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https://www.readbyqxmd.com/read/29758267/the-functional-architecture-of-axonal-actin
#1
REVIEW
Marie-Jeanne Papandréou, Christophe Leterrier
The cytoskeleton builds and supports the complex architecture of neurons. It orchestrates the specification, growth, and compartmentation of the axon: axon initial segment, axonal shaft, presynapses. The cytoskeleton must then maintain this intricate architecture for the whole life of its host, but also drive its adaptation to new network demands and changing physiological conditions. Microtubules are readily visible inside axon shafts by electron microscopy, whereas axonal actin study has long been focused on dynamic structures of the axon such as growth cones...
May 11, 2018: Molecular and Cellular Neurosciences
https://www.readbyqxmd.com/read/29752714/post-crossing-segment-of-di1-commissural-axons-forms-collateral-branches-to-motor-neurons-in-the-developing-spinal-cord
#2
Takeshi Kaneyama, Ryuichi Shirasaki
The dI1 commissural axons in the developing spinal cord, upon crossing the midline through the floor plate, make a sharp turn to grow rostrally. These post-crossing axons initially just extend adjacent to the floor plate without entering nearby motor columns. However, it remains poorly characterized how these post-crossing dI1 axons behave subsequently to this process. In the present study, to address this issue, we examined in detail the behavior of post-crossing dI1 axons in mice, using the Atoh1 enhancer-based conditional expression system that enables selective and sparse labeling of individual dI1 axons, together with Hb9 and ChAT immunohistochemistry for precise identification of spinal motor neurons (MNs)...
May 11, 2018: Journal of Comparative Neurology
https://www.readbyqxmd.com/read/29749636/axon-initial-segments-structure-function-and-disease
#3
REVIEW
Claire Yu-Mei Huang, Matthew N Rasband
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...
May 11, 2018: Annals of the New York Academy of Sciences
https://www.readbyqxmd.com/read/29730177/ankyrins-roles-in-synaptic-biology-and-pathology
#4
REVIEW
Katharine R Smith, Peter Penzes
Ankyrins are broadly expressed adaptors that organize diverse membrane proteins into specialized domains and link them to the sub-membranous cytoskeleton. In neurons, ankyrins are known to have essential roles in organizing the axon initial segment and nodes of Ranvier. However, recent studies have revealed novel functions for ankyrins at synapses, where they organize and stabilize neurotransmitter receptors, modulate dendritic spine morphology and control adhesion to the presynaptic site. Ankyrin genes have also been highly associated with a range of neurodevelopmental and psychiatric diseases, including bipolar disorder, schizophrenia and autism, which all demonstrate overlap in their genetics, mechanisms and phenotypes...
May 3, 2018: Molecular and Cellular Neurosciences
https://www.readbyqxmd.com/read/29729299/the-intriguing-nature-of-dorsal-root-ganglion-neurons-linking-structure-with-polarity-and-function
#5
REVIEW
Ana Isabel Nascimento, Fernando Milhazes Mar, Mónica Mendes Sousa
Dorsal root ganglion (DRG) neurons are the first neurons of the sensory pathway. They are activated by a variety of sensory stimuli that are then transmitted to the central nervous system. An important feature of DRG neurons is their unique morphology where a single process -the stem axon- bifurcates into a peripheral and a central axonal branch, with different functions and cellular properties. Distinctive structural aspects of the two DRG neuron branches may have important implications for their function in health and disease...
May 2, 2018: Progress in Neurobiology
https://www.readbyqxmd.com/read/29722300/bridging-the-gap-axonal-fusion-drives-rapid-functional-recovery-of-the-nervous-system
#6
REVIEW
Jean-Sébastien Teoh, Michelle Yu-Ying Wong, Tarika Vijayaraghavan, Brent Neumann
Injuries to the central or peripheral nervous system frequently cause long-term disabilities because damaged neurons are unable to efficiently self-repair. This inherent deficiency necessitates the need for new treatment options aimed at restoring lost function to patients. Compared to humans, a number of species possess far greater regenerative capabilities, and can therefore provide important insights into how our own nervous systems can be repaired. In particular, several invertebrate species have been shown to rapidly initiate regeneration post-injury, allowing separated axon segments to re-join...
April 2018: Neural Regeneration Research
https://www.readbyqxmd.com/read/29688272/cellular-plasticity-in-the-adult-murine-piriform-cortex-continuous-maturation-of-dormant-precursors-into-excitatory-neurons
#7
Peter Rotheneichner, Maria Belles, Bruno Benedetti, Richard König, Dominik Dannehl, Christina Kreutzer, Pia Zaunmair, Maren Engelhardt, Ludwig Aigner, Juan Nacher, Sebastien Couillard-Despres
Neurogenesis in the healthy adult murine brain is based on proliferation and integration of stem/progenitor cells and is thought to be restricted to 2 neurogenic niches: the subventricular zone and the dentate gyrus. Intriguingly, cells expressing the immature neuronal marker doublecortin (DCX) and the polysialylated-neural cell adhesion molecule reside in layer II of the piriform cortex. Apparently, these cells progressively disappear along the course of ageing, while their fate and function remain unclear...
April 21, 2018: Cerebral Cortex
https://www.readbyqxmd.com/read/29676260/embryonic-and-postnatal-neurogenesis-produce-functionally-distinct-subclasses-of-dopaminergic-neuron
#8
Elisa Galliano, Eleonora Franzoni, Marine Breton, Annisa N Chand, Darren J Byrne, Venkatesh N Murthy, Matthew Grubb
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)...
April 20, 2018: ELife
https://www.readbyqxmd.com/read/29616726/segmentation-of-the-chick-central-and-peripheral-nervous-systems
#9
Roger Keynes, Geoffrey Cook
The chick embryo has provided a prominent model system for the study of segmental patterning in the nervous system. During early development, motor and sensory axon growth cones traverse the anterior/rostral half of each somite, so avoiding the developing vertebral components and ensuring separation of spinal nerves from vertebral bones. A glycoprotein expressed on the surface of posterior half-somite cells confines growth cones to the anterior half-somites by a contact repulsive mechanism. Hindbrain segmentation is also a conspicuous feature of chick brain development...
2018: International Journal of Developmental Biology
https://www.readbyqxmd.com/read/29577375/ca2-calmodulin-dependent-protein-kinase-ii-and-dimethyl-sulfoxide-affect-the-sealing-frequencies-of-transected-hippocampal-neurons
#10
Andrew D Poon, Sarah H McGill, Solomon Raju Bhupanapadu Sunkesula, Zachary S Burgess, Patrick J Dunne, Edward E Kang, George D Bittner
Traumatic injury often results in axonal severance, initiating obligatory Wallerian degeneration of distal segments, whereas proximal segments often survive. Calcium ion (Ca2+ ) influx at severed proximal axonal ends activates pathways that can induce apoptosis. However, this same Ca2+ -influx also activates multiple parallel pathways that seal the plasmalemma by inducing accumulation and fusion of vesicles at the lesion site that reduce Ca2+ -influx and enhance survival. We examined whether various inhibitors of Ca2+ /calmodulin-dependent protein kinases (CaMKs), and/or dimethyl sulfoxide (DMSO), a common solvent for biologically active substances, affected the ability of a hippocampal-derived neuronal cell line (B104 cells) to seal membrane damage following axotomy...
March 26, 2018: Journal of Neuroscience Research
https://www.readbyqxmd.com/read/29562514/amyloid-%C3%AE-and-tau-in-alzheimer-s-disease-novel-pathomechanisms-and-non-pharmacological-treatment-strategies
#11
Rebecca M Nisbet, Jürgen Götz
Accumulation of the peptide amyloid-β (Aβ) and the protein tau in Alzheimer's disease (AD) brains is a gradual process that involves the post-translational modification and assembly of monomeric forms into larger structures that eventually form fibrillar inclusions. This process is thought to both drive and initiate AD. However, why the axonally enriched tau in the course of AD accumulates in the somatodendritic domain is not fully understood. We discuss new data that provide a possible explanation that involves de novo protein synthesis, induced by Aβ and mediated through the kinase Fyn...
March 16, 2018: Journal of Alzheimer's Disease: JAD
https://www.readbyqxmd.com/read/29562186/kv1-2-channels-promote-nonlinear-spiking-motoneurons-for-powering-up-locomotion
#12
Rémi Bos, Ronald M Harris-Warrick, Cécile Brocard, Liliia E Demianenko, Marin Manuel, Daniel Zytnicki, Sergiy M Korogod, Frédéric Brocard
Spinal motoneurons are endowed with nonlinear spiking behaviors manifested by a spike acceleration whose functional significance remains uncertain. Here, we show in rodent lumbar motoneurons that these nonlinear spiking properties do not rely only on activation of dendritic nifedipine-sensitive L-type Ca2+ channels, as assumed for decades, but also on the slow inactivation of a nifedipine-sensitive K+ current mediated by Kv1.2 channels that are highly expressed in axon initial segments. Specifically, the pharmacological and computational inhibition of Kv1...
March 20, 2018: Cell Reports
https://www.readbyqxmd.com/read/29554219/prrt2-controls-neuronal-excitability-by-negatively-modulating-na-channel-1-2-1-6-activity
#13
Floriana Fruscione, Pierluigi Valente, Bruno Sterlini, Alessandra Romei, Simona Baldassari, Manuela Fadda, Cosimo Prestigio, Giorgia Giansante, Jacopo Sartorelli, Pia Rossi, Alicia Rubio, Antonio Gambardella, Thierry Nieus, Vania Broccoli, Anna Fassio, Pietro Baldelli, Anna Corradi, Federico Zara, Fabio Benfenati
Proline-rich transmembrane protein 2 (PRRT2) is the causative gene for a heterogeneous group of familial paroxysmal neurological disorders that include seizures with onset in the first year of life (benign familial infantile seizures), paroxysmal kinesigenic dyskinesia or a combination of both. Most of the PRRT2 mutations are loss-of-function leading to haploinsufficiency and 80% of the patients carry the same frameshift mutation (c.649dupC; p.Arg217Profs*8), which leads to a premature stop codon. To model the disease and dissect the physiological role of PRRT2, we studied the phenotype of neurons differentiated from induced pluripotent stem cells from previously described heterozygous and homozygous siblings carrying the c...
March 15, 2018: Brain: a Journal of Neurology
https://www.readbyqxmd.com/read/29533849/the-electrical-significance-of-axon-location-diversity
#14
REVIEW
Maarten Hp Kole, Romain Brette
The axon initial segment (AIS) is a unique domain of the proximal axon serving critical electrical and structural roles including the initiation of action potentials and maintenance of cellular polarity. Recent experimental and theoretical advances demonstrate that the anatomical site for initiation is remarkably diverse. The AIS location varies not only axially, along the axon, but axons also emerge variably from either the soma or proximal dendrites. Here, we review the evidence that the diversity of AIS and axon location has a substantial impact on the electrical properties and speculate that the anatomical heterogeneity of axon locations expands synaptic integration within cell types and improves information processing in neural circuits...
March 10, 2018: Current Opinion in Neurobiology
https://www.readbyqxmd.com/read/29510294/local-mechanisms-regulating-selective-cargo-entry-and-long-range-trafficking-in-axons
#15
REVIEW
Laura F Gumy, Casper C Hoogenraad
The polarized long-distance transport of neuronal cargoes depends on the presence of functional and structural axonal subcompartments. Given the heterogeneity of neuronal cargoes, selective sorting and entry occurs in the proximal axon where multiple subcellular specializations such as the axon initial segment, the pre-axonal exclusion zone, the MAP2 pre-axonal filtering zone and the Tau diffusion barrier provide different levels of regulation. Cargoes allowed to pass through the proximal axon spread into the more distal parts...
March 3, 2018: Current Opinion in Neurobiology
https://www.readbyqxmd.com/read/29507421/three-dimensional-electron-microscopy-reveals-changing-axonal-and-myelin-morphology-along-normal-and-partially-injured-optic-nerves
#16
Marcus K Giacci, Carole A Bartlett, Minh Huynh, Matt R Kilburn, Sarah A Dunlop, Melinda Fitzgerald
Following injury to the central nervous system, axons and myelin distinct from the initial injury site undergo changes associated with compromised function. Quantifying such changes is important to understanding the pathophysiology of neurotrauma; however, most studies to date used 2 dimensional (D) electron microscopy to analyse single sections, thereby failing to capture changes along individual axons. We used serial block face scanning electron microscopy (SBF SEM) to undertake 3D reconstruction of axons and myelin, analysing optic nerves from normal uninjured female rats and following partial optic nerve transection...
March 5, 2018: Scientific Reports
https://www.readbyqxmd.com/read/29496363/simulated-auditory-nerve-axon-demyelination-alters-sensitivity-and-response-timing-to-extracellular-stimulation
#17
Jesse M Resnick, Gabrielle E O'Brien, Jay T Rubinstein
Since cochlear implant function involves direct depolarization of spiral ganglion neurons (SGNs) by applied current, SGN physiological health must be an important factor in cochlear implant (CI) outcomes. This expected relationship has, however, been difficult to confirm in implant recipients. Suggestively, animal studies have demonstrated both acute and progressive SGN ultrastructural changes (notably axon demyelination), even in the absence of soma death, and corresponding altered physiology following sensorineural deafening...
April 2018: Hearing Research
https://www.readbyqxmd.com/read/29494655/minimizing-activation-of-overlying-axons-with-epiretinal-stimulation-the-role-of-fiber-orientation-and-electrode-configuration
#18
Timothy B Esler, Robert R Kerr, Bahman Tahayori, David B Grayden, Hamish Meffin, Anthony N Burkitt
Currently, a challenge in electrical stimulation of the retina with a visual prosthesis (bionic eye) is to excite only the cells lying directly under the electrode in the ganglion cell layer, while avoiding excitation of axon bundles that pass over the surface of the retina in the nerve fiber layer. Stimulation of overlying axons results in irregular visual percepts, limiting perceptual efficacy. This research explores how differences in fiber orientation between the nerve fiber layer and ganglion cell layer leads to differences in the electrical activation of the axon initial segment and axons of passage...
2018: PloS One
https://www.readbyqxmd.com/read/29468458/axon-initial-segment-structural-plasticity-is-involved-in-seizure-susceptibility-in-a-rat-model-of-cortical-dysplasia
#19
Zong-Wei Yue, Ye-Lan Wang, Bo Xiao, Li Feng
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...
April 2018: Neurochemical Research
https://www.readbyqxmd.com/read/29454834/functional-implications-of-inhibitory-synapse-placement-on-signal-processing-in-pyramidal-neuron-dendrites
#20
REVIEW
Josiah R Boivin, Elly Nedivi
A rich literature describes inhibitory innervation of pyramidal neurons in terms of the distinct inhibitory cell types that target the soma, axon initial segment, or dendritic arbor. Less attention has been devoted to how localization of inhibition to specific parts of the pyramidal dendritic arbor influences dendritic signal detection and integration. The effect of inhibitory inputs can vary based on their placement on dendritic spines versus shaft, their distance from the soma, and the branch order of the dendrite they inhabit...
February 15, 2018: Current Opinion in Neurobiology
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