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axon initial segment

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https://www.readbyqxmd.com/read/28227742/a-computational-model-of-orientation-dependent-activation-of-retinal-ganglion-cells
#1
Timothy Esler, Anthony N Burkitt, David B Grayden, Robert R Kerr, Bahman Tahayori, Hamish Meffin, Timothy Esler, Anthony N Burkitt, David B Grayden, Robert R Kerr, Bahman Tahayori, Hamish Meffin, Anthony N Burkitt, Timothy Esler, Hamish Meffin, David B Grayden, Robert R Kerr, Bahman Tahayori
Currently, a challenge in electrical stimulation for epiretinal prostheses is the avoidance of stimulation of axons of passage in the nerve fiber layer that originate from distant regions of the ganglion cell layer. A computational model of extracellular stimulation that captures the effect of neurite orientation in anisotropic tissue is developed using a modified version of the standard volume conductor model, known as the cellular composite model, embedded in a four layer model of the retina. Simulations are conducted to investigate the interaction of neural tissue orientation, electrode placement, and stimulation pulse duration and amplitude...
August 2016: Conference Proceedings: Annual International Conference of the IEEE Engineering in Medicine and Biology Society
https://www.readbyqxmd.com/read/28184187/ankyrin-g-membrane-partners-drive-the-establishment-and-maintenance-of-the-axon-initial-segment
#2
Christophe Leterrier, Nadine Clerc, Fanny Rueda-Boroni, Audrey Montersino, Bénédicte Dargent, Francis Castets
The axon initial segment (AIS) is a highly specialized neuronal compartment that plays a key role in neuronal development and excitability. It concentrates multiple membrane proteins such as ion channels and cell adhesion molecules (CAMs) that are recruited to the AIS by the scaffold protein ankyrin G (ankG). The crucial function of ankG in the anchoring of AIS membrane components is well established, but a reciprocal role of membrane partners in ankG targeting and stabilization remained elusive. In rat cultured hippocampal neurons and cortical organotypic slices, we found that shRNA-mediated knockdown of ankG membrane partners (voltage-gated sodium channels (Nav) or neurofascin-186) led to a decrease of ankG concentration and perturbed the AIS formation and maintenance...
2017: Frontiers in Cellular Neuroscience
https://www.readbyqxmd.com/read/28181483/nf-%C3%AE%C2%BAb-regulates-neuronal-ankyrin-g-via-a-negative-feedback-loop
#3
Hans-Georg König, Robert Schwamborn, Silke Andresen, Sinéad Kinsella, Orla Watters, Beau Fenner, Jochen H M Prehn
The axon initial segment (AIS) is a neuronal compartment defined by ankyrin-G expression. We here demonstrate that the IKK-complex co-localizes and interacts with the cytoskeletal anchor protein ankyrin-G in immunoprecipitation and proximity-ligation experiments in cortical neurons. Overexpression of the 270 kDa variant of ankyrin-G suppressed, while gene-silencing of ankyrin-G expression increased nuclear factor-κB (NF-κB) activity in primary neurons, suggesting that ankyrin-G sequesters the transcription factor in the AIS...
February 9, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28179879/cannabinoid-receptors-modulate-neuronal-morphology-and-ankyring-density-at-the-axon-initial-segment
#4
Mónica Tapia, Ana Dominguez, Wei Zhang, Ana Del Puerto, María Ciorraga, María José Benitez, Carmen Guaza, Juan José Garrido
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...
2017: Frontiers in Cellular Neuroscience
https://www.readbyqxmd.com/read/28139716/adaptor-protein-2-ap-2-complex-is-essential-for-functional-axogenesis-in-hippocampal-neurons
#5
Jae Won Kyung, In Ha Cho, Sukmook Lee, Woo Keun Song, Timothy A Ryan, Michael B Hoppa, Sung Hyun Kim
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...
January 31, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28119345/heparan-sulfates-support-pyramidal-cell-excitability-synaptic-plasticity-and-context-discrimination
#6
Daniel Minge, Oleg Senkov, Rahul Kaushik, Michel K Herde, Olga Tikhobrazova, Andreas B Wulff, Andrey Mironov, Toin H van Kuppevelt, Arie Oosterhof, Gaga Kochlamazashvili, Alexander Dityatev, Christian Henneberger
Heparan sulfate (HS) proteoglycans represent a major component of the extracellular matrix and are critical for brain development. However, their function in the mature brain remains to be characterized. Here, acute enzymatic digestion of HS side chains was used to uncover how HSs support hippocampal function in vitro and in vivo. We found that long-term potentiation (LTP) of synaptic transmission at CA3-CA1 Schaffer collateral synapses was impaired after removal of highly sulfated HSs with heparinase 1. This reduction was associated with decreased Ca(2+) influx during LTP induction, which was the consequence of a reduced excitability of CA1 pyramidal neurons...
January 23, 2017: Cerebral Cortex
https://www.readbyqxmd.com/read/28091722/hyperphosphorylated-tau-causes-reduced-hippocampal-ca1-excitability-by-relocating-the-axon-initial-segment
#7
Robert John Hatch, Yan Wei, Di Xia, Jürgen Götz
Hyperphosphorylated tau has a critical role in tauopathies such as Alzheimer's disease and frontotemporal dementia, impairing neuronal function and eventually leading to neurodegeneration. A critical role for tau is supported by studies in transgenic mouse models that express the P301L tau mutation found in cases of familial frontotemporal dementia, with the accumulation of hyperphosphorylated tau in the hippocampus causing reductions in hippocampal long-term potentiation and impairments in spatial learning and memory...
January 16, 2017: Acta Neuropathologica
https://www.readbyqxmd.com/read/28068338/spikelets-in-pyramidal-neurons-action-potentials-initiated-in-the-axon-initial-segment-that-do-not-activate-the-soma
#8
Martina Michalikova, Michiel W H Remme, Richard Kempter
Spikelets are small spike-like depolarizations that can be measured in somatic intracellular recordings. Their origin in pyramidal neurons remains controversial. To explain spikelet generation, we propose a novel single-cell mechanism: somato-dendritic input generates action potentials at the axon initial segment that may fail to activate the soma and manifest as somatic spikelets. Using mathematical analysis and numerical simulations of compartmental neuron models, we identified four key factors controlling spikelet generation: (1) difference in firing threshold, (2) impedance mismatch, and (3) electrotonic separation between the soma and the axon initial segment, as well as (4) input amplitude...
January 2017: PLoS Computational Biology
https://www.readbyqxmd.com/read/27994149/fgf14-is-a-regulator-of-kcnq2-3-channels
#9
Juan Lorenzo Pablo, Geoffrey S Pitt
KCNQ2/3 (Kv7.2/7.3) channels and voltage-gated sodium channels (VGSCs) are enriched in the axon initial segment (AIS) where they bind to ankyrin-G and coregulate membrane potential in central nervous system neurons. The molecular mechanisms supporting coordinated regulation of KCNQ and VGSCs and the cellular mechanisms governing KCNQ trafficking to the AIS are incompletely understood. Here, we show that fibroblast growth factor 14 (FGF14), previously described as a VGSC regulator, also affects KCNQ function and localization...
January 3, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/27979964/schwannomin-interacting-protein-1-isoform-iqcj-schip1-is-a-multipartner-ankyrin-and-spectrin-binding-protein-involved-in-the-organization-of-nodes-of-ranvier
#10
Pierre-Marie Martin, Carmen Cifuentes-Diaz, Jérôme Devaux, Marta Garcia, Jocelyne Bureau, Sylvie Thomasseau, Esther Klingler, Jean-Antoine Girault, Laurence Goutebroze
The nodes of Ranvier are essential regions for action potential conduction in myelinated fibers. They are enriched in multimolecular complexes composed of voltage-gated Nav and Kv7 channels associated with cell adhesion molecules. Cytoskeletal proteins ankyrin-G (AnkG) and βIV-spectrin control the organization of these complexes and provide mechanical support to the plasma membrane. IQCJ-SCHIP1 is a cytoplasmic protein present in axon initial segments and nodes of Ranvier. It interacts with AnkG and is absent from nodes and axon initial segments of βIV-spectrin and AnkG mutant mice...
February 10, 2017: Journal of Biological Chemistry
https://www.readbyqxmd.com/read/27966487/expressions-of-visual-pigments-and-synaptic-proteins-in-neonatal-chick-retina-exposed-to-light-of-variable-photoperiods
#11
Kumar Abhiram Jha, Tapas C Nag, Shashi Wadhwa, Tara Sankar Roy
Light causes damage to the retina, which is one of the supposed factors for age-related macular degeneration in human. Some animal species show drastic retinal changes when exposed to intense light (e.g. albino rats). Although birds have a pigmented retina, few reports indicated its susceptibility to light damage. To know how light influences a cone-dominated retina (as is the case with human), we examined the effects of moderate light intensity on the retina of white Leghorn chicks (Gallus g. domesticus). The newly hatched chicks were initially acclimatized at 500 lux for 7 days in 12 h light: 12 h dark cycles (12L:12D)...
December 2016: Journal of Biosciences
https://www.readbyqxmd.com/read/27956739/ankyrin-g-isoform-imbalance-and-interneuronopathy-link-epilepsy-and-bipolar-disorder
#12
A Y Lopez, X Wang, M Xu, A Maheshwari, D Curry, S Lam, A M Adesina, J L Noebels, Q-Q Sun, E C Cooper
ANK3, encoding the adaptor protein Ankyrin-G (AnkG), has been implicated in bipolar disorder by genome-wide association studies. ANK3 has multiple alternative first exons, and a bipolar disorder-associated ANK3 variant has been shown to reduce the expression of exon 1b. Here we identify mechanisms through which reduced ANK3 exon 1b isoform expression disrupts neuronal excitation-inhibition balance. We find that parvalbumin (PV) interneurons and principal cells differentially express ANK3 first exon subtypes...
December 13, 2016: Molecular Psychiatry
https://www.readbyqxmd.com/read/27932952/evaluating-tools-for-live-imaging-of-structural-plasticity-at-the-axon-initial-segment
#13
Adna S Dumitrescu, Mark D Evans, Matthew S Grubb
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...
2016: Frontiers in Cellular Neuroscience
https://www.readbyqxmd.com/read/27930291/covariation-of-axon-initial-segment-location-and-dendritic-tree-normalizes-the-somatic-action-potential
#14
Mustafa S Hamada, Sarah Goethals, Sharon I de Vries, Romain Brette, Maarten H P Kole
In mammalian neurons, the axon initial segment (AIS) electrically connects the somatodendritic compartment with the axon and converts the incoming synaptic voltage changes into a temporally precise action potential (AP) output code. Although axons often emanate directly from the soma, they may also originate more distally from a dendrite, the implications of which are not well-understood. Here, we show that one-third of the thick-tufted layer 5 pyramidal neurons have an axon originating from a dendrite and are characterized by a reduced dendritic complexity and thinner main apical dendrite...
December 20, 2016: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/27911898/bilaterian-giant-ankyrins-have-a-common-evolutionary-origin-and-play-a-conserved-role-in-patterning-the-axon-initial-segment
#15
Timothy Jegla, Michelle M Nguyen, Chengye Feng, Daniel J Goetschius, Esteban Luna, Damian B van Rossum, Bishoy Kamel, Aditya Pisupati, Elliott S Milner, Melissa M Rolls
In vertebrate neurons, the axon initial segment (AIS) is specialized for action potential initiation. It is organized by a giant 480 Kd variant of ankyrin G (AnkG) that serves as an anchor for ion channels and is required for a plasma membrane diffusion barrier that excludes somatodendritic proteins from the axon. An unusually long exon required to encode this 480Kd variant is thought to have been inserted only recently during vertebrate evolution, so the giant ankyrin-based AIS scaffold has been viewed as a vertebrate adaptation for fast, precise signaling...
December 2016: PLoS Genetics
https://www.readbyqxmd.com/read/27884423/alterations-in-a-unique-class-of-cortical-chandelier-cell-axon-cartridges-in-schizophrenia
#16
Brad R Rocco, Adam M DeDionisio, David A Lewis, Kenneth N Fish
BACKGROUND: The axons of chandelier cells (ChCs) target the axon initial segment of pyramidal neurons, forming an array of boutons termed a cartridge. In schizophrenia, the density of cartridges detectable by gamma-aminobutyric acid (GABA) membrane transporter 1 immunoreactivity is lower, whereas the density of axon initial segments detectable by immunoreactivity for the α2 subunit of the GABAA receptor is higher in layers 2/superficial 3 of the prefrontal cortex. These findings were interpreted as compensatory responses to lower GABA levels in ChCs...
September 29, 2016: Biological Psychiatry
https://www.readbyqxmd.com/read/27881784/low-somatic-sodium-conductance-enhances-action-potential-precision-in-time-coding-auditory-neurons
#17
Yang Yang, Bina Ramamurthy, Andreas Neef, Matthew A Xu-Friedman
: Auditory nerve fibers encode sounds in the precise timing of action potentials (APs), which is used for such computations as sound localization. Timing information is relayed through several cell types in the auditory brainstem that share an unusual property: their APs are not overshooting, suggesting that the cells have very low somatic sodium conductance (gNa). However, it is not clear how gNa influences temporal precision. We addressed this by comparing bushy cells (BCs) in the mouse cochlear nucleus with T-stellate cells (SCs), which do have normal overshooting APs...
November 23, 2016: Journal of Neuroscience: the Official Journal of the Society for Neuroscience
https://www.readbyqxmd.com/read/27871891/long-term-alcohol-exposure-elicits-hippocampal-nonsynaptic-epileptiform-activity-changes-associated-with-expression-and-functional-changes-in-nkcc1-kcc2-co-transporters-and-na-k-atpase
#18
Luiz E C Santos, Antônio M Rodrigues, Mariana R Lopes, Victor D C Costa, Carla A Scorza, Fulvio A Scorza, Esper A Cavalheiro, Antônio-Carlos G Almeida
Nonsynaptic mechanism changes, particularly the enhancement of NKCC1 expression in the dentate gyrus (DG) after 4weeks of ethanol consumption, motivate the present work, in which rats were submitted to a period of chronic consumption (12weeks). Four groups of six animals (6-week-old male Wistar rats) were formed, including the control (C), ethanol 1 (E1), ethanol 2 (E2) and ethanol 3 (E3) groups. The rats in the E1, E2 and E3 groups were treated daily with a 30% v/v solution of ethanol, administered via oral gavage (1...
January 6, 2017: Neuroscience
https://www.readbyqxmd.com/read/27861786/infantile-spasms-and-encephalopathy-without-preceding-neonatal-seizures-caused-by-kcnq2-r198q-a-gain-of-function-variant
#19
John J Millichap, Francesco Miceli, Michela De Maria, Cynthia Keator, Nishtha Joshi, Baouyen Tran, Maria Virginia Soldovieri, Paolo Ambrosino, Vandana Shashi, Mohamad A Mikati, Edward C Cooper, Maurizio Taglialatela
Variants in KCNQ2 encoding for Kv 7.2 neuronal K(+) channel subunits lead to a spectrum of neonatal-onset epilepsies, ranging from self-limiting forms to severe epileptic encephalopathy. Most KCNQ2 pathogenic variants cause loss-of-function, whereas few increase channel activity (gain-of-function). We herein provide evidence for a new phenotypic and functional profile in KCNQ2-related epilepsy: infantile spasms without prior neonatal seizures associated with a gain-of-function gene variant. With use of an international registry, we identified four unrelated patients with the same de novo heterozygous KCNQ2 c...
January 2017: Epilepsia
https://www.readbyqxmd.com/read/27859267/human-motoneurone-excitability-is-depressed-by-activation-of-serotonin-1a-receptors-with-buspirone
#20
Jessica M D'Amico, Annie A Butler, Martin E Héroux, Florence Cotel, Jean-François M Perrier, Jane E Butler, Simon C Gandevia, Janet L Taylor
KEY POINTS: In the adult turtle spinal cord, action potential generation in motoneurones is inhibited by spillover of serotonin to extrasynaptic serotonin 1A (5-HT1A ) receptors at the axon initial segment. We explored whether ingestion of the 5-HT1A receptor partial agonist, buspirone, decreases motoneurone excitability in humans. Following ingestion of buspirone, two tests of motoneurone excitability showed decreases. F-wave areas and persistence in an intrinsic muscle of the hand were reduced, as was the area of cervicomedullary motor evoked potentials in biceps brachii...
November 17, 2016: Journal of Physiology
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