Recent advances in pathophysiology and treatment of spinal cord injury

Regeneration of the rat spinal cord after thoracic segmentectomy: Growth and restoration of nerve conductors

The results presented in our previous report (Morfologiya, 127, No. 2 (2005)) provided evidence that consolidation of the spinal cord (SC) after thoracic segmentectomy in rats occurs as a result of the formation of a connective tissue scar, which is quicker when the defect is filled with collagen gel. The present report describes analysis of semithin sections and transmission electron microscopy studies demonstrating that regenerating nerve conductors traverse connective tissue in structures whose organization is identical to that of peripheral nerves. In the zone of SC rarefaction caudal to the trauma site, myelination of growing axons is mediated by glial cells without the formation of nerve trunks. Large numbers of fine regenerating conductors were seen at the sites of degenerated myelin fibers in the fasciculi of the white matter in the lumbar segments of the SC.

Novel nerve guidance material prepared from bovine aponeurosis

Spinal cord injury (SCI) creates an adverse environment for axon regeneration. As a result, the axons at the injury sites begin to be atrophy, retract and lose their functions. Several strategies to promote axon regeneration at the injury site have been tested, but the progress is very limited. One of the major reasons is that the regenerated axons often extend randomly and do not reach the proper place. Fabricating linearly ordered materials as nerve guidance would be important to solve such problems. In this study, a novel type of nerve guidance material was prepared from the bovine aponeurosis, which mainly consisted of ordered collagen fibers. The processed material showed good cell compatibility and low immunogenisity. Moreover, the processed material guided the neurites outgrowth of in vitro cultured cortical neurons along its fibers. The results suggested that the processed aponeurosis would be a proper nerve guidance biomaterial for SCI repair.

Instrumental learning within the spinal cord: underlying mechanisms and implications for recovery after injury

Using spinally transected rats, research has shown that neurons within the L4-S2 spinal cord are sensitive to response-outcome (instrumental) relations. This learning depends on a form of N-methyl-D-aspartate (NMDA)-mediated plasticity. Instrumental training enables subsequent learning, and this effect has been linked to the expression of brain-derived neurotrophic factor. Rats given uncontrollable stimulation later exhibit impaired instrumental learning, and this deficit lasts up to 48 hr. The induction of the deficit can be blocked by prior training with controllable shock, the concurrent presentation of a tonic stimulus that induces antinociception, or pretreatment with an NMDA or gamma-aminobutyric acid-A antagonist. The expression of the deficit depends on a kappa opioid. Uncontrollable stimulation enhances mechanical reactivity (allodynia), and treatments that induce allodynia (e.g., inflammation) inhibit learning. In intact animals, descending serotonergic neurons exert a protective effect that blocks the adverse consequences of uncontrollable stimulation. Uncontrollable, but not controllable, stimulation impairs the recovery of function after a contusion injury.

Inhibition of EphA7 up-regulation after spinal cord injury reduces apoptosis and promotes locomotor recovery

Functional impairment after spinal cord injury (SCI) is partially attributed to neuronal cell death, with further degeneration caused by the accompanying apoptosis of myelin-forming oligodendrocytes. The Eph receptor protein tyrosine kinase family and its cognate ligands, the ephrins, have been identified to be involved in axonal outgrowth, synapse formation, and target recognition, mainly mediated by repulsive activity. Recent reports suggest that ephrin/Eph signaling might also play a role as a physiological trigger for apoptosis during embryonic development. Here, we investigated the expression profile of EphA7, after SCI, by using a combination of quantitative real-time PCR (QRT-PCR) and immunohistochemical techniques. QRT-PCR analysis showed an increase in the expression of full-length EphA7 at 7 days postinjury (DPI). Receptor immunoreactivity was shown mostly in astrocytes of the white matter at the injury epicenter. In control animals, EphA7 expression was observed predominantly in motor neurons of the ventral gray matter, although some immunoreactivity was seen in white matter. Furthermore, blocking the expression of EphA7 after SCI using antisense oligonucleotides resulted in significant acceleration of hindlimb locomotor recovery at 1 week. This was a transient effect; by 2 weeks postinjury, treated animals were not different from controls. Antisense treatment also produced a return of nerve conduction, with shorter latencies than in control treated animals after transcranial magnetic stimulation. We identified EphA7 receptors as putative regulators of apoptosis in the acute phase after SCI. These results suggest a functional role for EphA7 receptors in the early stages of SCI pathophysiology.

Astroglia-mediated effects of uric acid to protect spinal cord neurons from glutamate toxicity

Uric acid (UA) has been demonstrated to reduce damage to neurons elicited by oxidative stress. However, our studies utilizing cultures derived from embryonic rat spinal cord indicate that an astroglia-mediated mechanism is involved in the effects of UA to protect neurons from glutamate toxicity. The damage elicted by glutamate to neurons in a mixed culture of spinal cord cells can be reversed by UA. Furthermore, addition of UA after the termination of glutamate exposure suggests that UA plays an active role in mediating neuroprotection rather than purely binding peroxynitrite, as previously thought. Importantly, in pure neuron cultures from the same tissue, UA does not protect against glutamate toxicity. Addition of astroglia to the pure neuron cultures restores the ability of UA to protect the neurons from glutamate-induced toxicity. Our results also suggest that glia provide EAAT-1 and EAAT-2 glutamate transporters to protect neurons from glutamate, that functional EAATs may be necessary to mediate the effects of UA, and that treatment with UA results in upregulation of EAAT-1 protein. Taken together, our data strongly suggest that astroglia in mixed cultures are essential for mediating the effects of UA, revealing a novel mechanism by which UA, a naturally produced substance in the body, may act to protect neurons from damage during insults such as spinal cord injury.

Glutamine concentration and immune response of spinal cord-injured rats

BACKGROUND/OBJECTIVES

Glutamine plays a key role in immune response. Spinal cord injury (SCI) leads to severe loss of muscle mass and to a high incidence of infections. This study investigated the acute effect of SCI (2 and 5 days) on the plasma glutamine and skeletal muscle concentrations and immune responses in rats.

METHODS

A total of 29 adult male Wistar rats were divided as follows: control (C; n = 5), sham-operated (S2; n = 5) and spinal cord-transected (T2; n = 7). They were killed on day 2 after surgery/transection (acute phase). Another set was sham-operated (S5; n = 5), spinal cord-transected (T5; n = 7), and killed at day 5 after surgery/transection (secondary phase). Blood was collected; the white portion of the epitrochlearis and gastrocnemius muscles and the red portion of soleus muscles were dissected to measure the glutamine concentration. Gut-associated lymphocytes and peritoneal macrophages were obtained for immune parameters measurements.

RESULTS

Glutamine concentration in the plasma, gastrocnemius, and soleus muscles in rats with SCI were significantly reduced but not in the epitrochlearis muscle in the acute (2 days) and secondary (5 days) phases. Phagocytic response was reduced in the acute phase but increased in the secondary phase in rats with SCI. Superoxide production, on the other hand, was significantly increased at days 2 and 5 after SCI, and CD8+ lymphocytes subset decreased significantly on days 2 and 5.

CONCLUSIONS

Our results showed reduction in plasma glutamine and skeletal muscle concentrations after spinal cord transection. They also suggest that SCI and glutamine reduction contribute to an alteration in immune competence.

The long-term neurocompatibility of human fibrin sealant and equine collagen as biomatrices in experimental spinal cord injury

INTRODUCTION

While fibrin sealant (FS) and equine collagen (EC) have been used as scaffold materials in experimental spinal cord injury (SCI), questions concerning neurocompatibility still remain. In this study, we assessed potential adverse effects, as well as functional and histological impact of FS and EC in subtotal hemisection of the thoracic spinal cord (SC) in rats.

METHODS

124 male rats were randomly assigned to four main groups (n=31): Sham (SH), Lesion only (L), fibrin sealant (GFS) and equine collagen group (GEC). SH animals received laminectomy only; all other animals underwent subtotal lateral hemisection at T9. Treatment consisted of application of FS or EC into the lesion gap in GFS and GEC, which was left empty in L. GFS, GEC, L and SH were each further divided into 4 subgroups: One subgroup, consisting of 10 rats was subjected to behavioural and reflex testing before surgery and followed up on days 1,7, 14, 21, 28 post op and then sacrificed. Haemalaun or cresyl violet (CV) was used to identify neutrophils in parasagittal cord sections which were obtained on day 1 (n=7). Sections stained for quantification of microglia/macrophages using ED-1 on day 3 (n=7), day 7 (n=7) and day 28 (n=7 out of 10). Additionally, neural filament (NF) staining was chosen to detect axonal regeneration and the length of ingrowth into FS and EC, Luxol blue for myelination, Von Willebrand factor for vascularisation, and glial fibrillary acidic protein (GFAP) staining for detection of astrocytes in glial scars on day 28.

RESULTS

No adverse effects were observed in the treatment groups. Compared to L, GFS and GEC performed significantly better in the Basso, Beattie, Bresnahan (BBB) score and hopping responses. Proprioceptive placing was markedly improved in FS and EC compared to L. Axonal regrowth was found in GFS and GEC--the regrowth in the GFS was accompanied by myelination and vascularisation. Glial scarring occurred in all groups. Discussion Both biomatrices improved functional recovery compared to L and no adverse effects were perceived.

Donald Munro Lecture. Spinal cord injury--past, present, and future

This special report traces the path of spinal cord injury (SCI) from ancient times through the present and provides an optimistic overview of promising clinical trials and avenues of basic research. The spinal cord injuries of Lord Admiral Sir Horatio Nelson, President James A. Garfield, and General George Patton provide an interesting perspective on the evolution of the standard of care for SCI. The author details the contributions of a wide spectrum of professionals in the United States, Europe, and Australia, as well as the roles of various government and professional organizations, legislation, and overall advances in surgery, anesthesia, trauma care, imaging, pharmacology, and infection control, in the advancement of care for the individual with SCI.

Predifferentiated embryonic stem cells prevent chronic pain behaviors and restore sensory function following spinal cord injury in mice

Embryonic stem (ES) cells have been investigated in repair of the CNS following neuronal injury and disease; however, the efficacy of these cells in treatment of postinjury pain is far from clear. In this study, we evaluated the therapeutic potential of predifferentiated mouse ES cells to restore sensory deficits following spinal cord injury (SCI) in mice. The pain model used unilateral intraspinal injection of quisqualic acid (QUIS) into the dorsal horn between vertebral levels T13 and L1. Seven days later, 60,000 predifferentiated ES cells or media were transplanted into the site of the lesion. Histological analysis at 7, 14, and 60 days post-transplantation revealed that animals receiving ES cell transplants suffered significantly less tissue damage than animals receiving media alone. Transplanted cells provided immediate effects on both spontaneous and evoked pain behaviors. Treatment with ES cells resulted in 0% (n = 28) excessive grooming behavior versus 60% (18 of 30) in media-treated animals. In the acetone test (to assess thermal allodynia), mice recovered to preinjury levels by 12 days after ES cell transplant, whereas control animals injected with media after SCI did not show any improvement up to 60 days. Similarly, the von Frey test (to assess mechanical allodynia) and the formalin test (to assess nociceptive hyperalgesia) showed that transplantation of predifferentiated ES cells significantly reduced these pain behaviors following injury. Here we show that predifferentiated ES cells act in a neuroprotective manner and provide antinociceptive and therapeutic effects following excitotoxic SCI.

Regeneration of the rat spinal cord after thoracic segmentectomy: restoration of the anatomical integrity of the spinal cord

Segmentectomy of the spinal cord (SC) was performed in 28 rats at the level of the tenth thoracic vertebra. Scar formation at the operation site was studied, along with the completeness of the anatomical integrity of the SC, in control animals (group 1) and after filling of the defect with the neural matrix Spherogel (group 2) and with Spherogel containing embryonic nerve cells (group 3). The defect in the SC in animals of the control group was filled with fibrin masses by 1-2 weeks, while connective tissues scars were already formed by this time in rats of experimental groups 2 and 3. By 10-11 weeks, these animals showed partial recovery of movement in the three lower limb joints. The scar tissue and adjacent zones of the SC showed large quantities of regenerating fine myelinated nerve fibers. These were clearly evident in the zones of the cranial and caudal margins, to the extent of the appearance of typical SC tissue. In preparations obtained from control animals, fine myelinated fibers were noted in the immediate vicinity of SC substance, while nerve fibers were few in number in scar tissue and the cellular bands of the transitional zone.

6-Shogaol, a natural product, reduces cell death and restores motor function in rat spinal cord injury

Spinal cord injury (SCI) results in progressive waves of secondary injuries, which via the activation of a barrage of noxious pathological mechanisms exacerbate the injury to the spinal cord. Secondary injuries are associated with edema, inflammation, excitotoxicity, excessive cytokine release, caspase activation and cell apoptosis. This study was aimed at investigating the possible neuroprotective effects of 6-shogaol purified from Zingiber officinale by comparing an experimental SCI rat group with SCI control rats. Shogaol attenuated apoptotic cell death, including poly(ADP-ribose) polymerase activity, and reduced astrogliosis and hypomyelination which occurs in areas of active cell death in the spinal cords of SCI rats. The foremost protective effect of shogaol in SCI would therefore be manifested in the suppression of the acute secondary apoptotic cell death. However, it does not attenuate active microglia and macrophage infiltration. This finding is supported by a lack of histopathological changes in the areas of the lesion in the shogaol-treated SCI rats. Moreover, shogaol-mediated neuroprotection has been linked with shogaol's attenuation of p38 mitogen-activated protein kinase, p-SAPK/JNK and signal transducer, and with transcription-3 activation. Our results demonstrate that shogaol administrated immediately after SCI significantly diminishes functional deficits. The shogaol-treated group recovered hindlimb reflexes more rapidly and a higher percentage of these rats regained responses compared with the untreated injured rats. The overall hindlimb functional improvement of hindlimbs, as measured by the Basso, Beattie and Bresnahan scale, was significantly enhanced in the shogaol-treated group relative to the SCI control rats. Our data show that the therapeutic outcome of shogaol probably results from its comprehensive effects of blocking apoptotic cell death, resulting in the protection of white matter, oligodendrocytes and neurons, and inhibiting astrogliosis. Our finding that the administration of shogaol prevents secondary pathological events in traumatic SCIs and promotes recovery of motor functions in an animal model raises the issue of whether shogaol could be used therapeutically in humans after SCI.

Molecular insights of the injured lesions of rat spinal cords: Inflammation, apoptosis, and cell survival

Spinal cord injury (SCI) is a devastating neurologic injury with functional deficits. In the acute phase, which starts at the moment of the injury and extends over the first few days, numerous pathological processes begin. In this study, we made several additional advances to broaden our understanding of SCI-induced gene expression changes. We examined changes at multiple time points: 0, 6, 24, 48, and 72 h after injury, with the latter time period being added. Also, we utilized multiple analysis methods such as real-time RT-PCR, Western blot, and immunohistochemistry to increase confidence in our candidate gene and molecular processes. From the pool of information, we generated profiles of expression changes and molecular mechanisms of several injury processing. Early stages after the injury are characterized by the strong upregulation of genes involved in transcription, inflammation, and signaling proteins, and a general downregulation of neural function-related genes. In addition, edema of the spinal cord develops, and metabolic disturbances involving intra-neuronal Ca2+ accumulation occur. This translates into a general failure of normal neural functions and a stage of signal shock that lasts for a few days in experimental rat models. Traumatic injury to the spinal cord also leads to a strong inflammatory response with the recruitment of peripherally derived immature cells, such as ED1-positive macrophages. After the trauma, apoptotic cell death continues, and scarring and demyelination accompany Wallerian degeneration. Strong expression of transcription factors of the Janus-activated kinase (JAK) and signal transducer and activator of transcription (STAT) family represents an early attempt of spinal cord repair and regeneration. Our study allowed us to conclude that combined therapeutic strategies for enhanced recovery should be performed until the chronic phase of the injury in areas distal to the lesion epicenter of spinal cords.

Activation of Spinal GABA Receptors Attenuates Chronic Central Neuropathic Pain after Spinal Cord Injury

In this study, we investigated the role of the spinal GABAergic system in central neuropathic painlike outcomes following spinal cord injury (SCI) produced by a spinal hemitransection at T13 of the rat. After SCI, mechanical allodynia develops bilaterally in both hind paws of the rat, lasting longer than 40 days, as evidenced by an increase in paw withdrawal frequency in response to a weak von Frey filament. In naive rats, intrathecal (i.t.) administration in the lumbar spinal cord of GABAA and GABAB receptor antagonists, bicuculline (1-5 microg) and phaclofen (0.1-5 microg), respectively, causes a dose-dependent increase in the magnitude of mechanical allodynia. The SCI-induced mechanical allodynia in both hind-paws is attenuated by i.t. administration in the lumbar spinal cord of GABAA or GABAB receptor agonists, muscimol (1 microg) or baclofen (0.5 microg), respectively. In electrophysiological experiments, rats with SCI show a bilateral increase in hyperexcitability in response to natural stimuli in wide dynamic range (WDR) neurons in the lumbar spinal dorsal horn. The topical application of muscimol (1 microg) or baclofen (0.5 microg) onto the lumbar cord surface reduce the SCIinduced increased responsiveness of WDR neurons. Inhibitory effects of muscimol and baclofen on both the behavioral mechanical allodynia and the hyperexcitability in WDR neuron with SCI compared to controls, were antagonized by pre-treatment of bicuculline (10 microg) and phaclofen (5 microg), respectively. This study provides behavioral and electrophysiological evidence for the important role of the loss of spinal inhibitory tone, mediated by activation of both GABAA and GABAB receptors, in the development of central neuropathic pain following SCI.

Re-growth of catecholaminergic fibers and protection of cholinergic spinal cord neurons in spinal repaired rats

The extent of re-growth of catecholaminergic fibers, the survival of cholinergic neurons and the degree of autonomic dysreflexia were assessed in complete spinal cord-transected adult rats that received a repair treatment of peripheral nerve grafts and acidic fibroblast growth factor (aFGF). The rats were randomly divided into three groups: (1) sham control group (laminectomy only); (2) spinal cord transection at T8 (transected group); and (3) spinal cord transection at T8, followed by aFGF treatment and peripheral nerve graft (repaired group). The spinal cords and brains of all rats were collected at 6 months post-surgery. Immunohistochemistry for tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH), and fluoro-gold (FG) retrograde tracing were used to evaluate axon growth across the damage site, and immunocytochemistry for choline acetyl transferase (ChAT) was used to evaluate cholinergic neuronal cell survival following the injury and treatment. When comparing with the transected group, the repaired group showed: (1) lower elevation of mean arterial pressure during colorectal distension; (2) retrogradely labeled neurons in the hypothalamus, zona incerta, subcoeruleus nuclei and rostral ventrolateral medulla following application of FG below the repair site; (3) the presence of TH- and DBH-labeled axons below the lesion site; (4) higher numbers of ChAT-positive neurons in ventral horn and intermediolateral column near the lesion site. We conclude that peripheral nerve graft and aFGF treatments facilitate the re-growth of catecholaminergic fibers, also protect sympathetic preganglionic neurons and spinal motor neurons, and reduce autonomic dysfunction in a T-8 spinal cord-transected rat model.

Human fetal neural stem cells grafted into contusion-injured rat spinal cords improve behavior

Grafted human neural stem cells (hNSCs) may help to alleviate functional deficits resulting from spinal cord injury by bridging gaps, replacing lost neurons or oligodendrocytes, and providing neurotrophic factors. Previously, we showed that primed hNSCs differentiated into cholinergic neurons in an intact spinal cord. In this study, we tested the fate of hNSCs transplanted into a spinal cord T10 contusion injury model. When grafted into injured spinal cords of adult male rats on either the same day or 3 or 9 days after a moderate contusion injury, both primed and unprimed hNSCs survived for 3 months postengraftment only in animals that received grafts at 9 days postinjury. Histological analyses revealed that primed hNSCs tended to survive better and differentiated at higher rates into neurons and oligodendrocytes than did unprimed counterparts. Furthermore, only primed cells gave rise to cholinergic neurons. Animals receiving primed hNSC grafts on the ninth day postcontusion improved trunk stability, as determined by rearing activity measurements 3 months after grafting. This study indicates that human neural stem cell fate determination in vivo is influenced by the predifferentiation stage of stem cells prior to grafting. Furthermore, stem cell-mediated facilitation of functional improvement depends on the timing of transplantation after injury, the grafting sites, and the survival of newly differentiated neurons and oligodendrocytes.

Development of transplantable nervous tissue constructs comprised of stretch-grown axons

Pursuing a new approach to nervous system repair, fasciculated axon tracts grown in vitro were developed into nervous tissue constructs designed to span peripheral nerve or spinal cord lesions. We optimized the newfound process of extreme axon stretch growth to maximize the number and length of axon tracts, reach an unprecedented axon growth-rate of 1cm/day, and create 5cm long axon tracts in 8 days to serve as the core component of a living nervous tissue construct. Immunocytochemical analysis confirmed that elongating fibers were axons, and that all major cytoskeletal constituents were present across the stretch-growth regions. We formed a transplantable nervous tissue construct by encasing the elongated cells in an 80% collagen hydrogel, removing them from culture, and inserting them into a synthetic conduit. Alternatively, we induced axon stretch growth directly on a surgical membrane that could be removed from the elongation device, and formed into a cylindrical construct suitable for transplant. The ability to rapidly create living nervous tissue constructs that recapitulates the uniaxial orientations of the original nerve offers an unexplored and potentially complimentary direction in nerve repair. Ideally, bridging nerve damage with living axon tracts may serve to establish or promote new functional connections.

Upregulation of Group I metabotropic glutamate receptors in neurons and astrocytes in the dorsal horn following spinal cord injury

Of the glutamate receptor types, the metabotropic glutamate receptors (mGluRs) are G proteins coupled and can initiate a number of intracellular pathways leading to hyperexcitability of spinal neurons. In this study, we tested the expression of mGluRs to determine which cell types might contribute to sustained neuronal hyperexcitability in the lumbar enlargement with postoperative day (POD) 7 (early), 14 (late), and 30 (chronic phase) following spinal cord injury (SCI) by unilateral hemisection at T13 in Sprague-Dawley rats. Expression was determined by confocal analyses of immunocytochemical reaction product of neurons (NeuN positive) and astrocytes (GFAP positive) in the dorsal horn on both sides of the L4 segment. Neurons were divided into two sizes: small (<20 microm) and large (>35 microm), for physiological reasons. We report a significant increase of mGluR(1) expression in large and small neurons of the dorsal horn on both sides of the cord in late and chronic phases when compared to control sham groups. Expression of mGluR(2/3) significantly increased in large neurons on the ipsilateral (hemisected) side in the late phase. Expression of mGluR(5) significantly increased in large neurons in early, late, and chronic phases. In addition, mGluR(1) and mGluR(5) expression after hemisection was significantly increased in astrocytes in early, late, and chronic phases; whereas mGluR(2/3) did not display any significant changes. In conclusion, our data demonstrate long-term changes in expression levels of Group I mGluRs (mGluR(1) and mGluR(5)) in both neurons and astrocytes in segments below a unilateral SCI. Thus, permanent alterations in dorsal horn receptor expression may play important roles in transmission of nociceptive responses in the spinal cord following SCI.

Molecular targets in spinal cord injury

The spinal cord can be compared to a highway connecting the brain with the different body levels lying underneath, with the axons being the ultimate carriers of the electrical impulse. After spinal cord injury (SCI), many cells are lost because of the injury. To reconstitute function, damaged axons from surviving neurons have to grow through the lesion site to their initial targets. However, the territory they have to traverse has changed: the highway is full of inhibitory signals (myelin and scar components); the pavement itself has become bumpy (demyelination); and specialized cells are recruited to clear the way (inflammatory cells). Thus, actual strategies to treat spinal injuries aim at providing a permissive environment for regenerating axons and boosting the endogenous potential of axons to regenerate while limiting progression of secondary damage. Here we review some of the strategies currently under consideration to treat spinal injuries.

Upregulation of EphA3 Receptor after Spinal Cord Injury

Spinal cord injury (SCI) releases a cascade of events that leads to the onset of an inhibitory milieu for axonal regeneration. Some of these changes result from the presence of repulsive factors that may restrict axonal outgrowth after trauma. The Eph receptor tyrosine kinase (RTK) family has emerged as a key repellent cue known to be involved in neurite outgrowth, synapse formation, and axonal pathfinding during development. Given the nonpermissive environment for axonal regeneration after SCI, we questioned whether re-expression of one of these molecules occurs during regenerative failure. We examined the expression profile of EphA3 at the mRNA and protein levels after SCI, using the NYU contusion model. There is a differential distribution of this molecule in the adult spinal cord and EphA3 showed an increase in expression after several injury models like optic nerve and brain injury. Standardized semi-quantitative RT-PCR analysis demonstrated a time-dependent change in EphA3 mRNA levels, without alterations in beta-actin levels. The basal level of EphA3 mRNA in the adult spinal cord is low and its expression was induced 2 days after trauma (the earliest time point analyzed) and this upregulation persisted for 28 days post-injury (the latest time point examined). These results were corroborated at the protein level by immunohistochemical analysis and the cell phenotype identified by double labeling studies. In control animals, EphA3 immunoreactivity was observed in motor neurons of the ventral horn but not in lesioned animals. In addition, GFAP-positive cells were visualized in the ventral region of injured white matter. These results suggest that upregulation of EphA3 in reactive astrocytes may contribute to the repulsive environment for neurite outgrowth and may be involved in the pathophysiology generated after SCI.

Real-time quantitative PCR analysis of temporal-spatial alterations in gene expression after spinal cord contusion

Rat spinal cord contusion injury models the histopathology associated with much clinical spinal cord injury (SCI). Studies on altered gene expression after SCI in these models may identify therapeutic targets for reducing secondary injury after the initial trauma and/or enhancing recovery processes. However, complex spatial and temporal alterations after injury could complicate interpretation of changes in gene expression. To test this hypothesis, we selected six genes and studied their temporal and spatial patterns of expression at 1 h, 1, 3 and 7 days after a standardized spinal cord contusion produced by a weight drop device (10 g x 25 mm at T8). Real-time RT-PCR using TaqMan probes was employed to quantify mRNA for proteolipid protein, glyceraldehyde-3-phosphate dehydrogenase, glial fibrillary acidic protein, nestin, and the GluR2 and NR1 subunits of glutamate receptors. We found widely different temporal and spatial patterns of altered gene expression after SCI, including instances of opposing up- and down-regulation at different locations in tissue immediately adjacent to the injury site. We conclude that greater use of the reliable and extremely sensitive technique of quantitative real-time PCR for regional tissue analysis is important for understanding the altered gene expression that occurs after CNS trauma.

Uncontrollable stimulation undermines recovery after spinal cord injury

Prior studies have shown that neurons within the spinal cord are sensitive to response-outcome relations, a form of instrumental learning. Spinally transected rats that receive shock to one hind leg learn to maintain the leg in a flexed position that minimizes net shock exposure (controllable shock). Prior exposure to uncontrollable stimulation (intermittent shock) inhibits this spinally mediated learning. Here it is shown that uncontrollable stimulation undermines the recovery of function after a spinal contusion injury. Rats received a moderate injury (12.5 mm drop) and recovery was monitored for 6 weeks. In Experiment 1, rats received varying amounts of intermittent tailshock 1-2 days after injury. Just 6 min of intermittent shock impaired locomotor recovery. In Experiment 2, rats were shocked 1, 4, or 14 days after injury. Delaying the application of shock exposure reduced its negative effect on recovery. In Experiment 3, rats received controllable or uncontrollable shock 24 and 48 h after injury. Only uncontrollable shock disrupted recovery of locomotor function. Uncontrollably shocked rats also exhibited higher vocalization thresholds to aversive stimuli (heat and shock) applied below the injury. Across the three experiments, exposure to uncontrollable shock, (1) delayed the recovery of bladder function; (2) led to greater mortality and spasticity; and (3) increased tissue loss (white and gray matter) in the region of the injury. The results indicate that uncontrollable stimulation impairs recovery after spinal cord injury and suggest that reducing sources of uncontrolled afferent input (e.g., from peripheral tissue injury) could benefit patient recovery.

Glutathione monoethyl ester improves functional recovery, enhances neuron survival, and stabilizes spinal cord blood flow after spinal cord injury in rats

Secondary damage after spinal cord (SC) injury remains without a clinically effective drug treatment. To explore the neuroprotective effects of cell-permeable reduced glutathione monoethyl ester (GSHE), rats subjected to SC contusion using the New York University impactor were randomly assigned to receive intraperitoneally GSHE (total dose of 12 mg/kg), methylprednisolone sodium succinate (total dose of 120 mg/kg), or saline solution as vehicle. Motor function, assessed using the Basso-Beattie-Bresnahan scale for 8 weeks, was significantly better in GSHE (11.2+/-0.6, mean+/-S.E.M., n=8, at 8 weeks) than methylprednisolone (9.3+/-0.6) and vehicle (9.4+/-0.7) groups. The number of neurons in the red nuclei labeled with FluoroRuby placed caudally to the injury site was significantly higher in GSHE (158+/-9.3 mean+/-S.E.M., n=4) compared with methylprednisolone (53+/-14.7) and vehicle (46+/-16.4) groups. Differences in the amount of spared SC tissue at the epicenter and neighboring areas were not significant among experimental groups. In a second series of experiments, using similar treatment groups (n=6), regional changes in microvascular SC blood flow were evaluated for 100 min by laser-Doppler flowmetry after clip compression injury. SC blood flow fell in vehicle-treated rats 20% below baseline and increased significantly with methylprednisolone approximately 12% above baseline; changes were not greater than 5% in rats given GSHE. In conclusion, GSHE given to rats early after moderate SC contusion/compression improves functional outcome and red nuclei neuron survival significantly better than methylprednisolone and vehicle, and stabilizes SC blood flow. These results support further investigation of reduced glutathione supplementation after acute SC injury for future clinical application.

Targeting recovery: priorities of the spinal cord-injured population

In the United States alone, there are more than 200,000 individuals living with a chronic spinal cord injury (SCI). Healthcare for these individuals creates a significant economic burden for the country, not to mention the physiological, psychological, and social suffering these people endure everyday. Regaining partial function can lead to greater independence, thereby improving quality of life. To ascertain what functions are most important to the SCI population, in regard to enhancing quality of life, a novel survey was performed in which subjects were asked to rank seven functions in order of importance to their quality of life. The survey was distributed via email, postal mail, the internet, interview, and word of mouth to the SCI community at large. A total of 681 responses were completed. Regaining arm and hand function was most important to quadriplegics, while regaining sexual function was the highest priority for paraplegics. Improving bladder and bowel function was of shared importance to both injury groups. A longitudinal analysis revealed only slight differences between individuals injured <3 years compared to those injured >3 years. The majority of participants indicated that exercise was important to functional recovery, yet more than half either did not have access to exercise or did not have access to a trained therapist to oversee that exercise. In order to improve the relevance of research in this area, the concerns of the SCI population must be better known and taken into account. This approach is consistent with and emphasized by the new NIH roadmap to discovery.

Serum Biomarkers for Experimental Acute Spinal Cord Injury: Rapid Elevation of Neuron-specific Enolase and S-100β

OBJECTIVE

We evaluated whether serum levels of neuron-specific enolase (NSE) and S-100beta protein are biomarkers for traumatic injury in an animal model of spinal cord injury (SCI).

METHODS

Enzyme-linked immunosorbent assay serum measurements of NSE and S-100beta and assays of serum protein were compared at 6 and 24 hours after a graded contusive SCI (150 or 200 kdyn IH impactor injury (Infinite Horizons, L.L.C., Lexington, KY) or sham laminectomy at T9 in 30 female Sprague-Dawley rats. Serum from control animals was also analyzed.

RESULTS

Increases in serum levels of NSE were observed for 200-kdyn (3.1-fold, P < 0.001) and 150-kdyn (2.3-fold, P < 0.001) injury groups at 6 hours after injury, which decreased by 73.7% (P < 0.001) and 65.2% (P < 0.001) at 24 hours after SCI, respectively; the levels were still greater than in sham animals (P < 0.001, P = 0.001). The 200- and 150-kdyn injury groups were not different at either time point. S-100beta serum levels increased at 6 hours in the 200-kdyn injury group (P < 0.05), and no differences from sham levels were seen at 24 hours. No differences in total protein concentrations were observed between the injury and control groups.

CONCLUSION

Present data suggest that NSE and S-100beta serum levels may be useful experimental tools for the acute measurement of tissue loss after SCI. Despite significant shortcomings, NSE and S-100beta serum measurements in acute SCI patients with clinically defined functional deficits should allow comparisons with well-characterized SCI animal models. Future efforts to develop biomarkers that predict functional outcomes in the acute phase should focus on axon-specific proteins as markers of secondary axonal loss and regeneration.

Neurophysiological assessment of lower-limb voluntary control in incomplete spinal cord injury

STUDY DESIGN

Cross-sectional retrospective study of a neurophysiological method of voluntary motor control characterization.

OBJECTIVES

This study was undertaken to validate the surface electromyography (sEMG)-based voluntary response index (VRI) as an objective, quantitative, laboratory measure of spinal cord injury severity in terms of voluntary motor control disruption.

SETTING

VA Medical Centers in Houston and Dallas Texas, USA.

METHODS

A total of 67 subjects with incomplete spinal cord injury (iSCI), American Spinal Injury Association Impairment Scale (AIS)-C (n = 32) and -D (n = 35) were studied. sEMG recorded during a standardized protocol including eight lower-limb voluntary motor tasks was analyzed using the VRI method that relates multi-muscle activation patterns of SCI persons to those of healthy-subject prototypes (n = 15). The VRI is composed of a measure of the amount of the sEMG activity (magnitude) and the distribution of activity across muscle groups compared to that of healthy subjects for each motor task (similarity index, SI). These resulting VRI components, normalized magnitude and SI, were compared to AIS clinical findings in this study. Receiver operating characteristic analysis was performed to determine the SI values best separating AIS-C and AIS-D subjects.

RESULTS

Magnitude and SI for AIS-C subjects had mean values of 0.27 +/- 0.32 and 0.65 +/- 0.21, respectively. Both parameters were significantly larger in the AIS-D subjects (0.78 +/- 0.43 and 0.93 +/- 0.06), respectively (P < 0.01). An SI value of 0.85 was found to separate AIS-C and AIS-D groups with a sensitivity of 0.89 and a specificity of 0.81. Further, the VRI of each leg strongly correlated with the respective AIS motor score (0.80, r < 0.01).

CONCLUSIONS

In the domains of voluntary motor control, the sEMG-based VRI demonstrated adequate face validity and sensitivity to injury severity as currently measured by the AIS.

SPONSORSHIP

Veterans Affairs Medical Center.

Effect of age at time of spinal cord injury on behavioral outcomes in rat

Spinal cord injury (SCI) often leads to chronic central pain (CCP) syndromes such as allodynia and hyperalgesia. Although several experimental animal models for CCP studies exist, little is known about the effect of age on the development of CCP following SCI. In this study, we evaluated behavioral responses to mechanical and thermal stimuli following SCI using three different age groups of adult Sprague-Dawley rats: young (40 days), adult (60 days), and middle-age (12 months). SCI was produced by unilateral hemisection of the spinal cord at T13. Behavioral measures of locomotor function were assayed in open field tests and somatosensory function by paw withdrawal frequency (PWF) to innocuous mechanical stimuli and paw withdrawal latency (PWL) to radiant heat stimuli on both the forelimbs and hindlimbs. Prior to hemisection, the PWF was not different between the three groups; however, the PWL of the young group was significantly greater than the adult and middle-age group. After spinal hemisection, spontaneous locomotor recovery occurred more rapidly in young and adult than in middle-age rats. In both forelimbs and hindlimbs, the young group displayed a significant increase in PWF and a significant decrease in PWL compared to presurgical and sham values or values from the adult and middle-age groups. These results indicate that younger rats developed more robust neuropathic behaviors than middle-age rats, indicating that age selection is an important factor in animal models of CCP syndromes following SCI. Additionally, our data suggest that age at the time of injury may be one risk factor in predicting the development of CCP after SCI in people.

Cellular transplantation strategies for spinal cord injury and translational neurobiology

Basic science advances in spinal cord injury and regeneration research have led to a variety of novel experimental therapeutics designed to promote functionally effective axonal regrowth and sprouting. Among these interventions are cell-based approaches involving transplantation of neural and non-neural tissue elements that have potential for restoring damaged neural pathways or reconstructing intraspinal synaptic circuitries by either regeneration or neuronal/glial replacement. Notably, some of these strategies (e.g., grafts of peripheral nerve tissue, olfactory ensheathing glia, activated macrophages, marrow stromal cells, myelin-forming oligodendrocyte precursors or stem cells, and fetal spinal cord tissue) have already been translated to the clinical arena, whereas others have imminent likelihood of bench-to-bedside application. Although this progress has generated considerable enthusiasm about treating what once was thought to be a totally incurable condition, there are many issues to be considered relative to treatment safety and efficacy. The following review reflects on different experimental applications of intraspinal transplantation with consideration of the underlying pathological, pathophysiological, functional, and neuroplastic responses to spinal trauma that such treatments may target along with related issues of procedural and biological safety. The discussion then moves to an overview of ongoing and completed clinical trials to date. The pros and cons of these endeavors are considered, as well as what has been learned from them. Attention is primarily directed at preclinical animal modeling and the importance of patterning clinical trials, as much as possible, according to laboratory experiences.

Patterns of gene expression reveal a temporally orchestrated wound healing response in the injured spinal cord

Spinal cord injury (SCI) induces a progressive pathophysiology affecting cell survival and neurological integrity via complex and evolving molecular cascades whose interrelationships are not fully understood. The present experiments were designed to: (1) determine potential functional interactions within transcriptional expression profiles obtained after a clinically relevant SCI and (2) test the consistency of transcript expression after SCI in two genetically and immunologically diverse rat strains characterized by differences in T cell competence and associated inflammatory responses. By interrogating Affymetrix U34A rat genome GeneChip microarrays, we defined the transcriptional expression patterns in midcervical contusion lesion sites between 1 and 90 d postinjury of athymic nude (AN) and Sprague Dawley (SD) strains. Stringent statistical analyses detected significant changes in 3638 probe sets, with 80 genes differing between the AN and SD groups. Subsequent detailed functional categorization of these transcripts unveiled an overall tissue remodeling response that was common to both strains. The functionally organized gene profiles were temporally distinct and correlated with repair indices observed microscopically and by magnetic resonance microimaging. Our molecular and anatomical observations have identified a novel, longitudinal perspective of the post-SCI response, namely, that of a highly orchestrated tissue repair and remodeling repertoire with a prominent cutaneous wound healing signature that is conserved between two widely differing rat strains. These results have significant bearing on the continuing development of cellular and pharmacological therapeutics directed at tissue rescue and neuronal regeneration in the injured spinal cord.

Animal models of spinal cord injury for evaluation of tissue engineering treatment strategies

Tissue engineering approaches to spinal cord injury (SCI) treatment are attractive because they allow for manipulation of native regeneration processes involved in restoration of the integrity and function of damaged tissue. A clinically relevant spinal cord regeneration animal model requires that the model mimics specific pathologic processes that occur in human SCI. This manuscript discusses issues related to preclinical testing of tissue engineering spinal cord regeneration strategies from a number of perspectives. This discussion includes diverse causes, pathology and functional consequences of human SCI, general and species related considerations, technical and animal care considerations, and data analysis methods.

Minocycline inhibits contusion-triggered mitochondrial cytochrome c release and mitigates functional deficits after spinal cord injury

We investigated whether permeability transition-mediated release of mitochondrial cytochrome c is a potential therapeutic target for treating acute spinal cord injury (SCI). Based on previous reports, minocycline, a second-generation tetracycline, exerts neuroprotection partially by inhibiting mitochondrial cytochrome c release and reactive microgliosis. We first evaluated cytochrome c release at the injury epicenter after a T10 contusive SCI in rats. Cytochrome c release peaked at approximately 4-8 h postinjury. A dose-response study generated a safe pharmacological regimen that enabled i.p. minocycline to significantly lower cytosolic cytochrome c at the epicenter 4 h after SCI. In the long-term study, i.p. minocycline (90 mg/kg administered 1 h after SCI followed by 45 mg/kg administered every 12 h for 5 days) markedly enhanced long-term hind limb locomotion relative to that of controls. Coordinated motor function and hind limb reflex recoveries also were improved significantly. Histopathology suggested that minocycline treatment alleviated later-phase tissue loss, with significant sparing of white matter and ventral horn motoneurons at levels adjacent to the epicenter. Furthermore, glial fibrillary acidic protein and 2',3' cyclic nucleotide 3' phosphodiesterase immunocytochemistry showed an evident reduction in astrogliosis and enhanced survival of oligodendrocytes. Therefore, release of mitochondrial cytochrome c is an important secondary injury mechanism in SCI. Drugs with multifaceted effects in antagonizing this process and microgliosis may protect a proportion of spinal cord tissue that is clinically significant for functional recovery. Minocycline, with its proven clinical safety, capability to cross the blood-brain barrier, and demonstrated efficacy during a clinically relevant therapeutic window, may become an effective therapy for acute SCI.

NAD(P)H oxidase, superoxide dismutase, catalase, glutathione peroxidase and nitric oxide synthase expression in subacute spinal cord injury

Primary trauma to the spinal cord triggers a cascade of cellular and molecular events that promote continued tissue damage and expansion of the lesion for extended periods following the initial injury. Oxidative and nitrosative stresses play an important role in progression of spinal cord injury (SCI). In an attempt to explore the biochemical origin of oxidative/nitrosative stress associated with secondary SCI, we studied expression of the superoxide (O2*-)-generating enzyme, NAD(P)H oxidase, antioxidant enzymes [superoxide dismutase (CuZn SOD, Mn SOD), catalase, glutathione peroxidase (GPX)], nitric oxide synthases (NOS) and a byproduct of NO-O2*- interaction (nitrotyrosine) in the spinal cord tissues of rats 16 h and 14 days after surgical resections of a 5-mm segment of the cord below T8 or sham-operation. Immunodetectable NAD(P)H oxidase subunits (gp91phox and P67phox), Mn SOD, inducible NOS (iNOS), endothelial NOS (eNOS), and nitrotyrosine were elevated in the transected cords on day 1 and day 14. Neuronal NOS (nNOS) was unchanged on day 1 and significantly depressed on day 14. GPX was unchanged on day 1 and significantly elevated on day 14. Catalase was unchanged in the cord tissue surrounding the transection site at both points. Thus, concurrent upregulations of NAD(P)H oxidase, eNOS and iNOS (but not nNOS), work in concert to maintain oxidative and nitrosative stress in the injured cord tissue.

Inflammation, degeneration and regeneration in the injured spinal cord: insights from DNA microarrays

GeneChip microarrays have recently been introduced to the field of neurobiology to identify and monitor the expression levels of thousands of genes simultaneously. This powerful technique is now used for studying the pathophysiology of CNS injuries including spinal cord lesions. Early stages after injury are characterized by the strong upregulation of genes involved in transcription and inflammation and a general downregulation of structural proteins and proteins involved in neurotransmission. Later, an increase in the expression of growth factors, axonal guidance factors, extracellular matrix molecules and angiogenic factors reflects the attempts for repair, while upregulation of stress genes and proteases and downregulation of cytoskeletal and synaptic mRNA reflect the struggle of the tissue to survive. DNA microarrays have the potential to aid discovery of new targets for neuroprotective or restorative therapeutic approaches

Creatine diet supplement for spinal cord injury: influences on functional recovery and tissue sparing in rats

Creatine-supplemented diet significantly attenuates cortical damage after traumatic brain injury in rodents. The protective mechanism likely involves maintenance of mitochondrial homeostasis. In the present study, we used two separate contusion spinal cord injury (SCI) instruments--the NYU device and the PSI Infinite Horizon (IH) impactor--to assess the efficacy of creatine-supplemented diets on hind limb functional recovery and tissue sparing in adult rats. Rats were fed control versus 2% creatine-supplemented chow for 4-5 weeks prior to SCI (pre-fed), after which most resumed a control diet while some remained on a 2% creatine diet (pre & post-fed). Following long-term behavioral analysis (BBB), the amount of spared spinal cord tissue among the dietary regimen groups was assessed using stereology. Comparatively, both instruments caused similar amounts of gray matter damage while the NYU device rendered a greater loss of white matter, reflected in more severe hind limb functional deficits than with the IH impactor. Relative to the control fed groups injured with either instrument, none of the creatine fed animals showed improvements in hind limb function or white matter tissue sparing. Although creatine did not attenuate gray matter loss in the NYU cohort, it significantly spared gray matter in the IH cohort with pre-fed and pre & post-fed regimens. Such selective sparing of injured spinal cord gray matter with a dietary supplement yields a promising strategy to promote neuroprotection after SCI. The relationship between the efficacy of creatine and the magnitude of the insults is discussed.