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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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2
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Barlow BSM, Longtin A, Joós B. Impact on backpropagation of the spatial heterogeneity of sodium channel kinetics in the axon initial segment. PLoS Comput Biol 2024; 20:e1011846. [PMID: 38489374 PMCID: PMC10942053 DOI: 10.1371/journal.pcbi.1011846] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Accepted: 01/21/2024] [Indexed: 03/17/2024] Open
Abstract
In a variety of neurons, action potentials (APs) initiate at the proximal axon, within a region called the axon initial segment (AIS), which has a high density of voltage-gated sodium channels (NaVs) on its membrane. In pyramidal neurons, the proximal AIS has been reported to exhibit a higher proportion of NaVs with gating properties that are "right-shifted" to more depolarized voltages, compared to the distal AIS. Further, recent experiments have revealed that as neurons develop, the spatial distribution of NaV subtypes along the AIS can change substantially, suggesting that neurons tune their excitability by modifying said distribution. When neurons are stimulated axonally, computational modelling has shown that this spatial separation of gating properties in the AIS enhances the backpropagation of APs into the dendrites. In contrast, in the more natural scenario of somatic stimulation, our simulations show that the same distribution can impede backpropagation, suggesting that the choice of orthodromic versus antidromic stimulation can bias or even invert experimental findings regarding the role of NaV subtypes in the AIS. We implemented a range of hypothetical NaV distributions in the AIS of three multicompartmental pyramidal cell models and investigated the precise kinetic mechanisms underlying such effects, as the spatial distribution of NaV subtypes is varied. With axonal stimulation, proximal NaV availability dominates, such that concentrating right-shifted NaVs in the proximal AIS promotes backpropagation. However, with somatic stimulation, the models are insensitive to availability kinetics. Instead, the higher activation threshold of right-shifted NaVs in the AIS impedes backpropagation. Therefore, recently observed developmental changes to the spatial separation and relative proportions of NaV1.2 and NaV1.6 in the AIS differentially impact activation and availability. The observed effects on backpropagation, and potentially learning via its putative role in synaptic plasticity (e.g. through spike-timing-dependent plasticity), are opposite for orthodromic versus antidromic stimulation, which should inform hypotheses about the impact of the developmentally regulated subcellular localization of these NaV subtypes.
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Affiliation(s)
- Benjamin S. M. Barlow
- Department of Physics, University of Ottawa, STEM Complex, 150 Louis-Pasteur Pvt, Ottawa, Ontario, Canada
| | - André Longtin
- Department of Physics, University of Ottawa, STEM Complex, 150 Louis-Pasteur Pvt, Ottawa, Ontario, Canada
- Center for Neural Dynamics and AI, University of Ottawa, Ottawa, Ontario, Canada
- Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Béla Joós
- Department of Physics, University of Ottawa, STEM Complex, 150 Louis-Pasteur Pvt, Ottawa, Ontario, Canada
- Center for Neural Dynamics and AI, University of Ottawa, Ottawa, Ontario, Canada
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Gilloteaux J, De Swert K, Suain V, Nicaise C. Thalamic Neuron Resilience during Osmotic Demyelination Syndrome (ODS) Is Revealed by Primary Cilium Outgrowth and ADP-ribosylation factor-like protein 13B Labeling in Axon Initial Segment. Int J Mol Sci 2023; 24:16448. [PMID: 38003639 PMCID: PMC10671465 DOI: 10.3390/ijms242216448] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2023] [Revised: 11/10/2023] [Accepted: 11/13/2023] [Indexed: 11/26/2023] Open
Abstract
A murine osmotic demyelinating syndrome (ODS) model was developed through chronic hyponatremia, induced by desmopressin subcutaneous implants, followed by precipitous sodium restoration. The thalamic ventral posterolateral (VPL) and ventral posteromedial (VPM) relay nuclei were the most demyelinated regions where neuroglial damage could be evidenced without immune response. This report showed that following chronic hyponatremia, 12 h and 48 h time lapses after rebalancing osmolarity, amid the ODS-degraded outskirts, some resilient neuronal cell bodies built up primary cilium and axon hillock regions that extended into axon initial segments (AIS) where ADP-ribosylation factor-like protein 13B (ARL13B)-immunolabeled rod-like shape content was revealed. These AIS-labeled shaft lengths appeared proportional with the distance of neuronal cell bodies away from the ODS damaged epicenter and time lapses after correction of hyponatremia. Fine structure examination verified these neuron abundant transcriptions and translation regions marked by the ARL13B labeling associated with cell neurotubules and their complex cytoskeletal macromolecular architecture. This necessitated energetic transport to organize and restore those AIS away from the damaged ODS core demyelinated zone in the murine model. These labeled structures could substantiate how thalamic neuron resilience occurred as possible steps of a healing course out of ODS.
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Affiliation(s)
- Jacques Gilloteaux
- URPhyM, NARILIS, Université de Namur, Rue de Bruxelles 61, B-5000 Namur, Belgium; (J.G.); (K.D.S.)
- Department of Anatomical Sciences, St George’s University School of Medicine, Newcastle upon Tyne NE1 JG8, UK
| | - Kathleen De Swert
- URPhyM, NARILIS, Université de Namur, Rue de Bruxelles 61, B-5000 Namur, Belgium; (J.G.); (K.D.S.)
| | - Valérie Suain
- Laboratoire d’Histologie Générale, Université Libre de Bruxelles, Route de Lennik 808, B-1070 Bruxelles, Belgium;
| | - Charles Nicaise
- URPhyM, NARILIS, Université de Namur, Rue de Bruxelles 61, B-5000 Namur, Belgium; (J.G.); (K.D.S.)
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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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Bar L, Shalom L, Lezmy J, Peretz A, Attali B. Excitatory and inhibitory hippocampal neurons differ in their homeostatic adaptation to chronic M-channel modulation. Front Mol Neurosci 2022; 15:972023. [PMID: 36311018 PMCID: PMC9614320 DOI: 10.3389/fnmol.2022.972023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Accepted: 09/27/2022] [Indexed: 12/03/2022] Open
Abstract
A large body of studies has investigated bidirectional homeostatic plasticity both in vitro and in vivo using numerous pharmacological manipulations of activity or behavioral paradigms. However, these experiments rarely explored in the same cellular system the bidirectionality of the plasticity and simultaneously on excitatory and inhibitory neurons. M-channels are voltage-gated potassium channels that play a crucial role in regulating neuronal excitability and plasticity. In cultured hippocampal excitatory neurons, we previously showed that chronic exposure to the M-channel blocker XE991 leads to adaptative compensations, thereby triggering at different timescales intrinsic and synaptic homeostatic plasticity. This plastic adaptation barely occurs in hippocampal inhibitory neurons. In this study, we examined whether this homeostatic plasticity induced by M-channel inhibition was bidirectional by investigating the acute and chronic effects of the M-channel opener retigabine on hippocampal neuronal excitability. Acute retigabine exposure decreased excitability in both excitatory and inhibitory neurons. Chronic retigabine treatment triggered in excitatory neurons homeostatic adaptation of the threshold current and spontaneous firing rate at a time scale of 4–24 h. These plastic changes were accompanied by a substantial decrease in the M-current density and by a small, though significant, proximal relocation of Kv7.3-FGF14 segment along the axon initial segment. Thus, bidirectional homeostatic changes were observed in excitatory neurons though not symmetric in kinetics and mechanisms. Contrastingly, in inhibitory neurons, the compensatory changes in intrinsic excitability barely occurred after 48 h, while no homeostatic normalization of the spontaneous firing rate was observed. Our results indicate that excitatory and inhibitory hippocampal neurons differ in their adaptation to chronic alterations in neuronal excitability induced by M-channel bidirectional modulation.
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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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Jamann N, Dannehl D, Lehmann N, Wagener R, Thielemann C, Schultz C, Staiger J, Kole MHP, Engelhardt M. Sensory input drives rapid homeostatic scaling of the axon initial segment in mouse barrel cortex. Nat Commun 2021; 12:23. [PMID: 33397944 PMCID: PMC7782484 DOI: 10.1038/s41467-020-20232-x] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Accepted: 11/16/2020] [Indexed: 12/12/2022] Open
Abstract
The axon initial segment (AIS) is a critical microdomain for action potential initiation and implicated in the regulation of neuronal excitability during activity-dependent plasticity. While structural AIS plasticity has been suggested to fine-tune neuronal activity when network states change, whether it acts in vivo as a homeostatic regulatory mechanism in behaviorally relevant contexts remains poorly understood. Using the mouse whisker-to-barrel pathway as a model system in combination with immunofluorescence, confocal analysis and electrophysiological recordings, we observed bidirectional AIS plasticity in cortical pyramidal neurons. Furthermore, we find that structural and functional AIS remodeling occurs in distinct temporal domains: Long-term sensory deprivation elicits an AIS length increase, accompanied with an increase in neuronal excitability, while sensory enrichment results in a rapid AIS shortening, accompanied by a decrease in action potential generation. Our findings highlight a central role of the AIS in the homeostatic regulation of neuronal input-output relations.
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Affiliation(s)
- Nora Jamann
- Axonal Signaling Group, Netherlands Institute for Neurosciences (NIN), Royal Netherlands Academy for Arts and Sciences (KNAW), Amsterdam, The Netherlands
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Utrecht, The Netherlands
- Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Dominik Dannehl
- Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Nadja Lehmann
- Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Robin Wagener
- Clinic of Neurology, University Hospital Heidelberg, Heidelberg, Germany
| | - Corinna Thielemann
- Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Christian Schultz
- Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Jochen Staiger
- Institute of Neuroanatomy, University Medical Center, Georg August University of Göttingen, Göttingen, Germany
| | - Maarten H P Kole
- Axonal Signaling Group, Netherlands Institute for Neurosciences (NIN), Royal Netherlands Academy for Arts and Sciences (KNAW), Amsterdam, The Netherlands.
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Utrecht, The Netherlands.
| | - Maren Engelhardt
- Institute of Neuroanatomy, Mannheim Center for Translational Neuroscience (MCTN), Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany.
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Ghosh A, Malavasi EL, Sherman DL, Brophy PJ. Neurofascin and Kv7.3 are delivered to somatic and axon terminal surface membranes en route to the axon initial segment. eLife 2020; 9:60619. [PMID: 32903174 PMCID: PMC7511229 DOI: 10.7554/elife.60619] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Accepted: 09/08/2020] [Indexed: 12/15/2022] Open
Abstract
Ion channel complexes promote action potential initiation at the mammalian axon initial segment (AIS), and modulation of AIS size by recruitment or loss of proteins can influence neuron excitability. Although endocytosis contributes to AIS turnover, how membrane proteins traffic to this proximal axonal domain is incompletely understood. Neurofascin186 (Nfasc186) has an essential role in stabilising the AIS complex to the proximal axon, and the AIS channel protein Kv7.3 regulates neuron excitability. Therefore, we have studied how these proteins reach the AIS. Vesicles transport Nfasc186 to the soma and axon terminal where they fuse with the neuronal plasma membrane. Nfasc186 is highly mobile after insertion in the axonal membrane and diffuses bidirectionally until immobilised at the AIS through its interaction with AnkyrinG. Kv7.3 is similarly recruited to the AIS. This study reveals how key proteins are delivered to the AIS and thereby how they may contribute to its functional plasticity.
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Affiliation(s)
- Aniket Ghosh
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Elise Lv Malavasi
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Diane L Sherman
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Peter J Brophy
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom
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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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Lindroos R, Hellgren Kotaleski J. Predicting complex spikes in striatal projection neurons of the direct pathway following neuromodulation by acetylcholine and dopamine. Eur J Neurosci 2020; 53:2117-2134. [DOI: 10.1111/ejn.14891] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Revised: 06/15/2020] [Accepted: 06/25/2020] [Indexed: 02/03/2023]
Affiliation(s)
- Robert Lindroos
- Department of Neuroscience Karolinska Institutet Stockholm Sweden
| | - Jeanette Hellgren Kotaleski
- Department of Neuroscience Karolinska Institutet Stockholm Sweden
- Science for Life Laboratory Department of Computational Science and Technology The Royal Institute of Technology Stockholm Sweden
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11
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Develle Y, Leblond H. Biphasic Effect of Buspirone on the H-Reflex in Acute Spinal Decerebrated Mice. Front Cell Neurosci 2020; 13:573. [PMID: 32009904 PMCID: PMC6974439 DOI: 10.3389/fncel.2019.00573] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2019] [Accepted: 12/12/2019] [Indexed: 11/13/2022] Open
Abstract
Pharmacological treatment facilitating locomotor expression will also have some effects on reflex expression through the modulation of spinal circuitry. Buspirone, a partial serotonin receptor agonist (5-HT1 A), was recently shown to facilitate and even trigger locomotor movements in mice after complete spinal lesion (Tx). Here, we studied its effect on the H-reflex after acute Tx in adult mice. To avoid possible impacts of anesthetics on H-reflex depression, experiments were performed after decerebration in un-anesthetized mice (N = 20). The H-reflex in plantar muscles of the hind paw was recorded after tibial nerve stimulation 2 h after Tx at the 8th thoracic vertebrae and was compared before and every 10 min after buspirone (8 mg/kg, i.p.) for 60 min (N = 8). Frequency-dependent depression (FDD) of the H-reflex was assessed before and 60 min after buspirone. Before buspirone, a stable H-reflex could be elicited in acute spinal mice and FDD of the H-reflex was observed at 5 and 10 Hz relative to 0.2 Hz, FDD was still present 60 min after buspirone. Early after buspirone, the H-reflex was significantly decreased to 69% of pre-treatment, it then increased significantly 30-60 min after treatment, reaching 170% 60 min after injection. This effect was not observed in a control group (saline, N = 5) and was blocked when a 5-HT1 A antagonist (NAD-299) was administered with buspirone (N = 7). Altogether results suggest that the reported pro-locomotor effect of buspirone occurs at a time where there is a 5-HT1 A receptors mediated reflex depression followed by a second phase marked by enhancement of reflex excitability.
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Affiliation(s)
- Yann Develle
- Department of Anatomy, CogNAC Research Group, Université du Québec à Trois-Rivières, Trois-Rivières, QC, Canada
| | - Hugues Leblond
- Department of Anatomy, CogNAC Research Group, Université du Québec à Trois-Rivières, Trois-Rivières, QC, Canada
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Jin X, Chen Q, Song Y, Zheng J, Xiao K, Shao S, Fu Z, Yi M, Yang Y, Huang Z. Dopamine D2 receptors regulate the action potential threshold by modulating T‐type calcium channels in stellate cells of the medial entorhinal cortex. J Physiol 2019; 597:3363-3387. [PMID: 31049961 DOI: 10.1113/jp277976] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2019] [Accepted: 04/24/2019] [Indexed: 11/08/2022] Open
Affiliation(s)
- Xueqin Jin
- State Key Laboratory of Natural and Biomimetic DrugsDepartment of Molecular and Cellular PharmacologySchool of Pharmaceutical SciencesPeking University Health Science Centre Beijing 100191 China
| | - Qian Chen
- State Key Laboratory of Natural and Biomimetic DrugsDepartment of Molecular and Cellular PharmacologySchool of Pharmaceutical SciencesPeking University Health Science Centre Beijing 100191 China
| | - Yan Song
- State Key Laboratory of Natural and Biomimetic DrugsDepartment of Molecular and Cellular PharmacologySchool of Pharmaceutical SciencesPeking University Health Science Centre Beijing 100191 China
| | - Jie Zheng
- Neuroscience Research InstitutePeking University Health Science Center Beijing 100191 China
| | - Kuo Xiao
- State Key Laboratory of Natural and Biomimetic DrugsDepartment of Molecular and Cellular PharmacologySchool of Pharmaceutical SciencesPeking University Health Science Centre Beijing 100191 China
| | - Shan Shao
- Neuroscience Research InstitutePeking University Health Science Center Beijing 100191 China
| | - Zibing Fu
- Neuroscience Research InstitutePeking University Health Science Center Beijing 100191 China
| | - Ming Yi
- Neuroscience Research InstitutePeking University Health Science Center Beijing 100191 China
- Key Laboratory for NeuroscienceMinistry of Education/National Health and Family Planning CommissionPeking University Beijing 100191 China
| | - Yang Yang
- Department of Medicinal Chemistry and Molecular PharmacologyCollege of Pharmacy, Purdue University West Lafayette IN 47907 USA
- Purdue Institute for Integrative Neuroscience 575 Stadium Mall Drive West Lafayette IN 47907 USA
| | - Zhuo Huang
- State Key Laboratory of Natural and Biomimetic DrugsDepartment of Molecular and Cellular PharmacologySchool of Pharmaceutical SciencesPeking University Health Science Centre Beijing 100191 China
- Key Laboratory for NeuroscienceMinistry of Education/National Health and Family Planning CommissionPeking University Beijing 100191 China
- Department of Molecular and Cellular PharmacologyPeking University Health Science Center 38 Xue Yuan Road Beijing 100191 China
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13
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Burke KJ, Bender KJ. Modulation of Ion Channels in the Axon: Mechanisms and Function. Front Cell Neurosci 2019; 13:221. [PMID: 31156397 PMCID: PMC6533529 DOI: 10.3389/fncel.2019.00221] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Accepted: 05/01/2019] [Indexed: 12/11/2022] Open
Abstract
The axon is responsible for integrating synaptic signals, generating action potentials (APs), propagating those APs to downstream synapses and converting them into patterns of neurotransmitter vesicle release. This process is mediated by a rich assortment of voltage-gated ion channels whose function can be affected on short and long time scales by activity. Moreover, neuromodulators control the activity of these proteins through G-protein coupled receptor signaling cascades. Here, we review cellular mechanisms and signaling pathways involved in axonal ion channel modulation and examine how changes to ion channel function affect AP initiation, AP propagation, and the release of neurotransmitter. We then examine how these mechanisms could modulate synaptic function by focusing on three key features of synaptic information transmission: synaptic strength, synaptic variability, and short-term plasticity. Viewing these cellular mechanisms of neuromodulation from a functional perspective may assist in extending these findings to theories of neural circuit function and its neuromodulation.
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Affiliation(s)
| | - Kevin J. Bender
- Neuroscience Graduate Program and Department of Neurology, Kavli Institute for Fundamental Neuroscience, Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, United States
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14
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Axon initial segment plasticity accompanies enhanced excitation of visual cortical neurons in aged rats. Neuroreport 2019; 29:1537-1543. [PMID: 30320703 PMCID: PMC6250279 DOI: 10.1097/wnr.0000000000001145] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Recent studies have indicated that the structure of the axon initial segment (AIS) of neurons is highly plastic in response to changes in neuronal activity. Whether an age-related enhancement of neuronal responses in the visual cortex is coupled with plasticity of AISs is unknown. Here, we compare the AIS length and the distribution of Nav1.6, a key Na+ ion channel in action potential (AP) initiation, along the AIS of layer II/III neurons in the primary visual cortex (V1) of young adult and aged rats, which were examined previously in a single-unit recording study. In that study, we found that V1 neurons in aged rats showed a significantly higher spontaneous activity and stronger visually evoked responses than did neurons in young rats. Our present study shows that the mean AIS length of layer II/III neurons in the V1 area of aged rats was significantly shorter than that of young adult rats. Further, the proportion of AIS with the Nav1.6 distribution was also reduced significantly in aged rats relative to young rats, as indicated by a decrease in the mean Nav1.6 immunofluorescence optical density within AISs and a specific decrease in Nav1.6 immunofluorescence optical density near the proximal region of the AIS. Our results indicate that aging results in both shortening of AISs and reduction of Nav1.6 Na+ ion channel distribution along AISs, which accompanies enhanced neuronal activity. This age-related morphological plasticity may lower the AP amplitude by reducing Na+ ion entry during AP initiation, spare ATPs consumed by Na+ ion pumps during membrane potential restoration, and thus balance the energy expenditure caused by an increased firing rate of cortical neurons during the aging process.
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15
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Maturation Dynamics of the Axon Initial Segment (AIS) of Newborn Dentate Granule Cells in Young Adult C57BL/6J Mice. J Neurosci 2019; 39:1605-1620. [PMID: 30651327 DOI: 10.1523/jneurosci.2253-18.2019] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2018] [Revised: 12/27/2018] [Accepted: 01/04/2019] [Indexed: 01/07/2023] Open
Abstract
Newborn dentate granule cells (DGCs) are generated in the hippocampal dentate gyrus (DG) of rodents through a process called adult hippocampal neurogenesis, which is subjected to tight intrinsic and extrinsic regulation. The use of retroviruses encoding fluorescent proteins has allowed the characterization of the maturation dynamics of newborn DGCs, including their morphological development and the establishment and maturation of their afferent and efferent synaptic connections. However, the study of a crucial cellular compartment of these cells, namely, the axon initial segment (AIS), has remained unexplored to date. The AIS is not only the site of action potential initiation, but it also has a unique molecular identity that makes it one of the master regulators of neural plasticity and excitability. Here we examined the dynamics of AIS formation in newborn DGCs of young female adult C57BL/6J mice in vivo Our data reveal notable changes in AIS length and thickness throughout cell maturation under physiological conditions and show that the most remarkable structural changes coincide with periods of intense morphological and functional remodeling. Moreover, we demonstrate that AIS development can be modulated extrinsically by both neuroprotective (environmental enrichment) and detrimental (lipopolysaccharide from Escherichia coli) stimuli.SIGNIFICANCE STATEMENT The hippocampal dentate gyrus (DG) of rodents generates newborn dentate granule cells (DGCs) throughout life. This process, named adult hippocampal neurogenesis, confers a unique degree of plasticity to the hippocampal circuit, and it is crucial for learning and memory. Here we studied, for the first time, the formation of a key cellular compartment of newborn DGCs, namely, the axon initial segment (AIS) in vivo Our data reveal remarkable AIS structural remodeling throughout the maturation of these cells under physiological conditions. Moreover, AIS development can be modulated extrinsically by both neuroprotective (environmental enrichment) and detrimental (lipopolysaccharide from Escherichia coli) stimuli.
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16
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Tien NW, Kerschensteiner D. Homeostatic plasticity in neural development. Neural Dev 2018; 13:9. [PMID: 29855353 PMCID: PMC5984303 DOI: 10.1186/s13064-018-0105-x] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Accepted: 04/24/2018] [Indexed: 02/06/2023] Open
Abstract
Throughout life, neural circuits change their connectivity, especially during development, when neurons frequently extend and retract dendrites and axons, and form and eliminate synapses. In spite of their changing connectivity, neural circuits maintain relatively constant activity levels. Neural circuits achieve functional stability by homeostatic plasticity, which equipoises intrinsic excitability and synaptic strength, balances network excitation and inhibition, and coordinates changes in circuit connectivity. Here, we review how diverse mechanisms of homeostatic plasticity stabilize activity in developing neural circuits.
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Affiliation(s)
- Nai-Wen Tien
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Saint Louis, USA. .,Graduate Program in Neuroscience, Washington University School of Medicine, Saint Louis, USA.
| | - Daniel Kerschensteiner
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Saint Louis, USA. .,Department of Neuroscience, Washington University School of Medicine, Saint Louis, USA. .,Department of Biomedical Engineering, Washington University School of Medicine, Saint Louis, USA. .,Hope Center for Neurological Disorders, Washington University School of Medicine, Saint Louis, MO, 63110, USA.
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17
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The Axon Initial Segment: An Updated Viewpoint. J Neurosci 2018; 38:2135-2145. [PMID: 29378864 DOI: 10.1523/jneurosci.1922-17.2018] [Citation(s) in RCA: 164] [Impact Index Per Article: 27.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2017] [Revised: 01/20/2018] [Accepted: 01/25/2018] [Indexed: 12/20/2022] Open
Abstract
At the base of axons sits a unique compartment called the axon initial segment (AIS). The AIS generates and shapes the action potential before it is propagated along the axon. Neuronal excitability thus depends crucially on the AIS composition and position, and these adapt to developmental and physiological conditions. The AIS also demarcates the boundary between the somatodendritic and axonal compartments. Recent studies have brought insights into the molecular architecture of the AIS and how it regulates protein trafficking. This Viewpoints article summarizes current knowledge about the AIS and highlights future challenges in understanding this key actor of neuronal physiology.
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18
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Perrier JF, Rasmussen HB, Jørgensen LK, Berg RW. Intense Activity of the Raphe Spinal Pathway Depresses Motor Activity via a Serotonin Dependent Mechanism. Front Neural Circuits 2018; 11:111. [PMID: 29375322 PMCID: PMC5767281 DOI: 10.3389/fncir.2017.00111] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Accepted: 12/15/2017] [Indexed: 01/23/2023] Open
Abstract
Motor fatigue occurring during prolonged physical activity has both peripheral and central origins. It was previously demonstrated that the excitability of motoneurons was decreased when a spillover of serotonin could activate extrasynaptic 5-HT1A receptors at the axon initial segment (AIS) of motoneurons. Here we investigated the impact of massive synaptic release of serotonin on motor behavior in an integrated preparation of the adult turtle performing fictive scratching behaviors. We found that a prolonged electrical stimulation of the raphe spinal pathway induced a reversible inhibition of the motor behavior that lasted several tens of seconds. The effect disappeared when the spinal cord was perfused with an antagonist for 5-HT1A receptors. By demonstrating a direct impact of serotonin on motor behavior, we suggest a central role of this monoamine behind central fatigue.
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Affiliation(s)
- Jean-François Perrier
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Hanne B. Rasmussen
- Department of Biomedical Science, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Lone K. Jørgensen
- Department of Biomedical Science, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Rune W. Berg
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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19
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M-current inhibition rapidly induces a unique CK2-dependent plasticity of the axon initial segment. Proc Natl Acad Sci U S A 2017; 114:E10234-E10243. [PMID: 29109270 DOI: 10.1073/pnas.1708700114] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Alterations in synaptic input, persisting for hours to days, elicit homeostatic plastic changes in the axon initial segment (AIS), which is pivotal for spike generation. Here, in hippocampal pyramidal neurons of both primary cultures and slices, we triggered a unique form of AIS plasticity by selectively targeting M-type K+ channels, which predominantly localize to the AIS and are essential for tuning neuronal excitability. While acute M-current inhibition via cholinergic activation or direct channel block made neurons more excitable, minutes to hours of sustained M-current depression resulted in a gradual reduction in intrinsic excitability. Dual soma-axon patch-clamp recordings combined with axonal Na+ imaging and immunocytochemistry revealed that these compensatory alterations were associated with a distal shift of the spike trigger zone and distal relocation of FGF14, Na+, and Kv7 channels but not ankyrin G. The concomitant distal redistribution of FGF14 together with Nav and Kv7 segments along the AIS suggests that these channels relocate as a structural and functional unit. These fast homeostatic changes were independent of l-type Ca2+ channel activity but were contingent on the crucial AIS protein, protein kinase CK2. Using compartmental simulations, we examined the effects of varying the AIS position relative to the soma and found that AIS distal relocation of both Nav and Kv7 channels elicited a decrease in neuronal excitability. Thus, alterations in M-channel activity rapidly trigger unique AIS plasticity to stabilize network excitability.
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20
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Liu TT, Feng L, Liu HF, Shu Y, Xiao B. Altered axon initial segment in hippocampal newborn neurons, associated with recurrence of temporal lobe epilepsy in rats. Mol Med Rep 2017; 16:3169-3178. [PMID: 28713955 PMCID: PMC5547972 DOI: 10.3892/mmr.2017.7017] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2017] [Accepted: 07/06/2017] [Indexed: 01/23/2023] Open
Abstract
Hippocampal neurogenesis in temporal lobe epilepsy (TLE) may result in alteration of the excitability of neurons, which contributes to spontaneous recurrent seizures. Axon initial segment (AIS) structural and functional plasticity is important in the control of neuronal excitability. It remains to be elucidated whether the plasticity of AIS occurs in hippocampal newly-generated neurons that are involved in recurrent seizures following pilocarpine-induced status epilepticus (SE). The present study first established a pilocarpine-induced TLE rat model to assess the features of newborn neurons and AIS plasticity alterations using double immunofluorescence staining of Ankyrin G and doublecortin (DCX). AIS plasticity alterations include length and distance from soma in the hippocampal newly-generated neurons post-SE. The results of the present study demonstrated that pilocarpine-induced epileptic rats exhibited aberrant hippocampal neurogenesis and longer DCX-labeled cell dendrites in the dentate gyrus. Pilocarpine-induced epileptic rats demonstrated shortened lengths of AIS and an increased distance from the soma in hippocampal newborn neurons. Mibefradil, a T/L-type calcium blocker, reversed the alterations in length and position of AIS in hippocampal newborn neurons post-SE, accompanied by decreased long-term seizure activity without increased aberrant neurogenesis. These findings indicate that the plasticity of AIS in hippocampal neurogenesis may have profound consequences in epilepsy, at least in animals.
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Affiliation(s)
- Tian-Tian Liu
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China
| | - Li Feng
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China
| | - Heng-Fang Liu
- Department of Neurology, The Fifth Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Yi Shu
- Department of Neurology, The Second Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China
| | - Bo Xiao
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, P.R. China
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21
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Abstract
Motor neurons translate synaptic input from widely distributed premotor networks into patterns of action potentials that orchestrate motor unit force and motor behavior. Intercalated between the CNS and muscles, motor neurons add to and adjust the final motor command. The identity and functional properties of this facility in the path from synaptic sites to the motor axon is reviewed with emphasis on voltage sensitive ion channels and regulatory metabotropic transmitter pathways. The catalog of the intrinsic response properties, their underlying mechanisms, and regulation obtained from motoneurons in in vitro preparations is far from complete. Nevertheless, a foundation has been provided for pursuing functional significance of intrinsic response properties in motoneurons in vivo during motor behavior at levels from molecules to systems. © 2017 American Physiological Society. Compr Physiol 7:463-484, 2017.
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Affiliation(s)
- Jorn Hounsgaard
- Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
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22
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Griggs RB, Yermakov LM, Susuki K. Formation and disruption of functional domains in myelinated CNS axons. Neurosci Res 2016; 116:77-87. [PMID: 27717670 DOI: 10.1016/j.neures.2016.09.010] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 09/19/2016] [Accepted: 09/23/2016] [Indexed: 12/15/2022]
Abstract
Communication in the central nervous system (CNS) occurs through initiation and propagation of action potentials at excitable domains along axons. Action potentials generated at the axon initial segment (AIS) are regenerated at nodes of Ranvier through the process of saltatory conduction. Proper formation and maintenance of the molecular structure at the AIS and nodes are required for sustaining conduction fidelity. In myelinated CNS axons, paranodal junctions between the axolemma and myelinating oligodendrocytes delineate nodes of Ranvier and regulate the distribution and localization of specialized functional elements, such as voltage-gated sodium channels and mitochondria. Disruption of excitable domains and altered distribution of functional elements in CNS axons is associated with demyelinating diseases such as multiple sclerosis, and is likely a mechanism common to other neurological disorders. This review will provide a brief overview of the molecular structure of the AIS and nodes of Ranvier, as well as the distribution of mitochondria in myelinated axons. In addition, this review highlights important structural and functional changes within myelinated CNS axons that are associated with neurological dysfunction.
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Affiliation(s)
- Ryan B Griggs
- Department of Neuroscience, Cell Biology, and Physiology, Boonshoft School of Medicine, Wright State University, Dayton, OH, United States
| | - Leonid M Yermakov
- Department of Neuroscience, Cell Biology, and Physiology, Boonshoft School of Medicine, Wright State University, Dayton, OH, United States
| | - Keiichiro Susuki
- Department of Neuroscience, Cell Biology, and Physiology, Boonshoft School of Medicine, Wright State University, Dayton, OH, United States.
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