51
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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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52
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Goaillard JM, Moubarak E, Tapia M, Tell F. Diversity of Axonal and Dendritic Contributions to Neuronal Output. Front Cell Neurosci 2020; 13:570. [PMID: 32038171 PMCID: PMC6987044 DOI: 10.3389/fncel.2019.00570] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Accepted: 12/09/2019] [Indexed: 11/13/2022] Open
Abstract
Our general understanding of neuronal function is that dendrites receive information that is transmitted to the axon, where action potentials (APs) are initiated and propagated to eventually trigger neurotransmitter release at synaptic terminals. Even though this canonical division of labor is true for a number of neuronal types in the mammalian brain (including neocortical and hippocampal pyramidal neurons or cerebellar Purkinje neurons), many neuronal types do not comply with this classical polarity scheme. In fact, dendrites can be the site of AP initiation and propagation, and even neurotransmitter release. In several interneuron types, all functions are carried out by dendrites as these neurons are devoid of a canonical axon. In this article, we present a few examples of "misbehaving" neurons (with a non-canonical polarity scheme) to highlight the diversity of solutions that are used by mammalian neurons to transmit information. Moreover, we discuss how the contribution of dendrites and axons to neuronal excitability may impose constraints on the morphology of these compartments in specific functional contexts.
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Affiliation(s)
- Jean-Marc Goaillard
- UMR_S 1072, Aix Marseille Université, INSERM, Faculté de Médecine Secteur Nord, Marseille, France
| | - Estelle Moubarak
- UMR_S 1072, Aix Marseille Université, INSERM, Faculté de Médecine Secteur Nord, Marseille, France
| | - Mónica Tapia
- UMR_S 1072, Aix Marseille Université, INSERM, Faculté de Médecine Secteur Nord, Marseille, France
| | - Fabien Tell
- UMR_S 1072, Aix Marseille Université, INSERM, Faculté de Médecine Secteur Nord, Marseille, France
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53
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Iijima T, Yoshimura T. A Perspective on the Role of Dynamic Alternative RNA Splicing in the Development, Specification, and Function of Axon Initial Segment. Front Mol Neurosci 2019; 12:295. [PMID: 31866821 PMCID: PMC6906172 DOI: 10.3389/fnmol.2019.00295] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Accepted: 11/15/2019] [Indexed: 11/13/2022] Open
Abstract
Alternative splicing is a powerful mechanism for molecular and functional diversification. In neurons, alternative splicing extensively controls various developmental steps as well as the plasticity and remodeling of neuronal activity in the adult brain. The axon initial segment (AIS) is the specialized compartment of proximal axons that initiates action potential (AP). At the AIS, the ion channels and cell adhesion molecules (CAMs) required for AP initiation are densely clustered via the scaffolding and cytoskeletal proteins. Notably, recent studies have elucidated that multiple AIS proteins are controlled by extensive alternative splicing in developing and adult brains. Here, we argue the potential role of dynamic regulation of alternative splicing in the development, specification, and functions of the AIS. In particular, we propose the novel concept that alternative splicing potentially modulates the structural and functional plasticity at the AIS.
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Affiliation(s)
- Takatoshi Iijima
- Department of Molecular Life Science, Division of Basic Medical Science and Molecular Medicine, School of Medicine, Tokai University, Isehara, Japan
| | - Takeshi Yoshimura
- Department of Child Development and Molecular Brain Science, United Graduate School of Child Development, Osaka University, Suita, Japan
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54
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Dumenieu M, Senkov O, Mironov A, Bourinet E, Kreutz MR, Dityatev A, Heine M, Bikbaev A, Lopez-Rojas J. The Low-Threshold Calcium Channel Cav3.2 Mediates Burst Firing of Mature Dentate Granule Cells. Cereb Cortex 2019; 28:2594-2609. [PMID: 29790938 PMCID: PMC5998957 DOI: 10.1093/cercor/bhy084] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2018] [Indexed: 12/11/2022] Open
Abstract
Mature granule cells are poorly excitable neurons that were recently shown to fire action potentials, preferentially in bursts. It is believed that the particularly pronounced short-term facilitation of mossy fiber synapses makes granule cell bursting a very effective means of properly transferring information to CA3. However, the mechanism underlying the unique bursting behavior of mature granule cells is currently unknown. Here, we show that Cav3.2 T-type channels at the axon initial segment are responsible for burst firing of mature granule cells in rats and mice. Accordingly, Cav3.2 knockout mice fire tonic spikes and exhibit impaired bursting, synaptic plasticity and dentate-to-CA3 communication. The data show that Cav3.2 channels are strong modulators of bursting and can be considered a critical molecular switch that enables effective information transfer from mature granule cells to the CA3 pyramids.
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Affiliation(s)
- Mael Dumenieu
- Research Group Neuroplasticity, Leibniz Institute for Neurobiology, Brenneckestr. 6, Magdeburg, Germany
| | - Oleg Senkov
- Molecular Neuroplasticity Group, German Center for Neurodegenerative Diseases (DZNE), Magdeburg, Germany
| | - Andrey Mironov
- Molecular Neuroplasticity Group, German Center for Neurodegenerative Diseases (DZNE), Magdeburg, Germany.,Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russia.,Privolzhsky Research Medical University, Nizhny Novgorod, Russia
| | - Emmanuel Bourinet
- Calcium Channel Dynamics & Nociception Group, Institute of Functional Genomics, Montpellier, France
| | - Michael R Kreutz
- Research Group Neuroplasticity, Leibniz Institute for Neurobiology, Brenneckestr. 6, Magdeburg, Germany.,Leibniz Group "Dendritic Organelles and Synaptic Function," University Medical Center Hamburg-Eppendorf, Center for Molecular Neurobiology (ZMNH), Hamburg, Germany
| | - Alexander Dityatev
- Molecular Neuroplasticity Group, German Center for Neurodegenerative Diseases (DZNE), Magdeburg, Germany.,Center for Behavioral Brain Sciences (CBBS), Magdeburg, Germany.,Medical Faculty, Otto-von-Guericke University, Magdeburg, Germany
| | - Martin Heine
- Research Group Molecular Physiology, Leibniz Institute for Neurobiology, Brenneckestr. 6, Magdeburg, Germany
| | - Arthur Bikbaev
- Research Group Molecular Physiology, Leibniz Institute for Neurobiology, Brenneckestr. 6, Magdeburg, Germany
| | - Jeffrey Lopez-Rojas
- Research Group Neuroplasticity, Leibniz Institute for Neurobiology, Brenneckestr. 6, Magdeburg, Germany
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Neurodevelopmental mutation of giant ankyrin-G disrupts a core mechanism for axon initial segment assembly. Proc Natl Acad Sci U S A 2019; 116:19717-19726. [PMID: 31451636 PMCID: PMC6765234 DOI: 10.1073/pnas.1909989116] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Axon initial segments of vertebrate neurons integrate thousands of dendritic inputs and generate a single outgoing action potential. Giant ankyrin-G associates with most of the molecular components of axon initial segments and is required for their assembly. This study identified 3 human mutations of giant ankyrin-G resulting in impaired neurodevelopment in compound heterozygotes. These mutations prevent transition of giant ankyrin-G from a closed to an open conformation, which normally is regulated by phosphorylation of giant ankyrin-G during maturation of axon initial segments. Giant ankyrin-G thus functions in a signaling pathway that may contribute to activity-dependent plasticity of the axon initial segment as well as provide a therapeutic target for treatment of patients bearing giant ankyrin-G mutations. Giant ankyrin-G (gAnkG) coordinates assembly of axon initial segments (AISs), which are sites of action potential generation located in proximal axons of most vertebrate neurons. Here, we identify a mechanism required for normal neural development in humans that ensures ordered recruitment of gAnkG and β4-spectrin to the AIS. We identified 3 human neurodevelopmental missense mutations located in the neurospecific domain of gAnkG that prevent recruitment of β4-spectrin, resulting in a lower density and more elongated pattern for gAnkG and its partners than in the mature AIS. We found that these mutations inhibit transition of gAnkG from a closed configuration with close apposition of N- and C-terminal domains to an extended state that is required for binding and recruitment of β4-spectrin, and normally occurs early in development of the AIS. We further found that the neurospecific domain is highly phosphorylated in mouse brain, and that phosphorylation at 2 sites (S1982 and S2619) is required for the conformational change and for recruitment of β4-spectrin. Together, these findings resolve a discrete intermediate stage in formation of the AIS that is regulated through phosphorylation of the neurospecific domain of gAnkG.
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57
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Dynamic Gain Analysis Reveals Encoding Deficiencies in Cortical Neurons That Recover from Hypoxia-Induced Spreading Depolarizations. J Neurosci 2019; 39:7790-7800. [PMID: 31399533 DOI: 10.1523/jneurosci.3147-18.2019] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2018] [Revised: 07/23/2019] [Accepted: 07/23/2019] [Indexed: 11/21/2022] Open
Abstract
Cortical regions that are damaged by insults, such as ischemia, hypoxia, and trauma, frequently generate spreading depolarization (SD). At the neuronal level, SDs entail complete breakdown of ionic gradients, persisting for seconds to minutes. It is unclear whether these transient events have a more lasting influence on neuronal function. Here, we describe electrophysiological changes in cortical neurons after recovery from hypoxia-induced SD. When examined with standard measures of neuronal excitability several hours after recovery from SD, layer 5 pyramidal neurons in brain slices from mice of either sex appear surprisingly normal. However, we here introduce an additional parameter, dynamic gain, which characterizes the bandwidth of action potential encoding by a neuron, and thereby reflects its potential efficiency in a multineuronal circuit. We find that the ability of neurons that recover from SD to track high-frequency inputs is markedly curtailed; exposure to hypoxia did not have this effect when SD was prevented pharmacologically. Staining for Ankyrin G revealed at least a fourfold decrease in the number of intact axon initial segments in post-SD slices. Since this effect, along with the effect on encoding, was blocked by an inhibitor of the Ca2+-dependent enzyme, calpain, we conclude that both effects were mediated by the SD-induced rise in intracellular Ca2+ Although effects of calpain activation were detected in the axon initial segment, changes in soma-dendritic compartments may also be involved. Whatever the precise molecular mechanism, our findings indicate that in the context of cortical circuit function, effectiveness of neurons that survive SD may be limited.SIGNIFICANCE STATEMENT Spreading depolarization, which commonly accompanies cortical injury, entails transient massive breakdown of neuronal ionic gradients. The function of cortical neurons that recover from hypoxia-induced spreading depolarization is not obviously abnormal when tested for usual measures of neuronal excitability. However, we now demonstrate that they have a reduced bandwidth, reflecting a significant impairment of their ability to precisely encode high-frequency components of their synaptic input in output spike trains. Thus, neurons that recover from spreading depolarizations are less able to function normally as elements in the multineuronal cortical circuitry. These changes are correlated with activation of the calcium-dependent enzyme, calpain.
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58
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Cilia function is associated with axon initial segment morphology. Biochem Biophys Res Commun 2019; 516:15-21. [DOI: 10.1016/j.bbrc.2019.05.172] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Accepted: 05/29/2019] [Indexed: 12/25/2022]
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59
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The Autism-Associated Gene Scn2a Contributes to Dendritic Excitability and Synaptic Function in the Prefrontal Cortex. Neuron 2019; 103:673-685.e5. [PMID: 31230762 DOI: 10.1016/j.neuron.2019.05.037] [Citation(s) in RCA: 107] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2018] [Revised: 03/23/2019] [Accepted: 05/22/2019] [Indexed: 12/20/2022]
Abstract
Autism spectrum disorder (ASD) is strongly associated with de novo gene mutations. One of the most commonly affected genes is SCN2A. ASD-associated SCN2A mutations impair the encoded protein NaV1.2, a sodium channel important for action potential initiation and propagation in developing excitatory cortical neurons. The link between an axonal sodium channel and ASD, a disorder typically attributed to synaptic or transcriptional dysfunction, is unclear. Here we show that NaV1.2 is unexpectedly critical for dendritic excitability and synaptic function in mature pyramidal neurons in addition to regulating early developmental axonal excitability. NaV1.2 loss reduced action potential backpropagation into dendrites, impairing synaptic plasticity and synaptic strength, even when NaV1.2 expression was disrupted in a cell-autonomous fashion late in development. These results reveal a novel dendritic function for NaV1.2, providing insight into cellular mechanisms probably underlying circuit and behavioral dysfunction in ASD.
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60
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Noh W, Pak S, Choi G, Yang S, Yang S. Transient Potassium Channels: Therapeutic Targets for Brain Disorders. Front Cell Neurosci 2019; 13:265. [PMID: 31263403 PMCID: PMC6585177 DOI: 10.3389/fncel.2019.00265] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Accepted: 05/28/2019] [Indexed: 01/04/2023] Open
Abstract
Transient potassium current channels (IA channels), which are expressed in most brain areas, have a central role in modulating feedforward and feedback inhibition along the dendroaxonic axis. Loss of the modulatory channels is tightly associated with a number of brain diseases such as Alzheimer’s disease, epilepsy, fragile X syndrome (FXS), Parkinson’s disease, chronic pain, tinnitus, and ataxia. However, the functional significance of IA channels in these diseases has so far been underestimated. In this review, we discuss the distribution and function of IA channels. Particularly, we posit that downregulation of IA channels results in neuronal (mostly dendritic) hyperexcitability accompanied by the imbalanced excitation and inhibition ratio in the brain’s networks, eventually causing the brain diseases. Finally, we propose a potential therapeutic target: the enhanced action of IA channels to counteract Ca2+-permeable channels including NMDA receptors could be harnessed to restore dendritic excitability, leading to a balanced neuronal state.
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Affiliation(s)
- Wonjun Noh
- Department of Nano-Bioengineering, Incheon National University, Incheon, South Korea
| | - Sojeong Pak
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon, Hong Kong
| | - Geunho Choi
- Department of Computer Science and Engineering, Incheon National University, Incheon, South Korea
| | - Sungchil Yang
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon, Hong Kong
| | - Sunggu Yang
- Department of Nano-Bioengineering, Incheon National University, Incheon, South Korea
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61
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Shin W, Kweon H, Kang R, Kim D, Kim K, Kang M, Kim SY, Hwang SN, Kim JY, Yang E, Kim H, Kim E. Scn2a Haploinsufficiency in Mice Suppresses Hippocampal Neuronal Excitability, Excitatory Synaptic Drive, and Long-Term Potentiation, and Spatial Learning and Memory. Front Mol Neurosci 2019; 12:145. [PMID: 31249508 PMCID: PMC6582764 DOI: 10.3389/fnmol.2019.00145] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Accepted: 05/17/2019] [Indexed: 01/13/2023] Open
Abstract
Nav1.2, a voltage-gated sodium channel subunit encoded by the Scn2a gene, has been implicated in various brain disorders, including epilepsy, autism spectrum disorder, intellectual disability, and schizophrenia. Nav1.2 is known to regulate the generation of action potentials in the axon initial segment and their propagation along axonal pathways. Nav1.2 also regulates synaptic integration and plasticity by promoting back-propagation of action potentials to dendrites, but whether Nav1.2 deletion in mice affects neuronal excitability, synaptic transmission, synaptic plasticity, and/or disease-related animal behaviors remains largely unclear. Here, we report that mice heterozygous for the Scn2a gene (Scn2a+/- mice) show decreased neuronal excitability and suppressed excitatory synaptic transmission in the presence of network activity in the hippocampus. In addition, Scn2a+/- mice show suppressed hippocampal long-term potentiation (LTP) in association with impaired spatial learning and memory, but show largely normal locomotor activity, anxiety-like behavior, social interaction, repetitive behavior, and whole-brain excitation. These results suggest that Nav1.2 regulates hippocampal neuronal excitability, excitatory synaptic drive, LTP, and spatial learning and memory in mice.
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Affiliation(s)
- Wangyong Shin
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea
| | - Hanseul Kweon
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea
| | - Ryeonghwa Kang
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea
| | - Doyoun Kim
- Center for Synaptic Brain Dysfunctions, Institute for Basic Science, Daejeon, South Korea
| | - Kyungdeok Kim
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea
| | - Muwon Kang
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea
| | - Seo Yeong Kim
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea
| | - Sun Nam Hwang
- Center for Synaptic Brain Dysfunctions, Institute for Basic Science, Daejeon, South Korea
| | - Jin Yong Kim
- Department of Anatomy and Division of Brain Korea 21, Biomedical Science, College of Medicine, Korea University, Seoul, South Korea
| | - Esther Yang
- Department of Anatomy and Division of Brain Korea 21, Biomedical Science, College of Medicine, Korea University, Seoul, South Korea
| | - Hyun Kim
- Department of Anatomy and Division of Brain Korea 21, Biomedical Science, College of Medicine, Korea University, Seoul, South Korea
| | - Eunjoon Kim
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea.,Center for Synaptic Brain Dysfunctions, Institute for Basic Science, Daejeon, South Korea
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62
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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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63
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Alpizar SA, Baker AL, Gulledge AT, Hoppa MB. Loss of Neurofascin-186 Disrupts Alignment of AnkyrinG Relative to Its Binding Partners in the Axon Initial Segment. Front Cell Neurosci 2019; 13:1. [PMID: 30723396 PMCID: PMC6349729 DOI: 10.3389/fncel.2019.00001] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2018] [Accepted: 01/07/2019] [Indexed: 12/14/2022] Open
Abstract
The axon initial segment (AIS) is a specialized region within the proximal portion of the axon that initiates action potentials thanks in large part to an enrichment of sodium channels. The scaffolding protein ankyrinG (AnkG) is essential for the recruitment of sodium channels as well as several other intracellular and extracellular proteins to the AIS. In the present study, we explore the role of the cell adhesion molecule (CAM) neurofascin-186 (NF-186) in arranging the individual molecular components of the AIS in cultured rat hippocampal neurons. Using a CRISPR depletion strategy to ablate NF expression, we found that the loss of NF selectively perturbed AnkG accumulation and its relative proximal distribution within the AIS. We found that the overexpression of sodium channels could restore AnkG accumulation, but not its altered distribution within the AIS without NF present. We go on to show that although the loss of NF altered AnkG distribution, sodium channel function within the AIS remained normal. Taken together, these results demonstrate that the regulation of AnkG and sodium channel accumulation within the AIS can occur independently of one another, potentially mediated by other binding partners such as NF.
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Affiliation(s)
- Scott A Alpizar
- Department of Biological Sciences, Dartmouth College, Hanover, NH, United States
| | - Arielle L Baker
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth College, Hanover, NH, United States
| | - Allan T Gulledge
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth College, Hanover, NH, United States
| | - Michael B Hoppa
- Department of Biological Sciences, Dartmouth College, Hanover, NH, United States
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Raghavan M, Fee D, Barkhaus PE. Generation and propagation of the action potential. ACTA ACUST UNITED AC 2019; 160:3-22. [DOI: 10.1016/b978-0-444-64032-1.00001-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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65
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Yermakov LM, Hong LA, Drouet DE, Griggs RB, Susuki K. Functional Domains in Myelinated Axons. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1190:65-83. [PMID: 31760639 DOI: 10.1007/978-981-32-9636-7_6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Propagation of action potentials along axons is optimized through interactions between neurons and myelinating glial cells. Myelination drives division of the axons into distinct molecular domains including nodes of Ranvier. The high density of voltage-gated sodium channels at nodes generates action potentials allowing for rapid and efficient saltatory nerve conduction. At paranodes flanking both sides of the nodes, myelinating glial cells interact with axons, forming junctions that are essential for node formation and maintenance. Recent studies indicate that the disruption of these specialized axonal domains is involved in the pathophysiology of various neurological diseases. Loss of paranodal axoglial junctions due to genetic mutations or autoimmune attack against the paranodal proteins leads to nerve conduction failure and neurological symptoms. Breakdown of nodal and paranodal proteins by calpains, the calcium-dependent cysteine proteases, may be a common mechanism involved in various nervous system diseases and injuries. This chapter reviews recent progress in neurobiology and pathophysiology of specialized axonal domains along myelinated nerve fibers.
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Affiliation(s)
- Leonid M Yermakov
- Department of Neuroscience, Cell Biology, and Physiology, Boonshoft School of Medicine, Wright State University, Dayton, OH, USA
| | - Lulu A Hong
- Department of Neuroscience, Cell Biology, and Physiology, Boonshoft School of Medicine, Wright State University, Dayton, OH, USA
| | - Domenica E Drouet
- Department of Neuroscience, Cell Biology, and Physiology, Boonshoft School of Medicine, Wright State University, Dayton, OH, USA
| | - Ryan B Griggs
- Department of Neuroscience, Cell Biology, and Physiology, Boonshoft School of Medicine, Wright State University, Dayton, OH, USA
| | - Keiichiro Susuki
- Department of Neuroscience, Cell Biology, and Physiology, Boonshoft School of Medicine, Wright State University, Dayton, OH, USA.
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66
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Mechanisms of Axonal Sorting of Tau and Influence of the Axon Initial Segment on Tau Cell Polarity. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1184:69-77. [DOI: 10.1007/978-981-32-9358-8_6] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
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67
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Meredith FL, Rennie KJ. Regional and Developmental Differences in Na + Currents in Vestibular Primary Afferent Neurons. Front Cell Neurosci 2018; 12:423. [PMID: 30487736 PMCID: PMC6246661 DOI: 10.3389/fncel.2018.00423] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Accepted: 10/29/2018] [Indexed: 02/04/2023] Open
Abstract
The vestibular system relays information about head position via afferent nerve fibers to the brain in the form of action potentials. Voltage-gated Na+ channels in vestibular afferents drive the initiation and propagation of action potentials, but their expression during postnatal development and their contributions to firing in diverse mature afferent populations are unknown. Electrophysiological techniques were used to determine Na+ channel subunit types in vestibular calyx-bearing afferents at different stages of postnatal development. We used whole cell patch clamp recordings in thin slices of gerbil crista neuroepithelium to investigate Na+ channels and firing patterns in central zone (CZ) and peripheral zone (PZ) afferents. PZ afferents are exclusively dimorphic, innervating type I and type II hair cells, whereas CZ afferents can form dimorphs or calyx-only terminals which innervate type I hair cells alone. All afferents expressed tetrodotoxin (TTX)-sensitive Na+ currents, but TTX-sensitivity varied with age. During the fourth postnatal week, 200–300 nM TTX completely blocked sodium currents in PZ and CZ calyces. By contrast, in immature calyces [postnatal day (P) 5–11], a small component of peak sodium current remained in 200 nM TTX. Application of 1 μM TTX, or Jingzhaotoxin-III plus 200 nM TTX, abolished sodium current in immature calyces, suggesting the transient expression of voltage-gated sodium channel 1.5 (Nav1.5) during development. A similar TTX-insensitive current was found in early postnatal crista hair cells (P5–9) and constituted approximately one third of the total sodium current. The Nav1.6 channel blocker, 4,9-anhydrotetrodotoxin, reduced a component of sodium current in immature and mature calyces. At 100 nM 4,9-anhydrotetrodotoxin, peak sodium current was reduced on average by 20% in P5–14 calyces, by 37% in mature dimorphic PZ calyces, but by less than 15% in mature CZ calyx-only terminals. In mature PZ calyces, action potentials became shorter and broader in the presence of 4,9-anhydrotetrodotoxin implicating a role for Nav1.6 channels in firing in dimorphic afferents.
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Affiliation(s)
- Frances L Meredith
- Department of Otolaryngology, University of Colorado School of Medicine, Aurora, CO, United States
| | - Katherine J Rennie
- Department of Otolaryngology, University of Colorado School of Medicine, Aurora, CO, United States.,Department of Physiology & Biophysics, University of Colorado School of Medicine, Aurora, CO, United States
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Morphological and Biophysical Determinants of the Intracellular and Extracellular Waveforms in Nigral Dopaminergic Neurons: A Computational Study. J Neurosci 2018; 38:8295-8310. [PMID: 30104340 DOI: 10.1523/jneurosci.0651-18.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Revised: 07/12/2018] [Accepted: 08/09/2018] [Indexed: 11/21/2022] Open
Abstract
Action potentials (APs) in nigral dopaminergic neurons often exhibit two separate components: the first reflecting spike initiation in the dendritically located axon initial segment (AIS) and the second the subsequent dendro-somatic spike. These components are separated by a notch in the ascending phase of the somatic extracellular waveform and in the temporal derivative of the somatic intracellular waveform. Still, considerable variability exists in the presence and magnitude of the notch across neurons. To systematically address the contribution of AIS, dendritic and somatic compartments to shaping the two-component APs, we modeled APs of previously in vivo electrophysiologically characterized and 3D-reconstructed male mouse and rat dopaminergic neurons. A parsimonious two-domain model, with high (AIS) and lower (dendro-somatic) Na+ conductance, reproduced the notch in the temporal derivatives, but not in the extracellular APs, regardless of morphology. The notch was only revealed when somatic active currents were reduced, constraining the model to three domains. Thus, an initial AIS spike is followed by an actively generated spike by the axon-bearing dendrite (ABD), in turn followed mostly passively by the soma. The transition from being a source compartment for the AIS spike to a source compartment for the ABD spike satisfactorily explains the extracellular somatic notch. Larger AISs and thinner ABD (but not soma-to-AIS distance) accentuate the AIS component. We conclude that variability in AIS size and ABD caliber explains variability in AP extracellular waveform and separation of AIS and dendro-somatic components, given the presence of at least three functional domains with distinct excitability characteristics.SIGNIFICANCE STATEMENT Midbrain dopamine neurons make an important contribution to circuits mediating motivation and movement. Understanding the basic rules that govern the electrical activity of single dopaminergic neurons is therefore essential to reveal how they ultimately contribute to movement and motivation as well as what goes wrong in associated disorders. Our computational study focuses on the generation and propagation of action potentials and shows that different morphologies and excitability characteristics of the cell body, dendrites and proximal axon can explain the diversity of action potentials shapes in this population. These compartments likely make differential contributions both to normal dopaminergic signaling and could potentially underlie pathological dopaminergic signaling implicated in addiction, schizophrenia, Parkinson's disease, and other disorders.
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Xu M, Pan R, Zhu Y, Jiang D, Chen HY. Resistive Analysis of Hydrogen Peroxide in One Axon of Single Neuron with Nanopipets. Anal Chem 2018; 90:10117-10121. [DOI: 10.1021/acs.analchem.8b01539] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Mingchen Xu
- The State Key Lab of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, Jiangsu 210093, China
| | - Rongrong Pan
- The State Key Lab of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, Jiangsu 210093, China
| | - Yue Zhu
- Jiangsu Key Laboratory for High Technology Research of TCM Formulae and Jiangsu Collaborative Innovation Center of Chinese Medicinal Resources Industrialization, Nanjing University of Chinese Medicine, Nanjing, Jiangsu 210093, China
| | - Dechen Jiang
- The State Key Lab of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, Jiangsu 210093, China
| | - Hong-Yuan Chen
- The State Key Lab of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, Jiangsu 210093, China
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71
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Role of sodium channel subtype in action potential generation by neocortical pyramidal neurons. Proc Natl Acad Sci U S A 2018; 115:E7184-E7192. [PMID: 29991598 DOI: 10.1073/pnas.1720493115] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Neocortical pyramidal neurons express several distinct subtypes of voltage-gated Na+ channels. In mature cells, Nav1.6 is the dominant channel subtype in the axon initial segment (AIS) as well as in the nodes of Ranvier. Action potentials (APs) are initiated in the AIS, and it has been proposed that the high excitability of this region is related to the unique characteristics of the Nav1.6 channel. Knockout or loss-of-function mutation of the Scn8a gene is generally lethal early in life because of the importance of this subtype in noncortical regions of the nervous system. Using the Cre/loxP system, we selectively deleted Nav1.6 in excitatory neurons of the forebrain and characterized the excitability of Nav1.6-deficient layer 5 pyramidal neurons by patch-clamp and Na+ and Ca2+ imaging recordings. We now report that, in the absence of Nav1.6 expression, the AIS is occupied by Nav1.2 channels. However, APs are generated in the AIS, and differences in AP propagation to soma and dendrites are minimal. Moreover, the channels that are expressed in the AIS still show a clear hyperpolarizing shift in voltage dependence of activation, compared with somatic channels. The only major difference between Nav1.6-null and wild-type neurons was a strong reduction in persistent sodium current. We propose that the molecular environment of the AIS confers properties on whatever Na channel subtype is present and that some other benefit must be conferred by the selective axonal presence of the Nav1.6 channel.
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72
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Schlüter A, Del Turco D, Deller T, Gutzmann A, Schultz C, Engelhardt M. Structural Plasticity of Synaptopodin in the Axon Initial Segment during Visual Cortex Development. Cereb Cortex 2018; 27:4662-4675. [PMID: 28922860 DOI: 10.1093/cercor/bhx208] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2017] [Indexed: 12/12/2022] Open
Abstract
The axon initial segment (AIS) is essential for action potential generation. Recently, the AIS was identified as a site of neuronal plasticity. A subpopulation of AIS in cortical principal neurons contains stacks of endoplasmic reticulum (ER) forming the cisternal organelle (CO). The function of this organelle is poorly understood, but roles in local Ca2+-trafficking and AIS plasticity are discussed. To investigate whether the presence and/or the size of COs are linked to the development and maturation of AIS of cortical neurons, we analyzed the relationship between COs and the AIS during visual cortex development under control and visual deprivation conditions. In wildtype mice, immunolabeling for synaptopodin, ankyrin-G, and ßIV-spectrin were employed to label COs and the AIS, respectively. Dark rearing resulted in an increase in synaptopodin cluster sizes, suggesting a homeostatic function of the CO in this cellular compartment. In line with this observation, synaptopodin-deficient mice lacking the CO showed AIS shortening in the dark. Collectively, these data demonstrate that the CO is an essential part of the AIS machinery required for AIS plasticity during a critical developmental period of the visual cortex.
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Affiliation(s)
- Annabelle Schlüter
- Institute of Neuroanatomy, Centre for Biomedicine and Medical Technology Mannheim (CBTM), Medical Faculty Mannheim, Heidelberg University, Ludolf-Krehl-Str. 13-17, 68167 Mannheim, Germany.,Department of Neurobiology, Heidelberg University, Im Neuenheimer Feld 364, 69120 Heidelberg, Germany
| | - Domenico Del Turco
- Institute of Clinical Neuroanatomy, Neuroscience Center, Goethe-University Frankfurt, Theodor-Stern-Kai 7, 60590 Frankfurt am Main, Germany
| | - Thomas Deller
- Institute of Clinical Neuroanatomy, Neuroscience Center, Goethe-University Frankfurt, Theodor-Stern-Kai 7, 60590 Frankfurt am Main, Germany
| | - Annika Gutzmann
- Institute of Neuroanatomy, Centre for Biomedicine and Medical Technology Mannheim (CBTM), Medical Faculty Mannheim, Heidelberg University, Ludolf-Krehl-Str. 13-17, 68167 Mannheim, Germany
| | - Christian Schultz
- Institute of Neuroanatomy, Centre for Biomedicine and Medical Technology Mannheim (CBTM), Medical Faculty Mannheim, Heidelberg University, Ludolf-Krehl-Str. 13-17, 68167 Mannheim, Germany
| | - Maren Engelhardt
- Institute of Neuroanatomy, Centre for Biomedicine and Medical Technology Mannheim (CBTM), Medical Faculty Mannheim, Heidelberg University, Ludolf-Krehl-Str. 13-17, 68167 Mannheim, Germany
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73
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Yermakov LM, Drouet DE, Griggs RB, Elased KM, Susuki K. Type 2 Diabetes Leads to Axon Initial Segment Shortening in db/db Mice. Front Cell Neurosci 2018; 12:146. [PMID: 29937715 PMCID: PMC6002488 DOI: 10.3389/fncel.2018.00146] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Accepted: 05/14/2018] [Indexed: 01/09/2023] Open
Abstract
Cognitive and mood impairments are common central nervous system complications of type 2 diabetes, although the neuronal mechanism(s) remains elusive. Previous studies focused mainly on neuronal inputs such as altered synaptic plasticity. Axon initial segment (AIS) is a specialized functional domain within neurons that regulates neuronal outputs. Structural changes of AIS have been implicated as a key pathophysiological event in various psychiatric and neurological disorders. Here we evaluated the structural integrity of the AIS in brains of db/db mice, an established animal model of type 2 diabetes associated with cognitive and mood impairments. We assessed the AIS before (5 weeks of age) and after (10 weeks) the development of type 2 diabetes, and after daily exercise treatment of diabetic condition. We found that the development of type 2 diabetes is associated with significant AIS shortening in both medial prefrontal cortex and hippocampus, as evident by immunostaining of the AIS structural protein βIV spectrin. AIS shortening occurs in the absence of altered neuronal and AIS protein levels. We found no change in nodes of Ranvier, another neuronal functional domain sharing a molecular organization similar to the AIS. This is the first study to identify AIS alteration in type 2 diabetes condition. Since AIS shortening is known to lower neuronal excitability, our results may provide a new avenue for understanding and treating cognitive and mood impairments in type 2 diabetes.
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Affiliation(s)
- Leonid M Yermakov
- Department of Neuroscience, Cell Biology, and Physiology, Boonshoft School of Medicine, Wright State University, Dayton, OH, United States
| | - Domenica E Drouet
- Department of Neuroscience, Cell Biology, and Physiology, Boonshoft School of Medicine, Wright State University, Dayton, OH, United States
| | - Ryan B Griggs
- Department of Neuroscience, Cell Biology, and Physiology, Boonshoft School of Medicine, Wright State University, Dayton, OH, United States
| | - Khalid M Elased
- Department of Pharmacology and Toxicology, 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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74
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Huang CYM, Rasband MN. Axon initial segments: structure, function, and disease. Ann N Y Acad Sci 2018; 1420:46-61. [PMID: 29749636 DOI: 10.1111/nyas.13718] [Citation(s) in RCA: 106] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2018] [Revised: 03/13/2018] [Accepted: 03/17/2018] [Indexed: 11/28/2022]
Abstract
The axon initial segment (AIS) is located at the proximal axon and is the site of action potential initiation. This reflects the high density of ion channels found at the AIS. Adaptive changes to the location and length of the AIS can fine-tune the excitability of neurons and modulate plasticity in response to activity. The AIS plays an important role in maintaining neuronal polarity by regulating the trafficking and distribution of proteins that function in somatodendritic or axonal compartments of the neuron. In this review, we provide an overview of the AIS cytoarchitecture, mechanism of assembly, and recent studies revealing mechanisms of differential transport at the AIS that maintain axon and dendrite identities. We further discuss how genetic mutations in AIS components (i.e., ankyrins, ion channels, and spectrins) and injuries may cause neurological disorders.
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Affiliation(s)
| | - Matthew N Rasband
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas
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75
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Sanders SJ, Campbell AJ, Cottrell JR, Moller RS, Wagner FF, Auldridge AL, Bernier RA, Catterall WA, Chung WK, Empfield JR, George AL, Hipp JF, Khwaja O, Kiskinis E, Lal D, Malhotra D, Millichap JJ, Otis TS, Petrou S, Pitt G, Schust LF, Taylor CM, Tjernagel J, Spiro JE, Bender KJ. Progress in Understanding and Treating SCN2A-Mediated Disorders. Trends Neurosci 2018; 41:442-456. [PMID: 29691040 DOI: 10.1016/j.tins.2018.03.011] [Citation(s) in RCA: 181] [Impact Index Per Article: 30.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 03/09/2018] [Accepted: 03/14/2018] [Indexed: 01/20/2023]
Abstract
Advances in gene discovery for neurodevelopmental disorders have identified SCN2A dysfunction as a leading cause of infantile seizures, autism spectrum disorder, and intellectual disability. SCN2A encodes the neuronal sodium channel NaV1.2. Functional assays demonstrate strong correlation between genotype and phenotype. This insight can help guide therapeutic decisions and raises the possibility that ligands that selectively enhance or diminish channel function may improve symptoms. The well-defined function of sodium channels makes SCN2A an important test case for investigating the neurobiology of neurodevelopmental disorders more generally. Here, we discuss the progress made, through the concerted efforts of a diverse group of academic and industry scientists as well as policy advocates, in understanding and treating SCN2A-related disorders.
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Affiliation(s)
- Stephan J Sanders
- Department of Psychiatry, UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA 94158, USA.
| | - Arthur J Campbell
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, 75 Ames Street, Cambridge, MA 02142, USA
| | - Jeffrey R Cottrell
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, 75 Ames Street, Cambridge, MA 02142, USA
| | - Rikke S Moller
- The Danish Epilepsy Centre, Dianalund, Denmark; Institute for Regional Health Services, University of Southern Denmark, Campusvej 55, 5230 Odense, Denmark
| | - Florence F Wagner
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, 75 Ames Street, Cambridge, MA 02142, USA
| | - Angie L Auldridge
- FamilieSCN2a Foundation, P.O. Box 82, East Longmeadow, MA 01028, USA
| | - Raphael A Bernier
- Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, WA 98195, USA
| | - William A Catterall
- Department of Pharmacology, University of Washington, Seattle, WA 98195-7280, USA
| | - Wendy K Chung
- Simons Foundation, New York, NY 10010, USA; Department of Pediatrics and Medicine, Columbia University, New York, NY 10032, USA
| | - James R Empfield
- Xenon Pharmaceuticals Inc., 3650 Gilmore Way, Burnaby, BC V5G 4W8, Canada
| | - Alfred L George
- Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Joerg F Hipp
- Roche Innovation Center Basel, F. Hoffmann-La Roche Ltd, Basel, Switzerland
| | - Omar Khwaja
- Roche Innovation Center Basel, F. Hoffmann-La Roche Ltd, Basel, Switzerland
| | - Evangelos Kiskinis
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA; Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Dennis Lal
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, 75 Ames Street, Cambridge, MA 02142, USA
| | - Dheeraj Malhotra
- Roche Innovation Center Basel, F. Hoffmann-La Roche Ltd, Basel, Switzerland
| | - John J Millichap
- Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA; Epilepsy Center and Division of Neurology, Ann & Robert H. Lurie Children's Hospital of Chicago, IL 60611, USA; Department of Pediatrics, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Thomas S Otis
- Sainsbury Wellcome Centre for Neural Circuits and Behaviour, University College London, 25 Howland Street, London W1T 4JG, UK
| | - Steven Petrou
- Florey Institute of Neuroscience and Mental Health, The University of Melbourne, Parkville, VIC, Australia
| | - Geoffrey Pitt
- Cardiovascular Research Institute, Weill Cornell Medical College, Cornell University, New York, NY 10065, USA
| | - Leah F Schust
- FamilieSCN2a Foundation, P.O. Box 82, East Longmeadow, MA 01028, USA
| | - Cora M Taylor
- Geisinger Health System, 100 North Academy Avenue, Danville, PA 17822, USA
| | | | | | - Kevin J Bender
- Department of Neurology, UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA 94158, USA.
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76
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Galliano E, Franzoni E, Breton M, Chand AN, Byrne DJ, Murthy VN, Grubb MS. Embryonic and postnatal neurogenesis produce functionally distinct subclasses of dopaminergic neuron. eLife 2018; 7:e32373. [PMID: 29676260 PMCID: PMC5935487 DOI: 10.7554/elife.32373] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Accepted: 04/04/2018] [Indexed: 11/13/2022] Open
Abstract
Most neurogenesis in the mammalian brain is completed embryonically, but in certain areas the production of neurons continues throughout postnatal life. The functional properties of mature postnatally generated neurons often match those of their embryonically produced counterparts. However, we show here that in the olfactory bulb (OB), embryonic and postnatal neurogenesis produce functionally distinct subpopulations of dopaminergic (DA) neurons. We define two subclasses of OB DA neuron by the presence or absence of a key subcellular specialisation: the axon initial segment (AIS). Large AIS-positive axon-bearing DA neurons are exclusively produced during early embryonic stages, leaving small anaxonic AIS-negative cells as the only DA subtype generated via adult neurogenesis. These populations are functionally distinct: large DA cells are more excitable, yet display weaker and - for certain long-latency or inhibitory events - more broadly tuned responses to odorant stimuli. Embryonic and postnatal neurogenesis can therefore generate distinct neuronal subclasses, placing important constraints on the functional roles of adult-born neurons in sensory processing.
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Affiliation(s)
- Elisa Galliano
- Centre for Developmental NeurobiologyInstitute of Psychiatry, Psychology and Neuroscience, King’s College LondonLondonUnited Kingdom
- Department of Molecular and Cellular BiologyHarvard UniversityCambridgeUnited States
- Centre for Brain ScienceHarvard UniversityCambridgeUnited States
| | - Eleonora Franzoni
- Centre for Developmental NeurobiologyInstitute of Psychiatry, Psychology and Neuroscience, King’s College LondonLondonUnited Kingdom
| | - Marine Breton
- Centre for Developmental NeurobiologyInstitute of Psychiatry, Psychology and Neuroscience, King’s College LondonLondonUnited Kingdom
| | - Annisa N Chand
- Centre for Developmental NeurobiologyInstitute of Psychiatry, Psychology and Neuroscience, King’s College LondonLondonUnited Kingdom
| | - Darren J Byrne
- Centre for Developmental NeurobiologyInstitute of Psychiatry, Psychology and Neuroscience, King’s College LondonLondonUnited Kingdom
| | - Venkatesh N Murthy
- Department of Molecular and Cellular BiologyHarvard UniversityCambridgeUnited States
- Centre for Brain ScienceHarvard UniversityCambridgeUnited States
| | - Matthew S Grubb
- Centre for Developmental NeurobiologyInstitute of Psychiatry, Psychology and Neuroscience, King’s College LondonLondonUnited Kingdom
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77
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Hu W, Bean BP. Differential Control of Axonal and Somatic Resting Potential by Voltage-Dependent Conductances in Cortical Layer 5 Pyramidal Neurons. Neuron 2018. [PMID: 29526554 DOI: 10.1016/j.neuron.2018.02.016] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Voltage-dependent conductances not only drive action potentials but also help regulate neuronal resting potential. We found differential regulation of resting potential in the proximal axon of layer 5 pyramidal neurons compared to the soma. Axonal resting potential was more negative than the soma, reflecting differential control by multiple voltage-dependent channels, including sodium channels, Cav3 channels, Kv7 channels, and HCN channels. Kv7 current is highly localized to the axon and HCN current to the soma and dendrite. Because of impedance asymmetry between the soma and axon, axonal Kv7 current has little effect on somatic resting potential, while somatodendritic HCN current strongly influences the proximal axon. In fact, depolarizing somatodendritic HCN current is critical for resting activation of all the other voltage-dependent conductances, including Kv7 in the axon. These experiments reveal complex interactions among voltage-dependent conductances to control region-specific resting potential, with somatodendritic HCN channels playing a critical enabling role.
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Affiliation(s)
- Wenqin Hu
- Department of Neurobiology, Harvard Medical School, 220 Longwood Avenue, Boston, MA 02115, USA
| | - Bruce P Bean
- Department of Neurobiology, Harvard Medical School, 220 Longwood Avenue, Boston, MA 02115, USA.
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78
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Yue ZW, Wang YL, Xiao B, Feng L. Axon Initial Segment Structural Plasticity is Involved in Seizure Susceptibility in a Rat Model of Cortical Dysplasia. Neurochem Res 2018; 43:878-885. [PMID: 29468458 DOI: 10.1007/s11064-018-2493-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Revised: 01/30/2018] [Accepted: 02/02/2018] [Indexed: 11/28/2022]
Abstract
Cortical dysplasia is the most common etiology of intractable epilepsy. Both excitability changes in cortical neurons and neural network reconstitution play a role in cortical dysplasia epileptogenesis. Recent research shows that the axon initial segment, a subcompartment of the neuron important to the shaping of action potentials, adjusts its position in response to changes in input, which contributes to neuronal excitability and local circuit balance. It is unknown whether axon initial segment plasticity occurs in neurons involved in seizure susceptibility in cortical dysplasia. Here, we developed a "Carmustine"- "pilocarpine" rat model of cortical dysplasia and show that it exhibits a lower seizure threshold, as indicated by behavior studies and electroencephalogram monitoring. Using immunofluorescence, we measured the axon initial segment positions of deep L5 somatosensory neurons and show that it is positioned closer to the soma after acute seizure, and that this displacement is sustained in the chronic phase. We then show that Nifedipine has a dose-dependent protective effect against axon initial segment displacement and increased seizure susceptibility. These findings further our understanding of the pathophysiology of seizures in cortical dysplasia and suggests Nifedipine as a potential therapeutic agent.
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Affiliation(s)
- Zong-Wei Yue
- 1Neurology Department, Xiangya Hospital, Central South University, No. 87, Xiangya Road, Changsha, Hunan, China
| | - Ye-Lan Wang
- 1Neurology Department, Xiangya Hospital, Central South University, No. 87, Xiangya Road, Changsha, Hunan, China
| | - Bo Xiao
- 1Neurology Department, Xiangya Hospital, Central South University, No. 87, Xiangya Road, Changsha, Hunan, China.
| | - Li Feng
- 1Neurology Department, Xiangya Hospital, Central South University, No. 87, Xiangya Road, Changsha, Hunan, China.
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79
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Berger SL, Leo-Macias A, Yuen S, Khatri L, Pfennig S, Zhang Y, Agullo-Pascual E, Caillol G, Zhu MS, Rothenberg E, Melendez-Vasquez CV, Delmar M, Leterrier C, Salzer JL. Localized Myosin II Activity Regulates Assembly and Plasticity of the Axon Initial Segment. Neuron 2018; 97:555-570.e6. [PMID: 29395909 PMCID: PMC5805619 DOI: 10.1016/j.neuron.2017.12.039] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Revised: 08/24/2017] [Accepted: 12/22/2017] [Indexed: 01/08/2023]
Abstract
The axon initial segment (AIS) is the site of action potential generation and a locus of activity-dependent homeostatic plasticity. A multimeric complex of sodium channels, linked via a cytoskeletal scaffold of ankyrin G and beta IV spectrin to submembranous actin rings, mediates these functions. The mechanisms that specify the AIS complex to the proximal axon and underlie its plasticity remain poorly understood. Here we show phosphorylated myosin light chain (pMLC), an activator of contractile myosin II, is highly enriched in the assembling and mature AIS, where it associates with actin rings. MLC phosphorylation and myosin II contractile activity are required for AIS assembly, and they regulate the distribution of AIS components along the axon. pMLC is rapidly lost during depolarization, destabilizing actin and thereby providing a mechanism for activity-dependent structural plasticity of the AIS. Together, these results identify pMLC/myosin II activity as a common link between AIS assembly and plasticity.
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Affiliation(s)
- Stephen L Berger
- Neuroscience Institute and Department of Neuroscience and Physiology, NYU School of Medicine, New York, NY 10016, USA
| | | | - Stephanie Yuen
- Neuroscience Institute and Department of Neuroscience and Physiology, NYU School of Medicine, New York, NY 10016, USA
| | - Latika Khatri
- Neuroscience Institute and Department of Neuroscience and Physiology, NYU School of Medicine, New York, NY 10016, USA
| | - Sylvia Pfennig
- Neuroscience Institute and Department of Neuroscience and Physiology, NYU School of Medicine, New York, NY 10016, USA
| | - Yanqing Zhang
- Neuroscience Institute and Department of Neuroscience and Physiology, NYU School of Medicine, New York, NY 10016, USA
| | | | - Ghislaine Caillol
- Aix Marseille Université, CNRS, INP UMR7051, 13344 Cedex 15, Marseille, France
| | - Min-Sheng Zhu
- Model Animal Research Center and MOE Key Laboratory of Model Animal and Disease Study, Nanjing University, Nanjing 210061, China
| | - Eli Rothenberg
- Department of Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, NY 10016, USA
| | - Carmen V Melendez-Vasquez
- Department of Biological Sciences, Hunter College, New York, NY 10065, USA; Department of Molecular, Cellular, and Developmental Biology, The Graduate Center, The City University of New York, NY 10016, USA
| | - Mario Delmar
- Division of Cardiology, NYU School of Medicine, New York, NY 10016, USA
| | | | - James L Salzer
- Neuroscience Institute and Department of Neuroscience and Physiology, NYU School of Medicine, New York, NY 10016, USA.
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80
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Irie T, Trussell LO. Double-Nanodomain Coupling of Calcium Channels, Ryanodine Receptors, and BK Channels Controls the Generation of Burst Firing. Neuron 2017; 96:856-870.e4. [PMID: 29144974 DOI: 10.1016/j.neuron.2017.10.014] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 06/21/2017] [Accepted: 10/06/2017] [Indexed: 01/16/2023]
Abstract
Action potentials clustered into high-frequency bursts play distinct roles in neural computations. However, little is known about ionic currents that control the duration and probability of these bursts. We found that, in cartwheel inhibitory interneurons of the dorsal cochlear nucleus, the likelihood of bursts and the interval between their spikelets were controlled by Ca2+ acting across two nanodomains, one between plasma membrane P/Q Ca2+ channels and endoplasmic reticulum (ER) ryanodine receptors and another between ryanodine receptors and large-conductance, voltage- and Ca2+-activated K+ (BK) channels. Each spike triggered Ca2+-induced Ca2+ release (CICR) from the ER immediately beneath somatic, but not axonal or dendritic, plasma membrane. Moreover, immunolabeling demonstrated close apposition of ryanodine receptors and BK channels. Double-nanodomain coupling between somatic plasma membrane and hypolemmal ER cisterns provides a unique mechanism for rapid control of action potentials on the millisecond timescale.
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Affiliation(s)
- Tomohiko Irie
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, OR 97239, USA; Division of Pharmacology, National Institute of Health Sciences, Kanagawa 210-9501, Japan.
| | - Laurence O Trussell
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, OR 97239, USA; Vollum Institute, Oregon Health & Science University, Portland, OR 97239, USA.
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81
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Role of the Axon Initial Segment in the Control of Spontaneous Frequency of Nigral Dopaminergic Neurons In Vivo. J Neurosci 2017; 38:733-744. [PMID: 29217687 DOI: 10.1523/jneurosci.1432-17.2017] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Revised: 10/24/2017] [Accepted: 11/20/2017] [Indexed: 11/21/2022] Open
Abstract
The spontaneous tonic discharge activity of nigral dopamine neurons plays a fundamental role in dopaminergic signaling. To investigate the role of neuronal morphology and architecture with respect to spontaneous activity in this population, we visualized the 3D structure of the axon initial segment (AIS) along with the entire somatodendritic domain of adult male mouse dopaminergic neurons, previously recorded in vivo We observed a positive correlation of the firing rate with both proximity and size of the AIS. Computational modeling showed that the size of the AIS, but not its position within the somatodendritic domain, is the major causal determinant of the tonic firing rate in the intact model, by virtue of the higher intrinsic frequency of the isolated AIS. Further mechanistic analysis of the relationship between neuronal morphology and firing rate showed that dopaminergic neurons function as a coupled oscillator whose frequency of discharge results from a compromise between AIS and somatodendritic oscillators. Thus, morphology plays a critical role in setting the basal tonic firing rate, which in turn could control striatal dopaminergic signaling that mediates motivation and movement.SIGNIFICANCE STATEMENT The frequency at which nigral dopamine neurons discharge action potentials sets baseline dopamine levels in the brain, which enables activity in motor, cognitive, and motivational systems. Here, we demonstrate that the size of the axon initial segment, a subcellular compartment responsible for initiating action potentials, is a key determinant of the firing rate in these neurons. The axon initial segment and all the molecular components that underlie its critical function may provide a novel target for the regulation of dopamine levels in the brain.
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82
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Genetic disruption of ankyrin-G in adult mouse forebrain causes cortical synapse alteration and behavior reminiscent of bipolar disorder. Proc Natl Acad Sci U S A 2017; 114:10479-10484. [PMID: 28894008 DOI: 10.1073/pnas.1700689114] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Genome-wide association studies have implicated the ANK3 locus in bipolar disorder, a major human psychotic illness. ANK3 encodes ankyrin-G, which organizes the neuronal axon initial segment (AIS). We generated a mouse model with conditional disruption of ANK3 in pyramidal neurons of the adult forebrain (Ank-G cKO). This resulted in the expected loss of pyramidal neuron AIS voltage-gated sodium and potassium channels. There was also dramatic loss of markers of afferent GABAergic cartridge synapses, resembling the cortical microcircuitry changes in brains from psychotic patients, and suggesting disinhibition. Expression of c-fos was increased in cortical pyramidal neurons, consistent with increased neuronal activity due to disinhibition. The mice showed robust behavioral phenotypes reminiscent of aspects of human mania, ameliorated by antimania drugs lithium and valproate. Repeated social defeat stress resulted in repeated episodes of dramatic behavioral changes from hyperactivity to "depression-like" behavior, suggestive of some aspects of human bipolar disorder. Overall, we suggest that this Ank-G cKO mouse model recapitulates some of the core features of human bipolar disorder and indicates that cortical microcircuitry alterations during adulthood may be involved in pathogenesis. The model may be useful for studying disease pathophysiology and for developing experimental therapeutics.
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83
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Nirschl JJ, Ghiretti AE, Holzbaur ELF. The impact of cytoskeletal organization on the local regulation of neuronal transport. Nat Rev Neurosci 2017; 18:585-597. [PMID: 28855741 DOI: 10.1038/nrn.2017.100] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Neurons are akin to modern cities in that both are dependent on robust transport mechanisms. Like the best mass transit systems, trafficking in neurons must be tailored to respond to local requirements. Neurons depend on both high-speed, long-distance transport and localized dynamics to correctly deliver cargoes and to tune synaptic responses. Here, we focus on the mechanisms that provide localized regulation of the transport machinery, including the cytoskeleton and molecular motors, to yield compartment-specific trafficking in the axon initial segment, axon terminal, dendrites and spines. The synthesis of these mechanisms provides a sophisticated and responsive transit system for the cell.
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Affiliation(s)
- Jeffrey J Nirschl
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, 638A Clinical Research Building, 415 Curie Boulevard, Philadelphia, Pennsylvania 19104, USA
| | - Amy E Ghiretti
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, 638A Clinical Research Building, 415 Curie Boulevard, Philadelphia, Pennsylvania 19104, USA
| | - Erika L F Holzbaur
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, 638A Clinical Research Building, 415 Curie Boulevard, Philadelphia, Pennsylvania 19104, USA
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84
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Guo Y, Liu Z, Chen YK, Chai Z, Zhou C, Zhang Y. Neurons with Multiple Axons Have Functional Axon Initial Segments. Neurosci Bull 2017; 33:641-652. [PMID: 28828584 DOI: 10.1007/s12264-017-0169-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2016] [Accepted: 07/11/2017] [Indexed: 12/30/2022] Open
Abstract
Neurons grow multiple axons after treatment with glycogen synthase kinase-3 (GSK-3) inhibitors. However, whether they are electrically active is not known. Here, we examined the role of multiple axons as electrophysiological components during neuronal firing. Combining pharmacological, immunofluorescence, and electrophysiological methods, we found that more neurons had multiple axon initial segments (AISs) after inhibition of GSK-3 activity with SB415286. The multiple AISs induced by GSK-3 inhibition were enriched with voltage-gated sodium channels. The depolarization rate of the multiple-AIS neurons was increased, but their action potential threshold and half-width were normal. By calculating derivatives of the action-potential rising phase, an extra d2 V/dt 2 peak from the extra AIS was distinguished; this indicated that the extra AIS fired ahead of the soma and increased the rate of depolarization. Our study demonstrates that the multiple axons induced by GSK-3 inhibition have AIS structures that are electrically active, and provides insight for axon and AIS studies.
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Affiliation(s)
- Yu Guo
- State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, PKU-IDG/McGovern Institute for Brain Research, Beijing, 100871, China
| | - Zhuo Liu
- State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, PKU-IDG/McGovern Institute for Brain Research, Beijing, 100871, China.,Department of Forensic Science, People's Public Security University of China, Beijing, 100038, China
| | - Yi-Kun Chen
- State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, PKU-IDG/McGovern Institute for Brain Research, Beijing, 100871, China
| | - Zhen Chai
- State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, PKU-IDG/McGovern Institute for Brain Research, Beijing, 100871, China
| | - Chen Zhou
- State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, PKU-IDG/McGovern Institute for Brain Research, Beijing, 100871, China.
| | - Yan Zhang
- State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, PKU-IDG/McGovern Institute for Brain Research, Beijing, 100871, China.
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85
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González-Cabrera C, Meza R, Ulloa L, Merino-Sepúlveda P, Luco V, Sanhueza A, Oñate-Ponce A, Bolam JP, Henny P. Characterization of the axon initial segment of mice substantia nigra dopaminergic neurons. J Comp Neurol 2017; 525:3529-3542. [PMID: 28734032 DOI: 10.1002/cne.24288] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2017] [Revised: 07/08/2017] [Accepted: 07/10/2017] [Indexed: 12/11/2022]
Abstract
The axon initial segment (AIS) is the site of initiation of action potentials and influences action potential waveform, firing pattern, and rate. In view of the fundamental aspects of motor function and behavior that depend on the firing of substantia nigra pars compacta (SNc) dopaminergic neurons, we identified and characterized their AIS in the mouse. Immunostaining for tyrosine hydroxylase (TH), sodium channels (Nav ) and ankyrin-G (Ank-G) was used to visualize the AIS of dopaminergic neurons. Reconstructions of sampled AIS of dopaminergic neurons revealed variable lengths (12-60 μm) and diameters (0.2-0.8 μm), and an average of 50% reduction in diameter between their widest and thinnest parts. Ultrastructural analysis revealed submembranous localization of Ank-G at nodes of Ranvier and AIS. Serial ultrathin section analysis and 3D reconstructions revealed that Ank-G colocalized with TH only at the AIS. Few cases of synaptic innervation of the AIS of dopaminergic neurons were observed. mRNA in situ hybridization of brain-specific Nav subunits revealed the expression of Nav 1.2 by most SNc neurons and a small proportion expressing Nav 1.6. The presence of sodium channels, along with the submembranous location of Ank-G is consistent with the role of AIS in action potential generation. Differences in the size of the AIS likely underlie differences in firing pattern, while the tapering diameter of AIS may define a trigger zone for action potentials. Finally, the conspicuous expression of Nav 1.2 by the majority of dopaminergic neurons may explain their high threshold for firing and their low discharge rate.
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Affiliation(s)
- Cristian González-Cabrera
- Laboratorio de Neuroanatomía, Departamento de Anatomía, and Centro Interdisciplinario de Neurociencia, NeuroUC, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Rodrigo Meza
- Laboratorio de Neuroanatomía, Departamento de Anatomía, and Centro Interdisciplinario de Neurociencia, NeuroUC, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile.,Departamento de Fisiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Lorena Ulloa
- Laboratorio de Neuroanatomía, Departamento de Anatomía, and Centro Interdisciplinario de Neurociencia, NeuroUC, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Paulina Merino-Sepúlveda
- Laboratorio de Neuroanatomía, Departamento de Anatomía, and Centro Interdisciplinario de Neurociencia, NeuroUC, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Valentina Luco
- Laboratorio de Neuroanatomía, Departamento de Anatomía, and Centro Interdisciplinario de Neurociencia, NeuroUC, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Ana Sanhueza
- Laboratorio de Neuroanatomía, Departamento de Anatomía, and Centro Interdisciplinario de Neurociencia, NeuroUC, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Alejandro Oñate-Ponce
- Laboratorio de Neuroanatomía, Departamento de Anatomía, and Centro Interdisciplinario de Neurociencia, NeuroUC, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - J Paul Bolam
- MRC Brain Network Dynamics Unit, Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Pablo Henny
- Laboratorio de Neuroanatomía, Departamento de Anatomía, and Centro Interdisciplinario de Neurociencia, NeuroUC, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
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86
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Ben-Shalom R, Keeshen CM, Berrios KN, An JY, Sanders SJ, Bender KJ. Opposing Effects on Na V1.2 Function Underlie Differences Between SCN2A Variants Observed in Individuals With Autism Spectrum Disorder or Infantile Seizures. Biol Psychiatry 2017; 82:224-232. [PMID: 28256214 PMCID: PMC5796785 DOI: 10.1016/j.biopsych.2017.01.009] [Citation(s) in RCA: 164] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Revised: 12/14/2016] [Accepted: 01/10/2017] [Indexed: 01/02/2023]
Abstract
BACKGROUND Variants in the SCN2A gene that disrupt the encoded neuronal sodium channel NaV1.2 are important risk factors for autism spectrum disorder (ASD), developmental delay, and infantile seizures. Variants observed in infantile seizures are predominantly missense, leading to a gain of function and increased neuronal excitability. How variants associated with ASD affect NaV1.2 function and neuronal excitability are unclear. METHODS We examined the properties of 11 ASD-associated SCN2A variants in heterologous expression systems using whole-cell voltage-clamp electrophysiology and immunohistochemistry. Resultant data were incorporated into computational models of developing and mature cortical pyramidal cells that express NaV1.2. RESULTS In contrast to gain of function variants that contribute to seizure, we found that all ASD-associated variants dampened or eliminated channel function. Incorporating these electrophysiological results into a compartmental model of developing excitatory neurons demonstrated that all ASD variants, regardless of their mechanism of action, resulted in deficits in neuronal excitability. Corresponding analysis of mature neurons predicted minimal change in neuronal excitability. CONCLUSIONS This functional characterization thus identifies SCN2A mutation and NaV1.2 dysfunction as the most frequently observed ASD risk factor detectable by exome sequencing and suggests that associated changes in neuronal excitability, particularly in developing neurons, may contribute to ASD etiology.
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Affiliation(s)
- Roy Ben-Shalom
- Center for Integrative Neuroscience, Kavli Institute for Fundamental Neuroscience, Department of Neurology, San Francisco, San Francisco; Computational Research Division , Lawrence Berkeley National Laboratory, Berkeley, California
| | - Caroline M Keeshen
- Center for Integrative Neuroscience, Kavli Institute for Fundamental Neuroscience, Department of Neurology, San Francisco, San Francisco
| | - Kiara N Berrios
- Department of Chemistry, University of Puerto Rico, Río Piedras Campus, San Juan, Puerto Rico
| | - Joon Y An
- Department of Psychiatry, San Francisco, San Francisco; UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco
| | - Stephan J Sanders
- Department of Psychiatry, San Francisco, San Francisco; UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco
| | - Kevin J Bender
- Center for Integrative Neuroscience, Kavli Institute for Fundamental Neuroscience, Department of Neurology, San Francisco, San Francisco; UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco; Department of Chemistry, University of Puerto Rico, Río Piedras Campus, San Juan, Puerto Rico.
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87
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Jamann N, Jordan M, Engelhardt M. Activity-dependent axonal plasticity in sensory systems. Neuroscience 2017; 368:268-282. [PMID: 28739523 DOI: 10.1016/j.neuroscience.2017.07.035] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2017] [Revised: 06/23/2017] [Accepted: 07/14/2017] [Indexed: 12/21/2022]
Abstract
The rodent whisker-to-barrel cortex pathway is a classic model to study the effects of sensory experience and deprivation on neuronal circuit formation, not only during development but also in the adult. Decades of research have produced a vast body of evidence highlighting the fundamental role of neuronal activity (spontaneous and/or sensory-evoked) for circuit formation and function. In this context, it has become clear that neuronal adaptation and plasticity is not just a function of the neonatal brain, but persists into adulthood, especially after experience-driven modulation of network status. Mechanisms for structural remodeling of the somatodendritic or axonal domain include microscale alterations of neurites or synapses. At the same time, functional alterations at the nanoscale such as expression or activation changes of channels and receptors contribute to the modulation of intrinsic excitability or input-output relationships. However, it remains elusive how these forms of structural and functional plasticity come together to shape neuronal network formation and function. While specifically somatodendritic plasticity has been studied in great detail, the role of axonal plasticity, (e.g. at presynaptic boutons, branches or axonal microdomains), is rather poorly understood. Therefore, this review will only briefly highlight somatodendritic plasticity and instead focus on axonal plasticity. We discuss (i) the role of spontaneous and sensory-evoked plasticity during critical periods, (ii) the assembly of axonal presynaptic sites, (iii) axonal plasticity in the mature brain under baseline and sensory manipulation conditions, and finally (iv) plasticity of electrogenic axonal microdomains, namely the axon initial segment, during development and in the mature CNS.
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Affiliation(s)
- Nora Jamann
- Institute of Neuroanatomy, Medical Faculty Mannheim, CBTM, Heidelberg University, Germany
| | - Merryn Jordan
- Institute of Neuroanatomy, Medical Faculty Mannheim, CBTM, Heidelberg University, Germany
| | - Maren Engelhardt
- Institute of Neuroanatomy, Medical Faculty Mannheim, CBTM, Heidelberg University, Germany.
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88
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Rinetti-Vargas G, Phamluong K, Ron D, Bender KJ. Periadolescent Maturation of GABAergic Hyperpolarization at the Axon Initial Segment. Cell Rep 2017; 20:21-29. [PMID: 28683314 PMCID: PMC6483373 DOI: 10.1016/j.celrep.2017.06.030] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 05/15/2017] [Accepted: 06/11/2017] [Indexed: 10/25/2022] Open
Abstract
Neuronal chloride levels are developmentally regulated. Early in life, high intracellular concentrations support chloride efflux and depolarization at GABAergic synapses. In mouse, intracellular chloride decreases over the first postnatal week in the somatodendritic compartment, eventually supporting mature, hyperpolarizing GABAergic inhibition. In contrast to this dendritic switch, it is less clear how GABAergic signaling at the axon initial segment (AIS) functions in mature pyramidal cells, as reports of both depolarization and hyperpolarization have been reported in the AIS past the first postnatal week. Here, we show that GABAergic signaling at the AIS of prefrontal pyramidal cells, indeed, switches polarity from depolarizing to hyperpolarizing but does so over a protracted periadolescent period. This is the most delayed maturation in chloride reversal in any structure studied to date and suggests that chandelier cells, which mediate axo-axonic inhibition, play a unique role in the periadolescent maturation of prefrontal circuits.
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Affiliation(s)
- Gina Rinetti-Vargas
- Center for Integrative Neuroscience, University of California, San Francisco, San Francisco, CA 94143, USA; UCSF Weill Institute for Neuroscience, University of California, San Francisco, San Francisco, CA 94143, USA; Department of Neurology, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Khanhky Phamluong
- UCSF Weill Institute for Neuroscience, University of California, San Francisco, San Francisco, CA 94143, USA; Department of Neurology, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Dorit Ron
- UCSF Weill Institute for Neuroscience, University of California, San Francisco, San Francisco, CA 94143, USA; Department of Neurology, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Kevin J Bender
- Center for Integrative Neuroscience, University of California, San Francisco, San Francisco, CA 94143, USA; UCSF Weill Institute for Neuroscience, University of California, San Francisco, San Francisco, CA 94143, USA; Department of Neurology, University of California, San Francisco, San Francisco, CA 94143, USA.
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89
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Vascak M, Sun J, Baer M, Jacobs KM, Povlishock JT. Mild Traumatic Brain Injury Evokes Pyramidal Neuron Axon Initial Segment Plasticity and Diffuse Presynaptic Inhibitory Terminal Loss. Front Cell Neurosci 2017. [PMID: 28634442 PMCID: PMC5459898 DOI: 10.3389/fncel.2017.00157] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The axon initial segment (AIS) is the site of action potential (AP) initiation, thus a crucial regulator of neuronal activity. In excitatory pyramidal neurons, the high density of voltage-gated sodium channels (NaV1.6) at the distal AIS regulates AP initiation. A surrogate AIS marker, ankyrin-G (ankG) is a structural protein regulating neuronal functional via clustering voltage-gated ion channels. In neuronal circuits, changes in presynaptic input can alter postsynaptic output via AIS structural-functional plasticity. Recently, we showed experimental mild traumatic brain injury (mTBI) evokes neocortical circuit disruption via diffuse axonal injury (DAI) of excitatory and inhibitory neuronal systems. A key finding was that mTBI-induced neocortical electrophysiological changes involved non-DAI/ intact excitatory pyramidal neurons consistent with AIS-specific alterations. In the current study we employed Thy1-yellow fluorescent protein (YFP)-H mice to test if mTBI induces AIS structural and/or functional plasticity within intact pyramidal neurons 2 days after mTBI. We used confocal microscopy to assess intact YFP+ pyramidal neurons in layer 5 of primary somatosensory barrel field (S1BF), whose axons were continuous from the soma of origin to the subcortical white matter (SCWM). YFP+ axonal traces were superimposed on ankG and NaV1.6 immunofluorescent profiles to determine AIS position and length. We found that while mTBI had no effect on ankG start position, the length significantly decreased from the distal end, consistent with the site of AP initiation at the AIS. However, NaV1.6 structure did not change after mTBI, suggesting uncoupling from ankG. Parallel quantitative analysis of presynaptic inhibitory terminals along the postsynaptic perisomatic domain of these same intact YFP+ excitatory pyramidal neurons revealed a significant decrease in GABAergic bouton density. Also within this non-DAI population, patch-clamp recordings of intact YFP+ pyramidal neurons showed AP acceleration decreased 2 days post-mTBI, consistent with AIS functional plasticity. Simulations of realistic pyramidal neuron computational models using experimentally determined AIS lengths showed a subtle decrease is NaV1.6 density is sufficient to attenuate AP acceleration. Collectively, these findings highlight the complexity of mTBI-induced neocortical circuit disruption, involving changes in extrinsic/presynaptic inhibitory perisomatic input interfaced with intrinsic/postsynaptic intact excitatory neuron AIS output.
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Affiliation(s)
- Michal Vascak
- Department of Anatomy and Neurobiology, Virginia Commonwealth University School of MedicineRichmond, VA, United States
| | - Jianli Sun
- Department of Anatomy and Neurobiology, Virginia Commonwealth University School of MedicineRichmond, VA, United States
| | - Matthew Baer
- Department of Anatomy and Neurobiology, Virginia Commonwealth University School of MedicineRichmond, VA, United States
| | - Kimberle M Jacobs
- Department of Anatomy and Neurobiology, Virginia Commonwealth University School of MedicineRichmond, VA, United States
| | - John T Povlishock
- Department of Anatomy and Neurobiology, Virginia Commonwealth University School of MedicineRichmond, VA, United States
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90
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Zempel H, Dennissen FJA, Kumar Y, Luedtke J, Biernat J, Mandelkow EM, Mandelkow E. Axodendritic sorting and pathological missorting of Tau are isoform-specific and determined by axon initial segment architecture. J Biol Chem 2017; 292:12192-12207. [PMID: 28536263 DOI: 10.1074/jbc.m117.784702] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2017] [Revised: 05/21/2017] [Indexed: 11/06/2022] Open
Abstract
Subcellular mislocalization of the microtubule-associated protein Tau is a hallmark of Alzheimer disease (AD) and other tauopathies. Six Tau isoforms, differentiated by the presence or absence of a second repeat or of N-terminal inserts, exist in the human CNS, but their physiological and pathological differences have long remained elusive. Here, we investigated the properties and distributions of human and rodent Tau isoforms in primary forebrain rodent neurons. We found that the Tau diffusion barrier (TDB), located within the axon initial segment (AIS), controls retrograde (axon-to-soma) and anterograde (soma-to-axon) traffic of Tau. Tau isoforms without the N-terminal inserts were sorted efficiently into the axon. However, the longest isoform (2N4R-Tau) was partially retained in cell bodies and dendrites, where it accelerated spine and dendrite growth. The TDB (located within the AIS) was impaired when AIS components (ankyrin G, EB1) were knocked down or when glycogen synthase kinase-3β (GSK3β; an AD-associated kinase tethered to the AIS) was overexpressed. Using superresolution nanoscopy and live-cell imaging, we observed that microtubules within the AIS appeared highly dynamic, a feature essential for the TDB. Pathomechanistically, amyloid-β insult caused cofilin activation and F-actin remodeling and decreased microtubule dynamics in the AIS. Concomitantly with these amyloid-β-induced disruptions, the AIS/TDB sorting function failed, causing AD-like Tau missorting. In summary, we provide evidence that the human and rodent Tau isoforms differ in axodendritic sorting and amyloid-β-induced missorting and that the axodendritic distribution of Tau depends on AIS integrity.
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Affiliation(s)
- Hans Zempel
- German Center for Neurodegenerative Diseases (DZNE), 53127 Bonn, Germany; CAESAR Research Center, 53175 Bonn, Germany; Max Planck Institute for Metabolism Research, 50931 Cologne, Germany; University of Bonn, 53113 Bonn, Germany.
| | - Frank J A Dennissen
- German Center for Neurodegenerative Diseases (DZNE), 53127 Bonn, Germany; CAESAR Research Center, 53175 Bonn, Germany
| | - Yatender Kumar
- German Center for Neurodegenerative Diseases (DZNE), 53127 Bonn, Germany; Max Planck Institute for Metabolism Research, 50931 Cologne, Germany
| | - Julia Luedtke
- German Center for Neurodegenerative Diseases (DZNE), 53127 Bonn, Germany; CAESAR Research Center, 53175 Bonn, Germany
| | - Jacek Biernat
- German Center for Neurodegenerative Diseases (DZNE), 53127 Bonn, Germany; CAESAR Research Center, 53175 Bonn, Germany
| | - Eva-Maria Mandelkow
- German Center for Neurodegenerative Diseases (DZNE), 53127 Bonn, Germany; CAESAR Research Center, 53175 Bonn, Germany; Max Planck Institute for Metabolism Research, 50931 Cologne, Germany
| | - Eckhard Mandelkow
- German Center for Neurodegenerative Diseases (DZNE), 53127 Bonn, Germany; CAESAR Research Center, 53175 Bonn, Germany; Max Planck Institute for Metabolism Research, 50931 Cologne, Germany.
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91
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Evans MD, Tufo C, Dumitrescu AS, Grubb MS. Myosin II activity is required for structural plasticity at the axon initial segment. Eur J Neurosci 2017; 46:1751-1757. [PMID: 28452088 PMCID: PMC5573965 DOI: 10.1111/ejn.13597] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Revised: 03/29/2017] [Accepted: 04/20/2017] [Indexed: 12/21/2022]
Abstract
In neurons, axons possess a molecularly defined and highly organised proximal region – the axon initial segment (AIS) – that is a key regulator of both electrical excitability and cellular polarity. Despite existing as a large, dense structure with specialised cytoskeletal architecture, the AIS is surprisingly plastic, with sustained alterations in neuronal activity bringing about significant alterations to its position, length or molecular composition. However, although the upstream activity‐dependent signalling pathways that lead to such plasticity have begun to be elucidated, the downstream mechanisms that produce structural changes at the AIS are completely unknown. Here, we use dissociated cultures of rat hippocampus to show that two forms of AIS plasticity in dentate granule cells – long‐term relocation, and more rapid shortening – are completely blocked by treatment with blebbistatin, a potent and selective myosin II ATPase inhibitor. These data establish a link between myosin II and AIS function, and suggest that myosin II's primary role at the structure may be to effect activity‐dependent morphological alterations.
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Affiliation(s)
- Mark D Evans
- Centre for Developmental Neurobiology, King's College London, London, SE1 1UL, UK
| | - Candida Tufo
- Centre for Developmental Neurobiology, King's College London, London, SE1 1UL, UK
| | - Adna S Dumitrescu
- Centre for Developmental Neurobiology, King's College London, London, SE1 1UL, UK
| | - Matthew S Grubb
- Centre for Developmental Neurobiology, King's College London, London, SE1 1UL, UK.,FENS-Kavli Network of Excellence, Europe-wide
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92
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Nelson AD, Jenkins PM. Axonal Membranes and Their Domains: Assembly and Function of the Axon Initial Segment and Node of Ranvier. Front Cell Neurosci 2017; 11:136. [PMID: 28536506 PMCID: PMC5422562 DOI: 10.3389/fncel.2017.00136] [Citation(s) in RCA: 74] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 04/21/2017] [Indexed: 12/19/2022] Open
Abstract
Neurons are highly specialized cells of the nervous system that receive, process and transmit electrical signals critical for normal brain function. Here, we review the intricate organization of axonal membrane domains that facilitate rapid action potential conduction underlying communication between complex neuronal circuits. Two critical excitable domains of vertebrate axons are the axon initial segment (AIS) and the nodes of Ranvier, which are characterized by the high concentrations of voltage-gated ion channels, cell adhesion molecules and specialized cytoskeletal networks. The AIS is located at the proximal region of the axon and serves as the site of action potential initiation, while nodes of Ranvier, gaps between adjacent myelin sheaths, allow rapid propagation of the action potential through saltatory conduction. The AIS and nodes of Ranvier are assembled by ankyrins, spectrins and their associated binding partners through the clustering of membrane proteins and connection to the underlying cytoskeleton network. Although the AIS and nodes of Ranvier share similar protein composition, their mechanisms of assembly are strikingly different. Here we will cover the mechanisms of formation and maintenance of these axonal excitable membrane domains, specifically highlighting the similarities and differences between them. We will also discuss recent advances in super resolution fluorescence imaging which have elucidated the arrangement of the submembranous axonal cytoskeleton revealing a surprising structural organization necessary to maintain axonal organization and function. Finally, human mutations in axonal domain components have been associated with a growing number of neurological disorders including severe cognitive dysfunction, epilepsy, autism, neurodegenerative diseases and psychiatric disorders. Overall, this review highlights the assembly, maintenance and function of axonal excitable domains, particularly the AIS and nodes of Ranvier, and how abnormalities in these processes may contribute to disease.
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Affiliation(s)
- Andrew D Nelson
- Department of Pharmacology, University of Michigan Medical SchoolAnn Arbor, MI, USA
| | - Paul M Jenkins
- Department of Pharmacology, University of Michigan Medical SchoolAnn Arbor, MI, USA.,Department of Psychiatry, University of Michigan Medical SchoolAnn Arbor, MI, USA
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93
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Goetz SM, Deng ZD. The development and modelling of devices and paradigms for transcranial magnetic stimulation. Int Rev Psychiatry 2017; 29:115-145. [PMID: 28443696 PMCID: PMC5484089 DOI: 10.1080/09540261.2017.1305949] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Revised: 03/03/2017] [Accepted: 03/09/2017] [Indexed: 12/20/2022]
Abstract
Magnetic stimulation is a non-invasive neurostimulation technique that can evoke action potentials and modulate neural circuits through induced electric fields. Biophysical models of magnetic stimulation have become a major driver for technological developments and the understanding of the mechanisms of magnetic neurostimulation and neuromodulation. Major technological developments involve stimulation coils with different spatial characteristics and pulse sources to control the pulse waveform. While early technological developments were the result of manual design and invention processes, there is a trend in both stimulation coil and pulse source design to mathematically optimize parameters with the help of computational models. To date, macroscopically highly realistic spatial models of the brain, as well as peripheral targets, and user-friendly software packages enable researchers and practitioners to simulate the treatment-specific and induced electric field distribution in the brains of individual subjects and patients. Neuron models further introduce the microscopic level of neural activation to understand the influence of activation dynamics in response to different pulse shapes. A number of models that were designed for online calibration to extract otherwise covert information and biomarkers from the neural system recently form a third branch of modelling.
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Affiliation(s)
- Stefan M Goetz
- a Department of Psychiatry & Behavioral Sciences, Division for Brain Stimulation & Neurophysiology , Duke University , Durham , NC , USA
- b Department of Electrical & Computer Engineering , Duke University , Durham , NC , USA
- c Department of Neurosurgery , Duke University , Durham , NC , USA
| | - Zhi-De Deng
- a Department of Psychiatry & Behavioral Sciences, Division for Brain Stimulation & Neurophysiology , Duke University , Durham , NC , USA
- d Intramural Research Program, Experimental Therapeutics & Pathophysiology Branch, Noninvasive Neuromodulation Unit , National Institutes of Health, National Institute of Mental Health , Bethesda , MD , USA
- e Duke Institute for Brain Sciences , Duke University , Durham , NC , USA
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94
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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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95
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Connors BW. Synchrony and so much more: Diverse roles for electrical synapses in neural circuits. Dev Neurobiol 2017; 77:610-624. [PMID: 28245529 DOI: 10.1002/dneu.22493] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Revised: 02/05/2017] [Accepted: 02/14/2017] [Indexed: 11/09/2022]
Abstract
Electrical synapses are neuronal gap junctions that are ubiquitous across brain regions and species. The biophysical properties of most electrical synapses are relatively simple-transcellular channels allow nearly ohmic, bidirectional flow of ionic current. Yet these connections can play remarkably diverse roles in different neural circuit contexts. Recent findings illustrate how electrical synapses may excite or inhibit, synchronize or desynchronize, augment or diminish rhythms, phase-shift, detect coincidences, enhance signals relative to noise, adapt, and interact with nonlinear membrane and transmitter-release mechanisms. Most of these functions are likely to be widespread in central nervous systems. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 610-624, 2017.
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Affiliation(s)
- Barry W Connors
- Department of Neuroscience, Brown University, Providence, Rhode Island
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96
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Kyung JW, Cho IH, Lee S, Song WK, Ryan TA, Hoppa MB, Kim SH. Adaptor Protein 2 (AP-2) complex is essential for functional axogenesis in hippocampal neurons. Sci Rep 2017; 7:41620. [PMID: 28139716 PMCID: PMC5282494 DOI: 10.1038/srep41620] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2016] [Accepted: 12/21/2016] [Indexed: 11/18/2022] Open
Abstract
The complexity and diversity of a neural network requires regulated elongation and branching of axons, as well as the formation of synapses between neurons. In the present study we explore the role of AP-2, a key endocytic adaptor protein complex, in the development of rat hippocampal neurons. We found that the loss of AP-2 during the early stage of development resulted in impaired axon extension and failed maturation of the axon initial segment (AIS). Normally the AIS performs two tasks in concert, stabilizing neural polarity and generating action potentials. In AP-2 silenced axons polarity is established, however there is a failure to establish action potential firing. Consequently, this impairs activity-driven Ca2+ influx and exocytosis at nerve terminals. In contrast, removal of AP-2 from older neurons does not impair axonal growth or signaling and synaptic function. Our data reveal that AP-2 has important roles in functional axogenesis by proper extension of axon as well as the formation of AIS during the early step of neurodevelopment.
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Affiliation(s)
- Jae Won Kyung
- Department of Biomedical Science, Graduate School, Kyung Hee University, Seoul, 02447, South Korea
| | - In Ha Cho
- Department of Biology, Molecular Cellular Biology Program, Dartmouth College, Hanover, NH, 03755, USA
| | - Sukmook Lee
- Laboratory of Molecular Cancer Therapeutics, Scripps Korea Antibody Institute, Chuncheon, 24341, South Korea
| | - Woo Keun Song
- School of Life Science, Bioimaging Research Center, Gwangju Institute of Science and Technology (GIST), Gwangju, 61005, South Korea
| | - Timothy A Ryan
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, 10065, USA
| | - Michael B Hoppa
- Department of Biology, Molecular Cellular Biology Program, Dartmouth College, Hanover, NH, 03755, USA
| | - Sung Hyun Kim
- Department of Biomedical Science, Graduate School, Kyung Hee University, Seoul, 02447, South Korea.,Department of Physiology, Neurodegeneration Control Research Center, School of Medicine, Kyung Hee University, Seoul, 02447, South Korea
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97
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Tapia M, Dominguez A, Zhang W, Del Puerto A, Ciorraga M, Benitez MJ, Guaza C, Garrido JJ. Cannabinoid Receptors Modulate Neuronal Morphology and AnkyrinG Density at the Axon Initial Segment. Front Cell Neurosci 2017; 11:5. [PMID: 28179879 PMCID: PMC5263140 DOI: 10.3389/fncel.2017.00005] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Accepted: 01/10/2017] [Indexed: 12/27/2022] Open
Abstract
Neuronal polarization underlies the ability of neurons to integrate and transmit information. This process begins early in development with axon outgrowth, followed by dendritic growth and subsequent maturation. In between these two steps, the axon initial segment (AIS), a subcellular domain crucial for generating action potentials (APs) and maintaining the morphological and functional polarization, starts to develop. However, the cellular/molecular mechanisms and receptors involved in AIS initial development and maturation are mostly unknown. In this study, we have focused on the role of the type-1 cannabinoid receptor (CB1R), a highly abundant G-protein coupled receptor (GPCR) in the nervous system largely involved in different phases of neuronal development and differentiation. Although CB1R activity modulation has been related to changes in axons or dendrites, its possible role as a modulator of AIS development has not been yet explored. Here we analyzed the potential role of CB1R on neuronal morphology and AIS development using pharmacological and RNA interference approaches in cultured hippocampal neurons. CB1R inhibition, at a very early developmental stage, has no effect on axonal growth, yet CB1R activation can promote it. By contrast, subsequent dendritic growth is impaired by CB1R inhibition, which also reduces ankyrinG density at the AIS. Moreover, our data show a significant correlation between early dendritic growth and ankyrinG density. However, CB1R inhibition in later developmental stages after dendrites are formed only reduces ankyrinG accumulation at the AIS. In conclusion, our data suggest that neuronal CB1R basal activity plays a role in initial development of dendrites and indirectly in AIS proteins accumulation. Based on the lack of CB1R expression at the AIS, we hypothesize that CB1R mediated modulation of dendritic arbor size during early development indirectly determines the accumulation of ankyrinG and AIS development. Further studies will be necessary to determine which CB1R-dependent mechanisms can coordinate these two domains, and what may be the impact of these early developmental changes once neurons mature and are embedded in a functional brain network.
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Affiliation(s)
- Mónica Tapia
- Instituto Cajal, Consejo Superior de Investigaciones Científicas (CSIC) Madrid, Spain
| | - Ana Dominguez
- Instituto Cajal, Consejo Superior de Investigaciones Científicas (CSIC) Madrid, Spain
| | - Wei Zhang
- Instituto Cajal, Consejo Superior de Investigaciones Científicas (CSIC) Madrid, Spain
| | - Ana Del Puerto
- Instituto Cajal, Consejo Superior de Investigaciones Científicas (CSIC) Madrid, Spain
| | - María Ciorraga
- Instituto Cajal, Consejo Superior de Investigaciones Científicas (CSIC) Madrid, Spain
| | - María José Benitez
- Instituto Cajal, Consejo Superior de Investigaciones Científicas (CSIC)Madrid, Spain; Department of Quimica Fisica Aplicada, Universidad Autónoma de MadridMadrid, Spain
| | - Carmen Guaza
- Instituto Cajal, Consejo Superior de Investigaciones Científicas (CSIC) Madrid, Spain
| | - Juan José Garrido
- Instituto Cajal, Consejo Superior de Investigaciones Científicas (CSIC) Madrid, Spain
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98
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Jiang L, Ni H, Wang QY, Huang L, Zhao SD, Yu JD, Ge RJ. Dual face of axonal inhibitory inputs in the modulation of neuronal excitability in cortical pyramidal neurons. Neural Regen Res 2017; 12:1079-1085. [PMID: 28852389 PMCID: PMC5558486 DOI: 10.4103/1673-5374.211186] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Limited by the tiny structure of axons, the effects of these axonal hyperpolarizing inputs on neuronal activity have not been directly elucidated. Here, we imitated these processes by simultaneously recording the activities of the somas and proximal axons of cortical pyramidal neurons. We found that spikes and subthreshold potentials propagate between somas and axons with high fidelity. Furthermore, inhibitory inputs on axons have opposite effects on neuronal activity according to their temporal integration with upstream signals. Concurrent with somatic depolarization, inhibitory inputs on axons decrease neuronal excitability and impede spike generation. In addition, following action potentials, inhibitory inputs on an axon increase neuronal spike capacity and improve spike precision. These results indicate that inhibitory inputs on proximal axons have dual regulatory functions in neuronal activity (suppression or facilitation) according to neuronal network patterns.
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Affiliation(s)
- Lei Jiang
- Department of Pathophysiology, Bengbu Medical College, Bengbu, Anhui Province, China.,Department of General Surgery, The Second Affiliated Hospital of Bengbu Medical College, Bengbu, Anhui Province, China
| | - Hong Ni
- Department of Pathophysiology, Bengbu Medical College, Bengbu, Anhui Province, China
| | - Qi-Yi Wang
- Department of Physiology, Bengbu Medical College, Bengbu, Anhui Province, China
| | - Li Huang
- Department of Pathophysiology, Bengbu Medical College, Bengbu, Anhui Province, China
| | - Shi-di Zhao
- Department of Pathophysiology, Bengbu Medical College, Bengbu, Anhui Province, China
| | - Jian-Dong Yu
- Guangdong-Hongkong-Macau Institute of CNS Regeneration, Joint International Research Laboratory of CNS Regeneration, Ministry of Education, Jinan University, Guangzhou, Guangdong Province, China
| | - Rong-Jing Ge
- Department of Pathophysiology, Bengbu Medical College, Bengbu, Anhui Province, China
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99
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Dumitrescu AS, Evans MD, Grubb MS. Evaluating Tools for Live Imaging of Structural Plasticity at the Axon Initial Segment. Front Cell Neurosci 2016; 10:268. [PMID: 27932952 PMCID: PMC5120105 DOI: 10.3389/fncel.2016.00268] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Accepted: 11/04/2016] [Indexed: 11/20/2022] Open
Abstract
The axon initial segment (AIS) is a specialized neuronal compartment involved in the maintenance of axo-dendritic polarity and in the generation of action potentials. It is also a site of significant structural plasticity—manipulations of neuronal activity in vitro and in vivo can produce changes in AIS position and/or size that are associated with alterations in intrinsic excitability. However, to date all activity-dependent AIS changes have been observed in experiments carried out on fixed samples, offering only a snapshot, population-wide view of this form of plasticity. To extend these findings by following morphological changes at the AIS of individual neurons requires reliable means of labeling the structure in live preparations. Here, we assessed five different immunofluorescence-based and genetically-encoded tools for live-labeling the AIS of dentate granule cells (DGCs) in dissociated hippocampal cultures. We found that an antibody targeting the extracellular domain of neurofascin provided accurate live label of AIS structure at baseline, but could not follow rapid activity-dependent changes in AIS length. Three different fusion constructs of GFP with full-length AIS proteins also proved unsuitable: while neurofascin-186-GFP and NaVβ4-GFP did not localize to the AIS in our experimental conditions, overexpressing 270kDa-AnkyrinG-GFP produced abnormally elongated AISs in mature neurons. In contrast, a genetically-encoded construct consisting of a voltage-gated sodium channel intracellular domain fused to yellow fluorescent protein (YFP-NaVII–III) fulfilled all of our criteria for successful live AIS label: this construct specifically localized to the AIS, accurately revealed plastic changes at the structure within hours, and, crucially, did not alter normal cell firing properties. We therefore recommend this probe for future studies of live AIS plasticity in vitro and in vivo.
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Affiliation(s)
- Adna S Dumitrescu
- Centre for Developmental Neurobiology, King's College London London, UK
| | - Mark D Evans
- Centre for Developmental Neurobiology, King's College London London, UK
| | - Matthew S Grubb
- Centre for Developmental Neurobiology, King's College London London, UK
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100
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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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