Adjacent Axons Research Articles

Possible mechanism of action potential propagation mediated by static electric field: A novel assumption of understanding nerve interaction and ephaptic coupling

The generation and propagation of physical signals in living biosystems are continuous issues. Traditional Hodgkin-Huxley model based on ionic current conduction could not explain the fast transmission of action potential in myelinated axons and factors influencing action potential velocity. We propose that the ion flow induced by Nav channel generates near field quasi-static electric field at extracellular space, termed as an ephaptic field which is able to excite nearby passive axons. Our simulation indicates that the static electric field produced by sodium ion channels in one node of Ranvier is improbable to stimulate the ion channels in the adjacent neighboring node. However, the ion channel ring in one node of Ranvier could induce the shift of membrane potential (0.01 mV) on the node at nearby axons (100 μm) in a bundle of axon synchronously, suggesting zig-zag propagation of action potential. Together with the superposition effect of ephaptic feedback field generated by the synchronized movement of adjacent parallel axons stimulate the adjacent node of the original axon, strengthen the action potential to travel in a zig-zag pattern. Our model also provides an explanation for the rapid velocity of action potential propagation reported in experimental studies.

Structural reorganization of medullary dorsal horn astrocytes in a rat model of neuropathic pain.

Multiple studies have shown that astrocytes in the medullary dorsal horn (MDH) play an important role in the development of pathologic pain. However, little is known about the structural reorganization of the peripheral astrocytic processes (PAP), the main functional part of the astrocyte, in MDH in neuropathic state. For this, we investigated the structural relationship between PAP and their adjacent presynaptic axon terminals and postsynaptic dendrites in the superficial laminae of the MDH using electron microscopical immunohistochemistry for ezrin, a marker for PAP, and quantitative analysis in a rat model of neuropathic pain following chronic constriction injury of the infraorbital nerve (CCI-ION). We found that, compared to controls, in rats with CCI-ION, (1) the number, % area, surface density, and volume fraction of ezrin-positive (+) PAP, as well as the fraction of synaptic edge apposed by ezrin + PAP and the degree of its coverage of presynaptic axon terminals and postsynaptic dendrites increased significantly, (2) these effects were abolished by administration of the mGluR5 antagonist 2-methyl-6-(phenylethynyl) pyridine (MPEP). These findings indicate that PAP undergoes structural reorganization around the central synapses of sensory afferents following nerve injury, suggest that it may be mediated by mGluR5, and may represent the structural basis for enhancing astrocyte-neuron interaction in neuropathic pain.

Transsynaptic BMP Signaling Regulates Fine-Scale Topography between Adjacent Sensory Neurons.

Sensory axons projecting to the central nervous system are organized into topographic maps that represent the locations of sensory stimuli. In some sensory systems, even adjacent sensory axons are arranged topographically, forming "fine-scale" topographic maps. Although several broad molecular gradients are known to instruct coarse topography, we know little about the molecular signaling that regulates fine-scale topography at the level of two adjacent axons. Here, we provide evidence that transsynaptic bone morphogenetic protein (BMP) signaling mediates local interneuronal communication to regulate fine-scale topography in the nociceptive system of Drosophila larvae. We first show that the topographic separation of the axon terminals of adjacent nociceptors requires their common postsynaptic target, the A08n neurons. This phenotype is recapitulated by knockdown of the BMP ligand, Decapentaplegic (Dpp), in these neurons. In addition, removing the Type 2 BMP receptors or their effector (Mad transcription factor) in single nociceptors impairs the fine-scale topography, suggesting the contribution of BMP signaling originated from A08n. This signaling is likely mediated by phospho-Mad in the presynaptic terminals of nociceptors to ensure local interneuronal communication. Finally, reducing Dpp levels in A08n reduces the nociceptor-A08n synaptic contacts. Our data support that transsynaptic BMP signaling establishes the fine-scale topography by facilitating the formation of topographically correct synapses. Local BMP signaling for synapse formation may be a developmental strategy that independently regulates neighboring axon terminals for fine-scale topography.

Axonal autophagic vesicle transport in the rat optic nerve in vivo under normal conditions and during acute axonal degeneration

Neurons pose a particular challenge to degradative processes like autophagy due to their long and thin processes. Autophagic vesicles (AVs) are formed at the tip of the axon and transported back to the soma. This transport is essential since the final degradation of the vesicular content occurs only close to or in the soma. Here, we established an in vivo live-imaging model in the rat optic nerve using viral vector mediated LC3-labeling and two-photon-microscopy to analyze axonal transport of AVs. Under basal conditions in vivo, 50% of the AVs are moving with a majority of 85% being transported in the retrograde direction. Transport velocity is higher in the retrograde than in the anterograde direction. A crush lesion of the optic nerve results in a rapid breakdown of retrograde axonal transport while the anterograde transport stays intact over several hours. Close to the lesion site, the formation of AVs is upregulated within the first 6 h after crush, but the clearance of AVs and the levels of lysosomal markers in the adjacent axon are reduced. Expression of p150Glued, an adaptor protein of dynein, is significantly reduced after crush lesion. In vitro, fusion and colocalization of the lysosomal marker cathepsin D with AVs are reduced after axotomy. Taken together, we present here the first in vivo analysis of axonal AV transport in the mammalian CNS using live-imaging. We find that axotomy leads to severe defects of retrograde motility and a decreased clearance of AVs via the lysosomal system.

Altered projection-specific synaptic remodeling and its modification by oxytocin in an idiopathic autism marmoset model.

Alterations in the experience-dependent and autonomous elaboration of neural circuits are assumed to underlie autism spectrum disorder (ASD), though it is unclear what synaptic traits are responsible. Here, utilizing a valproic acid-induced ASD marmoset model, which shares common molecular features with idiopathic ASD, we investigate changes in the structural dynamics of tuft dendrites of upper-layer pyramidal neurons and adjacent axons in the dorsomedial prefrontal cortex through two-photon microscopy. In model marmosets, dendritic spine turnover is upregulated, and spines are generated in clusters and survived more often than in control marmosets. Presynaptic boutons in local axons, but not in commissural long-range axons, demonstrate hyperdynamic turnover in model marmosets, suggesting alterations in projection-specific plasticity. Intriguingly, nasal oxytocin administration attenuates clustered spine emergence in model marmosets. Enhanced clustered spine generation, possibly unique to certain presynaptic partners, may be associated with ASD and be a potential therapeutic target.

In Vivo Imaging of Secondary Neurodegeneration Associated With Phosphatidylserine Externalization Along Axotomized Axons.

Axonal degeneration in acute and chronic disorders is well-characterized, comprising retrograde (proximal) and Wallerian (distal) degeneration, but the mechanism of propagation remains less understood. Laser injury with a diode-pumped solid-state 532nm laser was used to axotomize retinal ganglion cell axons. We used confocal in vivo imaging to demonstrate that phosphatidylserine externalization is a biomarker of early axonal degeneration after selective intraretinal axotomy. Quantitative dynamic analysis revealed that the rate of axonal degeneration was fastest within 40minutes, then decreased exponentially afterwards. Axonal degeneration was constrained within the same axotomized axonal bundles. Remarkably, axon degeneration arising from the site of injury induced a secondary degeneration of distal normal axons. Axonal degeneration in vivo is a progressive process associated with phosphatidylserine externalization, which can propagate not only along the axon but to adjacent uninjured axons. This finding has implications for acute and chronic neurodegenerative disorders associated with axonal injury.

454 Effects of Human Brain Organoid Age on Post-Transplant Growth in the Rat Motor Cortex

INTRODUCTION: Human brain organoids have potential to be used as a substrate for brain repair following injury, however the factors affecting survival and integration of transplanted organoids are unknown. We hypothesized that organoids transplanted at an earlier time point would result in improved survival and integration into the motor cortex because of their greater growth potential. METHODS: Human forebrain organoids at two timepoints (d20-25, d55-60) were transplanted into the motor cortex of adult rats following an aspiration injury. The first cohort was survived for 1 month post transplantation (MPT, n = 6); the second cohort was survived for 2 MPT (n = 16). Quantification of organoid volume and immunohistochemistry were performed. RESULTS: Survival of organoids post-transplantation was >90%. Pre-transplantation organoid size at d20-25 was significantly smaller than d55-60 (p < 0.0001). Average organoid volume 2 MPT was 1.04E + 10 µm3, significantly increased from 1435.4 µm3 pre-transplant (p = 0.0156). 2 MPT was correlated with more growth than 1MPT, though not statistically significant (p = 0.2672). Younger organoids trended toward a larger end-volume with the mean d20-25 volume being 3.1x larger than d55-60 at 1MPT (p = 0.3211) and 1.74x larger at 2MPT (p = 0.5090). Axon projections were seen in the adjacent host cortex at both timepoints. Both organoid age groups contained neural progenitors (PAX6, Sox2) with d20-25 retaining areas reminiscent of neural progenitor zones at 1MPT. CONCLUSIONS: Survival of transplanted organoids following injury was successful with a vast majority of organoids experiencing rapid growth within the injury cavity. Both age cohorts demonstrated adjacent axon projection and the presence of neural progenitors. Though further investigation is needed to clarify the influence of organoid maturity on integration, the survival rate and degree of post-transplant growth is a promising first step.

Muliple Sclerosis, Corpus Callosum & Epilepsy

There is a difference in prevalence of Epilepsy in General population & MS patients. Interical Epileptiform Discharges (IED) positivity in EEG is also different in the above two populations. Demyelination slows down the conduction speed of axons and author is proposing that different speed of conduction in adjacent axons can generate re-entrant circuits. If the reentrant circuits involve Corpus callosum (CC) fibers, seizure activities of MS can be triggered. DBS applied to CC can terminate the seizure attack of MS like Vagal Nerve Simulator (VNS) in terminating seizure in general population.

Autofluorescence enhancement for label-free imaging of myelinated fibers in mammalian brains

Analyzing the structure of neuronal fibers with single axon resolution in large volumes is a challenge in connectomics. Different technologies try to address this goal; however, they are limited either by the ineffective labeling of the fibers or in the achievable resolution. The possibility of discriminating between different adjacent myelinated axons gives the opportunity of providing more information about the fiber composition and architecture within a specific area. Here, we propose MAGIC (Myelin Autofluorescence imaging by Glycerol Induced Contrast enhancement), a tissue preparation method to perform label-free fluorescence imaging of myelinated fibers that is user friendly and easy to handle. We exploit the high axial and radial resolution of two-photon fluorescence microscopy (TPFM) optical sectioning to decipher the mixture of various fiber orientations within the sample of interest. We demonstrate its broad applicability by performing mesoscopic reconstruction at a sub-micron resolution of mouse, rat, monkey, and human brain samples and by quantifying the different fiber organization in control and Reeler mouse's hippocampal sections. Our study provides a novel method for 3D label-free imaging of nerve fibers in fixed samples at high resolution, below micrometer level, that overcomes the limitation related to the myelinated axons exogenous labeling, improving the possibility of analyzing brain connectivity.

Schwann cell development: From neural crest to myelin sheath.

Vertebrate nervous system function requires glial cells, including myelinating glia that insulate axons and provide trophic support that allows for efficient signal propagation by neurons. In vertebrate peripheral nervous systems, neural crest-derived glial cells known as Schwann cells (SCs) generate myelin by encompassing and iteratively wrapping membrane around single axon segments. SC gliogenesis and neurogenesis are intimately linked and governed by a complex molecular environment that shapes their developmental trajectory. Changes in this external milieu drive developing SCs through a series of distinct morphological and transcriptional stages from the neural crest to a variety of glial derivatives, including the myelinating sublineage. Cues originate from the extracellular matrix, adjacent axons, and the developing SC basal lamina to trigger intracellular signaling cascades and gene expression changes that specify stages and transitions in SC development. Here, we integrate the findings from in vitro neuron-glia co-culture experiments with in vivo studies investigating SC development, particularly in zebrafish and mouse, to highlight critical factors that specify SC fate. Ultimately, we connect classic biochemical and mutant studies with modern genetic and visualization tools that have elucidated the dynamics of SC development. This article is categorized under: Signaling Pathways > Cell Fate Signaling Nervous System Development > Vertebrates: Regional Development.

AMPK Preferentially Depresses Retrograde Transport of Axonal Mitochondria during Localized Nutrient Deprivation

Mitochondrial clusters are found at regions of high-energy demand, allowing cells to meet local metabolic requirements while maintaining neuronal homeostasis. AMP-activated protein kinase (AMPK), a key energy stress sensor, responds to increases in AMP/ATP ratio by activating multiple signaling cascades to overcome the energetic deficiency. In many neurologic conditions, the distal axon experiences energetic stress independent of the soma. Here, we used microfluidic devices to physically isolate these two neuronal structures and to investigate whether localized AMPK signaling influenced axonal mitochondrial transport. Nucleofection of primary cortical neurons, derived from E16-18 mouse embryos (both sexes), with mito-GFP allowed monitoring of the transport dynamics of mitochondria within the axon, by confocal microscopy. Pharmacological activation of AMPK at the distal axon (0.1 mm 5-aminoimidazole-4-carboxamide riboside) induced a depression of the mean frequency, velocity, and distance of retrograde mitochondrial transport in the adjacent axon. Anterograde mitochondrial transport was less sensitive to local AMPK stimulus, with the imbalance of bidirectional mitochondrial transport resulting in accumulation of mitochondria at the region of energetic stress signal. Mitochondria in the axon-rich white matter of the brain rely heavily on lactate as a substrate for ATP synthesis. Interestingly, localized inhibition of lactate uptake (10 nm AR-C155858) reduced mitochondrial transport in the adjacent axon in all parameters measured, similar to that observed by 5-aminoimidazole-4-carboxamide riboside treatment. Coaddition of compound C restored all parameters measured to baseline levels, confirming the involvement of AMPK. This study highlights a role of AMPK signaling in the depression of axonal mitochondrial mobility during localized energetic stress.SIGNIFICANCE STATEMENT As the main providers of cellular energy, the dynamic transport of mitochondria within the neuron allows for clustering at regions of high-energy demand. Here we investigate whether acute changes in energetic stress signal in the spatially isolated axon would alter mitochondrial transport in this local region. Both direct and indirect activation of AMP-activated protein kinase isolated to the distal axon induced a rapid, marked depression in local mitochondrial transport. This work highlights the ability of acute localized AMP-activated protein kinase signaling to affect mitochondrial mobility within the axon, with important implications for white matter injury, axonal growth, and axonal degeneration.

A mathematical model of ephaptic interactions in neuronal fiber pathways: Could there be more than transmission along the tracts?

While numerous studies of ephaptic interactions have focused on either axons of peripheral nerves or on cortical structures, no attention has been given to the possibility of ephaptic interactions in white matter tracts. Inspired by the highly organized, tightly packed geometry of axons in fiber pathways, we aim to investigate the potential effects of ephaptic interactions along these structures that are resilient to experimental probing. We use axonal cable theory to derive a minimal model of a sheet of N ephaptically coupled axons. Numerical solutions of the proposed model are explored as ephaptic coupling is varied. We demonstrate that ephaptic interactions can lead to local phase locking between adjacent traveling impulses and that, as coupling is increased, traveling impulses trigger new impulses along adjacent axons, resulting in finite size traveling fronts. For strong enough coupling, impulses propagate laterally and backwards, resulting in complex spatiotemporal patterns. While common large-scale brain network models often model fiber pathways as simple relays of signals between different brain regions, our work calls for a closer reexamination of the validity of such a view. The results suggest that in the presence of significant ephaptic interactions, the brain fiber tracts can act as a dynamic active medium.

Terminal Schwann cell and vacant site mediated synapse elimination at developing neuromuscular junctions

Synapses undergo transition from polyinnervation by multiple axons to single innervation a few weeks after birth. Synaptic activity of axons and interaxonal competition are thought to drive this developmental synapse elimination and tested as key parameters in quantitative models for further understanding. Recent studies of muscle synapses (endplates) show that there are also terminal Schwann cells (tSCs), glial cells associated with motor neurons and their functions, and vacant sites (or vacancies) devoid of tSCs and axons proposing tSCs as key effectors of synapse elimination. However, there is no quantitative model that considers roles of tSCs including vacancies. Here we develop a stochastic model of tSC and vacancy mediated synapse elimination. It employs their areas on individual endplates quantified by electron microscopy-based analyses assuming that vacancies form randomly and are taken over by adjacent axons or tSCs. The model reliably reproduced synapse elimination whereas equal or random probability models, similar to classical interaxonal competition models, did not. Furthermore, the model showed that synapse elimination is accelerated by enhanced synaptic activity of one axon and also by increased areas of vacancies and tSCs suggesting that the areas are important structural correlates of the rate of synapse elimination.

Propagation and Selectivity of Axonal Loss in Leber Hereditary Optic Neuropathy

Leber hereditary optic neuropathy (LHON) is a syndrome of subacute loss of central vision associated with mutations in mitochondrial DNA coding for components of complex I. LHON preferentially involves small axons in the temporal optic nerve, but the reason is unclear. We performed a Monte Carlo simulation of the spread of injury in LHON axons to better understand the predilection for small axons. Optic nerve slices were modeled as grids containing axons with sizes from reported regional distributions. The propagation of injury from a localized concentration of superoxide was simulated as the spread via passive diffusion from one axon to adjacent axons, with basal production and scavenging rate proportional to axonal area and volume, respectively. Axonal degeneration occurred when intra-axonal concentrations reached a toxic threshold. Simulations demonstrated that almost all small and medium axons degenerated by the time steady-state was reached, but about 50% of large axons were preserved. The location of initial injury affected time to steady state, with nasal injuries reaching steady state faster than temporal injuries. The pattern of axonal degeneration in the simulations mirrored both visual fields and optic nerve histology from patients with LHON. These results provide insight into the nature of axonal loss in LHON.

Oligodendrocytes: Morphology, functions and involvement in neurodegenerative diseases

Oligodendrocytes (OLs) are myelinating cells of the central nervous system (CNS). They are a highly specialized type of glial cell in the CNS of vertebrates, which guarantee the transmission of action potentials over long distances by producing a myelin sheath that wraps adjacent axons. Although they are often credited merely with participation in myelination, recent research has led to a radical change in the understanding the role of these glial cells. OLs are currently understood to be plastic and adaptive cells, capable of responding quickly to changes taking place in the spatial neuronal network in the CNS. Due to their complex differentiation process and their physiology, OLs are among the most sensitive cells in the CNS. Finding answers about their interactions with other types of glial cells may result in benefits in the form of neuroprotection and axon plasticity. Damage to OLs and the myelin sheath is one of processes contributing to the development of crippling neurological diseases, although the role of these cells in neurodegeneration remains controversial. This article not only presents OLs as cells whose ultimate goal is to produce myelin sheaths, but also discusses their involvement in neurodegenerative diseases.

Distinct patterns of glia repair and remyelination in antibody-mediated demyelination models of multiple sclerosis and neuromyelitis optica.

Multiple sclerosis (MS) and neuromyelitis optica (NMO) are inflammatory demyelinating disorders of the central nervous system with evidence of antibody-mediated pathology. Using ex vivo organotypic mouse cerebellar slice cultures, we have demonstrated that recombinant antibodies (rAbs) cloned from cerebrospinal fluid plasmablasts of MS and NMO patients target myelin- and astrocyte-specific antigens to induce disease-specific oligodendrocyte loss and myelin degradation. In this study, we examined glial cell responses and myelin integrity during recovery from disease-specific antibody-mediated injury. Following exposure to MS rAb and human complement (HC) in cerebellar explants, myelinating oligodendrocytes repopulated the demyelinated tissue and formed new myelin sheaths along axons. Remyelination was accompanied by pronounced microglial activation. In contrast, following treatment with NMO rAb and HC, there was rapid regeneration of astrocytes and pre-myelinating oligodendrocytes but little formation of myelin sheaths on preserved axons. Deficient remyelination was associated with progressive axonal loss and the return of microglia to a resting state. Our results indicate that antibody-mediated demyelination in MS and NMO show distinct capacities for recovery associated with differential injury to adjacent axons and variable activation of microglia. Remyelination was rapid in MS rAb plus HC-induced demyelination. By contrast, oligodendrocyte maturation and remyelination failed following NMO rAb-mediated injury despite the rapid restoration of astrocytes and preservation of axons in early lesions.

An automated pipeline for bouton, spine, and synapse detection of in vivo two-photon images

BackgroundIn the nervous system, the neurons communicate through synapses. The size, morphology, and connectivity of these synapses are significant in determining the functional properties of the neural network. Therefore, they have always been a major focus of neuroscience research. Two-photon laser scanning microscopy allows the visualization of synaptic structures in vivo, leading to many important findings. However, the identification and quantification of structural imaging data currently rely heavily on manual annotation, a method that is both time-consuming and prone to bias.ResultsWe present an automated approach for the identification of synaptic structures in two-photon images. Axon boutons and dendritic spines are structurally distinct. They can be detected automatically using this image processing method. Then, synapses can be identified by integrating information from adjacent axon boutons and dendritic spines. In this study, we first detected the axonal boutons and dendritic spines respectively, and then identified synapses based on these results. Experimental results were validated manually, and the effectiveness of our proposed method was demonstrated.ConclusionsThis approach will helpful for neuroscientists to automatically analyze and quantify the formation, elimination and destabilization of the axonal boutons, dendritic spines and synapses.

Recent Advances in the Study of Bipolar/Rod-Shaped Microglia and their Roles in Neurodegeneration.

Microglia are the resident immune cells of the central nervous system (CNS) and they contribute to primary inflammatory responses following CNS injuries. The morphology of microglia is closely associated with their functional activities. Most previous research efforts have attempted to delineate the role of ramified and amoeboid microglia in the pathogenesis of neurodegenerative diseases. In addition to ramified and amoeboid microglia, bipolar/rod-shaped microglia were first described by Franz Nissl in 1899 and their presence in the brain was closely associated with the pathology of infectious diseases and sleeping disorders. However, studies relating to bipolar/rod-shaped microglia are very limited, largely due to the lack of appropriate in vitro and in vivo experimental models. Recent studies have reported the formation of bipolar/rod-shaped microglia trains in in vivo models of CNS injury, including diffuse brain injury, focal transient ischemia, optic nerve transection and laser-induced ocular hypertension (OHT). These bipolar/rod-shaped microglia formed end-to-end alignments in close proximity to the adjacent injured axons, but they showed no interactions with blood vessels or other types of glial cell. Recent studies have also reported on a highly reproducible in vitro culture model system to enrich bipolar/rod-shaped microglia that acts as a powerful tool with which to characterize this form of microglia. The molecular aspects of bipolar/rod-shaped microglia are of great interest in the field of CNS repair. This review article focuses on studies relating to the morphology and transformation of microglia into the bipolar/rod-shaped form, along with the differential gene expression and spatial distribution of bipolar/rod-shaped microglia in normal and pathological CNSs. The spatial arrangement of bipolar/rod-shaped microglia is crucial in the reorganization and remodeling of neuronal and synaptic circuitry following CNS injuries. Finally, we discuss the potential neuroprotective roles of bipolar/rod-shaped microglia, and the possibility of transforming ramified/amoeboid microglia into bipolar/rod-shaped microglia. This will be of considerable clinical benefit in the development of novel therapeutic strategies for treating various neurodegenerative diseases and promoting CNS repair after injury.

Rat odontoblasts may use glutamate to signal dentin injury

Accumulating evidence indicates that odontoblasts act as sensor cells, capable of triggering action potentials in adjacent pulpal nociceptive axons, suggesting a paracrine signaling via a currently unknown mediator. Since glutamate can mediate signaling by non-neuronal cells, and peripheral axons may express glutamate receptors (GluR), we hypothesized that the expression of high levels of glutamate, and of sensory receptors in odontoblasts, combined with an expression of GluR in adjacent pulpal axons, is the morphological basis for odontoblastic sensory signaling. To test this hypothesis, we investigated the expression of glutamate, the thermo- and mechanosensitive ion channels transient receptor potential vanilloid 1 (TRPV1), transient receptor potential ankyrin 1 (TRPA1), and TWIK-1-related K+channel (TREK-1), and the glutamate receptor mGluR5, in a normal rat dental pulp, and following dentin injury. We also examined the glutamate release from odontoblast in cell culture.Odontoblasts were enriched with glutamate, at the level as high as in adjacent pulpal axons, and showed immunoreactivity for TRPV1, TRPA1, and TREK-1. Pulpal sensory axons adjacent to odontoblasts expressed mGluR5. Both the levels of glutamate in odontoblasts, and the expression of mGluR5 in nearby axons, were upregulated following dentin injury. The extracellular glutamate concentration was increased significantly after treating of odontoblast cell line with calcium permeable ionophore, suggesting glutamate release from odontoblasts.These findings lend morphological support to the hypothesis that odontoblasts contain glutamate as a potential neuroactive substance that may activate adjacent pulpal axons, and thus contribute to dental pain and hypersensitivity.

Attenuation of Axonal Degeneration by Calcium Channel Inhibitors Improves Retinal Ganglion Cell Survival and Regeneration After Optic Nerve Crush.

Axonal degeneration is one of the initial steps in many traumatic and neurodegenerative central nervous system (CNS) disorders and thus a promising therapeutic target. A focal axonal lesion is followed by acute axonal degeneration (AAD) of both adjacent axon parts, before proximal and distal parts follow different degenerative fates at later time points. Blocking calcium influx by calcium channel inhibitors was previously shown to attenuate AAD after optic nerve crush (ONC). However, it remains unclear whether the attenuation of AAD also promotes consecutive axonal regeneration. Here, we used a rat ONC model to study the effects of calcium channel inhibitors on axonal degeneration, retinal ganglion cell (RGC) survival, and axonal regeneration, as well as the molecular mechanisms involved. Application of calcium channel inhibitors attenuated AAD after ONC and preserved axonal integrity as visualized by live imaging of optic nerve axons. Consecutively, this resulted in improved survival of RGCs and improved axonal regeneration at 28days after ONC. We show further that calcium channel inhibition attenuated lesion-induced calpain activation in the proximity of the crush and inhibited the activation of the c-Jun N-terminal kinase pathway. Pro-survival signaling via Akt in the retina was also increased. Our data thus show that attenuation of AAD improves consecutive neuronal survival and axonal regeneration and that calcium channel inhibitors could be valuable tools for therapeutic interventions in traumatic and degenerative CNS disorders.