Sodium channel blockade with phenytoin protects spinal cord axons, enhances axonal conduction, and improves functional motor recovery after contusion SCI

Thermosensitive collagen/fibrinogen gels loaded with decorin suppress lesion site cavitation and promote functional recovery after spinal cord injury

The treatment of spinal cord injury (SCI) is a complex challenge in regenerative medicine, complicated by the low intrinsic capacity of CNS neurons to regenerate their axons and the heterogeneity in size, shape and extent of human injuries. For example, some contusion injuries do not compromise the dura mater and in such cases implantation of preformed scaffolds or drug delivery systems may cause further damage. Injectable in situ thermosensitive scaffolds are therefore a less invasive alternative. In this study, we report the development of a novel, flowable, thermosensitive, injectable drug delivery system comprising bovine collagen (BC) and fibrinogen (FB) that forms a solid BC/FB gel (Gel) immediately upon exposure to physiological conditions and can be used to deliver reparative drugs, such as the naturally occurring anti-inflammatory, anti-scarring agent Decorin, into adult rat spinal cord lesion sites. In dorsal column lesions of adult rats treated with the Gel + Decorin, cavitation was completely suppressed and instead lesion sites became filled with injury-responsive cells and extracellular matrix materials, including collagen and laminin. Decorin increased the intrinsic potential of dorsal root ganglion neurons (DRGN) by increasing their expression of regeneration associated genes (RAGs), enhanced local axon regeneration/sprouting, as evidenced both histologically and by improved electrophysiological, locomotor and sensory function recovery. These results suggest that this drug formulated, injectable hydrogel has the potential to be further studied and translated into the clinic.

Overexpression of Reticulon 3 Enhances CNS Axon Regeneration and Functional Recovery after Traumatic Injury

CNS neurons are generally incapable of regenerating their axons after injury due to several intrinsic and extrinsic factors, including the presence of axon growth inhibitory molecules. One such potent inhibitor of CNS axon regeneration is Reticulon (RTN) 4 or Nogo-A. Here, we focused on RTN3 as its contribution to CNS axon regeneration is currently unknown. We found that RTN3 expression correlated with an axon regenerative phenotype in dorsal root ganglion neurons (DRGN) after injury to the dorsal columns, a well-characterised model of spinal cord injury. Overexpression of RTN3 promoted disinhibited DRGN neurite outgrowth in vitro and dorsal column axon regeneration/sprouting and electrophysiological, sensory and locomotor functional recovery after injury in vivo. Knockdown of protrudin, however, ablated RTN3-enhanced neurite outgrowth/axon regeneration in vitro and in vivo. Moreover, overexpression of RTN3 in a second model of CNS injury, the optic nerve crush injury model, enhanced retinal ganglion cell (RGC) survival, disinhibited neurite outgrowth in vitro and survival and axon regeneration in vivo, an effect that was also dependent on protrudin. These results demonstrate that RTN3 enhances neurite outgrowth/axon regeneration in a protrudin-dependent manner after both spinal cord and optic nerve injury.

Targeting Aquaporin-4 Subcellular Localization to Treat Central Nervous System Edema

Swelling of the brain or spinal cord (CNS edema) affects millions of people every year. All potential pharmacological interventions have failed in clinical trials, meaning that symptom management is the only treatment option. The water channel protein aquaporin-4 (AQP4) is expressed in astrocytes and mediates water flux across the blood-brain and blood-spinal cord barriers. Here we show that AQP4 cell-surface abundance increases in response to hypoxia-induced cell swelling in a calmodulin-dependent manner. Calmodulin directly binds the AQP4 carboxyl terminus, causing a specific conformational change and driving AQP4 cell-surface localization. Inhibition of calmodulin in a rat spinal cord injury model with the licensed drug trifluoperazine inhibited AQP4 localization to the blood-spinal cord barrier, ablated CNS edema, and led to accelerated functional recovery compared with untreated animals. We propose that targeting the mechanism of calmodulin-mediated cell-surface localization of AQP4 is a viable strategy for development of CNS edema therapies.

Phenytoin - An anti-seizure drug: Overview of its chemistry, pharmacology and toxicology

Phenytoin is a long-standing, anti-seizure drug widely used in clinical practice. It has also been evaluated in the context of many other illnesses in addition to its original epilepsy indication. The narrow therapeutic index of phenytoin and its ubiquitous daily use pose a high risk of poisoning. This review article focuses on the chemistry, pharmacokinetics, and toxicology of phenytoin, with a special focus on its mutagenicity, carcinogenicity, and teratogenicity. The side effects on human health associated with phenytoin use are thoroughly described. In particular, DRESS syndrome and cerebellar atrophy are addressed. This review will help in further understanding the benefits phenytoin use in the treatment of epilepsy.

The fate and function of oligodendrocyte progenitor cells after traumatic spinal cord injury

Oligodendrocyte progenitor cells (OPCs) are the most proliferative and dispersed population of progenitor cells in the adult central nervous system, which allows these cells to rapidly respond to damage. Oligodendrocytes and myelin are lost after traumatic spinal cord injury (SCI), compromising efficient conduction and, potentially, the long-term health of axons. In response, OPCs proliferate and then differentiate into new oligodendrocytes and Schwann cells to remyelinate axons. This culminates in highly efficient remyelination following experimental SCI in which nearly all intact demyelinated axons are remyelinated in rodent models. However, myelin regeneration comprises only one role of OPCs following SCI. OPCs contribute to scar formation after SCI and restrict the regeneration of injured axons. Moreover, OPCs alter their gene expression following demyelination, express cytokines and perpetuate the immune response. Here, we review the functional contribution of myelin regeneration and other recently uncovered roles of OPCs and their progeny to repair following SCI.

Attenuating the DNA damage response to double-strand breaks restores function in models of CNS neurodegeneration

DNA double-strand breaks are a feature of many acute and long-term neurological disorders, including neurodegeneration, following neurotrauma and after stroke. Persistent activation of the DNA damage response in response to double-strand breaks contributes to neural dysfunction and pathology as it can force post-mitotic neurons to re-enter the cell cycle leading to senescence or apoptosis. Mature, non-dividing neurons may tolerate low levels of DNA damage, in which case muting the DNA damage response might be neuroprotective. Here, we show that attenuating the DNA damage response by targeting the meiotic recombination 11, Rad50, Nijmegen breakage syndrome 1 complex, which is involved in double-strand break recognition, is neuroprotective in three neurodegeneration models in Drosophila and prevents Aβ_1-42-induced loss of synapses in embryonic hippocampal neurons. Attenuating the DNA damage response after optic nerve injury is also neuroprotective to retinal ganglion cells and promotes dramatic regeneration of their neurites both in vitro and in vivo. Dorsal root ganglion neurons similarly regenerate when the DNA damage response is targeted in vitro and in vivo and this strategy also induces significant restoration of lost function after spinal cord injury. We conclude that muting the DNA damage response in the nervous system is neuroprotective in multiple neurological disorders. Our results point to new therapies to maintain or repair the nervous system.

The Effect of Non-Gabapentinoid Anticonvulsants on Sensorimotor Recovery After Human Spinal Cord Injury

BACKGROUND

Recent observational studies have shown an association between gabapentinoid anticonvulsants and greater motor recovery after spinal cord injury. There is preclinical evidence to suggest that other anticonvulsants, such as sodium channel blockers, may also confer beneficial effects.

PURPOSE

The aim of the current study was to determine if non-gabapentinoid anticonvulsants were associated with neurological recovery after acute, traumatic spinal cord injury.

METHODS

This was an observational cohort study using data from the Sygen clinical trial. The primary outcome was total motor score recovery in the first year after injury. Anticonvulsant use was extracted from concomitant medication records; individuals were classified based on early administration (within 30 days of injury), or late/no administration. Motor recovery was compared using linear mixed effects regression models with a drug-by-time interaction, and adjustment for confounders. A secondary analysis incorporated a propensity score matched cohort.

RESULTS

Of the cohort (n = 570), 6% received anticonvulsants (carbamazepine, phenytoin, clonazepam, phenobarbital, and valproic acid) early after injury. After adjustments for initial injury level and severity, early exposure to non-gabapentinoid anticonvulsants was not associated with motor neurological outcomes (p = 0.38 for all anticonvulsants, p = 0.83 for sodium channel blockers, p = 0.82 in propensity-matched cohort).

CONCLUSION

Non-gabapentinoid anticonvulsant exposure was not associated with greater or lesser neurological recovery. This suggests that these medications, as administered for the acute management of spinal cord injury, do not impact long-term neurological outcomes.

BMP4/Smad1 Signalling Promotes Spinal Dorsal Column Axon Regeneration and Functional Recovery After Injury

Signalling through the BMP4/Smad1 pathway promotes corticospinal tract axon regeneration and functional recovery in mice. However, unlike humans and rats, mice do not cavitate. Here, we investigated if activation of the BMP4/Smad1 pathway promotes axon regeneration and functional recovery in a rat model that cavitates. We show that dorsal root ganglion neurons (DRGN) in injury models, including the non-regenerating dorsal column (DC) and the regenerating sciatic nerve (SN) crush and preconditioning (p) SN + DC (pSN + DC) paradigms, regulate the BMP4/Smad1 signalling pathway. For example, mRNA expression of positive regulators of the BMP4/Smad1 pathway was highly up-regulated whilst negative regulators were significantly down-regulated in DRGN in the regenerating SN and pSN + DC models compared to non-regenerating DC models, matched by concomitant changes in protein expression detected in DRGN by immunohistochemistry. BMP4 peptide promoted significant DRGN survival and disinhibited neurite outgrowth in vitro, whilst AAV-BMP4 delivery in vivo stimulated DC axon regeneration and functional recovery in a model that cavitates. Our results show that activation of the BMP4/Smad1 pathway is a potential therapeutic target in the search for axon regenerative signalling pathways in the CNS.

Non-viral-mediated suppression of AMIGO3 promotes disinhibited NT3-mediated regeneration of spinal cord dorsal column axons

After injury to the mature central nervous system (CNS), myelin-derived inhibitory ligands bind to the Nogo-66 tripartite receptor complex expressed on axonal growth cones, comprised of LINGO-1 and p75NTR/TROY and induce growth cone collapse through the RhoA pathway. We have also shown that amphoterin-induced gene and open reading frame-3 (AMIGO3) substitutes for LINGO-1 and can signal axon growth cone collapse. Here, we investigated the regeneration of dorsal root ganglion neuron (DRGN) axons/neurites after treatment with a short hairpin RNA (sh) AMIGO3 plasmid delivered with a non-viral in vivo-jetPEI vector, and the pro-survival/axogenic neurotrophin (NT) 3 in vitro and in vivo. A bicistronic plasmid, containing both shAMIGO3 and NT3 knocked down >75% of AMIGO3 mRNA in cultured DRGN and significantly overexpressed NT3 production. In vivo, intra-DRG injection of in vivo-jetPEI plasmids containing shAMIGO3/gfp and shAMIGO3/nt3 both knocked down AMIGO3 expression in DRGN and, in combination with NT3 overexpression, promoted DC axon regeneration, recovery of conduction of compound action potentials across the lesion site and improvements in sensory and locomotor function. These findings demonstrate that in vivo-jetPEI is a potential non-viral, translatable DRGN delivery vehicle in vivo and that suppression of AMIGO3 disinhibits the growth of axotomised DRGN enabling NT3 to stimulate the regeneration of their DC axons and enhances functional recovery.

Microenvironment Imbalance of Spinal Cord Injury

Spinal cord injury (SCI), for which there currently is no cure, is a heavy burden on patient physiology and psychology. The microenvironment of the injured spinal cord is complicated. According to our previous work and the advancements in SCI research, ‘microenvironment imbalance’ is the main cause of the poor regeneration and recovery of SCI. Microenvironment imbalance is defined as an increase in inhibitory factors and decrease in promoting factors for tissues, cells and molecules at different times and spaces. There are imbalance of hemorrhage and ischemia, glial scar formation, demyelination and re-myelination at the tissue’s level. The cellular level imbalance involves an imbalance in the differentiation of endogenous stem cells and the transformation phenotypes of microglia and macrophages. The molecular level includes an imbalance of neurotrophic factors and their pro-peptides, cytokines, and chemokines. The imbalanced microenvironment of the spinal cord impairs regeneration and functional recovery. This review will aid in the understanding of the pathological processes involved in and the development of comprehensive treatments for SCI.

RGMa inhibition with human monoclonal antibodies promotes regeneration, plasticity and repair, and attenuates neuropathic pain after spinal cord injury

Traumatic spinal cord injury (SCI) causes a cascade of degenerative events including cell death, axonal damage, and the upregulation of inhibitory molecules which prevent regeneration and limit recovery. Repulsive guidance molecule A (RGMa) is a potent neurite growth inhibitor in the central nervous system, exerting its repulsive activity by binding the Neogenin receptor. Here, we show for the first time that inhibitory RGMa is markedly upregulated in multiple cell types after clinically relevant impact-compression SCI in rats, and importantly, also in the injured human spinal cord. To neutralize inhibitory RGMa, clinically relevant human monoclonal antibodies were systemically administered after acute SCI, and were detected in serum, cerebrospinal fluid, and in the injured tissue. Rats treated with RGMa blocking antibodies showed significantly improved recovery of motor function and gait. Furthermore, RGMa blocking antibodies promoted neuronal survival, and enhanced the plasticity of descending serotonergic pathways and corticospinal tract axonal regeneration. RGMa antibody also attenuated neuropathic pain responses, which was associated with fewer activated microglia and reduced CGRP expression in the dorsal horn caudal to the lesion. These results show the therapeutic potential of the first human RGMa antibody for SCI and uncovers a new role for the RGMa/Neogenin pathway on neuropathic pain.

Activity of NaV1.2 promotes neurodegeneration in an animal model of multiple sclerosis

Counteracting the progressive neurological disability caused by neuronal and axonal loss is the major unmet clinical need in multiple sclerosis therapy. However, the mechanisms underlying irreversible neuroaxonal degeneration in multiple sclerosis and its animal model experimental autoimmune encephalomyelitis (EAE) are not well understood. A long-standing hypothesis holds that the distribution of voltage-gated sodium channels along demyelinated axons contributes to neurodegeneration by increasing neuroaxonal sodium influx and energy demand during CNS inflammation. Here, we tested this hypothesis in vivo by inserting a human gain-of-function mutation in the mouse Na_V1.2-encoding gene Scn2a that is known to increase Na_V1.2-mediated persistent sodium currents. In mutant mice, CNS inflammation during EAE leads to elevated neuroaxonal degeneration and increased disability and lethality compared with wild-type littermate controls. Importantly, immune cell infiltrates were not different between mutant EAE mice and wild-type EAE mice. Thus, this study shows that increased neuronal Na_V1.2 activity exacerbates inflammation-induced neurodegeneration irrespective of immune cell alterations and identifies Na_V1.2 as a promising neuroprotective drug target in multiple sclerosis.

Sodium channels in astroglia and microglia

Voltage-gated sodium channels are required for electrogenesis in excitable cells. Their activation, triggered by membrane depolarization, generates transient sodium currents that initiate action potentials in neurons, cardiac, and skeletal muscle cells. Cells that have not traditionally been considered to be excitable (nonexcitable cells), including glial cells, also express sodium channels in physiological conditions as well as in pathological conditions. These channels contribute to multiple functional roles that are seemingly unrelated to the generation of action potentials. Here, we discuss the dynamics of sodium channel expression in astrocytes and microglia, and review evidence for noncanonical roles in effector functions of these cells including phagocytosis, migration, proliferation, ionic homeostasis, and secretion of chemokines/cytokines. We also examine possible mechanisms by which sodium channels contribute to the activity of glial cells, with an eye toward therapeutic implications for central nervous system disease. GLIA 2016;64:1628-1645.

Spinal electro-magnetic stimulation combined with transgene delivery of neurotrophin NT-3 and exercise: novel combination therapy for spinal contusion injury

Our recent terminal experiments revealed that administration of a single train of repetitive spinal electromagnetic stimulation (sEMS; 35 min) enhanced synaptic plasticity in spinal circuitry following lateral hemisection spinal cord injury. In the current study, we have examined effects of repetitive sEMS applied as a single train and chronically (5 wk, every other day) following thoracic T10 contusion. Chronic studies involved examination of systematic sEMS administration alone and combined with exercise training and transgene delivery of neurotrophin [adeno-associated virus 10-neurotrophin 3 (AAV10-NT3)]. Electrophysiological intracellular/extracellular recordings, immunohistochemistry, behavioral testing, and anatomical tracing were performed to assess effects of treatments. We found that administration of a single sEMS train induced transient facilitation of transmission through preserved lateral white matter to motoneurons and hindlimb muscles in chronically contused rats with effects lasting for at least 2 h. These physiological changes associated with increased immunoreactivity of GluR1 and GluR2/3 glutamate receptors in lumbar neurons. Systematic administration of sEMS alone for 5 wk, however, was unable to induce cumulative improvements of transmission in spinomuscular circuitry or improve impaired motor function following thoracic contusion. Encouragingly, chronic administration of sEMS, followed by exercise training (running in an exercise ball and swimming), induced the following: 1) sustained strengthening of transmission to lumbar motoneurons and hindlimb muscles, 2) better retrograde transport of anatomical tracer, and 3) improved locomotor function. Greatest improvements were seen in the group that received exercise combined with sEMS and AAV-NT3.

Myelin damage and repair in pathologic CNS: challenges and prospects

Injury to the central nervous system (CNS) results in oligodendrocyte cell death and progressive demyelination. Demyelinated axons undergo considerable physiological changes and molecular reorganizations that collectively result in axonal dysfunction, degeneration and loss of sensory and motor functions. Endogenous adult oligodendrocyte precursor cells and neural stem/progenitor cells contribute to the replacement of oligodendrocytes, however, the extent and quality of endogenous remyelination is suboptimal. Emerging evidence indicates that optimal remyelination is restricted by multiple factors including (i) low levels of factors that promote oligodendrogenesis; (ii) cell death among newly generated oligodendrocytes, (iii) inhibitory factors in the post-injury milieu that impede remyelination, and (iv) deficient expression of key growth factors essential for proper re-construction of a highly organized myelin sheath. Considering these challenges, over the past several years, a number of cell-based strategies have been developed to optimize remyelination therapeutically. Outcomes of these basic and preclinical discoveries are promising and signify the importance of remyelination as a mechanism for improving functions in CNS injuries. In this review, we provide an overview on: (1) the precise organization of myelinated axons and the reciprocal axo-myelin interactions that warrant properly balanced physiological activities within the CNS; (2) underlying cause of demyelination and the structural and functional consequences of demyelination in axons following injury and disease; (3) the endogenous mechanisms of oligodendrocyte replacement; (4) the modulatory role of reactive astrocytes and inflammatory cells in remyelination; and (5) the current status of cell-based therapies for promoting remyelination. Careful elucidation of the cellular and molecular mechanisms of demyelination in the pathologic CNS is a key to better understanding the impact of remyelination for CNS repair.

Challenges of animal models in SCI research: Effects of pre-injury task-specific training in adult rats before lesion

A rarely explored subject in animal research is the effect of pre-injury variables on behavioral outcome post-SCI. Low reporting of such variables may underlie some discrepancies in findings between laboratories. Particularly, intensive task-specific training before a SCI might be important, considering that sports injuries are one of the leading causes of SCI. Thus, individuals with SCI often underwent rigorous training before their injuries. In the present study, we asked whether training before SCI on a grasping task or a swimming task would influence motor recovery in rats. Swim pre-training impaired recovery of swimming 2 and 4 weeks post-injury. This result fits with the idea of motor learning interference, which posits that learning something new may disrupt learning of a new task; in this case, learning strategies to compensate for functional loss after SCI. In contrast to swimming, grasp pre-training did not influence grasping ability after SCI at any time point. However, grasp pre-trained rats attempted to grasp more times than untrained rats in the first 4 weeks post-injury. Also, lesion volume of grasp pre-trained rats was greater than that of untrained rats, a finding which may be related to stress or activity. The increased participation in rehabilitative training of the pre-trained rats in the early weeks post-injury may have potentiated spontaneous plasticity in the spinal cord and counteracted the deleterious effect of interference and bigger lesions. Thus, our findings suggest that pre-training plays a significant role in recovery after CNS damage and needs to be carefully controlled for.

Repair of spinal cord injury by implantation of bFGF-incorporated HEMA-MOETACL hydrogel in rats

There is no effective strategy for the treatment of spinal cord injury (SCI). An appropriate combination of hydrogel materials and neurotrophic factor therapy is currently thought to be a promising approach. In this study, we performed experiments to evaluate the synergic effect of implanting hydroxyl ethyl methacrylate [2-(methacryloyloxy)ethyl] trimethylammonium chloride (HEMA-MOETACL) hydrogel incorporated with basic fibroblast growth factor (bFGF) into the site of surgically induced SCI. Prior to implantation, the combined hydrogel was surrounded by an acellular vascular matrix. Sprague-Dawley rats underwent complete spinal cord transection at the T-9 level, followed by implantation of bFGF/HEMA-MOETACL 5 days after transection surgery. Our results showed that the bFGF/HEMA-MOETACL transplant provided a scaffold for the ingrowth of regenerating tissue eight weeks after implantation. Furthermore, this newly designed implant promoted both nerve tissue regeneration and functional recovery following SCI. These results indicate that HEMA-MOETACL hydrogel is a promising scaffold for intrathecal, localized and sustained delivery of bFGF to the injured spinal cord and provide evidence for the possibility that this approach may have clinical applications in the treatment of SCI.

Functional changes in deep dorsal horn interneurons following spinal cord injury are enhanced with different durations of exercise training

KEY POINTS

Exercise training after spinal cord injury (SCI) enhances collateral sprouting from axons near the injury and is thought to promote intraspinal circuit reorganisation that effectively bridges the SCI. The effects of exercise training, and its duration, on interneurons in these de novo intraspinal circuits are poorly understood. In an adult mouse hemisection model of SCI, we used whole-cell patch-clamp electrophysiology to examine changes in the intrinsic and synaptic properties of deep dorsal horn interneurons in the vicinity of a SCI in response to the injury, and after 3 and 6 weeks of treadmill exercise training. SCI alone exerted powerful effects on the intrinsic and synaptic properties of interneurons near the lesion. Importantly, synaptic activity, both local and descending, was preferentially enhanced by exercise training, suggesting that exercise promotes synaptic plasticity in spinal cord interneurons that are ideally placed to form new intraspinal circuits after SCI. Following incomplete spinal cord injury (SCI), collaterals sprout from intact and injured axons in the vicinity of the lesion. These sprouts are thought to form new synaptic contacts that effectively bypass the lesion epicentre and contribute to improved functional recovery. Such anatomical changes are known to be enhanced by exercise training; however, the mechanisms underlying exercise-mediated plasticity are poorly understood. Specifically, we do not know how SCI alone or SCI combined with exercise alters the intrinsic and synaptic properties of interneurons in the vicinity of a SCI. Here we use a hemisection model of incomplete SCI in adult mice and whole-cell patch-clamp recording in a horizontal spinal cord slice preparation to examine the functional properties of deep dorsal horn (DDH) interneurons located in the vicinity of a SCI following 3 or 6 weeks of treadmill exercise training. We examined the functional properties of local and descending excitatory synaptic connections by recording spontaneous excitatory postsynaptic currents (sEPSCs) and responses to dorsal column stimulation, respectively. We find that SCI in untrained animals exerts powerful effects on intrinsic, and especially, synaptic properties of DDH interneurons. Plasticity in intrinsic properties was most prominent at 3 weeks post SCI, whereas synaptic plasticity was greatest at 6 weeks post injury. Exercise training did not markedly affect intrinsic membrane properties; however, local and descending excitatory synaptic drive were enhanced by 3 and 6 weeks of training. These results suggest exercise promotes synaptic plasticity in spinal cord interneurons that are ideally placed to form new intraspinal circuits after SCI.

Voltage-gated sodium channel Nav 1.5 contributes to astrogliosis in an in vitro model of glial injury via reverse Na+ /Ca2+ exchange

Astrogliosis is a prominent feature of many, if not all, pathologies of the brain and spinal cord, yet a detailed understanding of the underlying molecular pathways involved in the transformation from quiescent to reactive astrocyte remains elusive. We investigated the contribution of voltage-gated sodium channels to astrogliosis in an in vitro model of mechanical injury to astrocytes. Previous studies have shown that a scratch injury to astrocytes invokes dual mechanisms of migration and proliferation in these cells. Our results demonstrate that wound closure after mechanical injury, involving both migration and proliferation, is attenuated by pharmacological treatment with tetrodotoxin (TTX) and KB-R7943, at a dose that blocks reverse mode of the Na(+) /Ca(2+) exchanger (NCX), and by knockdown of Nav 1.5 mRNA. We also show that astrocytes display a robust [Ca(2+) ]i transient after mechanical injury and demonstrate that this [Ca(2+) ]i response is also attenuated by TTX, KB-R7943, and Nav 1.5 mRNA knockdown. Our results suggest that Nav 1.5 and NCX are potential targets for modulation of astrogliosis after injury via their effect on [Ca(2+) ]i .

Sodium channels contribute to degeneration of dorsal root ganglion neurites induced by mitochondrial dysfunction in an in vitro model of axonal injury

Axonal degeneration occurs in multiple neurodegenerative disorders of the central and peripheral nervous system. Although the underlying molecular pathways leading to axonal degeneration are incompletely understood, accumulating evidence suggests contributions of impaired mitochondrial function, disrupted axonal transport, and/or dysfunctional intracellular Ca(2+)-homeostasis in the injurious cascade associated with axonal degeneration. Utilizing an in vitro model of axonal degeneration, we studied a subset of mouse peripheral sensory neurons in which neurites were exposed selectively to conditions associated with the pathogenesis of axonal neuropathies in vivo. Rotenone-induced mitochondrial dysfunction resulted in neurite degeneration accompanied by reduced ATP levels and increased ROS levels in neurites. Blockade of voltage-gated sodium channels with TTX and reverse (Ca(2+)-importing) mode of the sodium-calcium exchanger (NCX) with KB-R7943 partially protected rotenone-treated neurites from degeneration, suggesting a contribution of sodium channels and reverse NCX activity to the degeneration of neurites resulting from impaired mitochondrial function. Pharmacological inhibition of the Na(+)/K(+)-ATPase with ouabain induced neurite degeneration, which was attenuated by TTX and KB-R7943, supporting a contribution of sodium channels in axonal degenerative pathways accompanying impaired Na(+)/K(+)-ATPase activity. Conversely, oxidant stress (H2O2)-induced neurite degeneration was not attenuated by TTX. Our results demonstrate that both energetic and oxidative stress targeted selectively to neurites induces neurite degeneration and that blockade of sodium channels and of reverse NCX activity blockade partially protects neurites from injury due to energetic stress, but not from oxidative stress induced by H2O2.

A computational model coupling mechanics and electrophysiology in spinal cord injury

Traumatic brain injury and spinal cord injury have recently been put under the spotlight as major causes of death and disability in the developed world. Despite the important ongoing experimental and modeling campaigns aimed at understanding the mechanics of tissue and cell damage typically observed in such events, the differentiated roles of strain, stress and their corresponding loading rates on the damage level itself remain unclear. More specifically, the direct relations between brain and spinal cord tissue or cell damage, and electrophysiological functions are still to be unraveled. Whereas mechanical modeling efforts are focusing mainly on stress distribution and mechanistic-based damage criteria, simulated function-based damage criteria are still missing. Here, we propose a new multiscale model of myelinated axon associating electrophysiological impairment to structural damage as a function of strain and strain rate. This multiscale approach provides a new framework for damage evaluation directly relating neuron mechanics and electrophysiological properties, thus providing a link between mechanical trauma and subsequent functional deficits.

Force spectroscopy measurements show that cortical neurons exposed to excitotoxic agonists stiffen before showing evidence of bleb damage

In ischemic and traumatic brain injury, hyperactivated glutamate (N-methyl-D-aspartic acid, NMDA) and sodium (Nav) channels trigger excitotoxic neuron death. Na⁺, Ca⁺⁺ and H₂O influx into affected neurons elicits swelling (increased cell volume) and pathological blebbing (disassociation of the plasma membrane’s bilayer from its spectrin-actomyosin matrix). Though usually conflated in injured tissue, cell swelling and blebbing are distinct processes. Around an injury core, salvageable neurons could be mildly swollen without yet having suffered the bleb-type membrane damage that, by rendering channels leaky and pumps dysfunctional, exacerbates the excitotoxic positive feedback spiral. Recognizing when neuronal inflation signifies non-lethal osmotic swelling versus blebbing should further efforts to salvage injury-penumbra neurons. To assess whether the mechanical properties of osmotically-swollen versus excitotoxically-blebbing neurons might be cytomechanically distinguishable, we measured cortical neuron elasticity (gauged via atomic force microscopy (AFM)-based force spectroscopy) upon brief exposure to hypotonicity or to excitotoxic agonists (glutamate and Nav channel activators, NMDA and veratridine). Though unperturbed by solution exchange per se, elasticity increased abruptly with hypotonicity, with NMDA and with veratridine. Neurons then invariably softened towards or below the pre-treatment level, sometimes starting before the washout. The initial channel-mediated stiffening bespeaks an abrupt elevation of hydrostatic pressure linked to NMDA or Nav channel-mediated ion/H₂O fluxes, together with increased [Ca⁺⁺]_int-mediated submembrane actomyosin contractility. The subsequent softening to below-control levels is consistent with the onset of a lethal level of bleb damage. These findings indicate that dissection/identification of molecular events during the excitotoxic transition from stiff/swollen to soft/blebbing is warranted and should be feasible.

Updates in the management of the small animal patient with neurologic trauma

Neurologic trauma, encompassing traumatic brain injury (TBI) and acute spinal cord injury (SCI), is a cause of significant morbidity and mortality in veterinary patients. Acute SCIs occurring secondary to trauma are also common. Essential to the management of TBI and SCI is a thorough understanding of the pathophysiology of the primary and secondary injury that occurs following trauma. This article reviews the pathophysiology of this primary and secondary injury, as well as recommendations regarding clinical assessment, diagnostics, pharmacologic and nonpharmacologic therapy, and prognosis.

Neural stem-like cells derived from human amnion tissue are effective in treating traumatic brain injury in rat

Although human amnion derived mesenchymal stem cells (AMSC) are a promising source of stem cells, their therapeutic potential for traumatic brain injury (TBI) has not been widely investigated. In this study, we evaluated the therapeutic potential of AMSC using a rat TBI model. AMSC were isolated from human amniotic membrane and characterized by flow cytometry. After induction, AMSC differentiated in vitro into neural stem-like cells (AM-NSC) that expressed higher levels of the neural stem cell markers, nestin, sox2 and musashi, in comparison to undifferentiated AMSC. Interestingly, the neurotrophic factors, brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), neurotrophin 3 (NT-3), glial cell derived neurotrophic factor (GDNF) and ciliary neurotrophic factor (CNTF) were markedly upregulated after neural stem cell induction. Following transplantation in a rat TBI model, significant improvements in neurological function, brain tissue morphology, and higher levels of BDNF, NGF, NT-3, GDNF and CNTF, were observed in the AM-NSC group compared with the AMSC and Matrigel groups. However, few grafted cells survived with minimal differentiation into neural-like cells. Together, our results suggest that transplantation of AM-NSC promotes functional rehabilitation of rats with TBI, with enhanced expression of neurotrophic factors a likely mechanistic pathway.

A combination of taxol infusion and human umbilical cord mesenchymal stem cells transplantation for the treatment of rat spinal cord injury

BACKGROUND AND PURPOSE

Studies have shown that the administration of Taxol, an anti-cancer drug, inhibited scar formation, promoted axonal elongation and improved locomotor recovery in rats after spinal cord injury (SCI). We hypothesized that combining Taxol with another promising therapy, transplantation of human umbilical mesenchymal stem cells (hUCMSCs), might further improve the degree of locomotor recovery. The present study examined whether Taxol combined with transplantation of hUCMSCs would produce synergistic effects on recovery and which mechanisms were involved in the effect.

METHODS

A total of 32 rats subjected to SCI procedures were assigned to one of the following four treatment groups: phosphate-buffered saline (PBS, control), hUCMSCs, Taxol, or Taxol+hUCMSCs. Immediately after injury, hUCMSCs were transplanted into the injury site and Taxol was administered intrathecally for 4 weeks. Locomotor recovery was evaluated using the Basso, Beattie and Bresnahan locomotor (BBB) rating scale. Survival of the transplanted human cells and the host glial reaction in the injured spinal cord were studied by immunohistochemistry.

RESULTS

Treatment with Taxol, hUCMSCs or Taxol+hUCMSCs reduced the extent of astrocytic activation, increased axonal preservation and decreased the number of caspase-3(+) and ED-1(+) cells, but these effects were more pronounced in the Taxol+hUCMSCs group. Behavioral analyses showed that rats in the Taxol+hUCMSCs group showed better motor performance than rats treated with hUCMSCs or Taxol only.

CONCLUSIONS

The combination of Taxol and hUCMSCs produced beneficial effects in rats with regard to functional recovery following SCI through the enhancement of anti-inflammatory, anti-astrogliosis, anti-apoptotic and axonal preservation effects.

Axonal protection achieved by blockade of sodium/calcium exchange in a new model of ischemia in vivo

Ischemic white matter injury has been relatively little studied despite its importance to the outcome of stroke. To aid such research a new rat model has been developed in vivo and used to assess whether blockade of the sodium/calcium exchanger is effective in protecting central axons from ischemic injury. Vasoconstrictive agent endothelin-1 was injected into the rat spinal cord to induce ischemia. KB-R7943 or SEA0400 was administered systemically to block the operation of the sodium/calcium exchanger. Endothelin-1 caused profound reduction of local blood perfusion and resulted in a prompt loss of axonal conduction. Whereas recovery of conduction following vehicle administration was only to 10.5 ± 9% of baseline (n = 8) 4.5 h after endothelin-1 injection, recovery following KB-R7943 (30 mg/kg, i.a.) administration was increased to 35 ± 9% of baseline (n = 6; P < 0.001). SEA0400 (30 mg/kg, i.a.) was also protective (33.2 ± 6% of baseline, n = 4; P < 0.001). Neither drug improved conduction by diminishing the severity of the ischemia. The protective effect of KB-R7943 persisted for at least 3 days after ischemia, as it improved axonal conduction (76.3 ± 11% for KB-R7943 vs. 51.0 ± 19% for vehicle; P < 0.01) and reduced lesion area (55.6 ± 15% for KB-R7943 vs. 77.9 ± 9% for vehicle; P < 0.01) at this time. In conclusion, a new model of white matter ischemia has been introduced suitable for both structural and functional studies in vivo. Blocking the sodium/calcium exchanger protects central axons from ischemic injury in vivo.

Repetitive spinal electromagnetic stimulation opens a window of synaptic plasticity in damaged spinal cord: role of NMDA receptors

As we reported previously, propagation of action potentials through surviving axons is impaired dramatically, resulting in reduced transmission to lumbar motoneurons after midthoracic lateral hemisection (HX) in rats. The aim of the present study was to evoke action potentials through the spared fibers using noninvasive electromagnetic stimulation (EMS) over intact T2 vertebrae in an attempt to activate synaptic inputs to lumbar motoneurons and thus to enhance plasticity of spinal neural circuits after HX. We found that EMS was able to activate synaptic inputs to lumbar motoneurons and motor-evoked potentials (MEP) in hindlimb muscles in adult anesthetized rats. Amplitude of MEP was attenuated in parallel with the decline of responses recorded from the motoneuron pool after HX. Repetitive EMS (50 min, 0.2 Hz) facilitated the amplitudes of responses elicited by electric stimulation of lateral white matter or dorsal corticospinal tracts in HX rats. Facilitation sustained for at least 1.5 h after termination of EMS. The N-methyl-d-aspartate (NMDA) receptor blocker MK-801, injected intraspinally close to the recording electrode prior to EMS, did not alter these responses but blocked the EMS-induced facilitation, suggesting that activation of NMDA receptors is required to initiate an EMS-evoked increase. When MK-801 was administered after EMS-induced facilitation was established, it induced depression of these elevated responses. Results suggest that repetitive EMS over intact vertebrae could be used as a therapeutic approach to open a window of synaptic plasticity after incomplete midthoracic injuries, i.e., to activate NMDA receptors in the lumbar motoneuron pool at synaptic inputs and to strengthen transmission in damaged spinal cord.

Conduction failure following spinal cord injury: functional and anatomical changes from acute to chronic stages

In the majority of spinal cord injuries (SCIs), some axonal projections remain intact. We examined the functional status of these surviving axons since they represent a prime therapeutic target. Using a novel electrophysiological preparation, adapted from techniques used to study primary demyelination, we quantified conduction failure across a SCI and studied conduction changes over time in adult rats with a moderate severity spinal contusion (150 kdyn; Infinite Horizon impactor). By recording antidromically activated single units from teased dorsal root filaments, we demonstrate complete conduction block in ascending dorsal column axons acutely (1-7 d) after injury, followed by a period of restored conduction over the subacute phase (2-4 weeks), with no further improvements in conduction at chronic stages (3-6 months). By cooling the lesion site, additional conducting fibers could be recruited, thus revealing a population of axons that are viable but unable to conduct under normal physiological conditions. Importantly, this phenomenon is still apparent at the most chronic (6 month) time point. The time course of conduction changes corresponded with changes in behavioral function, and ultrastructural analysis of dorsal column axons revealed extensive demyelination during the period of conduction block, followed by progressive remyelination. A proportion of dorsal column axons remained chronically demyelinated, suggesting that these are the axons recruited with the cooling paradigm. Thus, using a clinically relevant SCI model, we have identified a population of axons present at chronic injury stages that are intact but fail to conduct and are therefore a prime target for therapeutic strategies to restore function.

Differential protection of neuromuscular sensory and motor axons and their endings in Wld(S) mutant mice

Orthograde Wallerian degeneration normally brings about fragmentation of peripheral nerve axons and their sensory or motor endings within 24-48 h in mice. However, neuronal expression of the chimaeric, Wld(S) gene mutation extends survival of functioning axons and their distal endings for up to 3 weeks after nerve section. Here we studied the pattern and rate of degeneration of sensory axons and their annulospiral endings in deep lumbrical muscles of Wld(S) mice, and compared these with motor axons and their terminals, using neurone-specific transgenic expression of the fluorescent proteins yellow fluorescent protein (YFP) or cyan fluorescent protein (CFP) as morphological reporters. Surprisingly, sensory endings were preserved for up to 20 days, at least twice as long as the most resilient motor nerve terminals. Protection of sensory endings and axons was also much less sensitive to Wld(S) gene-copy number or age than motor axons and their endings. Protection of γ-motor axons and their terminals innervating the juxtaequatorial and polar regions of the spindles was less than sensory axons but greater than α-motor axons. The differences between sensory and motor axon protection persisted in electrically silent, organotypic nerve-explant cultures suggesting that residual axonal activity does not contribute to the sensory-motor axon differences in vivo. Quantitative, Wld(S)-specific immunostaining of dorsal root ganglion (DRG) neurones and motor neurones in homozygous Wld(S) mice suggested that the nuclei of large DRG neurones contain about 2.4 times as much Wld(S) protein as motor neurones. By contrast, nuclear fluorescence of DRG neurones in homozygotes was only 1.5 times brighter than in heterozygotes stained under identical conditions. Thus, differences in axonal or synaptic protection within the same Wld(S) mouse may most simply be explained by differences in expression level of Wld(S) protein between neurones. Mimicry of Wld(S)-induced protection may also have applications in treatment of neurotoxicity or peripheral neuropathies in which the integrity of sensory endings may be especially implicated.

Delayed axonal degeneration in slow Wallerian degeneration mutant mice detected using diffusion tensor imaging

Previous studies have shown the feasibility of using diffusion tensor imaging (DTI) as a noninvasive imaging modality to evaluate neurodegeneration in humans and animals. The axial and radial diffusivities derived from DTI were demonstrated to be sensitive markers for axonal and myelin damage, respectively. This study used DTI to evaluate optic nerve degeneration in wild-type and slow Wallerian degeneration (Wld(S)) mutant mice. Longitudinal DTI was performed on optic nerves following high intraocular pressure-induced transient retinal ischemia. The axial diffusivity of wild-type nerves decreased 30% (P<0.05) at 3 days and 40% (P<0.05) at 5-30 days after transient elevation of intraocular pressure. In contrast, the axial diffusivity of Wld(S) nerves did not change at 3 days; decreased by 20% (P<0.05) at 5 days, and continued to decrease by 30% (P<0.05) at 15 days and 40% (P<0.05) at 30 days after transient intraocular pressure elevation, suggesting delayed axonal damage in Wld(S) mice. Radial diffusivity increased 200% (P<0.05) at 15-30 days in the wild-type mice and 100% (P<0.05) at 30 days in the Wld(S) mice after transient intraocular pressure elevation, suggesting delayed myelin damage in Wld(S) mice. DTI detected damage was confirmed with immunohistochemistry using phosphorylated neurofilament and myelin basic protein for assessing axonal and myelin integrity, respectively. These findings support the use of DTI not only to evaluate the progression of neurodegeneration but also to noninvasively demonstrate Wld(S) mutation to delay the Wallerian degeneration.

Role of acid-sensing ion channel 1a in the secondary damage of traumatic spinal cord injury

OBJECTIVE

To determine the cellular and molecular mechanisms by which acid-sensing ion channel 1a (ASIC1a) plays its role in the secondary injury after traumatic spinal cord injury (SCI), and validate the neuroprotective effect of ASIC1a suppression in SCI model in vivo.

BACKGROUND

Secondary damage after traumatic SCI contributes to the exacerbation of cellular insult and thereby contributes to spinal cord dysfunction. However, the underlying mechanisms remain largely unknown. Acidosis is commonly involved in the secondary injury process after the injury of central nervous system, but whether ASIC1a is involved in secondary injury after SCI is unclear.

METHODS

Male Sprague-Dawley rats were subjected to spinal contusion using a weight-drop injury approach. Western blotting and immunofluorescence assays were used to observe the change of ASIC1a expression after SCI. The TUNEL staining in vivo as well as the cell viability and death assays in spinal neuronal culture were employed to assess the role of ASIC1a in the secondary spinal neuronal injury. The electrophysiological recording and Ca(2+) imaging were performed to reveal the possible underlying mechanism. The antagonists and antisense oligonucleotide for ASIC1a, lesion volume assessment assay and behavior test were used to estimate the therapeutic effect of ASIC1a on SCI.

RESULTS

We show that ASIC1a expression is markedly increased in the peri-injury zone after traumatic SCI. Consistent with the change of ASIC1a expression in injured spinal neurons, both ASIC1a-mediated whole-cell currents and ASIC1a-mediated Ca(2+) entry are significantly enhanced after injury. We also show that increased activity of ASIC1a contributes to SCI-induced neuronal death. Importantly, our results indicate that down-regulation of ASIC1a by antagonists or antisense oligonucleotide reduces tissue damage and promotes the recovery of neurological function after SCI.

CONCLUSION

This study reveals a cellular and molecular mechanism by which ASIC1a is involved in the secondary damage process after traumatic SCI. Our results suggest that blockade of Ca(2+) -permeable ASIC1a may be a potential neuroprotection strategy for the treatment of SCI patients.

Acrolein-mediated injury in nervous system trauma and diseases

Acrolein, an α,β-unsaturated aldehyde, is a ubiquitous pollutant that is also produced endogenously through lipid peroxidation. This compound is hundreds of times more reactive than other aldehydes such as 4-hydroxynonenal, is produced at much higher concentrations, and persists in solution for much longer than better known free radicals. It has been implicated in disease states known to involve chronic oxidative stress, particularly spinal cord injury and multiple sclerosis. Acrolein may overwhelm the anti-oxidative systems of any cell by depleting glutathione reserves, preventing glutathione regeneration, and inactivating protective enzymes. On the cellular level, acrolein exposure can cause membrane damage, mitochondrial dysfunction, and myelin disruption. Such pathologies can be exacerbated by increased concentrations or duration of exposure, and can occur in normal tissue incubated with injured spinal cord, showing that acrolein can act as a diffusive agent, spreading secondary injury. Several chemical species are capable of binding and inactivating acrolein. Hydralazine in particular can reduce acrolein concentrations and inhibit acrolein-mediated pathologies in vivo. Acrolein scavenging appears to be a novel effective treatment, which is primed for rapid translation to the clinic.

Comparison of transdifferentiated and untransdifferentiated human umbilical mesenchymal stem cells in rats after traumatic brain injury

Transdifferentiated and untransdifferentiated mesenchymal stem cells (MSCs) have shown therapeutic benefits in central nervous system (CNS) injury. However, it is unclear which would be more appropriate for transplantation. To address this question, we transplanted untransdifferentiated human umbilical mesenchymal stem cells (HUMSCs) and transdifferentiated HUMSCs (HUMSC-derived neurospheres, HUMSC-NSs) into a rat model of traumatic brain injury. Cognitive function, cell survival and differentiation, brain tissue morphology and neurotrophin expression were compared between groups. Significant improvements in cognitive function and brain tissue morphology were seen in the HUMSCs group compared with HUMSC-NSs group, which was accompanied by increased neurotrophin expression. Moreover, only few grafted cells survived in both the HUMSCs and HUMSC-NSs groups, with very few of the cells differentiating into neural-like cells. These findings indicate that HUMSCs are more appropriate for transplantation and their therapeutic benefits may be associated with neuroprotection rather than cell replacement.

NT-3-secreting human umbilical cord mesenchymal stromal cell transplantation for the treatment of acute spinal cord injury in rats

An animal model for clip spinal cord injury (SCI) was used to determine whether Neurotrophin-3 (NT-3) genetically modified human umbilical mesenchymal stem cells (NT-3-HUMSCs) could promote the morphologic and functional recovery of injured spinal cords. Using the Basso, Beattie, and Bresnahan scores and a grid test, the rats in the HUMSC-treated and NT-3-HUMSCs groups had significantly improved locomotor functional recovery more than the control group. In comparison, the NT-3-HUMSCs group achieved better functional recovery than the HUMSCs group at the end of 12 weeks after SCI. The functional recovery was accompanied by increased intensity of 5-HT fibers, increased volume of spared myelination, and decreased area of the cystic cavity in the NT-3-HUMSCs group compared with the HUMSCs group. Moreover, transplanted NT-3-HUMSCs survived and produced larger amounts of NT-3 than the HUMSCs in the host spinal cord. These results show that NT-3 enhanced the therapeutic effects of HUMSCs after clip injury of the spinal cord.

Alterations of action potentials and the localization of Nav1.6 sodium channels in spared axons after hemisection injury of the spinal cord in adult rats

Previously, we reported a pronounced reduction in transmission through surviving axons contralateral to chronic hemisection (HX) of adult rat spinal cord. To examine the cellular and molecular mechanisms responsible for this diminished transmission, we recorded intracellularly from lumbar lateral white matter axons in deeply anesthetized adult rats in vivo and measured the propagation of action potentials (APs) through rubrospinal/reticulospinal tract (RST/RtST) axons contralateral to chronic HX at T10. We found decreased excitability in these axons, manifested by an increased rheobase to trigger APs and longer latency for AP propagation passing the injury level, without significant differences in axonal resting membrane potential and input resistance. These electrophysiological changes were associated with altered spatial localization of Nav1.6 sodium channels along axons: a subset of axons contralateral to the injury exhibited a diffuse localization (>10 μm spread) of Nav1.6 channels, a pattern characteristic of demyelinated axons (Craner MJ, Newcombe J, Black JA, Hartle C, Cuzner ML, Waxman SG. Proc Natl Acad Sci USA 101: 8168-8173, 2004b). This result was substantiated by ultrastructural changes seen with electron microscopy, in which an increased number of large-caliber, demyelinated RST axons were found contralateral to the chronic HX. Therefore, an increased rheobase, pathological changes in the distribution of Nav1.6 sodium channels, and the demyelination of contralateral RST axons are likely responsible for their decreased conduction chronically after HX and thus may provide novel targets for strategies to improve function following incomplete spinal cord injury.

THE ROLE OF INTRACELLULAR SODIUM (Na) IN THE REGULATION OF CALCIUM (Ca)-MEDIATED SIGNALING AND TOXICITY

It is known that activated N-methyl-D-aspartate receptors (NMDARs) are a major route of excessive calcium ion (Ca(2+)) entry in central neurons, which may activate degradative processes and thereby cause cell death. Therefore, NMDARs are now recognized to play a key role in the development of many diseases associated with injuries to the central nervous system (CNS). However, it remains a mystery how NMDAR activity is recruited in the cellular processes leading to excitotoxicity and how NMDAR activity can be controlled at a physiological level. The sodium ion (Na(+)) is the major cation in extracellular space. With its entry into the cell, Na(+) can act as a critical intracellular second messenger that regulates many cellular functions. Recent data have shown that intracellular Na(+) can be an important signaling factor underlying the up-regulation of NMDARs. While Ca(2+) influx during the activation of NMDARs down-regulates NMDAR activity, Na(+) influx provides an essential positive feedback mechanism to overcome Ca(2+)-induced inhibition and thereby potentiate both NMDAR activity and inward Ca(2+) flow. Extensive investigations have been conducted to clarify mechanisms underlying Ca(2+)-mediated signaling. This review focuses on the roles of Na(+) in the regulation of Ca(2+)-mediated NMDAR signaling and toxicity.

Cografted Wharton's jelly cells-derived neurospheres and BDNF promote functional recovery after rat spinal cord transection

An animal model of transected spinal cord injury (SCI) was used to test the hypothesis that cografted human umbilical mesenchymal stem cells-derived neurospheres (HUMSC-NSs) and BDNF can promote morphologic and functional recoveries of injured spinal cord. In vitro, HUMSC-NSs terminally differentiated into higher percentages of cells expressing neuronal markers: beta-tubulin III and MAP2ab by the supplement with BDNF. Following grafted into injured spinal cord, very few grafted cells survived in the HUMSC-NSs + BDNF-treated (<3%) and HUMSC-NSs-treated (<1%) groups. The survived cells were differentiated into various cells, which were confirmed by double staining of BrdU and neural or glia markers. In comparison, more grafted cells in the HUMSC-NSs + BDNF group transformed into mature neural-like cells, while more grafted cells in the HUMSC-NSs group transformed into oligodendrocyte-like cells. HUMSC-NSs + BDNF-treated group had more greatly improved BBB scores, compared with HUMSC-NSs-treated and medium-treated groups. Additionally, axonal regeneration showed significant improvement in rats receiving HUMSC-NSs + BDNF, compared with HUMSC-NSs-treated and medium-treated groups, as demonstrated by the NF-200-positive staining and Fluorogold (FG) retrograde tracing study. Lastly, a significant reduction in the percentage cavitation was seen in the two cell-treated groups compared with medium control group. These results means BDNF could promote the neural differentiation of HUMSC-NSs in vitro and in vivo. However, cellular replacement is unlikely to explain the improvement in functional outcome. The functional recovery might more rely on the axonal regeneration and neuroprotective action that active by the grafted cells. Cografted HUMSCs and BDNF is a potential therapy for SCI.

Loss of Na+ channel beta2 subunits is neuroprotective in a mouse model of multiple sclerosis

Multiple sclerosis (MS) is a CNS disease that includes demyelination and axonal degeneration. Voltage-gated Na+ channels are abnormally expressed and distributed in MS and its animal model, Experimental Allergic Encephalomyelitis (EAE). Up-regulation of Na+ channels along demyelinated axons is proposed to lead to axonal loss in MS/EAE. We hypothesized that Na+ channel beta2 subunits (encoded by Scn2b) are involved in MS/EAE pathogenesis, as beta2 is responsible for regulating levels of channel cell surface expression in neurons. We induced non-relapsing EAE in Scn2b(+/+) and Scn2b(-/-) mice on the C57BL/6 background. Scn2b(-/-) mice display a dramatic reduction in EAE symptom severity and lethality as compared to wildtype, with significant decreases in axonal degeneration and axonal loss. Scn2b(-/-) mice show normal peripheral immune cell populations, T cell proliferation, cytokine release, and immune cell infiltration into the CNS in response to EAE, suggesting that Scn2b inactivation does not compromise immune function. Our data suggest that loss of beta2 is neuroprotective in EAE by prevention of Na+ channel up-regulation in response to demyelination.

Small-molecule protein tyrosine phosphatase inhibition as a neuroprotective treatment after spinal cord injury in adult rats

Spinal cord injury causes progressive secondary tissue degeneration, leaving many injured people with neurological disabilities. There are no satisfactory neuroprotective treatments. Protein tyrosine phosphatases inactivate neurotrophic factor receptors and downstream intracellular signaling molecules. Thus, we tested whether the peroxovanadium compound potassium bisperoxo(1,10-phenanthroline)oxovanadate (V) [bpV(phen)], a stable, potent and selective protein tyrosine phosphatase inhibitor, would be neuroprotective after a thoracic spinal cord contusion in adult rats. Intrathecal bpV(phen) infusions through a lumbar puncture rescued dorsal column sensory axons innervating the nucleus gracilis and white matter at the injury epicenter. At the most effective dose, essentially all of these axons and most of the white matter at the epicenter were spared (vs approximately 60% with control infusions). bpV(phen) treatments started 4 h after contusion were fully effective. This treatment greatly improved and normalized sensorimotor function in a grid-walking test and provided complete axonal protection over 6 weeks. The treatment rescued sensory-evoked potentials that disappeared after dorsal column transection. bpV(phen) affected early degenerative mechanisms, because the main effects were seen at 7 d and lasted beyond the treatment period. The neuroprotection appeared to be mediated by rescue of blood vessels. bpV(phen) reduced apoptosis of cultured endothelial cells. These results show that a small molecule, used in a clinically relevant manner, reduces loss of long-projecting axons, myelin, blood vessels, and function in a model relevant to the most common type of spinal cord injury in humans. They reveal a novel mechanism of spinal cord degeneration involving protein tyrosine phosphatases that can be targeted with therapeutic drugs.

Phenytoin protects central axons in experimental autoimmune encephalomyelitis

Axon degeneration is a major contributor to non-remitting deficits in multiple sclerosis (MS). Thus the development of therapies to provide protection of axons has elicited considerable interest. Voltage-gated sodium channels have been implicated in the injury cascade leading to axonal damage, and sodium-channel blockers have shown efficacy in ameliorating axonal damage in disease models following anoxia, trauma and damaging levels of nitric oxide (NO). Here we discuss studies in our laboratory that examined the protective effects of phenytoin, a well-characterized sodium-channel blocker, in the inflammatory/demyelinating disorder experimental autoimmune encephalomyelitis (EAE), a model of MS. Administration of phenytoin to C57/Bl6 mice inoculated with rat myelin oligodendrocyte glycoprotein (MOG) provides improved clinical status, preservation of axons, enhanced action potential conduction and reduced immune infiltrates compared to untreated mice with EAE. Moreover, continuous treatment with phenytoin provides these protective actions for at least 180 days post-MOG injection. The withdrawal of phenytoin from mice inoculated with MOG, however, is accompanied by acute exacerbation of EAE, with significant mortality and infiltration of immune cells in the CNS. Our studies demonstrate the efficacy of phenytoin as a neuroprotectant in EAE. Our results also, however, indicate that we need to learn more about the long-term effects of sodium-channel blockers, and of their withdrawal, in neuroinflammatory disorders.

Reimplantation of avulsed lumbosacral ventral roots in the rat ameliorates injury-induced degeneration of primary afferent axon collaterals in the spinal dorsal columns

Injuries to the cauda equina/conus medullaris portion of the spinal cord can result in motor, sensory, and autonomic dysfunction, and neuropathic pain. In rats, unilateral avulsion of the motor efferents from the lumbosacral spinal cord results in at-level allodynia, along with a corresponding glial and inflammatory response in the dorsal horn of the spinal cord segments immediately rostral to the lesion. Here, we investigated the fate of intramedullary primary sensory projections following a motor efferent lesion. The lumbosacral (L6 and S1) ventral roots were unilaterally avulsed from the rat spinal cord (VRA; n=9). A second experimental group had the avulsed roots acutely reimplanted into the lateral funiculus (Imp; n=5), as this neural repair strategy is neuroprotective, and promotes the functional reinnervation of peripheral targets. A laminectomy-only group served as controls (Lam; n=7). At 8 weeks post-lesion, immunohistochemical examination showed a 42% reduction (P<0.001) in the number of RT97-positive axons in the ascending tracts of the dorsal funiculus of the L4-5 spinal segment in VRA rats. Evidence for degenerating myelin was also present. Reimplantation of the avulsed roots ameliorated axon and myelin degeneration. Axons in the descending dorsal corticospinal tract were unaffected in all groups, suggesting a specificity of this lesion for spinal primary sensory afferents. These results show for the first time that a lesion restricted to motor roots can induce the degeneration of intramedullary sensory afferents. Importantly, reimplantation of the lesioned motor roots ameliorated sensory axon degeneration. These data further support the therapeutic potential for reimplantation of avulsed ventral roots following trauma to the cauda equina/conus medullaris.