays key roles in sodium channel clustering, action potential initiation, and signal propagation of neuronal outputs. Mutations in constitutive genes of the AIS, such as ANK3, have been identified in patients with neurodevelopmental disorders. Nevertheless, morphological changes in the AIS in neurodevelopmental disorders have not been characterized. In this study, we investigated the length of the AIS in rodent models of attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). We observed abnormalities in AIS length in both animal models. In ADHD model rodents, we observed shorter AIS length in layer 2/3 (L2/3) neurons of the medial prefrontal cortex (mPFC) and primary somatosensory barrel field (S1BF). Further, we observed shorter AIS length in S1BF L5 neurons. In ASD model mice, we observed shorter AIS length in L2/3 and L5 neurons of the S1BF. These results suggest that impairments in AIS length are common phenomena in neurodevelopmental disorders such as ADHD and ASD and may be conserved across species. Our findings provide novel insight into the potential contribution of the AIS to the pathophysiology and pathogenesis of neurodevelopmental disorders.
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Affiliation(s)
- Noriyoshi Usui
- Department of Neuroscience and Cell Biology, Graduate School of Medicine, Osaka University, Suita, 565-0871, Japan; United Graduate School of Child Development, Osaka University, Suita, 565-0871, Japan; Global Center for Medical Engineering and Informatics, Osaka University, Suita, 565-0871, Japan; Addiction Research Unit, Osaka Psychiatric Research Center, Osaka Psychiatric Medical Center, Hirakata, 573-0022, Japan.
| | - Xiaoye Tian
- Department of Child Development and Molecular Brain Science, United Graduate School of Child Development, Osaka University, Suita, 565-0871, Japan
| | - Wakana Harigai
- Department of Child Development and Molecular Brain Science, United Graduate School of Child Development, Osaka University, Suita, 565-0871, Japan
| | - Shogo Togawa
- Department of Neuroscience and Cell Biology, Graduate School of Medicine, Osaka University, Suita, 565-0871, Japan; Division of Neuroanatomy, Department of Neuroscience, Yamaguchi University Graduate School of Medicine, Yamaguchi, 755-8505, Japan
| | - Ryo Utsunomiya
- Department of Molecular and Cellular Physiology, Graduate School of Medicine, Ehime University, Ehime, 791-0295, Japan
| | - Tomomi Doi
- Department of Molecular and Cellular Physiology, Graduate School of Medicine, Ehime University, Ehime, 791-0295, Japan
| | - Ko Miyoshi
- Department of Child Development and Molecular Brain Science, United Graduate School of Child Development, Osaka University, Suita, 565-0871, Japan
| | - Koh Shinoda
- Division of Neuroanatomy, Department of Neuroscience, Yamaguchi University Graduate School of Medicine, Yamaguchi, 755-8505, Japan
| | - Junya Tanaka
- Department of Molecular and Cellular Physiology, Graduate School of Medicine, Ehime University, Ehime, 791-0295, Japan
| | - Shoichi Shimada
- Department of Neuroscience and Cell Biology, Graduate School of Medicine, Osaka University, Suita, 565-0871, Japan; United Graduate School of Child Development, Osaka University, Suita, 565-0871, Japan; Addiction Research Unit, Osaka Psychiatric Research Center, Osaka Psychiatric Medical Center, Hirakata, 573-0022, Japan
| | - Taiichi Katayama
- Department of Child Development and Molecular Brain Science, United Graduate School of Child Development, Osaka University, Suita, 565-0871, Japan
| | - Takeshi Yoshimura
- Department of Child Development and Molecular Brain Science, United Graduate School of Child Development, Osaka University, Suita, 565-0871, Japan.
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23
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Sajedi S, Fellner A, Werginz P, Rattay F. Block Phenomena During Electric Micro-Stimulation of Pyramidal Cells and Retinal Ganglion Cells. Front Cell Neurosci 2021; 15:771600. [PMID: 34899192 PMCID: PMC8663762 DOI: 10.3389/fncel.2021.771600] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Accepted: 11/08/2021] [Indexed: 11/13/2022] Open
Abstract
Electric micro-stimulation of the nervous system is a means to restore various body functions. The stimulus amplitude necessary to generate action potentials, the lower threshold (LT), is well characterized for many neuronal populations. However, electric overstimulation above an upper threshold (UT) prevents action potential generation and therefore hinders optimal neuro-rehabilitation. Previous studies demonstrated the impact of the UT in micro-stimulation of retinal ganglion cells (RGCs). The observed phenomenon is mostly explained by (i) reversed sodium ion flow in the soma membrane, and (ii) anodal surround block that hinders spike conduction in strongly hyperpolarized regions of the axon at high stimulus intensities. However, up to now, no detailed study of the nature of these phenomena has been presented, particularly for different cell types. Here, we present computational analyses of LT and UT for layer 5 pyramidal cells (PCs) as well as alpha RGCs. Model neurons were stimulated in close vicinity to the cell body and LTs and UTs as well as the ratio UT/LT were compared. Aside from a simple point source electrode and monophasic stimuli also realistic electrode and pulse configurations were examined. The analysis showed: (i) in RGCs, the soma contributed to action potential initiation and block for small electrode distances, whereas in PCs the soma played no role in LTs or UTs. (ii) In both cell types, action potential always initiated within the axon initial segment at LT. (iii) In contrast to a complete block of spike conductance at UT that occurred in RGCs, an incomplete block of spiking appeared in PC axon collaterals. (iv) PC axon collateral arrangement influenced UTs but had small impact on LTs. (v) Population responses of RGCs change from circular regions of activation to ring-shaped patterns for increasing stimulus amplitude. A better understanding of the stimulation window that can reliably activate target neurons will benefit the future development of neuroprostheses.
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Affiliation(s)
- Sogand Sajedi
- Institute for Analysis and Scientific Computing, Vienna University of Technology, Vienna, Austria
| | - Andreas Fellner
- Institute for Analysis and Scientific Computing, Vienna University of Technology, Vienna, Austria
| | - Paul Werginz
- Institute for Analysis and Scientific Computing, Vienna University of Technology, Vienna, Austria
| | - Frank Rattay
- Institute for Analysis and Scientific Computing, Vienna University of Technology, Vienna, Austria
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24
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Zhang W, Ciorraga M, Mendez P, Retana D, Boumedine-Guignon N, Achón B, Russier M, Debanne D, Garrido JJ. Formin Activity and mDia1 Contribute to Maintain Axon Initial Segment Composition and Structure. Mol Neurobiol 2021; 58:6153-6169. [PMID: 34458961 PMCID: PMC8639558 DOI: 10.1007/s12035-021-02531-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Accepted: 08/11/2021] [Indexed: 10/29/2022]
Abstract
The axon initial segment (AIS) is essential for maintaining neuronal polarity, modulating protein transport into the axon, and action potential generation. These functions are supported by a distinctive actin and microtubule cytoskeleton that controls axonal trafficking and maintains a high density of voltage-gated ion channels linked by scaffold proteins to the AIS cytoskeleton. However, our knowledge of the mechanisms and proteins involved in AIS cytoskeleton regulation to maintain or modulate AIS structure is limited. In this context, formins play a significant role in the modulation of actin and microtubules. We show that pharmacological inhibition of formins modifies AIS actin and microtubule characteristics in cultured hippocampal neurons, reducing F-actin density and decreasing microtubule acetylation. Moreover, formin inhibition diminishes sodium channels, ankyrinG and βIV-spectrin AIS density, and AIS length, in cultured neurons and brain slices, accompanied by decreased neuronal excitability. We show that genetic downregulation of the mDia1 formin by interference RNAs also decreases AIS protein density and shortens AIS length. The ankyrinG decrease and AIS shortening observed in pharmacologically inhibited neurons and neuron-expressing mDia1 shRNAs were impaired by HDAC6 downregulation or EB1-GFP expression, known to increase microtubule acetylation or stability. However, actin stabilization only partially prevented AIS shortening without affecting AIS protein density loss. These results suggest that mDia1 maintain AIS composition and length contributing to the stability of AIS microtubules.
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Affiliation(s)
- Wei Zhang
- Instituto Cajal, CSIC, 28002 Madrid, Spain
- Present Address: College of Chemistry and Molecular Engineering, Peking University, Beijing, China
| | | | | | | | | | | | - Michaël Russier
- UNIS, INSERM, UMR 1072, Aix-Marseille Université, 13015 Marseille, France
| | - Dominique Debanne
- UNIS, INSERM, UMR 1072, Aix-Marseille Université, 13015 Marseille, France
| | - Juan José Garrido
- Instituto Cajal, CSIC, 28002 Madrid, Spain
- Alzheimer’s Disease and Other Degenerative Dementias, Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED), Madrid, Spain
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25
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Rotterman TM, Carrasco DI, Housley SN, Nardelli P, Powers RK, Cope TC. Axon initial segment geometry in relation to motoneuron excitability. PLoS One 2021; 16:e0259918. [PMID: 34797870 PMCID: PMC8604372 DOI: 10.1371/journal.pone.0259918] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Accepted: 10/28/2021] [Indexed: 12/12/2022] Open
Abstract
The axon initial segment (AIS) responsible for action potential initiation is a dynamic structure that varies and changes together with neuronal excitability. Like other neuron types, alpha motoneurons in the mammalian spinal cord express heterogeneity and plasticity in AIS geometry, including length (AISl) and distance from soma (AISd). The present study aimed to establish the relationship of AIS geometry with a measure of intrinsic excitability, rheobase current, that varies by 20-fold or more among normal motoneurons. We began by determining whether AIS length or distance differed for motoneurons in motor pools that exhibit different activity profiles. Motoneurons sampled from the medial gastrocnemius (MG) motor pool exhibited values for average AISd that were significantly greater than that for motoneurons from the soleus (SOL) motor pool, which is more readily recruited in low-level activities. Next, we tested whether AISd covaried with intrinsic excitability of individual motoneurons. In anesthetized rats, we measured rheobase current intracellularly from MG motoneurons in vivo before labeling them for immunohistochemical study of AIS structure. For 16 motoneurons sampled from the MG motor pool, this combinatory approach revealed that AISd, but not AISl, was significantly related to rheobase, as AIS tended to be located further from the soma on motoneurons that were less excitable. Although a causal relation with excitability seems unlikely, AISd falls among a constellation of properties related to the recruitability of motor units and their parent motoneurons.
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Affiliation(s)
- Travis M. Rotterman
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, United States of America
- * E-mail: (TMR); (TCC)
| | - Darío I. Carrasco
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, United States of America
| | - Stephen N. Housley
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, United States of America
| | - Paul Nardelli
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, United States of America
| | - Randall K. Powers
- Department of Physiology and Biophysics, University of Washington, Seattle, WA, United States of America
| | - Timothy C. Cope
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, United States of America
- W.H. Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, United States of America
- * E-mail: (TMR); (TCC)
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26
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Bagheri S, Haddadi R, Saki S, Kourosh-Arami M, Komaki A. The effect of sodium channels on neurological/neuronal disorders: A systematic review. Int J Dev Neurosci 2021; 81:669-685. [PMID: 34687079 DOI: 10.1002/jdn.10153] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 10/06/2021] [Accepted: 10/19/2021] [Indexed: 12/19/2022] Open
Abstract
Neurological and neuronal disorders are associated with structural, biochemical, or electrical abnormalities in the nervous system. Many neurological diseases have not yet been discovered. Interventions used for the treatment of these disorders include avoidance measures, lifestyle changes, physiotherapy, neurorehabilitation, pain management, medication, and surgery. In the sodium channelopathies, alterations in the structure, expression, and function of voltage-gated sodium channels (VGSCs) are considered as the causes of neurological and neuronal diseases. Online databases, including Scopus, Science Direct, Google Scholar, and PubMed were assessed for studies published between 1977 and 2020 using the keywords of review, sodium channels blocker, neurological diseases, and neuronal diseases. VGSCs consist of one α subunit and two β subunits. These subunits are known to regulate the gating kinetics, functional characteristics, and localization of the ion channel. These channels are involved in cell migration, cellular connections, neuronal pathfinding, and neurite outgrowth. Through the VGSC, the action potential is triggered and propagated in the neurons. Action potentials are physiological functions and passage of impermeable ions. The electrophysiological properties of these channels and their relationship with neurological and neuronal disorders have been identified. Subunit mutations are involved in the development of diseases, such as epilepsy, multiple sclerosis, autism, and Alzheimer's disease. Accordingly, we conducted a review of the link between VGSCs and neurological and neuronal diseases. Also, novel therapeutic targets were introduced for future drug discoveries.
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Affiliation(s)
- Shokufeh Bagheri
- Neurophysiology Research Center, Hamadan University of Medical Sciences, Hamadan, Iran.,Department of Neuroscience, School of Science and Advanced Technologies in Medicine, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Rasool Haddadi
- Department of Pharmacology, School of Pharmacy, Hamadan University of Medical Science, Hamadan, Iran
| | - Sahar Saki
- Vice-Chancellor for Research and Technology, Hamadan University of Medical Science, Hamadan, Iran
| | - Masoumeh Kourosh-Arami
- Department of Neuroscience, School of Advanced Technologies in Medicine, Iran University of Medical Sciences, Tehran, Iran
| | - Alireza Komaki
- Neurophysiology Research Center, Hamadan University of Medical Sciences, Hamadan, Iran.,Department of Neuroscience, School of Science and Advanced Technologies in Medicine, Hamadan University of Medical Sciences, Hamadan, Iran
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27
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Chang CW, Evans MD, Yu X, Yu GQ, Mucke L. Tau reduction affects excitatory and inhibitory neurons differently, reduces excitation/inhibition ratios, and counteracts network hypersynchrony. Cell Rep 2021; 37:109855. [PMID: 34686344 PMCID: PMC8648275 DOI: 10.1016/j.celrep.2021.109855] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 08/04/2021] [Accepted: 09/27/2021] [Indexed: 11/27/2022] Open
Abstract
The protein tau has been implicated in many brain disorders. In animal models, tau reduction suppresses epileptogenesis of diverse causes and ameliorates synaptic and behavioral abnormalities in various conditions associated with excessive excitation-inhibition (E/I) ratios. However, the underlying mechanisms are unknown. Global genetic ablation of tau in mice reduces the action potential (AP) firing and E/I ratio of pyramidal cells in acute cortical slices without affecting the excitability of these cells. Tau ablation reduces the excitatory inputs to inhibitory neurons, increases the excitability of these cells, and structurally alters their axon initial segments (AISs). In primary neuronal cultures subjected to prolonged overstimulation, tau ablation diminishes the homeostatic response of AISs in inhibitory neurons, promotes inhibition, and suppresses hypersynchrony. Together, these differential alterations in excitatory and inhibitory neurons help explain how tau reduction prevents network hypersynchrony and counteracts brain disorders causing abnormally increased E/I ratios.
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Affiliation(s)
- Che-Wei Chang
- Gladstone Institute of Neurological Disease, Gladstone Institutes, San Francisco, CA 94158, USA
| | - Mark D Evans
- Gladstone Institute of Neurological Disease, Gladstone Institutes, San Francisco, CA 94158, USA
| | - Xinxing Yu
- Gladstone Institute of Neurological Disease, Gladstone Institutes, San Francisco, CA 94158, USA
| | - Gui-Qiu Yu
- Gladstone Institute of Neurological Disease, Gladstone Institutes, San Francisco, CA 94158, USA
| | - Lennart Mucke
- Gladstone Institute of Neurological Disease, Gladstone Institutes, San Francisco, CA 94158, USA; Department of Neurology and Weill Institute for Neurosciences, University of California, San Francisco, CA 94158, USA.
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28
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The Type 2 Diabetes Factor Methylglyoxal Mediates Axon Initial Segment Shortening and Alters Neuronal Function at the Cellular and Network Levels. eNeuro 2021; 8:ENEURO.0201-21.2021. [PMID: 34531281 PMCID: PMC8496204 DOI: 10.1523/eneuro.0201-21.2021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Revised: 08/23/2021] [Accepted: 09/07/2021] [Indexed: 02/02/2023] Open
Abstract
Recent evidence suggests that alteration of axon initial segment (AIS) geometry (i.e., length or location along the axon) contributes to CNS dysfunction in neurological diseases. For example, AIS length is shorter in the prefrontal cortex of type 2 diabetic mice with cognitive impairment. To determine the key type 2 diabetes-related factor that produces AIS shortening we modified levels of insulin, glucose, or the reactive glucose metabolite methylglyoxal in cultures of dissociated cortices from male and female mice and quantified AIS geometry using immunofluorescent imaging of the AIS proteins AnkyrinG and βIV spectrin. Neither insulin nor glucose modification altered AIS length. Exposure to 100 but not 1 or 10 μm methylglyoxal for 24 h resulted in accumulation of the methylglyoxal-derived advanced glycation end-product hydroimidazolone and produced reversible AIS shortening without cell death. Methylglyoxal-evoked AIS shortening occurred in both excitatory and putative inhibitory neuron populations and in the presence of tetrodotoxin (TTX). In single-cell recordings resting membrane potential was depolarized at 0.5-3 h and returned to normal at 24 h. In multielectrode array (MEA) recordings methylglyoxal produced an immediate ∼300% increase in spiking and bursting rates that returned to normal within 2 min, followed by a ∼20% reduction of network activity at 0.5-3 h and restoration of activity to baseline levels at 24 h. AIS length was unchanged at 0.5-3 h despite the presence of depolarization and network activity reduction. Nevertheless, these results suggest that methylglyoxal could be a key mediator of AIS shortening and disruptor of neuronal function during type 2 diabetes.
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29
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Liang L, Fazel Darbandi S, Pochareddy S, Gulden FO, Gilson MC, Sheppard BK, Sahagun A, An JY, Werling DM, Rubenstein JLR, Sestan N, Bender KJ, Sanders SJ. Developmental dynamics of voltage-gated sodium channel isoform expression in the human and mouse brain. Genome Med 2021; 13:135. [PMID: 34425903 PMCID: PMC8383430 DOI: 10.1186/s13073-021-00949-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2020] [Accepted: 08/05/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Genetic variants in the voltage-gated sodium channels SCN1A, SCN2A, SCN3A, and SCN8A are leading causes of epilepsy, developmental delay, and autism spectrum disorder. The mRNA splicing patterns of all four genes vary across development in the rodent brain, including mutually exclusive copies of the fifth protein-coding exon detected in the neonate (5N) and adult (5A). A second pair of mutually exclusive exons is reported in SCN8A only (18N and 18A). We aimed to quantify the expression of individual exons in the developing human brain. METHODS RNA-seq data from 783 human brain samples across development were analyzed to estimate exon-level expression. Developmental changes in exon utilization were validated by assessing intron splicing. Exon expression was also estimated in RNA-seq data from 58 developing mouse neocortical samples. RESULTS In the mature human neocortex, exon 5A is consistently expressed at least 4-fold higher than exon 5N in all four genes. For SCN2A, SCN3A, and SCN8A, a brain-wide synchronized 5N to 5A transition occurs between 24 post-conceptual weeks (2nd trimester) and 6 years of age. In mice, the equivalent 5N to 5A transition begins at or before embryonic day 15.5. In SCN8A, over 90% of transcripts in the mature human cortex include exon 18A. Early in fetal development, most transcripts include 18N or skip both 18N and 18A, with a transition to 18A inclusion occurring from 13 post-conceptual weeks to 6 months of age. No other protein-coding exons showed comparably dynamic developmental trajectories. CONCLUSIONS Exon usage in SCN1A, SCN2A, SCN3A, and SCN8A changes dramatically during human brain development. These splice isoforms, which alter the biophysical properties of the encoded channels, may account for some of the observed phenotypic differences across development and between specific variants. Manipulation of the proportion of splicing isoforms at appropriate stages of development may act as a therapeutic strategy for specific mutations or even epilepsy in general.
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Affiliation(s)
- Lindsay Liang
- Department of Psychiatry and Behavioral Sciences, UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, 94158, USA
| | - Siavash Fazel Darbandi
- Department of Psychiatry and Behavioral Sciences, UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, 94158, USA
| | - Sirisha Pochareddy
- Department of Neuroscience and Kavli Institute for Neuroscience, Yale School of Medicine, New Haven, CT, 06510, USA
| | - Forrest O Gulden
- Department of Neuroscience and Kavli Institute for Neuroscience, Yale School of Medicine, New Haven, CT, 06510, USA
| | - Michael C Gilson
- Department of Psychiatry and Behavioral Sciences, UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, 94158, USA
| | - Brooke K Sheppard
- Department of Psychiatry and Behavioral Sciences, UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, 94158, USA
| | - Atehsa Sahagun
- Department of Neurology, UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, 94158, USA
| | - Joon-Yong An
- School of Biosystem and Biomedical Science, College of Health Science, Korea University, Seoul, 02841, Republic of Korea
| | - Donna M Werling
- Laboratory of Genetics, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - John L R Rubenstein
- Department of Psychiatry and Behavioral Sciences, UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, 94158, USA
| | - Nenad Sestan
- Department of Neuroscience and Kavli Institute for Neuroscience, Yale School of Medicine, New Haven, CT, 06510, USA
- Program in Cellular Neuroscience, Neurodegeneration, and Repair and Yale Child Study Center, Yale School of Medicine, New Haven, CT, 06510, USA
- Department of Psychiatry, Yale University School of Medicine, New Haven, CT, 06520, USA
- Department of Genetics, Yale University School of Medicine, New Haven, CT, 06520, USA
- Department of Comparative Medicine, Program in Integrative Cell Signaling and Neurobiology of Metabolism, Yale School of Medicine, New Haven, CT, 06510, USA
| | - Kevin J Bender
- Department of Neurology, UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, 94158, USA
| | - Stephan J Sanders
- Department of Psychiatry and Behavioral Sciences, UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, 94158, USA.
- Institute for Human Genetics, University of California, San Francisco, San Francisco, CA, 94158, USA.
- Bakar Computational Health Sciences Institute, University of California, San Francisco, San Francisco, CA, 94158, USA.
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30
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Neural excitability increases with axonal resistance between soma and axon initial segment. Proc Natl Acad Sci U S A 2021; 118:2102217118. [PMID: 34389672 DOI: 10.1073/pnas.2102217118] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The position of the axon initial segment (AIS) is thought to play a critical role in neuronal excitability. Previous experimental studies have found that a distal shift in AIS position correlates with a reduction in excitability. Yet theoretical work has suggested the opposite, because of increased electrical isolation. A distal shift in AIS position corresponds to an elevation of axial resistance R a We therefore examined how changes in R a at the axon hillock impact the voltage threshold (Vth) of the somatic action potential in L5 pyramidal neurons. Increasing R a by mechanically pinching the axon between the soma and the AIS was found to lower Vth by ∼6 mV. Conversely, decreasing R a by substituting internal ions with higher mobility elevated Vth All R a -dependent changes in Vth could be reproduced in a Hodgkin-Huxley compartmental model. We conclude that in L5 pyramidal neurons, excitability increases with axial resistance and therefore with a distal shift of the AIS.
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31
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Fujitani M, Otani Y, Miyajima H. Pathophysiological Roles of Abnormal Axon Initial Segments in Neurodevelopmental Disorders. Cells 2021; 10:2110. [PMID: 34440880 PMCID: PMC8392614 DOI: 10.3390/cells10082110] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Revised: 08/13/2021] [Accepted: 08/15/2021] [Indexed: 11/17/2022] Open
Abstract
The 20-60 μm axon initial segment (AIS) is proximally located at the interface between the axon and cell body. AIS has characteristic molecular and structural properties regulated by the crucial protein, ankyrin-G. The AIS contains a high density of Na+ channels relative to the cell body, which allows low thresholds for the initiation of action potential (AP). Molecular and physiological studies have shown that the AIS is also a key domain for the control of neuronal excitability by homeostatic mechanisms. The AIS has high plasticity in normal developmental processes and pathological activities, such as injury, neurodegeneration, and neurodevelopmental disorders (NDDs). In the first half of this review, we provide an overview of the molecular, structural, and ion-channel characteristics of AIS, AIS regulation through axo-axonic synapses, and axo-glial interactions. In the second half, to understand the relationship between NDDs and AIS, we discuss the activity-dependent plasticity of AIS, the human mutation of AIS regulatory genes, and the pathophysiological role of an abnormal AIS in NDD model animals and patients. We propose that the AIS may provide a potentially valuable structural biomarker in response to abnormal network activity in vivo as well as a new treatment concept at the neural circuit level.
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Affiliation(s)
- Masashi Fujitani
- Department of Anatomy and Neuroscience, Faculty of Medicine, Shimane University, 89-1 Enya-cho, Izumo-shi 693-8501, Shimane, Japan; (Y.O.); (H.M.)
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32
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Zhang J, Chen X, Eaton M, Wu J, Ma Z, Lai S, Park A, Ahmad TS, Que Z, Lee JH, Xiao T, Li Y, Wang Y, Olivero-Acosta MI, Schaber JA, Jayant K, Yuan C, Huang Z, Lanman NA, Skarnes WC, Yang Y. Severe deficiency of the voltage-gated sodium channel Na V1.2 elevates neuronal excitability in adult mice. Cell Rep 2021; 36:109495. [PMID: 34348148 PMCID: PMC8382316 DOI: 10.1016/j.celrep.2021.109495] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Revised: 06/30/2021] [Accepted: 07/14/2021] [Indexed: 12/13/2022] Open
Abstract
Scn2a encodes the voltage-gated sodium channel NaV1.2, a main mediator of neuronal action potential firing. The current paradigm suggests that NaV1.2 gain-of-function variants enhance neuronal excitability, resulting in epilepsy, whereas NaV1.2 deficiency impairs neuronal excitability, contributing to autism. However, this paradigm does not explain why ∼20%-30% of individuals with NaV1.2 deficiency still develop seizures. Here, we report the counterintuitive finding that severe NaV1.2 deficiency results in increased neuronal excitability. Using a NaV1.2-deficient mouse model, we show enhanced intrinsic excitability of principal neurons in the prefrontal cortex and striatum, brain regions known to be involved in Scn2a-related seizures. This increased excitability is autonomous and reversible by genetic restoration of Scn2a expression in adult mice. RNA sequencing reveals downregulation of multiple potassium channels, including KV1.1. Correspondingly, KV channel openers alleviate the hyperexcitability of NaV1.2-deficient neurons. This unexpected neuronal hyperexcitability may serve as a cellular basis underlying NaV1.2 deficiency-related seizures.
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Affiliation(s)
- Jingliang Zhang
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
| | - Xiaoling Chen
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA; Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, USA
| | - Muriel Eaton
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
| | - Jiaxiang Wu
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
| | - Zhixiong Ma
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
| | - Shirong Lai
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
| | - Anthony Park
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
| | - Talha S Ahmad
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
| | - Zhefu Que
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
| | - Ji Hea Lee
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
| | - Tiange Xiao
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
| | - Yuansong Li
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
| | - Yujia Wang
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
| | - Maria I Olivero-Acosta
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA
| | - James A Schaber
- Bioscience Imaging Facility, Bindley Bioscience Center, Purdue University, West Lafayette, IN 47907, USA
| | - Krishna Jayant
- Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA; Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, USA
| | - Chongli Yuan
- Davidson School of Chemical Engineering, Purdue University, West Lafayette, IN 47907, USA
| | - Zhuo Huang
- Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking University Health Science Center, Beijing 100191, China
| | - Nadia A Lanman
- Department of Comparative Pathobiology, Purdue University, West Lafayette, IN 47907, USA; Purdue Center for Cancer Research, Purdue University, West Lafayette, IN 47907, USA
| | - William C Skarnes
- The Jackson Laboratory for Genomic Medicine, Farmington, CT 06032, USA
| | - Yang Yang
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA; Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, IN 47907, USA.
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33
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Quistgaard EM, Nissen JD, Hansen S, Nissen P. Mind the Gap: Molecular Architecture of the Axon Initial Segment - From Fold Prediction to a Mechanistic Model of Function? J Mol Biol 2021; 433:167176. [PMID: 34303720 DOI: 10.1016/j.jmb.2021.167176] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Revised: 07/14/2021] [Accepted: 07/14/2021] [Indexed: 11/28/2022]
Abstract
The axon initial segment (AIS) is a distinct neuronal domain, which is responsible for initiating action potentials, and therefore of key importance to neuronal signaling. To determine how it functions, it is necessary to establish which proteins reside there, how they are organized, and what the dynamic features are. Great strides have been made in recent years, and it is now clear that several AIS cytoskeletal and membrane proteins interact to form a higher-order periodic structure. Here we briefly describe AIS function, protein composition and molecular architecture, and discuss perspectives for future structural characterization, and if structure predictions will be able to model complex higher-order assemblies.
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Affiliation(s)
- Esben M Quistgaard
- DANDRITE - Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Dept. Molecular Biology and Genetics, DK - 8000 Aarhus C, Denmark
| | - Josephine Dannersø Nissen
- DANDRITE - Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Dept. Molecular Biology and Genetics, DK - 8000 Aarhus C, Denmark
| | - Sean Hansen
- DANDRITE - Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Dept. Molecular Biology and Genetics, DK - 8000 Aarhus C, Denmark
| | - Poul Nissen
- DANDRITE - Nordic EMBL Partnership for Molecular Medicine, Aarhus University, Dept. Molecular Biology and Genetics, DK - 8000 Aarhus C, Denmark.
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34
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Plasmalogens regulate the AKT-ULK1 signaling pathway to control the position of the axon initial segment. Prog Neurobiol 2021; 205:102123. [PMID: 34302896 DOI: 10.1016/j.pneurobio.2021.102123] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Revised: 06/11/2021] [Accepted: 07/14/2021] [Indexed: 01/04/2023]
Abstract
The axon initial segment (AIS) is a specialized region in neurons that encompasses two essential functions, the generation of action potentials and the regulation of the axodendritic polarity. The mechanism controlling the position of the axon initial segment to allow plasticity and regulation of neuron excitability is unclear. Here we demonstrate that plasmalogens, the most abundant ether-phospholipid, are essential for the homeostatic positioning of the AIS. Plasmalogen deficiency is a hallmark of Rhizomelic Chondrodysplasia Punctata (RCDP) and Zellweger spectrum disorders, but Alzheimer's and Parkinson's disease, are also characterized by plasmalogen defects. Neurons lacking plasmalogens displaced the AIS to more distal positions and were characterized by reduced excitability. Treatment with a short-chain alkyl glycerol was able to rescue AIS positioning. Plasmalogen deficiency impaired AKT activation, and we show that inhibition of AKT phosphorylation at Ser473 and Thr308 is sufficient to induce a distal relocation of the AIS. Pathway analysis revealed that downstream of AKT, overtly active ULK1 mediates AIS repositioning. Rescuing the impaired AKT signaling pathway was able to normalize AIS position independently of the biochemical defect. These results unveil a previously unknown mechanism that couples the phospholipid composition of the neuronal membrane to the positional assembly of the AIS.
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35
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Zybura A, Hudmon A, Cummins TR. Distinctive Properties and Powerful Neuromodulation of Na v1.6 Sodium Channels Regulates Neuronal Excitability. Cells 2021; 10:cells10071595. [PMID: 34202119 PMCID: PMC8307729 DOI: 10.3390/cells10071595] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 06/20/2021] [Accepted: 06/21/2021] [Indexed: 12/19/2022] Open
Abstract
Voltage-gated sodium channels (Navs) are critical determinants of cellular excitability. These ion channels exist as large heteromultimeric structures and their activity is tightly controlled. In neurons, the isoform Nav1.6 is highly enriched at the axon initial segment and nodes, making it critical for the initiation and propagation of neuronal impulses. Changes in Nav1.6 expression and function profoundly impact the input-output properties of neurons in normal and pathological conditions. While mutations in Nav1.6 may cause channel dysfunction, aberrant changes may also be the result of complex modes of regulation, including various protein-protein interactions and post-translational modifications, which can alter membrane excitability and neuronal firing properties. Despite decades of research, the complexities of Nav1.6 modulation in health and disease are still being determined. While some modulatory mechanisms have similar effects on other Nav isoforms, others are isoform-specific. Additionally, considerable progress has been made toward understanding how individual protein interactions and/or modifications affect Nav1.6 function. However, there is still more to be learned about how these different modes of modulation interact. Here, we examine the role of Nav1.6 in neuronal function and provide a thorough review of this channel’s complex regulatory mechanisms and how they may contribute to neuromodulation.
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Affiliation(s)
- Agnes Zybura
- Program in Medical Neuroscience, Paul and Carole Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, IN 46202, USA;
- Biology Department, School of Science, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202, USA
| | - Andy Hudmon
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA;
| | - Theodore R. Cummins
- Program in Medical Neuroscience, Paul and Carole Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, IN 46202, USA;
- Biology Department, School of Science, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202, USA
- Correspondence:
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36
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Franken TP, Bondy BJ, Haimes DB, Goldwyn JH, Golding NL, Smith PH, Joris PX. Glycinergic axonal inhibition subserves acute spatial sensitivity to sudden increases in sound intensity. eLife 2021; 10:62183. [PMID: 34121662 PMCID: PMC8238506 DOI: 10.7554/elife.62183] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Accepted: 06/12/2021] [Indexed: 11/20/2022] Open
Abstract
Locomotion generates adventitious sounds which enable detection and localization of predators and prey. Such sounds contain brisk changes or transients in amplitude. We investigated the hypothesis that ill-understood temporal specializations in binaural circuits subserve lateralization of such sound transients, based on different time of arrival at the ears (interaural time differences, ITDs). We find that Lateral Superior Olive (LSO) neurons show exquisite ITD-sensitivity, reflecting extreme precision and reliability of excitatory and inhibitory postsynaptic potentials, in contrast to Medial Superior Olive neurons, traditionally viewed as the ultimate ITD-detectors. In vivo, inhibition blocks LSO excitation over an extremely short window, which, in vitro, required synaptically evoked inhibition. Light and electron microscopy revealed inhibitory synapses on the axon initial segment as the structural basis of this observation. These results reveal a neural vetoing mechanism with extreme temporal and spatial precision and establish the LSO as the primary nucleus for binaural processing of sound transients.
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Affiliation(s)
- Tom P Franken
- Department of Neurosciences, Katholieke Universiteit Leuven, Leuven, Belgium.,Systems Neurobiology Laboratory, The Salk Institute for Biological Studies, La Jolla, United States
| | - Brian J Bondy
- Department of Neuroscience, University of Texas at Austin, Austin, United States
| | - David B Haimes
- Department of Neuroscience, University of Texas at Austin, Austin, United States
| | - Joshua H Goldwyn
- Department of Mathematics and Statistics, Swarthmore College, Swarthmore, United States
| | - Nace L Golding
- Department of Neuroscience, University of Texas at Austin, Austin, United States
| | - Philip H Smith
- Department of Neuroscience, University of Wisconsin-Madison, Madison, United States
| | - Philip X Joris
- Department of Neurosciences, Katholieke Universiteit Leuven, Leuven, Belgium
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37
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Goethals S, Sierksma MC, Nicol X, Réaux-Le Goazigo A, Brette R. Electrical match between initial segment and somatodendritic compartment for action potential backpropagation in retinal ganglion cells. J Neurophysiol 2021; 126:28-46. [PMID: 34038184 DOI: 10.1152/jn.00005.2021] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The action potential of most vertebrate neurons initiates in the axon initial segment (AIS) and is then transmitted to the soma where it is regenerated by somatodendritic sodium channels. For successful transmission, the AIS must produce a strong axial current, so as to depolarize the soma to the threshold for somatic regeneration. Theoretically, this axial current depends on AIS geometry and Na+ conductance density. We measured the axial current of mouse retinal ganglion cells using whole cell recordings with post hoc AIS labeling. We found that this current is large, implying high Na+ conductance density, and carries a charge that covaries with capacitance so as to depolarize the soma by ∼30 mV. Additionally, we observed that the axial current attenuates strongly with depolarization, consistent with sodium channel inactivation, but temporally broadens so as to preserve the transmitted charge. Thus, the AIS appears to be organized so as to reliably backpropagate the axonal action potential.NEW & NOTEWORTHY We measured the axial current produced at spike initiation by the axon initial segment of mouse retinal ganglion cells. We found that it is a large current, requiring high sodium channel conductance density, which covaries with cell capacitance so as to ensure a ∼30 mV depolarization. During sustained depolarization the current attenuated, but it broadened to preserve somatic depolarization. Thus, properties of the initial segment are adjusted to ensure backpropagation of the axonal action potential.
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Affiliation(s)
- Sarah Goethals
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
| | - Martijn C Sierksma
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France.,Department of Neuroscience, Erasmus MC, Erasmus University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Xavier Nicol
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
| | | | - Romain Brette
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
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38
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Lipkin AM, Cunniff MM, Spratt PWE, Lemke SM, Bender KJ. Functional Microstructure of Ca V-Mediated Calcium Signaling in the Axon Initial Segment. J Neurosci 2021; 41:3764-3776. [PMID: 33731449 PMCID: PMC8084313 DOI: 10.1523/jneurosci.2843-20.2021] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 02/15/2021] [Accepted: 03/09/2021] [Indexed: 01/12/2023] Open
Abstract
The axon initial segment (AIS) is a specialized neuronal compartment in which synaptic input is converted into action potential (AP) output. This process is supported by a diverse complement of sodium, potassium, and calcium channels (CaV). Different classes of sodium and potassium channels are scaffolded at specific sites within the AIS, conferring unique functions, but how calcium channels are functionally distributed within the AIS is unclear. Here, we use conventional two-photon laser scanning and diffraction-limited, high-speed spot two-photon imaging to resolve AP-evoked calcium dynamics in the AIS with high spatiotemporal resolution. In mouse layer 5 prefrontal pyramidal neurons, calcium influx was mediated by a mix of CaV2 and CaV3 channels that differentially localized to discrete regions. CaV3 functionally localized to produce nanodomain hotspots of calcium influx that coupled to ryanodine-sensitive stores, whereas CaV2 localized to non-hotspot regions. Thus, different pools of CaVs appear to play distinct roles in AIS function.SIGNIFICANCE STATEMENT The axon initial segment (AIS) is the site where synaptic input is transformed into action potential (AP) output. It achieves this function through a diverse complement of sodium, potassium, and calcium channels (CaV). While the localization and function of sodium channels and potassium channels at the AIS is well described, less is known about the functional distribution of CaVs. We used high-speed two-photon imaging to understand activity-dependent calcium dynamics in the AIS of mouse neocortical pyramidal neurons. Surprisingly, we found that calcium influx occurred in two distinct domains: CaV3 generates hotspot regions of calcium influx coupled to calcium stores, whereas CaV2 channels underlie diffuse calcium influx between hotspots. Therefore, different CaV classes localize to distinct AIS subdomains, possibly regulating distinct cellular processes.
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Affiliation(s)
- Anna M Lipkin
- Neuroscience Graduate Program, University of California, San Francisco, California 94158
| | - Margaret M Cunniff
- Neuroscience Graduate Program, University of California, San Francisco, California 94158
| | - Perry W E Spratt
- Neuroscience Graduate Program, University of California, San Francisco, California 94158
| | - Stefan M Lemke
- Neuroscience Graduate Program, University of California, San Francisco, California 94158
| | - Kevin J Bender
- Neuroscience Graduate Program, University of California, San Francisco, California 94158
- Department of Neurology, Kavli Institute for Fundamental Neuroscience, Weill Institute for Neurosciences, University of California, San Francisco, California 94158
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39
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Liu W, Luque M, Li H, Schrott-Fischer A, Glueckert R, Tylstedt S, Rajan G, Ladak H, Agrawal S, Rask-Andersen H. Spike Generators and Cell Signaling in the Human Auditory Nerve: An Ultrastructural, Super-Resolution, and Gene Hybridization Study. Front Cell Neurosci 2021; 15:642211. [PMID: 33796009 PMCID: PMC8008129 DOI: 10.3389/fncel.2021.642211] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Accepted: 02/22/2021] [Indexed: 11/23/2022] Open
Abstract
Background: The human auditory nerve contains 30,000 nerve fibers (NFs) that relay complex speech information to the brain with spectacular acuity. How speech is coded and influenced by various conditions is not known. It is also uncertain whether human nerve signaling involves exclusive proteins and gene manifestations compared with that of other species. Such information is difficult to determine due to the vulnerable, "esoteric," and encapsulated human ear surrounded by the hardest bone in the body. We collected human inner ear material for nanoscale visualization combining transmission electron microscopy (TEM), super-resolution structured illumination microscopy (SR-SIM), and RNA-scope analysis for the first time. Our aim was to gain information about the molecular instruments in human auditory nerve processing and deviations, and ways to perform electric modeling of prosthetic devices. Material and Methods: Human tissue was collected during trans-cochlear procedures to remove petro-clival meningioma after ethical permission. Cochlear neurons were processed for electron microscopy, confocal microscopy (CM), SR-SIM, and high-sensitive in situ hybridization for labeling single mRNA transcripts to detect ion channel and transporter proteins associated with nerve signal initiation and conductance. Results: Transport proteins and RNA transcripts were localized at the subcellular level. Hemi-nodal proteins were identified beneath the inner hair cells (IHCs). Voltage-gated ion channels (VGICs) were expressed in the spiral ganglion (SG) and axonal initial segments (AISs). Nodes of Ranvier (NR) expressed Nav1.6 proteins, and encoding genes critical for inter-cellular coupling were disclosed. Discussion: Our results suggest that initial spike generators are located beneath the IHCs in humans. The first NRs appear at different places. Additional spike generators and transcellular communication may boost, sharpen, and synchronize afferent signals by cell clusters at different frequency bands. These instruments may be essential for the filtering of complex sounds and may be challenged by various pathological conditions.
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Affiliation(s)
- Wei Liu
- Section of Otolaryngology, Department of Surgical Sciences, Head and Neck Surgery, Uppsala University Hospital, Uppsala, Sweden
| | - Maria Luque
- Department of Otorhinolaryngology, Medical University of Innsbruck, Innsbruck, Austria
| | - Hao Li
- Section of Otolaryngology, Department of Surgical Sciences, Head and Neck Surgery, Uppsala University Hospital, Uppsala, Sweden
| | | | - Rudolf Glueckert
- Department of Otorhinolaryngology, Medical University of Innsbruck, Innsbruck, Austria
| | - Sven Tylstedt
- Department of Olaryngology, Västerviks Hospital, Västervik, Sweden
| | - Gunesh Rajan
- Department of Otolaryngology, Head & Neck Surgery, Luzerner Kantonsspital, Luzern, Switzerland
- Department of Otolaryngology, Head & Neck Surgery, Division of Surgery, Medical School, University of Western Australia, Perth, WA, Australia
| | - Hanif Ladak
- Department of Otolaryngology-Head and Neck Surgery, Department of Medical Biophysics and Department of Electrical and Computer Engineering, Western University, London, ON, Canada
| | - Sumit Agrawal
- Department of Otolaryngology-Head and Neck Surgery, Western University, London, ON, Canada
| | - Helge Rask-Andersen
- Section of Otolaryngology, Department of Surgical Sciences, Head and Neck Surgery, Uppsala University Hospital, Uppsala, Sweden
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40
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Galliano E, Hahn C, Browne LP, R Villamayor P, Tufo C, Crespo A, Grubb MS. Brief Sensory Deprivation Triggers Cell Type-Specific Structural and Functional Plasticity in Olfactory Bulb Neurons. J Neurosci 2021; 41:2135-2151. [PMID: 33483429 PMCID: PMC8018761 DOI: 10.1523/jneurosci.1606-20.2020] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Revised: 11/11/2020] [Accepted: 11/17/2020] [Indexed: 02/03/2023] Open
Abstract
Can alterations in experience trigger different plastic modifications in neuronal structure and function, and if so, how do they integrate at the cellular level? To address this question, we interrogated circuitry in the mouse olfactory bulb responsible for the earliest steps in odor processing. We induced experience-dependent plasticity in mice of either sex by blocking one nostril for one day, a minimally invasive manipulation that leaves the sensory organ undamaged and is akin to the natural transient blockage suffered during common mild rhinal infections. We found that such brief sensory deprivation produced structural and functional plasticity in one highly specialized bulbar cell type: axon-bearing dopaminergic neurons in the glomerular layer. After 24 h naris occlusion, the axon initial segment (AIS) in bulbar dopaminergic neurons became significantly shorter, a structural modification that was also associated with a decrease in intrinsic excitability. These effects were specific to the AIS-positive dopaminergic subpopulation because no experience-dependent alterations in intrinsic excitability were observed in AIS-negative dopaminergic cells. Moreover, 24 h naris occlusion produced no structural changes at the AIS of bulbar excitatory neurons, mitral/tufted and external tufted cells, nor did it alter their intrinsic excitability. By targeting excitability in one specialized dopaminergic subpopulation, experience-dependent plasticity in early olfactory networks might act to fine-tune sensory processing in the face of continually fluctuating inputs.SIGNIFICANCE STATEMENT Sensory networks need to be plastic so they can adapt to changes in incoming stimuli. To see how cells in mouse olfactory circuits can change in response to sensory challenges, we blocked a nostril for just one day, a naturally relevant manipulation akin to the deprivation that occurs with a mild cold. We found that this brief deprivation induces forms of axonal and intrinsic functional plasticity in one specific olfactory bulb cell subtype: axon-bearing dopaminergic interneurons. In contrast, intrinsic properties of axon-lacking bulbar dopaminergic neurons and neighboring excitatory neurons remained unchanged. Within the same sensory circuits, specific cell types can therefore make distinct plastic changes in response to an ever-changing external landscape.
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Affiliation(s)
- Elisa Galliano
- Centre for Developmental Neurobiology, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, SE1 1UL, United Kingdom
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, CB2 3DY, United Kingdom
| | - Christiane Hahn
- Centre for Developmental Neurobiology, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, SE1 1UL, United Kingdom
| | - Lorcan P Browne
- Centre for Developmental Neurobiology, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, SE1 1UL, United Kingdom
| | - Paula R Villamayor
- Centre for Developmental Neurobiology, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, SE1 1UL, United Kingdom
| | - Candida Tufo
- Centre for Developmental Neurobiology, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, SE1 1UL, United Kingdom
| | - Andres Crespo
- Centre for Developmental Neurobiology, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, SE1 1UL, United Kingdom
| | - Matthew S Grubb
- Centre for Developmental Neurobiology, Institute of Psychiatry, Psychology & Neuroscience, King's College London, London, SE1 1UL, United Kingdom
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41
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Zhao YF, Tang Y, Illes P. Astrocytic and Oligodendrocytic P2X7 Receptors Determine Neuronal Functions in the CNS. Front Mol Neurosci 2021; 14:641570. [PMID: 33642994 PMCID: PMC7906075 DOI: 10.3389/fnmol.2021.641570] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Accepted: 01/19/2021] [Indexed: 12/20/2022] Open
Abstract
P2X7 receptors are members of the ATP-gated cationic channel family with a preferential localization at the microglial cells, the resident macrophages of the brain. However, these receptors are also present at neuroglia (astrocytes, oligodendrocytes) although at a considerably lower density. They mediate necrosis/apoptosis by the release of pro-inflammatory cytokines/chemokines, reactive oxygen species (ROS) as well as the excitotoxic (glio)transmitters glutamate and ATP. Besides mediating cell damage i.e., superimposed upon chronic neurodegenerative processes in Alzheimer’s Disease, Parkinson’s Disease, multiple sclerosis, and amyotrophic lateral sclerosis, they may also participate in neuroglial signaling to neurons under conditions of high ATP concentrations during any other form of neuroinflammation/neurodegeneration. It is a pertinent open question whether P2X7Rs are localized on neurons, or whether only neuroglia/microglia possess this receptor-type causing indirect effects by releasing the above-mentioned signaling molecules. We suggest as based on molecular biology and functional evidence that neurons are devoid of P2X7Rs although the existence of neuronal P2X7Rs cannot be excluded with absolute certainty.
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Affiliation(s)
- Ya-Fei Zhao
- School of Acupuncture and Tuina, Chengdu University of Traditional Chinese Medicine, Chengdu, China
| | - Yong Tang
- School of Acupuncture and Tuina, Chengdu University of Traditional Chinese Medicine, Chengdu, China.,International Collaborative Center on Big Science Plan for Purine Signaling, Chengdu University of Traditional Chinese Medicine, Chengdu, China
| | - Peter Illes
- School of Acupuncture and Tuina, Chengdu University of Traditional Chinese Medicine, Chengdu, China.,International Collaborative Center on Big Science Plan for Purine Signaling, Chengdu University of Traditional Chinese Medicine, Chengdu, China.,Rudolf Boehm Institute for Pharmacology and Toxicology, University of Leipzig, Leipzig, Germany
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42
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Stone MC, Kothe GO, Rolls MM, Jegla T. Cytoskeletal and synaptic polarity of LWamide-like+ ganglion neurons in the sea anemone Nematostella vectensis. J Exp Biol 2020; 223:jeb233197. [PMID: 32968001 PMCID: PMC7673360 DOI: 10.1242/jeb.233197] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2020] [Accepted: 09/14/2020] [Indexed: 12/22/2022]
Abstract
The centralized nervous systems of bilaterian animals rely on directional signaling facilitated by polarized neurons with specialized axons and dendrites. It is not known whether axo-dendritic polarity is exclusive to bilaterians or was already present in early metazoans. We therefore examined neurite polarity in the starlet sea anemone Nematostella vectensis (Cnidaria). Cnidarians form a sister clade to bilaterians and share many neuronal building blocks characteristic of bilaterians, including channels, receptors and synaptic proteins, but their nervous systems comprise a comparatively simple net distributed throughout the body. We developed a tool kit of fluorescent polarity markers for live imaging analysis of polarity in an identified neuron type, large ganglion cells of the body column nerve net that express the LWamide-like neuropeptide. Microtubule polarity differs in bilaterian axons and dendrites, and this in part underlies polarized distribution of cargo to the two types of processes. However, in LWamide-like+ neurons, all neurites had axon-like microtubule polarity suggesting that they may have similar contents. Indeed, presynaptic and postsynaptic markers trafficked to all neurites and accumulated at varicosities where neurites from different neurons often crossed, suggesting the presence of bidirectional synaptic contacts. Furthermore, we could not identify a diffusion barrier in the plasma membrane of any of the neurites like the axon initial segment barrier that separates the axonal and somatodendritic compartments in bilaterian neurons. We conclude that at least one type of neuron in Nematostella vectensis lacks the axo-dendritic polarity characteristic of bilaterian neurons.
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Affiliation(s)
- Michelle C Stone
- Department of Biochemistry and Molecular Biology and the Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA
| | - Gregory O Kothe
- Department of Biochemistry and Molecular Biology and the Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA
| | - Melissa M Rolls
- Department of Biochemistry and Molecular Biology and the Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA
| | - Timothy Jegla
- Department of Biology and the Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA
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43
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Petrone P, Giordano G, Vezzoli E, Pensa A, Castaldo G, Graziano V, Sirano F, Capasso E, Quaremba G, Vona A, Miano MG, Savino S, Niola M. Preservation of neurons in an AD 79 vitrified human brain. PLoS One 2020; 15:e0240017. [PMID: 33022024 PMCID: PMC7537897 DOI: 10.1371/journal.pone.0240017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Accepted: 09/17/2020] [Indexed: 12/03/2022] Open
Abstract
Detecting the ultrastructure of brain tissue in human archaeological remains is a rare event that can offer unique insights into the structure of the ancient central nervous system (CNS). Yet ancient brains reported in the literature show only poor preservation of neuronal structures. Using scanning electron microscopy (SEM) and advanced image processing tools, we describe the direct visualization of neuronal tissue in vitrified brain and spinal cord remains which we discovered in a male victim of the AD 79 eruption in Herculaneum. We show exceptionally well preserved ancient neurons from different regions of the human CNS at unprecedented resolution. This tissue typically consists of organic matter, as detected using energy-dispersive X-ray spectroscopy. By means of a self-developed neural image processing network, we also show specific details of the neuronal nanomorphology, like the typical myelin periodicity evidenced in the brain axons. The perfect state of preservation of these structures is due to the unique process of vitrification which occurred at Herculaneum. The discovery of proteins whose genes are expressed in the different region of the human adult brain further agree with the neuronal origin of the unusual archaeological find. The conversion of human tissue into glass is the result of sudden exposure to scorching volcanic ash and the concomitant rapid drop in temperature. The eruptive-induced process of natural vitrification, locking the cellular structure of the CNS, allowed us to study possibly the best known example in archaeology of extraordinarily well-preserved human neuronal tissue from the brain and spinal cord.
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Affiliation(s)
- Pierpaolo Petrone
- Dipartimento di Scienze Biomediche Avanzate, Università di Napoli Federico II, Naples, Italy
| | - Guido Giordano
- Dipartimento di Scienze, Università degli Studi Roma Tre, Rome, Italy
| | - Elena Vezzoli
- Dipartimento di Scienze Biomediche per la Salute, Università di Milano, Milan, Italy
| | - Alessandra Pensa
- Dipartimento di Scienze, Università degli Studi Roma Tre, Rome, Italy
| | | | - Vincenzo Graziano
- Dipartimento di Scienze Biomediche Avanzate, Università di Napoli Federico II, Naples, Italy
| | | | - Emanuele Capasso
- Dipartimento di Scienze Biomediche Avanzate, Università di Napoli Federico II, Naples, Italy
| | - Giuseppe Quaremba
- Dipartimento di Scienze Biomediche Avanzate, Università di Napoli Federico II, Naples, Italy
- Dipartimento di Ingegneria Industriale, Università di Napoli Federico II, Naples, Italy
| | - Alessandro Vona
- Dipartimento di Scienze, Università degli Studi Roma Tre, Rome, Italy
| | - Maria Giuseppina Miano
- Istituto di Genetica e Biofisica "Adriano Buzzati-Traverso”, Consiglio Nazionale delle Ricerche (CNR), Naples, Italy
| | - Sergio Savino
- Dipartimento di Ingegneria Industriale, Università di Napoli Federico II, Naples, Italy
| | - Massimo Niola
- Dipartimento di Scienze Biomediche Avanzate, Università di Napoli Federico II, Naples, Italy
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Werginz P, Raghuram V, Fried SI. Tailoring of the axon initial segment shapes the conversion of synaptic inputs into spiking output in OFF-α T retinal ganglion cells. SCIENCE ADVANCES 2020; 6:6/37/eabb6642. [PMID: 32917708 PMCID: PMC7486099 DOI: 10.1126/sciadv.abb6642] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Accepted: 07/29/2020] [Indexed: 06/11/2023]
Abstract
Recently, mouse OFF-α transient (OFF-α T) retinal ganglion cells (RGCs) were shown to display a gradient of light responses as a function of position along the dorsal-ventral axis; response differences were correlated to differences in the level of excitatory presynaptic input. Here, we show that postsynaptic differences between cells also make a strong contribution to response differences. Cells in the dorsal retina had longer axon initial segments (AISs)-the greater number of Nav1.6 channels in longer AISs directly mediates higher rates of spiking and helps avoid depolarization block that terminates spiking in ventral cells with shorter AISs. The pre- and postsynaptic specializations that shape the output of OFF-α T RGCs interact in different ways: In dorsal cells, strong inputs and the long AISs are both necessary to generate their strong, sustained spiking outputs, while in ventral cells, weak inputs or the short AISs are both sufficient to limit the spiking signal.
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Affiliation(s)
- Paul Werginz
- Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
- Institute for Analysis and Scientific Computing, Vienna University of Technology, 1040 Vienna, Austria
| | - Vineeth Raghuram
- Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
- Boston VA Healthcare System, Rehabilitation, Research and Development, Boston, MA 02130, USA
- Department of Biomedical Engineering, Tufts University, Medford, MA 02155, USA
| | - Shelley I Fried
- Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
- Boston VA Healthcare System, Rehabilitation, Research and Development, Boston, MA 02130, USA
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45
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Werginz P, Raghuram V, Fried SI. The relationship between morphological properties and thresholds to extracellular electric stimulation in α RGCs. J Neural Eng 2020; 17:045015. [PMID: 32736374 DOI: 10.1088/1741-2552/abab47] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
OBJECTIVE Retinal prostheses strive to restore vison to patients that are blind from retinal degeneration by electrically stimulating surviving retinal ganglion cells (RGCs). The quality of elicited percepts remains limited however and it is desirable to develop improved stimulation strategies. Here, we examine how the anatomical and biophysical properties of RGCs influence activation thresholds, including the effects of variations found naturally. APPROACH Detailed reconstructions were made of a large number of mouse α RGCs and were used to create an array of model cells; the models were used to study the effects of individual anatomical features on activation threshold to electric stimulation. Stimulation was delivered epiretinally from a point-source or disk electrode and consisted of monophasic or biphasic rectangular pulses. MAIN RESULTS Modeling results show that the region of minimum threshold always is within the axon initial segment (AIS). The properties of this region as well as the absolute value of the minimum threshold are dependent on the length of the AIS as well as on the relative composition of sodium channels within the AIS. Other morphological features, including cell size, dendritic field size and the distance between the AIS and the soma had only a minimal influence on thresholds. Introducing even a small number of low-threshold Nav1.6 channels into the AIS was sufficient to lower minimum thresholds substantially although further increases in Nav1.6 had diminishing effects. The distance between the AIS and the electrode affects threshold levels while alignment of the electrode with the axon or dendritic parts of the RGC can result in lower thresholds, even if the distance to the cell remains the same. SIGNIFICANCE Intrinsic morphological features can influence activation thresholds with the AIS having the strongest influence. However, the combined influence remains limited and may not be large enough to allow for selective activation between different RGC types.
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Affiliation(s)
- Paul Werginz
- Institute for Analysis and Scientific Computing, Vienna University of Technology, Vienna, Austria. Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States of America. Author to whom any correspondence should be addressed
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Benedetti B, Dannehl D, Janssen JM, Corcelli C, Couillard-Després S, Engelhardt M. Structural and Functional Maturation of Rat Primary Motor Cortex Layer V Neurons. Int J Mol Sci 2020; 21:E6101. [PMID: 32847128 PMCID: PMC7503395 DOI: 10.3390/ijms21176101] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Revised: 08/13/2020] [Accepted: 08/22/2020] [Indexed: 11/22/2022] Open
Abstract
Rodent neocortical neurons undergo prominent postnatal development and maturation. The process is associated with structural and functional maturation of the axon initial segment (AIS), the site of action potential initiation. In this regard, cell size and optimal AIS length are interconnected. In sensory cortices, developmental onset of sensory input and consequent changes in network activity cause phasic AIS plasticity that can also control functional output. In non-sensory cortices, network input driving phasic events should be less prominent. We, therefore, explored the relationship between postnatal functional maturation and AIS maturation in principal neurons of the primary motor cortex layer V (M1LV), a non-sensory area of the rat brain. We hypothesized that a rather continuous process of AIS maturation and elongation would reflect cell growth, accompanied by progressive refinement of functional output properties. We found that, in the first two postnatal weeks, cell growth prompted substantial decline of neuronal input resistance, such that older neurons needed larger input current to reach rheobase and fire action potentials. In the same period, we observed the most prominent AIS elongation and significant maturation of functional output properties. Alternating phases of AIS plasticity did not occur, and changes in functional output properties were largely justified by AIS elongation. From the third postnatal week up to five months of age, cell growth, AIS elongation, and functional output maturation were marginal. Thus, AIS maturation in M1LV is a continuous process that attunes the functional output of pyramidal neurons and associates with early postnatal development to counterbalance increasing electrical leakage due to cell growth.
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Affiliation(s)
- Bruno Benedetti
- Spinal Cord Injury and Tissue Regeneration Center Salzburg (SCI-TReCS), 5020 Salzburg, Austria; (D.D.); (S.C.-D.)
- Institute of Experimental Neuroregeneration, Paracelsus Medical University, 5020 Salzburg, Austria
- Austrian Cluster for Tissue Regeneration, 1000 Vienna, Austria
| | - Dominik Dannehl
- Spinal Cord Injury and Tissue Regeneration Center Salzburg (SCI-TReCS), 5020 Salzburg, Austria; (D.D.); (S.C.-D.)
- Institute of Experimental Neuroregeneration, Paracelsus Medical University, 5020 Salzburg, Austria
- Institute of Neuroanatomy, Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany; (J.M.J.); (C.C.)
- Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
| | - Jan Maximilian Janssen
- Institute of Neuroanatomy, Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany; (J.M.J.); (C.C.)
- Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
| | - Corinna Corcelli
- Institute of Neuroanatomy, Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany; (J.M.J.); (C.C.)
- Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
| | - Sébastien Couillard-Després
- Spinal Cord Injury and Tissue Regeneration Center Salzburg (SCI-TReCS), 5020 Salzburg, Austria; (D.D.); (S.C.-D.)
- Institute of Experimental Neuroregeneration, Paracelsus Medical University, 5020 Salzburg, Austria
- Austrian Cluster for Tissue Regeneration, 1000 Vienna, Austria
| | - Maren Engelhardt
- Institute of Neuroanatomy, Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany; (J.M.J.); (C.C.)
- Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, 68167 Mannheim, Germany
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Lipkin AM, Bender KJ. Flipping the Switch: Homeostatic Tuning of Chandelier Synapses Follows Developmental Changes in GABA Polarity. Neuron 2020; 106:199-201. [PMID: 32325052 DOI: 10.1016/j.neuron.2020.03.036] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Homeostatic plasticity rules are well described for glutamatergic synapses but less clear for GABAergic synapses. In this issue of Neuron, Pan-Vazquez et al. (2020) leverage the precise targeting of chandelier-to-pyramidal cell connectivity to understand how homeostatic plasticity regulates GABAergic synapses, showing that these synapses maintain homeostatic rules even as they flip from exciting to inhibiting pyramidal cells.
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Affiliation(s)
- Anna M Lipkin
- Neuroscience Graduate Program, University of California, San Francisco, San Francisco, CA, USA; Weill Institute for Neurosciences, Kavli Institute for Fundamental Neuroscience, Department of Neurology, University of California, San Francisco, San Francisco, CA, USA
| | - Kevin J Bender
- Weill Institute for Neurosciences, Kavli Institute for Fundamental Neuroscience, Department of Neurology, University of California, San Francisco, San Francisco, CA, USA.
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48
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Park DI. Genomics, transcriptomics, proteomics and big data analysis in the discovery of new diagnostic markers and targets for therapy development. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2020; 173:61-90. [PMID: 32711818 DOI: 10.1016/bs.pmbts.2020.04.017] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Highly complex endophenotypes and underlying molecular mechanisms have prevented effective diagnosis and treatment of autism spectrum disorder. Despite extensive studies to identify relevant biosignatures, no biomarker and therapeutic targets are available in the current clinical practice. While our current knowledge is still largely incomplete, -omics technology and machine learning-based big data analysis have provided novel insights on the etiology of autism spectrum disorders, elucidating systemic impairments that can be translated into biomarker and therapy target candidates. However, more integrated and sophisticated approaches are vital to realize molecular stratification and individualized treatment strategy. Ultimately, systemic approaches based on -omics and big data analysis will significantly contribute to more effective biomarker and therapy development for autism spectrum disorder.
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Affiliation(s)
- Dong Ik Park
- Danish Research Institute of Translational Neuroscience (DANDRITE)-Nordic EMBL Partnership for Molecular Medicine, Department of Biomedicine, Aarhus University, Aarhus, Denmark; The Danish National Research Foundation Center, PROMEMO, Department of Biomedicine, Aarhus University, Aarhus, Denmark.
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49
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Kruth KA, Grisolano TM, Ahern CA, Williams AJ. SCN2A channelopathies in the autism spectrum of neuropsychiatric disorders: a role for pluripotent stem cells? Mol Autism 2020; 11:23. [PMID: 32264956 PMCID: PMC7140374 DOI: 10.1186/s13229-020-00330-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Accepted: 03/25/2020] [Indexed: 12/12/2022] Open
Abstract
Efforts to identify the causes of autism spectrum disorders have highlighted the importance of both genetics and environment, but the lack of human models for many of these disorders limits researchers’ attempts to understand the mechanisms of disease and to develop new treatments. Induced pluripotent stem cells offer the opportunity to study specific genetic and environmental risk factors, but the heterogeneity of donor genetics may obscure important findings. Diseases associated with unusually high rates of autism, such as SCN2A syndromes, provide an opportunity to study specific mutations with high effect sizes in a human genetic context and may reveal biological insights applicable to more common forms of autism. Loss-of-function mutations in the SCN2A gene, which encodes the voltage-gated sodium channel NaV1.2, are associated with autism rates up to 50%. Here, we review the findings from experimental models of SCN2A syndromes, including mouse and human cell studies, highlighting the potential role for patient-derived induced pluripotent stem cell technology to identify the molecular and cellular substrates of autism.
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Affiliation(s)
- Karina A Kruth
- Department of Psychiatry, Iowa Neuroscience Institute, University of Iowa, 169 Newton Rd, 2326 PBDB, Iowa City, IA, 52242, USA
| | - Tierney M Grisolano
- Department of Molecular Physiology and Biophysics, Iowa Neuroscience Institute, University of Iowa, 169 Newton Rd, 2312 PBDB, Iowa City, IA, 52242, USA
| | - Christopher A Ahern
- Department of Molecular Physiology and Biophysics, Iowa Neuroscience Institute, University of Iowa, 169 Newton Rd, 2312 PBDB, Iowa City, IA, 52242, USA
| | - Aislinn J Williams
- Department of Psychiatry, Iowa Neuroscience Institute, University of Iowa, 169 Newton Rd, 2326 PBDB, Iowa City, IA, 52242, USA.
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50
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Goethals S, Brette R. Theoretical relation between axon initial segment geometry and excitability. eLife 2020; 9:53432. [PMID: 32223890 PMCID: PMC7170651 DOI: 10.7554/elife.53432] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2019] [Accepted: 03/30/2020] [Indexed: 12/29/2022] Open
Abstract
In most vertebrate neurons, action potentials are triggered at the distal end of the axon initial segment (AIS). Both position and length of the AIS vary across and within neuron types, with activity, development and pathology. What is the impact of AIS geometry on excitability? Direct empirical assessment has proven difficult because of the many potential confounding factors. Here, we carried a principled theoretical analysis to answer this question. We provide a simple formula relating AIS geometry and sodium conductance density to the somatic voltage threshold. A distal shift of the AIS normally produces a (modest) increase in excitability, but we explain how this pattern can reverse if a hyperpolarizing current is present at the AIS, due to resistive coupling with the soma. This work provides a theoretical tool to assess the significance of structural AIS plasticity for electrical function.
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Affiliation(s)
- Sarah Goethals
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
| | - Romain Brette
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
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