Temporal changes in the expression of TGF-beta 1 and EGF in the ventral horn of the spinal cord and associated precentral gyrus in adult Rhesus monkeys subjected to cord hemisection

It is well known that some growth factors can not only rescue neurons from death, but also improve motor functions following spinal cord injury. However, their cellular distribution in situ and temporal expressions following spinal cord injury have not been determined, especially in primates. This study investigated the temporal changes in the expression of two growth factors--epidermal growth factor (EGF) and transforming growth factor-beta 1 (TGF-beta1) in the injured motoneurons of the spinal cord and the associated precentral gyrus in adult Rhesus monkeys subjected to spinal cord hemisection. Animals were allowed to survive 7, 14, 30 and 90 days post operation (dpo). Functional recovery of the hindlimbs was assessed using Tarlov scale. The immunohistological expressions of EGF and TGF-beta1 in the ventral horn motoneurons decreased sharply at 7 dpo in the cord segments caudal to the lesion site, which was followed by an increase and a peak between 14 and 30 dpo for EGF and at 90 dpo for TGF-beta1. Changes in the expression of EGF in the precentral gyrus were similar to that in the spinal cord. No TGF-beta1 immunoreactive neurons were detected in the precentral gyrus. In the spinal segments rostral to the lesion, the expressions of EGF and TGF-beta1 peaked at 30 dpo. The mRNA of EGF was detected in both spinal motoneurons and the precentral gyrus, while that of TGF-beta1, only in the spinal motoneuons, suggesting that the spinal motoneurons themselves could synthesize both the growth factors. Partial locomotor recovery in hindlimbs was seen, especially after 14 dpo. It was concluded that a possible association existed between the modulation of EGF and TGF-beta1 and the recovery of locomotor function, and their roles differed somewhat in the neuroplasticity observed after spinal cord injury in primates.     

Novel intrathecal delivery system for treatment of spinal cord injury

A novel, localized method for potential delivery of therapeutic agents to the injured spinal cord was investigated. The strategy consists of a polymeric drug solution that gels after injection into the subarachnoid space (SAS). By dispersing therapeutic agents in the polymeric solution, a method is provided for localized delivery to the spinal cord. To determine whether intrathecal injection of this drug delivery system (DDS) would affect cerebrospinal fluid (CSF) flow, a spinal canal model was built using dimensional analysis. Blocking up to 52% of the modeled subarachnoid space of the spinal canal caused minimal pressure differences (9.22 +/- 1.45 Pa), suggesting that implantation of a DDS would not subject the spinal cord to increased pressure. The safety of the DDS was also assessed in vivo by injecting collagen into the SAS of Sprague Dawley rats. Controls received injections of artificial CSF (aCSF). Collagen or aCSF was injected at the T2-T3 spinal level of both uninjured rats and rats injured with a 20g compression clip. The injected collagen persisted in the SAS for at least 8 weeks post-implantation and did not elicit an inflammatory reaction in either uninjured or injured animals. Long-term functional behavior was evaluated with the Basso, Beattie, and Bresnahan (BBB) scale weekly for 8 weeks. Functional behavior was similar in the collagen and aCSF groups, also indicating that the DDS was safe. This minimally invasive DDS may provide an alternative, safe method to deliver therapeutic agents intrathecally.     

Quantitative analysis of vascularization and cytochrome oxidase following fetal transplantation in the contused rat spinal cord

In the normal adult central nervous system, a coupling between energy consumption and vascular density is well established. Likewise, the survival of fetal neural tissue grafts is highly dependent on the establishment of functional vascular integration with the host. However, to what degree graft vascularization and tissue metabolism influence the normal host response to traumatic injury has not been extensively studied. In the present report, embryonic day 14 fetal spinal cord suspension grafts were made into the lesion epicenter of subchronic (10 days) contusion-injured rats. Three months later, intraspinal transplants were analyzed using correlative cytochrome oxidase histochemistry and vascular morphometric analysis. The same approaches were applied to the host spinal cord and injured, non-transplanted animals in order to determine the ability of a graft to alter the level of post-injury vascularization and/or metabolism. In general, graft vascular density was increased over that measured in normal or injured gray matter. Vascular density in gray matter near the host/graft interface was markedly increased when compared to either gray matter of the same spinal level in injured non-grafted animals or normal control spinal gray matter. Vascular changes were not noted in gray matter 3 mm distal to the lesion epicenter (rostral or caudal) in all groups analyzed. Cytochrome oxidase was up-regulated at this time in the graft and gray matter at the host/graft interfaces when compared to either gray matter of the same spinal level in injured, non-grafted animals or that of uninjured controls. These data indicate that an intraspinal transplant placed into the contused adult rat spinal cord reaches a metabolic capacity that is likely to be associated with high levels of oxidative metabolism in the well-vascularized graft neuropil. In addition, transplantation chronically alters vascularization and metabolic patterns of adjacent spinal gray matter following contusion injury. © 1996 Wiley-Liss, Inc.     

Effects of cyclosporin-A on immune response,tissue protection and motor function of rats subjected to spinal cord injury

The aim of this work was to test the effect of cyclosporin-A (CsA) on some immunological, morphological and functional aspects developed after spinal cord injury. The specific cellular immune response against spinal cord constituents, the amount of spared tissue and myelination at the site of injury, and the motor function outcome were assessed in a first series of experiments. Rats were subjected to spinal cord compression and treated with cyclosporin-A before lesion and during the entire study. A specific lymphocyte response against spinal cord antigens was found in untreated spinal cord injured rats but not in cyclosporine-A treated injured rats. A significantly better myelination index was also found in injured cyclosporin-A-treated rats, as compared to untreated animals. The amount of spared spinal cord tissue at the epicenter was not significantly different comparing CsA-treated with vehicle-treated rats. Looking for a potential therapeutic use of CsA, in a second series of experiments, rats were subjected to spinal cord contusion and treated with cyclosporin-A from 1 to 72 h after lesion. Motor recovery and red nuclei neurons survival, were evaluated, and found to be significantly better in spinal cord injured rats treated with cyclosporin-A than in injured-untreated rats. This work confirms the existence of an autoimmune cellular reaction after injury that can be inhibited by cyclosporin-A treatment. Furthermore, cyclosporin-A promotes neuroprotection by diminishing both demyelination and neuronal cell death, resulting in a better motor outcome after spinal cord injury.     

Transplantation of bone marrow mesenchymal stem cells reduces lesion volume and induces axonal regrowth of injured spinal cord

It has been demonstrated that transplantation of bone marrow mesenchymal stem cells (BMSCs) improves recovery of injured spinal cord in animal models. However, the mechanism of how BMSCs promote repair of injured spinal cord remains under investigation. The present study investigated the neural differentiation of BMSCs, the lesion volume and axonal regrowth of injured spinal cord after transplantation. Seven days after spinal cord injury, 3 × 10⁵ BMSCs or PBS (control) was delivered into the injury epicenter of the spinal cord. At 8 weeks after spinal cord injury, transplantation of BMSCs reduced the volume of cavity and increased spared white matter as compared to the control. BMSCs did not express the cell marker of neurons, astrocytes and oligodendrocytes in injured spinal cord. Transmission electron microscopic examination displayed an increase in the number of axons in BMSC rats. The effect of BMSCs on growth of neuronal process was further investigated by using a coculture system. The length and the number of neurites from spinal neurons significantly increased when they cocultured with BMSCs. PCR and immunochemical analysis showed that BMSCs expressed brain‐derived neurotrophic factor (BDNF) and glia cell line‐derived neurotrophic factor (GDNF). These findings demonstrate that transplantation of BMSCs reduces lesion volume and promotes axonal regrowth of injured spinal cord.     

Robust Growth of Chronically Injured Spinal Cord Axons Induced by Grafts of Genetically Modified NGF-Secreting Cells

Little spontaneous regeneration of axons occurs after acute and chronic injury to the CNS. Previously we have shown that the continuous local delivery of neurotrophic factors to the acutely injured spinal cord induces robust growth of spinal and supraspinal axons. In the present study we examined whetherchronicallyinjured axons also demonstrate significant neurotrophin responsiveness. Adult rats underwent bilateral dorsal hemisection lesions that axotomize descending supraspinal pathways, including the corticospinal, rubrospinal, and cerulospinal tracts, and ascending dorsal spinal sensory projections. One to three months later, injured rats received grafts of syngenic fibroblasts genetically modified to produce nerve growth factor (NGF). Control subjects received unmodified cell grafts or cells transduced to express the reporter gene β-galactosidase. Three to five months after grafting, animals that received NGF-secreting grafts showed dense growth of putative cerulospinal axons and primary sensory axons of the dorsolateral fasciculus into the grafted lesion site. Growth from corticospinal, raphaespinal, and local motor axons was not detected. Thus, robust growth of defined populations of supraspinal and spinal axons can be elicited in chronic stages after spinal cord injury by localized, continuous transgenic delivery of neurotrophic factors.     

Fetal Transplantation Following Spinal Contusion Injury Results in Chronic Alterations in CNS Glucose Metabolism

Glucose utilization of the injured rat spinal cord was determined using the autoradiographic technique of Sokoloff et al. (33). Animals were analyzed chronically (2 and 3 months) after spinal contusion injury alone or when a spinal lesion was followed by subchronic (10 day) intraparenchymal fetal spinal transplantation. At 2 and 3 months postinjury, spinal glucose utilization was reduced in dorsal gray and white matter above and below the lesion site. In addition, sensory regions of the forebrain and brain stem (e.g., nucleus gracilis and ventral posterior medial nucleus of the thalamus) had a lower basal metabolic rate than control animals. Decreased metabolic rates in supraspinal regions were reversed by the presence of a spinal graft at 3 but not at 2 months postinjury. Furthermore, gray matter in animals receiving an intraspinal transplant had elevated glucose utilization rates for several spinal segments rostral and caudal to the lesion epicenter. Graft glucose utilization was higher at 2 months (80-90 μmol/100 g/min) than at 3 months (60-70 μmol/100 g/min) posttransplantation. These data are the first quantitative metabolic imaging of spinal and brain metabolism following spinal contusion injury and fetal transplantation. The study suggests that intraspinal transplants can become functionally integrated with adjacent host gray matter and can chronically alter specific postinjury metabolic patterns.     

NGF mRNA is expressed in the dorsal root ganglia after spinal cord injury in the rat

Nerve growth factor (NGF) mRNA is expressed in a variety of cell types in the injured spinal cord and its protein implicated in both positive and negative neurological outcomes of cord injury. Here we demonstrate that NGF mRNA is also upregulated in dorsal root ganglion (DRG) neurons after spinal cord injury and that the percentage of sensory neurons expressing NGF mRNA correlates with proximity to the lesion epicenter. Our data suggest that, in DRG, NGF gene expression may be upregulated by damage to the central processes of sensory neurons.     

A Quantitative Spatial Analysis of the Blood–Spinal Cord Barrier: II. Permeability after Intraspinal Fetal Transplantation

In previous experiments we utilized quantitative autoradiography to temporally describe vascular permeability of a radiolabeled vascular tracer following spinal contusion injury in the rat. In the present report we compare these findings with permeability assessments following fetal grafting in the contused rat spinal cord. At 10 days postinjury, Embryonic Day 14 spinal tissue was grafted into the lesioned spinal cord of Sprague–Dawley rats. At 7, 14, and 28 days postgrafting the α-aminoisobutyric acid (AIB) technique was used to assess blood-to-tissue transfer rates in graft and host tissue over several segments of the injured spinal cord. Regional changes in permeability were assessed using four distinct image analysis techniques. Using these methods, we have previously shown that contusion injury alone results in a chronic relapse in vascular permeability. The present data indicate that fetal transplants at 7 days postgrafting have AIB transfer rates that are significantly above uninjured control levels and are similar in magnitude to neighboring host spinal tissue. In addition, permeability in 14- and 28-day intraspinal grafts decreased relative to that of the 7-day transplant group, but remained significantly elevated at and rostral to the injury epicenter. Alternately, graft and host tissue in regions caudal to the injury epicenter (e.g., T₁₀–L₂) acquired a functional barrier to AIB as early as 14 days posttransplantation. These experiments suggest that graft development occurs in a different manner or at a different rate in segments of the injured spinal cord rostral and caudal to the injury site. Additionally, it appears that vascular permeability of the injured spinal cord can be influenced by the process of intraspinal transplantation.     

Self‐assembling peptide amphiphile promotes plasticity of serotonergic fibers following spinal cord injury

Injection into the injured spinal cord of peptide amphiphile (PA) molecules that self‐assemble and display the laminin epitope IKVAV at high density improved functional recovery after spinal cord injury (SCI) in two different species, rat and mouse, and in two different injury models, contusion and compression. The improvement required the IKVAV epitope and was not observed with the injection of an amphiphile displaying a nonbioactive sequence. To explore the mechanisms underlying these improvements, the number of serotonergic fibers in the lesioned spinal cord was compared in animals receiving the IKVAV‐PA, a nonbioactive PA (PA control), or sham injection. Serotonergic fibers were distributed equally in all three groups rostral to the injury but showed a significantly higher density caudal to the injury site in the IKVAV PA‐injected group. Furthermore, this difference was not present in the subacute phase following injury but appeared in the chronically injured cord. The IKVAV PA‐injected groups also trended higher both in the total number neurons adjacent to the lesion and in the number of long propriospinal tract connections from the thoracic to the lumbar cord. IKVAV PA injection did not alter myelin thickness, total axon number caudal to the lesion, axon size distribution, or total axon area. Serotonin can promote stepping even in complete transection models, so the improved function produced by the IKVAV PA treatment may reflect the increased serotonergic innervation caudal to the lesion in addition to the previously demonstrated regeneration of motor and sensory axons through the lesion. © 2010 Wiley‐Liss, Inc..     

Neuroprotective effects of a novel NMDA antagonist, Gacyclidine, after experimental contusive spinal cord injury in adult rats

The aim of this study was to analyze the optimal time-window for neuroprotection by a novel NMDA antagonist, Gacyclidine, after experimental spinal cord injury, in terms of its functional, histopathological and electrophysiological effects. This molecule has already demonstrated its capacity for reducing the extent of an ischemic lesion and is currently experimented in a clinical trial of spinal cord injury. In this study, the spinal cord of rats was damaged by a contusive method and the animals were treated by saline or 1 mg/kg of Gacyclidine i.v., 10, 30, 60 and 120 min after injury. The time-course of the motor score was evaluated on days 1, 7 and 18 after injury, and somatosensory evoked potentials were determined on day 20. The animals were then killed and the cross-sectional area of the spinal cord (at the epicenter of the injury, above and below the injury), was measured. Walking recovery was better (P<0.0125) in the group treated 10 min after injury than in the untreated injured animals after 18 days of injury. Motor performances were related to the preservation of a larger undamaged area of spinal cord at the level of the injury (P<0.0125). Somatosensory evoked potential amplitudes were also higher in this group. These results confirm that Gacyclidine attenuates spinal cord damage after an experimental spinal cord lesion. Recovery was better within the group treated 10 min after injury compared with the other groups, which certainly confirms that the acute time-course of glutamate release requires rapid pharmacological intervention to achieve good results.     

Time course study of GFRalpha-1 expression in an animal model of stroke

Alterations in the expression of ionotropic glutamate receptors (GluR) contribute to neuronal loss after brain ischemia and epilepsy. In order to determine whether altered expression of GluR subunits might contribute to cell loss after spinal cord injury (SCI), we performed a time course study of subunit mRNA expression using quantitative in situ hybridization. Expression was studied in ventral horn motor neurons (VMN) and glia in adjacent ventral white matter at 15 min and 4, 8, and 24 h after SCI in tissue sections 4 mm rostral and caudal to the injury epicenter. We found that the AMPA subunit GluR2 was significantly down-regulated in VMN at 24 h, but not at the earlier times examined, although half the loss of VMN in these locations occurs by 8 h after injury. No changes in the normal expression of GluR2 or GluR4 were found in white matter where glial loss occurs after SCI. NMDA subunits NR1 and NR2A were significantly and rapidly up-regulated in VMN after SCI, but only caudal to the lesion site, while VMN loss is similar rostral and caudal to the epicenter. Thus, the temporal pattern of AMPA and the spatial pattern of NMDA subunit expression changes were distinct from the pattern of VMN loss after SCI. We conclude that altered GluR subunit expression after SCI is unlikely to be involved in secondary cell loss and instead may be involved with plasticity and reorganization of the injured spinal cord.     

Up-regulation of macrophage migration-inhibitory factor expression after compression-induced spinal cord injury in rats

Macrophage migration inhibitory factor (MIF) is a multipotential protein that acts as a pro-inflammatory cytokine, pituitary hormone, immunoregulator, and mitogen. To elucidate function of MIF in spinal cord injury, we examined expression of MIF after compression-induced spinal cord injury using Northern blot analysis, in situ hybridization and immunohistochemistry. The MIF mRNA was up-regulated in injured spinal cord, peaking 3 days after injury shown by Northern blot analysis. In situ hybridization revealed up-regulation of MIF in microglia accumulating in the lesion epicenter 3 days after injury and astrocytes around the cystic cavity 1 week after injury. Double staining showed co-localization of MIF and tomato lectin in the lesioned site, indicating that microglia accumulating to the lesion epicenter express MIF. The time course of MIF expression is different from that of previous reports about cytokine expression peaking at earlier time points; thus, it is unlikely that MIF acts as a pro-inflammatory factor in the present study. The MIF may contribute to proliferation of astrocytes around the lesioned site in spinal cord injury because of its cell proliferation-promoting property.     

Differences in cytokine gene expression profile between acute and secondary injury in adult rat spinal cord

It is likely that the environment within the injured spinal cord influences the capacity of fetal spinal cord transplants to support axonal growth. We have recently demonstrated that fetal spinal cord transplants and neurotrophin administration support axonal regeneration after spinal cord transection, and that the distance and amount of axonal growth is greater when these treatments are delayed by several weeks after injury. In this study, we sought to determine whether differences in inflammatory mediators exist between the acutely injured spinal cord and the spinal cord after a second injury and re-section, which could provide a more favorable environment for the axonal re-growth. The results of this study show a more rapid induction of transforming growth factor (TGF) beta1 mRNA expression in the re-injured spinal cord than the acutely injured spinal cord and an attenuation of proinflammatory cytokine mRNA expression. Furthermore, there was a rapid recruitment of activated microglia/macrophages in the degenerating white matter rostral and caudal to the injury but fewer within the lesion site itself. These findings suggest that the augmentation of TGFbeta-1 gene expression and the attenuation of pro-inflammatory cytokine gene expression combined with an altered distribution of activated microglia/macrophages in the re-injured spinal cord might create a more favorable milieu for transplants and axonal regrowth as compared to the acutely injured spinal cord.     

Localization of transforming growth factor-beta1 and receptor mRNA after experimental spinal cord injury

Transforming growth factor-beta1 (TGFbeta1) is a cytokine/growth factor found within the pathological central nervous system. TGFbeta1 has been shown to inhibit the release of cytotoxic molecules from microglia and macrophages, decrease astrocyte proliferation, and promote neuron survival. Because of the relevance of these actions to spinal cord injury, we examined TGFbeta1 and its receptors betaRI and betaRII mRNA levels and localization within the contused rat spinal cord using in situ hybridization. At the lesion site, TGFbeta1 mRNA peaked at 7 days postinjury and declined thereafter. Temporal and spatial localization of the betaRI and betaRII receptor mRNA closely mimicked that for TGFbeta1 in the epicenter. TGFbeta1, betaRI, and betaRII mRNAs also were elevated rostral and caudal to the injury, especially in regions known to contain activated microglia and degenerating axon profiles. Immunohistochemical staining of nearby sections confirmed that the highest levels of TGFbeta1 and receptor mRNA corresponded to regions filled with activated microglia and macrophages. The similar expression pattern of TGFbeta1, betaRI, and betaRII mRNA within the injured spinal cord suggests a local site of action. Since TGFbeta1 can act as an immunosuppressant as well as a stimulant for growth factors and neurite sprouting, it likely plays an important role, both temporally and spatially, in orchestrating postinjury events within the spinal cord.     

Responses of spinal neurones to cutaneous and dorsal root stimuli in rats with mechanical allodynia after contusive spinal cord injury

The firing of neurones in spinal segments adjacent to a contusive T13 spinal cord injury was characterised in anaesthetised rats. Three groups of rats were examined: (1) allodynic spinally injured, (2) non-allodynic spinally injured and (3) normal, uninjured. Spinal cord field potentials evoked by electrical dorsal root stimulation and the responses of 207 dorsal horn neurones to mechanical stimuli applied to the skin were studied. Within the lesioned spinal segment few active neurones were encountered and field potentials were absent. Depolarising field potentials recorded rostral to the lesion were reduced in both allodynic and non-allodynic animals compared to uninjured controls, while those recorded in caudal segments were enhanced in allodynic animals. Neuronal recordings revealed that allodynia was associated with exaggerated responses, including afterdischarges, to innocuous and noxious mechanical stimuli in a proportion of wide dynamic range, but not low threshold, neurones. These changes were observed both rostral and caudal to the site of injury. The results suggest that an increased responsiveness of some dorsal horn neurones in segments neighbouring a contusive spinal cord injury may contribute to the expression of mechanical allodynia. It is proposed that a relative lack of inhibition underlies altered cell responses.     

NT-3 gene delivery elicits growth of chronically injured corticospinal axons and modestly improves functional deficits after chronic scar resection

Nervous system growth factors promote axonal growth following acute spinal cord injury. In the present experiment, we examined whether delivery of neurotrophic factors after chronic spinal cord injury would also promote axonal growth and influence functional outcomes. Adult Fischer 344 rats underwent mid-thoracic spinal cord dorsal hemisection lesions. Three months later, primary fibroblasts genetically modified to express human neurotrophin-3 (NT-3) were placed in, and distal to, the lesion cavity. Upon sacrifice 3 months later (6 months following the initial lesion), NT-3-grafted animals exhibited significant growth of corticospinal axons up to 15 mm distal to the lesion site and showed a modest but significant 1.5-point improvement in locomotor scores (P < 0.05) on the BBB scale, compared to control-grafted animals. Thus, growth factor gene delivery can elicit growth of corticospinal axons in chronic stages of injury and improves functional outcomes compared to non-growth-factor-treated animals.     

Endogenous recovery of injured spinal cord: longitudinal in vivo magnetic resonance imaging

Pathological changes were followed longitudinally with in vivo magnetic resonance imaging (MRI) and behavioral studies in experimental spinal cord injury (SCI). MRI-observed pathology was correlated with histology. On MRI, the cavitated regions of the injured cord were gradually filled with viable tissue between two and 8 weeks postinjury, and a concomitant improvement was observed in the neurobehavioral scores. By weeks 3-6, on MRI, the gray matter (GM) returned in the segments caudal, but not rostral, to the injury site. The corresponding histological sections revealed motor neurons as well as other nuclei in the gray matter immediately caudal to the epicenter, but not at the site of injury, suggesting neuronal recovery in perilesioned areas. The neuronal and neurological recovery appeared to occur about the same time as neovasculature that was reported on the contrast-enhanced MRI, suggesting a role for angiogenesis in recovery from SCI. The role of angiogenesis in neuronal recovery is further supported by the immunohistochemical observation of greater bromodeoxyuridine uptake by blood vessels near the lesion site compared with uninjured cords.     

Regeneration and Sprouting of Chronically Injured Corticospinal Tract Fibers in Adult Rats Promoted by NT-3 and the mAb IN-1, Which Neutralizes Myelin-Associated Neurite Growth Inhibitors

Myelin-associated inhibitors of neurite growth play an important role in the regenerative failure after injury in the adult mammalian CNS. The application of the mAb IN-1, which efficiently neutralizes the NI-250/35 inhibitory proteins, alone or in combination with neurotrophin-3 (NT-3), has been shown to promote axonal regeneration when applied in acute injury models. To test whether IN-1 application can induce axonal growth also in a chronic injury model, we treated rats with IN-1 and NT-3 starting 2 or 8 weeks after injury. Rats underwent bilateral dorsal hemisection of the spinal cord at the age of 5–6 weeks. Regeneration of corticospinal (CST) fibers into the caudal spinal cord was observed in three of eight of those animals with a 2-week delay between lesion and treatment. CST fibers regenerated for 2–11.4 mm. In the control group sprouting occurred rostral to the lesion but no long-distance regeneration occurred. In animals where treatment started at 8 weeks after injury the longest fibers observed grew up to 2 mm into the caudal spinal cord. The results show that transected corticospinal axons retain the ability to regenerate at least for a few weeks after injury. Functional analysis of these animals showed a slight improvement of functional recovery.     

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

Accumulation of intracellular sodium through voltage-gated sodium channels (VGSCs) is an important event in the cascade leading to anatomic degeneration of spinal cord axons and poor functional outcome following traumatic spinal cord injury (SCI). In this study, we hypothesized that phenytoin, a sodium channel blocker, would result in protection of axons with concomitant improvement of functional recovery after SCI. Adult male Sprague-Dawley rats underwent T9 contusion SCI after being fed normal chow or chow containing phenytoin; serum levels of phenytoin were within therapeutic range at the time of injury. At various timepoints after injury, quantitative assessment of lesion volumes, axonal degeneration, axonal conduction, and functional locomotor recovery were performed. When compared to controls, phenytoin-treated animals demonstrated reductions in the degree of destruction of gray and white matter surrounding the lesion epicenter, sparing of axons within the dorsal corticospinal tract (dCST) and dorsal column (DC) system rostral to the lesion site, and within the dorsolateral funiculus (DLF) caudal to the lesion site, and enhanced axonal conduction across the lesion site. Improved performance in measures of skilled locomotor function was observed in phenytoin-treated animals. Based on these results, we conclude that phenytoin provides neuroprotection and improves functional outcome after experimental SCI, and that it merits further examination as a potential treatment strategy in human SCI.