Cellular morphology of chronic spinal cord injury in the cat: analysis of myelinated axons by line-sampling

Vestibular-evoked muscle responses in patients with spinal cord injury

The vestibular system was activated by galvanic electrical stimulation in 22 patients with spinal cord injury. Three patients were studied standing and all were studied sitting. Electromyographic responses recorded in soleus (standing patients) and the erectores spinae (all patients) were compared with data from 18 control subjects. The vestibular stimulus polarity and head position were arranged so as to produce excitatory medium latency muscle responses in the controls. Responses in the patient group were present bilaterally, present unilaterally or absent below the level of injury. The amplitude of response recorded in erectores spinae at lumbar levels below the lesion in 21 patients (left and right side responses summed) and five control subjects was positively correlated with American Spinal Injuries Association (ASIA) grade: the smallest amplitudes were found in patients with the most severe impairment (Spearman rank correlation coefficient rs = 0.59; P = 0.002, two-tailed). The latency of response (averaged for both sides) was negatively correlated with ASIA grade in 21 patients: the longest latencies were found in patients with the most severe impairment (rs = -0.57; P < 0.01, two-tailed). Amplitude and latency were negatively correlated (rs = -0.72, P < 0.002, two-tailed). The latencies of responses recorded in the erectores spinae at different vertebral levels were linearly related to the vertical distance from the inion to the recording site in both patient and control groups. The conduction velocities of the spinal pathways activated by vestibular stimulation were 4.6 and 10.4 m/s in patient (recording below lesion) and control groups, respectively. Both clinical status (patients recording below lesion, patients recording above lesion and controls) and distance were significant predictors of latency (general linear model, P < 0.0005). It is concluded that measurement of vestibular-evoked responses could provide information on the level and density of spinal cord lesions.

Apoptosis of auditory neurons following central process injury

Although apoptotic changes in auditory neurons induced by injury to peripheral processes (dendrites) have been intensively studied, apoptotic changes in auditory neurons induced by injury to central processes (axons of spiral ganglion cells, SGCs) have not been reported previously, probably due to lack of an experimental model. The present study reports for the first time the appearance, extent, and time course of SGC apoptosis following injury to the central processes. Apoptosis was studied in a rat model that consisted of compression of the auditory nerve in the cerebellopontine (CP) angle cistern with intraoperative recordings of auditory nerve compound action potentials (CAPs) to ensure highly reproducible results. Rats were killed between day 0 and day 14 after compression and apoptosis of SGCs was evaluated quantitatively as well as qualitatively by terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) staining, anti-activated caspase-3 immunostaining, Hoechst 33342 staining, and electron microscopy. The average number of TUNEL-positive apoptotic SGCs in each cochlear turn increased from day 1 to day 5 and then decreased gradually to an undetectable level on day 14 after compression. The average proportion of apoptotic SGCs identified in any cochlear turn on any day was always lower than 10%. The results of our present study should be useful in determining the therapeutic time window for rescuing auditory neurons undergoing apoptosis due to injury during surgery in the CP angle.

Repair of the Injured Spinal Cord and the Potential of Embryonic Stem Cell Transplantation

Traditionally, treatment of spinal cord injury seemed frustrating and hopeless because of the remarkable morbidity and mortality, and restricted therapeutic options. Recent advances in neural injury and repair, and the progress towards development of neuroprotective and regenerative interventions are basis for increased optimism. Neural stem cells have opened a new arena of discovery for the field of regenerative science and medicine. Embryonic stem (ES) cells can give rise to all neural progenitors and they represent an important scientific tool for approaching neural repair. The growing number of dedicated regeneration centers worldwide exemplifies the changing perception towards the do-ability of spinal cord repair and this review was born from a presentation at one such leading center, the Kentucky Spinal Cord Injury Research Center. Current concepts of the pathophysiology, repair, and restoration of function in the damaged spinal cord are presented with an overlay of how neural stem cells, particularly ES cells, fit into the picture as important scientific tools and therapeutic targets. We focus on the use of genetically tagged and selectable ES cell lines for neural induction and transplantation. Unique features of ES cells, including indefinite replication, pluripotency, and genetic flexibility, provide strong tools to address questions of neural repair. Selective marker expression in transplanted ES cell derived neural cells is providing new insights into transplantation and repair not possible previously. These features of ES cells will produce a predictable and explosive growth in scientific tools that will translate into discoveries and rapid progress in neural repair.

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.

Motor evoked potential monitoring for spinal cord and brain stem surgery

Intraoperative Neurophysiology (ION) has established itself as one of the means by which modern neurosurgery can improve surgical results while minimizing morbidity. The advent of motor evoked potential (MEP) monitoring represents a landmark in this recent progress. ION consists of monitoring (the continuous "on-line" assessment of the functional integrity of neural pathways) and mapping (the functional identification and preservation of anatomically ambiguous nervous tissue) techniques. In this chapter we have attempted to critically review the evolution of MEP use during monitoring and mapping techniques for neurosurgical procedures in the brainstem and the spinal cord, providing the neurophysiological theoretical background and practical aspects of clinical applications. According to the experience from our and other groups involved in ION, we suggest the following: 1) ION is mandatory whenever neurological complications are expected as predicted by a known pathophysiological mechanism. It is therefore advisable to perform ION when dealing with brain stem and intramedullary spinal cord lesions. 2) MEP monitoring after transcranial electrical stimulation is today a feasible and reliable technique for use under general anesthesia. MEP monitoring is the most appropriate technique to assess the functional integrity of descending motor pathways in the brainstem and, foremost, in the spinal cord. 3) Mapping of the corticospinal tract at the level of the cerebral peduncle as well as mapping of the VII, IX-X and XII cranial nerve motor nuclei on the floor of the fourth ventricle is of great value with which to identify "safe entry zones" into the brainstem. 4) Other techniques, although safe and feasible, still lack rigorous validation in terms of prognostic value and correlation with the postoperative neurological outcome. These techniques include mapping of the corticospinal tract within the spinal cord and monitoring of the corticobulbar tracts. These techniques, however, are expected to open new perspectives in the near future.

Transplantation of oligodendrocyte precursors and sonic hedgehog results in improved function and white matter sparing in the spinal cords of adult rats after contusion

BACKGROUND CONTEXT

A substantial cause of neurological disability in spinal cord injury is oligodendrocyte death leading to demyelination and axonal degeneration. Rescuing oligodendrocytes and preserving myelin is expected to result in significant improvement in functional outcome after spinal cord injury. Although previous investigators have used cellular transplantation of xenografted pluripotent embryonic stem cells and observed improved functional outcome, these transplants have required steroid administration and only a minority of these cells develop into oligodendrocytes.

PURPOSE

The objective of the present study was to determine whether allografts of oligodendrocyte precursors transplanted into an area of incomplete spinal cord contusion would improve behavioral and electrophysiological measures of spinal cord function. Additional treatment incorporated the use of the glycoprotein molecule Sonic hedgehog (Shh), which has been shown to play a critical role in oligodendroglial development and induce proliferation of endogenous neural precursors after spinal cord injury.

SETTING

Laboratory study.

METHODS

Moderate spinal cord contusion injury was produced in 39 adult rats at T9-T10. Ten animals died during the course of the study. Nine rats served as contusion controls (Group 1). Six rats were treated with oligodendrocyte precursor transplantation 5 days after injury (Group 2). The transplanted cells were isolated from newborn rat pups using immunopanning techniques. Another eight rats received an injection of recombinant Shh along with the oligodendrocyte precursors (Group 3), while six more rats were treated with Shh alone (Group 4). Eight additional rats received only T9 laminectomies to serve as noninjured controls (Group 0). Animals were followed for 28 days.

RESULTS

After an initial complete hindlimb paralysis, rats of all groups receiving a contusive injury recovered substantial function within 1 week. By 28 days, rats in Groups 2 and 3 scored 4.7 and 5.8 points better on the Basso, Beattie, Bresnahan (BBB) open field locomotor score than rats in group 1 (Groups 2 and 3=18.2 and 19.4 points, respectively, after 28 days vs. Group 1=13.6 points; p=.015). Rats in Group 4 scored no better than those in Group 1 (BBB=16.4). Motor evoked potential (MEP) recordings revealed a strong trend towards significant improvement in latency measurements in all treatment groups compared with controls at 28 days, although three animals in Group 1 and two animals in Group 3 were not recordable. Histological examination demonstrated significantly more spared white matter in the same groups that correlated with the improvements in BBB scores and MEP latencies. Immunohistochemical analysis showed the survival, proliferation and migration of the transplanted cells, as well as the induction of proliferating endogenous neural precursor cells in animals treated with Shh.

CONCLUSIONS

These findings suggest that the transplantation of oligodendrocyte precursors may improve axonal conduction and spinal cord function in the injured spinal cord. The benefits seem more pronounced with the addition of Shh, and the addition of Shh alone results in the proliferation of an endogenous population of neural precursor cells.

An adverse role for matrix metalloproteinase 12 after spinal cord injury in mice

We investigated the role of matrix metalloproteinases (MMPs) in acute spinal cord injury (SCI). Transcripts encoding 22 of the 23 known mammalian MMPs were measured in the mouse spinal cord at various time points after injury. Although there were significant changes in the expression levels of multiple MMPs, MMP-12 was increased 189-fold over normal levels, the highest of all MMPs examined. To evaluate the role of MMP-12 in SCI, spinal cord compression was performed in wild-type (WT) and MMP-12 null mice. Behavioral analyses were conducted for 4 weeks using the Basso-Beattie-Bresnahan (BBB) locomotor rating scale as well as the inclined plane test. The results show that MMP-12 null mice exhibited significantly improved functional recovery compared with WT controls. Twenty-eight days after injury, the BBB score in the MMP-12 group was 7, representing extensive movement of all three hindlimb joints, compared with 4 in the WT group, representing only slight movement of these joints. Furthermore, MMP-12 null mice showed recovery of hindlimb strength more rapidly than control mice, with significantly higher inclined plane scores on days 14 and 21 after SCI. Mechanistically, there was decreased permeability of the blood-spinal barrier and reduced microglial and macrophage density in MMP-12 null mice compared with WT controls. This is the first study to profile the expression patterns of a majority of the known MMPs after spinal cord compression. The data indicate that MMP-12 expression after spinal cord trauma is deleterious and contributes to the development of secondary injury in SCI.

Spinal cord injury: promising interventions and realistic goals

Long regarded as impossible, spinal cord repair is approaching the realm of reality as efforts to bridge the gap between bench and bedside point to novel approaches to treatment. It is important to recognize that the research playing field is rapidly changing and that new mechanisms of resource development are required to effectively make the transition from basic science discoveries to effective clinical treatments. This article reviews recent laboratory studies and phase 1 clinical trials in neural and nonneural cell transplantation, stressing that the transition from basic science to clinical applications requires a parallel rather than serial approach, with continuous, two-way feedback to most efficiently translate basic science findings, through evaluation and optimization, to clinical treatments. An example of mobilizing endogenous stem cells for repair is reviewed, with emphasis on the rapid application of basic science to clinical therapy. Successful and efficient transition from basic science to clinical applications requires (1) a parallel rather than a serial approach; (2) development of centers that integrate three spheres of science, translational, transitional, and clinical trials; and (3) development of novel resources to fund the most critically limited step of transitional to clinical trials.

Effects of 4-aminopyridine on stretched mammalian spinal cord: the role of potassium channels in axonal conduction

Axonal conduction deficit is a major contributor to various degrees of disability after spinal cord injury. 4-aminopyridine (4-AP), a potassium channel blocker, has been shown to restore some conduction and improve neurological function in both animal and human studies. Using a double sucrose-gap recording device, we have examined the effects of 4-AP on isolated guinea pig spinal cord white matter after stretch injury. At a concentration of 100 microM, 4-AP increased the amplitude of the compound action potential by 100% while 1 microM 4-AP increased it by 43%, a larger response than seen following compression injury. The length of affected tissue is suggested as a potential explanation of this differential sensitivity to 4-AP. Plastic sections taken from the injury site revealed severe myelin damage, especially in the paranodal area, which may also partially explain why 4-AP has more effect on conduction after stretch injury than compression. In addition, we have shown that while enhancing conductivity in some axons, 4-AP significantly reduced the overall responsiveness to multiple stimuli, as evidenced by increase of the refractory period in response to dual stimuli and the decreased ability to follow repetitive stimuli. This increased refractoriness may be largely attributed to residual deficits in fibers newly recruited by 4-AP treatment.

Rats and mice exhibit distinct inflammatory reactions after spinal cord injury

Spinal contusion pathology in rats and mice is distinct. Cystic cavities form at the impact site in rats while a dense connective tissue matrix occupies the injury site in mice. Because inflammatory cells coordinate mechanisms of tissue injury and repair, we evaluated whether the unique anatomical presentation in spinally injured rats and mice is associated with a species-specific inflammatory response. Immunohistochemistry was used to compare the leukocytic infiltrate between rats and mice. Microglia/macrophage reactions were similar between species; however, the onset and magnitude of lymphocyte and dendritic cell (DC) infiltration were markedly different. In rats, T-cell numbers were highest between 3 and 7 days postinjury and declined by 50% over the next 3 weeks. In mice, significant T-cell entry was not evident until 14 days postinjury, with T-cell numbers doubling between 2 and 6 weeks. Dendritic cell influx paralleled T-cell infiltration in rats but was absent in mouse spinal cord. De novo expression of major histocompatability class II molecules was increased in both species but to a greater extent in mice. Unique to mice were cells that resembled lymphocytes but did not express lymphocyte-specific markers. These cells extended from blood vessels within the fibrotic tissue matrix and expressed fibronectin, collagen I, CD11b, CD34, CD13, and CD45. This phenotype is characteristic of fibrocytes, specialized blood-borne cells involved in wound healing and immunity. Thus, species-specific neuroinflammation may contribute to the formation of distinct tissue environments at the site of spinal cord injury in mice and rats.

Efficacy and safety of 4-aminopyridine in patients with long-term spinal cord injury: a randomized, double-blind, placebo-controlled trial

OBJECTIVES

To study the efficacy and safety of 4-aminopyridine (4-AP), and to document sensorimotor changes after discontinuation of the drug in patients with long-term spinal cord injury.

DESIGN

Randomized, double-blind, placebo-controlled trial.

SETTING

Clinical research unit.

PATIENTS

Twenty-seven patients with long-term spinal cord injury.

INTERVENTION

Patients were randomized to receive either oral 4-AP 5 mg/day, which was increased by 5 mg/week to a maximum dosage of 30 mg/day, or placebo for 12 weeks. They switched to the opposite treatment for the next 12 weeks.

MEASUREMENTS AND MAIN RESULTS

Twenty-five patients finished the study. The results from the first 12 weeks were used to test efficacy. Positive gains in motor function, sensation, and independence occurred more frequently in patients receiving 4-AP (69%) than those receiving placebo (46%). Significant functional improvement was also noted in those treated with 4-AP (chi2, p=0.042). When each evaluation scale was considered separately, significant improvement was seen only in motor function (4-AP 92% vs placebo 46%, Fisher exact test, p=0.03). Persistent effects of the drug were assessed at week 24 in the group that initially received 4-AP. A persistent, significant 4-AP effect was observed in evaluations of sensation and independence (67% and 83% of patients, respectively; Wilcoxon signed rank test, p=0.032 and 0.042, respectively). Fourteen (56%) patients had 26 adverse reactions. One moderate adverse reaction--posterior tibial artery vasospasm--and 25 mild adverse reactions, such as dry mouth, dizziness, nausea, gastritis, oral and peripheral paresthesia, resolved adequately. Six (24%) patients experienced transitory alterations of enzyme levels (alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and creatine kinase) and thrombocytopenia.

CONCLUSION

Patients who received 4-AP showed significant improvement in motor function, and a persistent effect on sensation and independent function occurred. The drug is safe; however, after starting 4-AP therapy, patients must be carefully monitored for the possible occurrence of peripheral vasospasm.

Primary cortical motor neurons undergo apoptosis after axotomizing spinal cord injury

Spinal cord injury (SCI) results in loss of voluntary motor control followed by incomplete recovery, which is partly mediated by the descending corticospinal tract (CST). This system is an important target for therapeutic repair strategies after SCI; however, the question of whether apoptotic cell death occurs in these axotomized neurons remains unanswered. In this study, adult (150-175 g) male Sprague-Dawley rats underwent T9 transection of the dorsal funiculus, which axotomizes the dorsal CST, and introduction of the retrograde tracer Fluoro-Gold into the lesion site. Primary motor cortex (M1) was then examined for evidence of apoptosis weekly for 4 weeks after injury. Axotomized pyramidal cells, identified by retrograde transport of Fluoro-Gold, were found in M1 (57.5 +/- 9.6/median section, 6127 +/- 292 total), and a significant proportion were terminal deoxynucleotidyl transferase (TdT) -mediated deoxyuridine triphosphate (dUTP)-rhodamine nick end labeling (TUNEL) -positive at 1 week after injury (39.3 +/- 5.6%), compared with animals undergoing sham surgery (1.2 +/- 1.4%). At 2-4 weeks, fewer cells were Fluoro-Gold-positive (24.6 +/- 65.06 to 25.3 +/- 6.4/median section, 2338 +/- 233 to 2393 +/- 124 total), of which very few were TUNEL-positive. In TUNEL-positive cells, Hoechst 33342 staining revealed nuclear morphology consistent with apoptosis, chromatin condensation, and formation of apoptotic bodies. Fluoro-Gold-positive cells showed increased caspase-3 and Bax immunoreactivity. Hematoxylin and eosin staining revealed similar nuclear changes and dystrophic cells. Internucleosomal DNA fragmentation was detected by gel electrophoresis at the 1-week time point. Lesioned animals not receiving Fluoro-Gold exhibited the same markers of apoptosis. These results document, for the first time, features of apoptotic cell death in a proportion of axotomized cortical motor neurons after SCI, suggesting that protection from apoptosis may be a prerequisite for regenerative approaches to SCI.

Restoring function after spinal cord injury

BACKGROUND

By affecting young people during the most productive period of their lives, spinal cord injury is a devastating problem for modern society. A decade ago, treating SCI seemed frustrating and hopeless because of the tremendous morbidity and mortality, life-shattering impact, and limited therapeutic options associated with the condition. Today, however, an understanding of the underlying pathophysiological mechanisms, the development of neuroprotective interventions, and progress toward regenerative interventions are increasing hope for functional restoration.

REVIEW SUMMARY

This study addresses the present understanding of SCI, including the etiology, pathophysiology, treatment, and scientific advances. The discussion of treatment options includes a critical review of high-dose methylprednisolone and GM-1 ganglioside therapy. The concept that limited rebuilding can provide a disproportionate improvement in quality of life is emphasized throughout.

CONCLUSIONS

New surgical procedures, pharmacologic treatments, and functional neuromuscular stimulation methods have evolved over the last decades that can improve functional outcomes after spinal cord injury, but limiting secondary injury remains the primary goal. Tissue replacement strategies, including the use of embryonic stem cells, become an important tool and can restore function in animal models. Controlled clinical trials are now required to confirm these observations. The ultimate goal is to harness the body's own potential to replace lost central nervous system cells by activation of endogenous progenitor cell repair mechanisms.

Therapeutic vaccination for spinal cord injury: helping the body to cure itself

Inflammation is thought to exacerbate the outcome of spinal cord injury. However, our findings have led us to view inflammation as a healing response that needs the help of a systemic immune response mediated by T helper 1 (Th1) cells that are specific to the abundant antigens residing in the lesion site. Strains differ in their ability to manifest, at the right time and intensity, a spontaneous T-cell response to antigens at the lesion site and therefore in their ability to generate a local inflammatory response whose outcome is beneficial (maintenance and repair). All strains, however, can benefit from immune intervention that boosts and regulates the inflammatory response. Because recovery comprises multi-step processes, pharmacological intervention will be less effective than well-synchronized, self-healing immune activity. Risk-free neuroprotective intervention might be achieved by post-traumatic vaccination with a weak, non-pathogenic, auto-antigen, causing autoimmune T cells to home to the lesion site where they become activated and therefore activate local phagocytic cells to remove hostile elements and provide growth factors.

Repairing the damaged spinal cord: a summary of our early success with embryonic stem cell transplantation and remyelination

Demyelination contributes to the loss of function consequent to central nervous system (CNS) injury. Optimizing remyelination through transplantation of myelin-producing cells may offer a pragmatic approach to restoring meaningful neurological function. An unlimited source of cell suitable for such transplantation therapy can be derived from embryonic stem (ES) cells, which are both pluripotent and genetically flexible. Here we review work from our group showing that neural precursor cells can be derived from ES cells and that transplantation of these cells into the injured spinal cord leads to some recovery of function. We have further examined and optimized methods for enriching oligodendrocyte differentiation from ES cells. ES cell-derived oligodendrocytes are capable of rapid differentiation and myelination in mixed neuron/glia cultures. When transplanted into the injured spinal cord of adult rodents, the neural-induced precursor cells are capable of differentiating into oligodendrocytes and myelinating host axons. The role of myelination and remyelination will be discussed in the context of regeneration strategies.

Secondary injury mechanisms of spinal cord trauma: a novel therapeutic approach for the management of secondary pathophysiology with the sodium channel blocker riluzole

Traumatic spinal cord injury is a consequence of a primary mechanical insult and a sequence of progressive secondary pathophysiological events that confound efforts to mitigate neurological deficits. Pharmacotherapy aimed at reducing the secondary injury is limited by a narrow therapeutic window. Thus, novel drug strategies must target early pathological mechanisms in order to realize the promise of efficacy for this form of neurotrauma. Research has shown that an accumulation of intracellular sodium as a result of trauma-induced perturbation of voltage-sensitive sodium channel activity is a key early mechanism in the secondary injury cascade. As such, voltage-sensitive sodium channels are an important therapeutic target for the treatment of spinal cord trauma. This review describes the evolution of acute spinal cord injury and provides a rationale for the clinical utility of sodium channel blockers, particularly riluzole, in the management of spinal cord trauma.

Recent advances in pathophysiology and treatment of spinal cord injury

Thirty years ago, patients with spinal cord injury (SCI) and their families were told "nothing can be done" to improve function. Since the SCI patient population is reaching normal life expectancy through better health care, it has become an obviously worthwhile enterprise to devote considerable research effort to SCI. Targets for intervention in SCI toward improved function have been identified using basic research approaches and can be simplified into a list: (1) reduction of edema and free-radical production, (2) rescue of neural tissue at risk of dying in secondary processes such as abnormally high extracellular glutamate concentrations, (3) control of inflammation, (4) rescue of neuronal/glial populations at risk of continued apoptosis, (5) repair of demyelination and conduction deficits, (6) promotion of neurite growth through improved extracellular environment, (7) cell replacement therapies, (8) efforts to bridge the gap with transplantation approaches, (9) efforts to retrain and relearn motor tasks, (10) restoration of lost function by electrical stimulation, and (11) relief of chronic pain syndromes. Currently, over 70 clinical trials are in progress worldwide. Consequently, in this millennium, unlike in the last, no SCI patient will have to hear "nothing can be done."

Mechanisms of signal change during intraoperative somatosensory evoked potential monitoring of the spinal cord

In scoliosis surgery, intraoperative somatosensory evoked potential (SSEP) monitoring has reduced the incidence of postoperative neurologic deficits. Many factors affect the amplitude and latency of SSEP waveforms during surgery. Somatosensory evoked potential amplitude decreases with ischemia and anoxia because of temporal dispersion of the afferent volley and conduction block in damaged axons. In conjunction with surgical manipulations, minor drops in blood pressure may result in substantial SSEP changes that reverse when perfusion pressure is increased. Irreversible anoxic injury to central nervous system white matter with loss of SSEP waveforms is dependent on calcium influx into the intracellular space. Somatosensory evoked potential monitoring may be less sensitive for detecting acute insults in the presence of preexisting white matter lesions. Increased extracellular potassium from acute baro-trauma can block axonal conduction transiently even when there is no axonal disruption. Marked temperature-related drops in SSEP amplitude may occur after exposure of the spine but before instrumentation and deformity correction. Hypothermia may increase false-negative outcomes. Short-interval double-pulse stimulation may improve the sensitivity of the SSEP in detecting early ischemic changes. For neurosurgical procedures on the spinal cord the use of SSEP monitoring in improving postoperative outcome is less well established.

Resistance of isolated mammalian spinal cord white matter to oxygen-glucose deprivation

We found that isolated guinea pig spinal cord white matter is resistant to acute oxygen-glucose deprivation. Sixty minutes of oxygen-glucose deprivation resulted in a 60% reduction of compound action potential (CAP) conductance, and there was a near complete recovery after 60 min reperfusion. Corresponding horseradish peroxidase-exclusion assay showed little axonal membrane damage. To further deprive the axons of metabolic substrate, we added 2 mM sodium cyanide or 2 mM sodium azide, both mitochondrial suppressors, to the ischemic medium, which completely abolished CAP and resulted in a 15 to approximately 30% recovery postreperfusion. Both compounds preferentially reduced the conductance of large diameter axons. We suggest the residual ATP in our ischemic model can protect anatomic integrity and physiological functioning of spinal axons following ischemic insult. This further suggests that oxygen-glucose deprivation alone cannot be solely responsible for short-term functional and anatomic damage. The damaging effects of ischemia in vivo may be mediated by factors originating from the gray matter of the cord or other systemic factors; both were largely eliminated in our in vitro white matter preparation.

Late recovery following spinal cord injury. Case report and review of the literature

The authors of this prospective, single-case study evaluated the potential for functional recovery from chronic spinal cord injury (SCI). The patient was motor complete with minimal and transient sensory perception in the left hemibody. His condition was classified as C-2 American Spinal Injury Association (ASIA) Grade A and he had experienced no substantial recovery in the first 5 years after traumatic SCI. Clinical experience and evidence from the scientific literature suggest that further recovery would not take place. When the study began in 1999, the patient was tetraplegic and unable to breathe without assisted ventilation; his condition classification persisted as C-2 ASIA Grade A. Magnetic resonance imaging revealed severe injury at the C-2 level that had left a central fluid-filled cyst surrounded by a narrow donutlike rim of white matter. Five years after the injury a program known as "activity-based recovery" was instituted. The hypothesis was that patterned neural activity might stimulate the central nervous system to become more functional, as it does during development. Over a 3-year period (5-8 years after injury), the patient's condition improved from ASIA Grade A to ASIA Grade C, an improvement of two ASIA grades. Motor scores improved from 0/100 to 20/100, and sensory scores rose from 5-7/112 to 58-77/112. Using electromyography, the authors documented voluntary control over important muscle groups, including the right hemidiaphragm (C3-5), extensor carpi radialis (C-6), and vastus medialis (L2-4). Reversal of osteoporosis and an increase in muscle mass was associated with this recovery. Moreover, spasticity decreased, the incidence of medical complications fell dramatically, and the incidence of infections and use of antibiotic medications was reduced by over 90%. These improvements occurred despite the fact that less than 25 mm2 of tissue (approximately 25%) of the outer cord (presumably white matter) had survived at the injury level. The primary novelty of this report is the demonstration that substantial recovery of function (two ASIA grades) is possible in a patient with severe C-2 ASIA Grade A injury, long after the initial SCI. Less severely injured (lower injury level, clinically incomplete lesions) individuals might achieve even more meaningful recovery. The role of patterned neural activity in regeneration and recovery of function after SCI therefore appears a fruitful area for future investigation.

Olfactory ensheathing cells: their potential use for repairing the injured spinal cord

STUDY DESIGN

The literature concerning the potential use of olfactory ensheathing cells for repairing damaged spinal cord was reviewed.

OBJECTIVE

To engender a better understanding of the role that olfactory ensheathing cells play in spinal cord regeneration.

SUMMARY OF BACKGROUND DATA

Intraspinal transplants (e.g., fetal neuronal cells, progenitor stem cells, and olfactory ensheathing cells) have been used to restore intraspinal circuitry or to serve as a "bridge" for damaged axons. Among these transplants, olfactory ensheathing cells provide a particularly favorable substrate for spinal axonal regeneration because these cells can secrete extracellular molecules and neurotrophic factors and have the ability to migrate into gliotic scar tissue, an important attribute that might be associated with high potential for axonal regeneration.

METHODS

Recent advances using centrally and peripherally derived olfactory ensheathing cells to promote spinal cord regeneration were reviewed.

RESULTS

Both centrally and peripherally derived olfactory ensheathing cells can lead to a degree of functional and anatomic recovery after spinal cord injury in adult animals.

CONCLUSION

Olfactory ensheathing cells from olfactory lamina propria in the nose are among the best transplants for "bridging" descending and ascending pathways in damaged spinal cord.

Functional recovery following traumatic spinal cord injury mediated by a unique polymer scaffold seeded with neural stem cells

To better direct repair following spinal cord injury (SCI), we designed an implant modeled after the intact spinal cord consisting of a multicomponent polymer scaffold seeded with neural stem cells. Implantation of the scaffold-neural stem cells unit into an adult rat hemisection model of SCI promoted long-term improvement in function (persistent for 1 year in some animals) relative to a lesion-control group. At 70 days postinjury, animals implanted with scaffold-plus-cells exhibited coordinated, weight-bearing hindlimb stepping. Histology and immunocytochemical analysis suggested that this recovery might be attributable partly to a reduction in tissue loss from secondary injury processes as well as in diminished glial scarring. Tract tracing demonstrated corticospinal tract fibers passing through the injury epicenter to the caudal cord, a phenomenon not present in untreated groups. Together with evidence of enhanced local GAP-43 expression not seen in controls, these findings suggest a possible regeneration component. These results may suggest a new approach to SCI and, more broadly, may serve as a prototype for multidisciplinary strategies against complex neurological problems.

Survival and regeneration of rubrospinal neurons 1 year after spinal cord injury

Scientific interest to find a treatment for spinal cord injuries has led to the development of numerous experimental strategies to promote axonal regeneration across the spinal cord injury site. Although these strategies have been developed in acute injury paradigms and hold promise for individuals with spinal cord injuries in the future, little is known about their applicability for the vast majority of paralyzed individuals whose injury occurred long ago and who are considered to have a chronic injury. Some studies have shown that the effectiveness of these approaches diminishes dramatically within weeks after injury. Here we investigated the regenerative capacity of rat rubrospinal neurons whose axons were cut in the cervical spinal cord 1 year before. Contrary to earlier reports, we found that rubrospinal neurons do not die after axotomy but, rather, they undergo massive atrophy that can be reversed by applying brain-derived neurotrophic factor to the cell bodies in the midbrain. This administration of neurotrophic factor to the cell body resulted in increased expression of growth-associated protein-43 and Talpha1 tubulin, genes thought to be related to axonal regeneration. This treatment promoted the regeneration of these chronically injured rubrospinal axons into peripheral nerve transplants engrafted at the spinal cord injury site. This outcome is a demonstration of the regenerative capacity of spinal cord projection neurons a full year after axotomy.

A quantitative morphometric analysis of rat spinal cord remyelination following transplantation of allogenic Schwann cells

Quantitative morphometric techniques were used to assess the extent and pattern of remyelination produced by transplanting allogenic Schwann cells into demyelinated lesions in adult rat spinal cords. The effects of donor age, prior culturing of donor cells, prior lesioning of donor nerves, and host immunosuppression were evaluated by transplanting suspensions of 30,000 acutely dissociated or cultured Schwann cells from neonatal, young adult, or aged adult rat sciatic nerves into X-irradiation and ethidium bromide-induced demyelinated dorsal column lesions, with or without co-transplantation of neonatal optic nerve astrocytes. Three weeks after transplantation, spinal cords were processed for histological analysis. Under all Schwann cell transplant protocols, large areas containing many Schwann cell-like myelinated axon profiles could be readily observed throughout most of the lesion length. Within these "myelin-rich" regions, the vast majority of detectable axons showed a peripheral-like pattern of myelination. However, interaxonal spacing also increased, resulting in densities of myelinated axons that were more similar to peripheral nerve than intact dorsal columns. Freshly isolated Schwann cells remyelinated more axonal length than cultured Schwann cells, and cells from younger donors remyelinated slightly more axon length than cells from older donors, but all Schwann cell transplant protocols remyelinated tens of thousands of millimeters of axon length and remyelinated axons at similar densities. These results indicate that Schwann cells prepared under a variety of conditions are capable of eliciting remyelination, but that the density of remyelinated axons is much lower than the myelinated axon density in intact spinal cords.

Spinal-cord injury

More than a decade ago, spinal-cord injury meant confinement to a wheelchair and a lifetime of medical comorbidity. The physician's armamentarium of treatments was very limited, and provision of care for individuals with spinal-cord injury was usually met with frustration. Advances in the neurosciences have drawn attention to research into spinal-cord injury. Nowadays, advanced interventions provide high hope for regeneration and functional restoration. As scientific advances become more frequent, scepticism is giving way to the ideas that spinal-cord injury will eventually be repairable and that strategies to restore function are within our grasp. We address the present understanding of spinal-cord injury, its cause, pathophysiology, diagnosis, and treatment, and look at promising research avenues. We also discuss new treatment options, including functional electric stimulation and part-weight-supported walking.

Kinematic analyses of air-stepping of neonatal rats after mid-thoracic spinal cord compression

Although human infants suffer traumatic spinal cord injury, appropriate animal models have not been developed. The consequences of neonatal injury are not necessarily the same as in adults, so treatments designed for adults may not generalize to infants. Therefore, understanding the effects of traumatic injury to the developing cord is important. In this experiment, mid-thoracic spinal cords of 4-day-old rats were compressed with forceps by 0% (sham), 90% or 95% of the uncompressed width. On postoperative day (POD) 1 or 11, rats were suspended in harnesses and administered L-DOPA to activate locomotor circuits. Slight modifications of interlimb coordination remained on POD 11 following the lesser compression, whereas the amount of hindlimb air-stepping, step rates, step lengths and coordination were reduced and declined post-operatively following the greater compression. Lesions were proportional to severity of compression. Progressive motor dysfunction during air-stepping revealed deficits in descending control of lumbar circuits, whereas previous reports of recovery of overground walking probably reflect activation of reflex mechanisms caudal to the transection.

Changes in axonal physiology and morphology after chronic compressive injury of the rat thoracic spinal cord

The spinal cord is rarely transected after spinal cord injury. Dysfunction of surviving axons, which traverse the site of spinal cord injury, appears to contribute to post-traumatic neurological deficits, although the underlying mechanisms remain unclear. The subpial rim frequently contains thinly myelinated axons which appear to conduct signals abnormally, although it is uncertain whether this truly reflects maladaptive alterations in conduction properties of injured axons during the chronic phase of spinal cord injury or whether this is merely the result of the selective survival of a subpopulation of axons. In the present study, we examined the changes in axonal conduction properties after chronic clip compression injury of the rat thoracic spinal cord, using the sucrose gap technique and quantitatively examined changes in the morphological and ultrastructural features of injured axonal fibers in order to clarify these issues. Chronically injured dorsal columns had a markedly reduced compound action potential amplitude (8.3% of control) and exhibited significantly reduced excitability. Other dysfunctional conduction properties of injured axons included a slower population conduction velocity, a longer refractory period and a greater degree of high-frequency conduction block at 200 Hz. Light microscopic and ultrastructural analysis showed numerous axons with abnormally thin myelin sheaths as well as unmyelinated axons in the injured spinal cord. The ventral column showed a reduced median axonal diameter and the lateral and dorsal columns showed increased median diameters, with evidence of abnormally large swollen axons. Plots of axonal diameter versus myelination ratio showed that post-injury, dorsal column axons of all diameters had thinner myelin sheaths. Noninjured dorsal column axons had a median myelination ratio (1.56) which was within the optimal range (1.43-1.67) for axonal conduction, whereas injured dorsal column axons had a median myelination ratio (1.33) below the optimal value. These data suggest that maladaptive alterations occur postinjury to myelin sheath thickness which reduce the efficiency of axonal signal transmission.In conclusion, chronically injured dorsal column axons show physiological evidence of dysfunction and morphological changes in axonal diameter and reduced myelination ratio. These maladaptive alterations to injured axons, including decrease in myelin thickness and the appearance of axonal swellings, contribute to the decreased excitability of chronically injured axons. These results further clarify the mechanisms underlying neurological dysfunction after chronic neurotrauma and have significant implications regarding approaches to augment neural repair and regeneration.

The role of intraoperative neurophysiology in the protection or documentation of surgically induced injury to the spinal cord

Playing both neuroprotective and educational roles, intraoperative neurophysiology has become an intrinsic part of modern neurosurgery. In this article, we present evidence substantiating the neuroprotective role of intraoperative neurophysiology, specifically its capacity to help prevent injury to the corticospinal tracts and the dorsal columns during spinal cord injury.

Effects of red nucleus ablation and exogenous neurotrophin-3 on corticospinal axon terminal distribution in the adult rat

Collateral sprouting of undamaged descending axons is one potential mechanism for recovery of function after incomplete spinal cord injury. In this study, we have investigated whether terminals of the intact corticospinal tract in the rat would sprout following ablation of a parallel descending pathway, the rubrospinal tract. No sprouting was detected after this injury alone. However, the combination of rubrospinal tract ablation with administration of 100ng neurotrophin-3 to neurons of the corticospinal tract resulted in marked increased density of corticospinal innervation in the superficial dorsal horn. There was no effect of administration of neurotrophin-3 alone and increase in axon density was not detected in the deep dorsal horn. These results imply that spontaneous sprouting of undamaged corticospinal axons does not occur following ablation of a parallel tract system, although collateral sprouting can be induced through a combination of the lesion plus exogenous growth factor. Induced change in corticospinal terminal density is detected in the superficial dorsal horn only, supporting the hypothesis that this is an area particularly supportive of circuit reorganisation.

Caspase-3 apoptotic signaling following injury to the central nervous system

Apoptotic cell death is a fundamental and highly regulated biological process in which a cell is instructed to participate actively in its own demise. This process of cellular suicide is activated by developmental and environmental cues and normally plays an essential role in eliminating superfluous, damaged, and senescent cells of many tissue types. In recent years, a number of experimental studies have provided evidence of widespread neuronal and glial apoptosis following injury to the central nervous system (CNS). These studies indicate that injury-induced apoptosis can be detected from hours to days following injury and may contribute to neurological dysfunction. Given these findings, understanding the biochemical signaling events controlling apoptosis is a first step towards developing therapeutic agents which would target this cell death process. This review will focus on the molecular cell death pathways responsible for generating the apoptotic phenotype, summarize what is currently known about apoptotic signals activated in the injured CNS, and what potential strategies might be pursued to reduce this cell death process as a means to promote functional recovery.

Evaluation of the neuroprotective effects of sodium channel blockers after spinal cord injury: improved behavioral and neuroanatomical recovery with riluzole

OBJECT

Persistent activation of voltage-sensitive Na+ channels is associated with cellular toxicity and may contribute to the degeneration of neural tissue following traumatic brain and spinal cord injury (SCI). Pharmacological blockade of these channels can attenuate secondary pathophysiology and reduce functional deficits acutely.

METHODS

To determine the therapeutic effects of Na+ channel blockers on long-term tissue sparing and functional neurological recovery after traumatic SCI, the authors injected Wistar rats intraperitoneally with riluzole (5 mg/kg), phenytoin (30 mg/kg), CNS5546A, a novel Na+ channel blocker (15 mg/kg), or vehicle (2-HP3CD; 5 mg/kg) 15 minutes after induction of compressive SCI at C7-T1. Functional neurological recovery of coordinated hindlimb function and strength, assessed 1 week postinjury and weekly thereafter for 6 weeks, was significantly enhanced in animals treated with riluzole compared with the other treatment groups. Seven weeks postinjury the preservation of residual tissue and integrity of descending axons were determined with digital morphometrical and fluorescent histochemical analysis. All three Na+ channel blockers significantly enhanced residual tissue area at the injury epicenter compared with control. Riluzole significantly reduced tissue loss in rostrocaudal regions surrounding the epicenter, with overall sparing of gray matter and selective sparing of white matter. Also, counts of red nuclei neurons retrogradely labeled with fluorogold introduced caudal to the injury site were significantly increased in the riluzole group.

CONCLUSIONS

Systemic Na+ channel blockers, in particular riluzole, can confer significant neuroprotection after in vivo SCI and result in behavioral recovery and sparing of both gray and white matter.

Delayed glial cell death following wallerian degeneration in white matter tracts after spinal cord dorsal column cordotomy in adult rats

The devastating consequences of spinal cord injury (SCI) result primarily from damage to long tracts in the spinal white matter. To elucidate the secondary injury processes occurring after SCI, we investigated the relationship between apoptosis and Wallerian degeneration in spinal white matter tracts. In the rat spinal cord, the corticospinal tract (CST) and the dorsal ascending tract (DAT) are separated from each other in the dorsal column and relay information in opposite directions. A dorsal column cordotomy at the eighth thoracic (T8) level simultaneously induces Wallerian degeneration in the CST caudal to and in the DAT rostral to the injury. Using the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) method, we demonstrate that apoptosis occurred in areas of Wallerian degeneration in both tracts throughout the length of the cord segments studied (from T3 to T12). This delayed cell death, more apparent in the DAT, began at 7 days after injury and peaked at 14 days for the DAT and 28 days for the CST. Although a few TUNEL+ cells, slightly above the noninjury control level, were found in intact areas of both tracts, statistically significant differences in the number of TUNEL+ cells were found between the intact and the lesioned tract segments (CST, F < 0.01; DAT, F < 0.001). Within a particular spinal segment, a mean number of 64 and 939 TUNEL+ cells in the degenerating CST and DAT, respectively, were estimated stereologically at 14 days postinjury. TUNEL+ cells in degenerating tracts outnumber their intact counterparts by 3.8:1 in the CST and 4.1:1 in the DAT, although a statistically significant difference between the two was only found in the DAT at this time point (P < 0.05). Finally, we demonstrated that oligodendrocytes, the myelin-forming cells in the central nervous system, constitute at least a portion of the cells undergoing apoptosis within areas of Wallerian degeneration.

Spontaneous corticospinal axonal plasticity and functional recovery after adult central nervous system injury

Although it is believed that little recovery occurs after adult mammalian spinal cord injury, in fact significant spontaneous functional improvement commonly occurs after spinal cord injury in humans. To investigate potential mechanisms underlying spontaneous recovery, lesions of defined components of the corticospinal motor pathway were made in adult rats in the rostral cervical spinal cord or caudal medulla. Following complete lesions of the dorsal corticospinal motor pathway, which contains more than 95% of all corticospinal axons, spontaneous sprouting from the ventral corticospinal tract occurred onto medial motoneuron pools in the cervical spinal cord; this sprouting was paralleled by functional recovery. Combined lesions of both dorsal and ventral corticospinal tract components eliminated sprouting and functional recovery. In addition, functional recovery was also abolished if dorsal corticospinal tract lesions were followed 5 weeks later by ventral corticospinal tract lesions. We found extensive spontaneous structural plasticity as a mechanism correlating with functional recovery in motor systems in the adult central nervous system. Experimental enhancement of spontaneous plasticity may be useful to promote further recovery after adult central nervous system injury.

Short-Term and medium-term effects of spinal cord tract transections on soleus H-reflex in freely moving rats

Spinal cord function is normally influenced by descending activity from supraspinal structures. When injury removes or distorts this influence, function changes and spasticity and other disabling problems eventually appear. Understanding how descending activity affects spinal cord function could lead to new means for inducing, guiding, and assessing recovery after injury. In this study, we investigated the short-term and medium-term effects of spinal cord bilateral dorsal column (DC), unilateral (ipsilateral) lateral column (LC), bilateral dorsal column ascending tract (DA), or bilateral dorsal column corticospinal tract (CST) transection at vertebral level T8-T9 on the soleus H-reflex in freely moving rats. Data were collected continuously for 10-20 days before and for 20-155 days after bilateral DC (13 rats), DA (10 rats), CST (eight rats), or ipsilateral LC (seven rats) transection. Histological examination showed that transections were 98(+/- 3 SD)% complete for DC rats, 80(+/- 20)% complete for LC rats, 91(+/- 13 SD)% complete for DA rats, and 95(+/-13)% complete for CST rats. LC, CST, and DA transections produced an immediate (i.e., first-day) increase in H-reflex amplitude. LC transection also produced a small decrease in background activity in the first few posttransection days. Other than this small decrease, none of the transections produced evidence for the phenomenon of spinal shock. For all transections, all measures returned to or neared pretransection values within 2 weeks. DA and LC transections were associated with modest increase in H-reflex amplitude 1-3 months after transection. These medium-term effects must be taken into account when assessing transection effects on operant conditioning of the H-reflex. At the same time, the results are consistent with other evidence that, while H-reflex rate dependence and H-reflex operant conditioning are sensitive measures of spinal cord injury, the H-reflex itself is not.

Reconstruction of the transected cat spinal cord following NeuroGel implantation: axonal tracing, immunohistochemical and ultrastructural studies

This study examined the ability of NeuroGel, a biocompatible porous poly [N-(2-hydroxypropyl) methacrylamide] hydrogel, to establish a permissive environment across a 3 mm gap in the cat spinal cord in order to promote tissue reconstitution and axonal regeneration across the lesion. Animals with NeuroGel implants were compared to transection-only controls and observed for 21 months. The hydrogel formed a stable bridge between the cord segments. Six months after reconstructive surgery, it was densely infiltrated by a reparative tissue composed of glial cells, capillary vessels and axonal fibres. Axonal labelling and double immunostaining for neurofilaments and myelin basic protein, showed that descending supraspinal axons of the ventral funiculus and afferent fibres of the dorsal column regenerated across the reconstructed lesion. Fifteen months after reconstructive surgery, axons had grown, at least, 12 mm into the distal cord tissue, and in the rostral cord there was labelling of neurons of the intermediate gray matter. Electron microscopy showed that after 9 months, most of the regenerating axons were myelinated, principally by Schwann cells. Newly formed neurons presumably from precursor cells of the ependyma and/or migrating neurons were observed within the reparative tissue after 21 months. Results indicate that functional deficit, as assessed by treadmill training, and morphological changes following double transection of the spinal cord can be modified by the implantation of NeuroGel. This technology offers the potential to promote the formation of a neural tissue equivalent via a reparative neohistogenesis process, that facilitates and supports regenerative growth of axons.

Methylprednisolone ameliorates cochlear nerve degeneration following mechanical injury

We investigated whether methylprednisolone sodium succinate can ameliorate cochlear nerve degeneration following compression injury on the cerebellopontine angle portion of the cochlear nerve, using a quantitative animal experimental model that we have developed recently. In this model, cochlear nerve degeneration after compression could be quantitatively evaluated, while cochlear ischemia induced by the compression carefully maintained below the critical limit that causes irreversible damage to the cochlea. Eleven rats were treated with methylprednisolone during the pre- and post-compression period. Two weeks after compression, the numbers of SGC were compared between the rats that received the compression without and with methylprednisolone treatment. Methylprednisolone treatment improved the survival of SGC following cochlear nerve injury statistically highly significantly in the basal turn where the traumatic stress had been less than in the other cochlear turns in our experimental setting. Although it was not statistically significant, greater survival was also observed in the other cochlear turns. The results of this experimental study indicated that at least a portion of injured cochlear nerve had been potentially treatable, and that methylprednisolone might prevent such cochlear neurons from entering into the vicious process of irreversible damaging process.

Olfactory ensheathing cells: bridging the gap in spinal cord injury

Spinal cord injury (SCI) continues to be an insidious and challenging problem for scientists and clinicians. Recent neuroscientific advances have changed the pessimistic notion that axons are not capable of significant extension after transection. The challenges of recovering from SCI have been broadly divided into four areas: 1) cell survival; 2) axon regeneration (growth); 3) correct targeting by growing axons; and 4) establishment of correct and functional synaptic appositions. After acute SCI, there seems to be a therapeutic window of opportunity within which the devastating consequences of the secondary injury can be ameliorated. This is supported by several observations in which apoptotic glial cells have been identified up to 1 week after acute SCI. Moreover, autopsy studies have identified anatomically preserved but unmyelinated axons that could potentially subserve normal physiological properties. These observations suggest that therapeutic strategies after SCI can be directed into two broad modalities: 1) prevention or amelioration of the secondary injury, and 2) restorative or regenerative interventions. Intraspinal transplants have been used after SCI as a means for restoring the severed neuraxis. Fetal cell transplants and, more recently, progenitor cells have been used to restore intraspinal circuitry or to serve as relay for damaged axons. In an attempt to remyelinate anatomically preserved but physiologically disrupted axons, newer therapeutic interventions have incorporated the transplantation of myelinating cells, such as Schwann cells, oligodendrocytes, and olfactory ensheathing cells. Of these cells, the olfactory ensheathing cells have become a more favorable candidate for extensive remyelination and axonal regeneration. Olfactory ensheathing cells are found along the full length of the olfactory nerve, from the basal lamina of the epithelium to the olfactory bulb, crossing the peripheral nervous system-central nervous system junction. In vitro, these cells promote robust axonal growth, in part through cell adhesion molecules and possibly by secretion of neurotrophic growth factors that support axonal elongation and extension. In animal models of SCI, transplantation of ensheathing cells supports axonal remyelination and extensive migration throughout the length of the spinal cord. Although the specific properties of these cells that govern enhanced axon regeneration remain to be elucidated, it seems certain that they will contribute to the establishment of new horizons in SCI research.

Extensive injury of descending neurons demonstrated by retrograde labeling in a virus-induced murine model of chronic inflammatory demyelination

Persistent Theiler's virus infection of SJL/J mice was used as a model to quantitatively assess the extent of descending neuron injury by chronic inflammatory demyelination of the spinal cord. By 9 months postinfection, inflammatory demyelinating lesions were present throughout the spinal cord, affecting up to 31% of the cross-sectional area of the ventrolateral columns. Axon dropout was evident in the lesions by electron microscopy and by quantitation of axons in normal-appearing white matter. Axon number in the ventrolateral columns at L1/L2 was reduced by 23% and total axon area was reduced by 37%, compared with uninfected mice. The most informative data on descending neuron injury, however, was a reduction in retrograde. Fluoro-Gold labeling. Labeling from T11/T12 of rubrospinal, reticulospinal/raphespinal, and vestibulospinal neurons was reduced by 60%, 70%, and 93%, respectively. Retrograde responses to axonal injury were observed, consisting of atrophied cell bodies, indented nuclei, and abundant lipofuscin, but cell body dropout was minimal. The number of cell bodies of vestibulospinal neurons was reduced by only 35%, whereas the number of cell bodies of rubrospinal neurons was unchanged. These results demonstrate that chronic inflammatory demyelination can severely injure axons and emphasize the need to design neuroprotective therapies in human multiple sclerosis.

Axonal loss results in spinal cord atrophy, electrophysiological abnormalities and neurological deficits following demyelination in a chronic inflammatory model of multiple sclerosis

Recent pathological studies have re-emphasized that axonal injury is present in patients with multiple sclerosis, the most common demyelinating disease of the CNS in humans. However, the temporal profile of demyelination and axonal loss in multiple sclerosis patients and their independent contributions to clinical and electrophysiological abnormalities are not completely understood. In this study, we used the Theiler's murine encephalomyelitis virus model of progressive CNS inflammatory demyelination to demonstrate that demyelination in the spinal cord is followed by a loss of medium to large myelinated fibres. By measuring spinal cord areas, motor-evoked potentials, and motor coordination and balance, we determined that axonal loss following demyelination was associated with electrophysiological abnormalities and correlated strongly with reduced motor coordination and spinal cord atrophy. These findings demonstrate that axonal loss can follow primary, immune-mediated demyelination in the CNS and that the severity of axonal loss correlates almost perfectly with the degree of spinal cord atrophy and neurological deficits.

GABA increases refractoriness of adult rat dorsal column axons

We applied randomized double pulse stimulation for assessing the effects of GABA and a GABAA antagonist on compound action potentials in dorsal column axons isolated from adult rat. We stimulated the axons with double pulses at 0.2 Hz and randomly varied interpulse intervals between 3, 4, 5, 8, 10, 20, 30, 50 and 80 ms. Action potentials were measured using glass micropipettes. The first pulse was used to condition the response activated by the second test pulse. Concentrations of GABA of 1 mM, 100 microM and 10 microM did not affect action potential amplitudes or latencies activated by conditioning pulses. In the control studies, before drug administration, test pulses induced response amplitudes that were significantly decreased at 3-, 4- and 5-ms interpulse intervals. The test action potential amplitudes were 84.6 +/- 2.5%, 89.0 +/- 3.9% and 93.3 +/- 3.6% (mean +/- S.E.M.) of conditioning pulse levels, respectively. At 3-ms interpulse intervals, test response latencies were prolonged to 104.3 +/- 1.0%, but were unchanged at the other interpulse intervals. The 10 microM, 100 microM and 1 mM concentrations of GABA affected test response amplitudes. Application of 100 microM GABA reduced the amplitudes of test responses at 3-, 4-, 5- and 8-ms interpulse intervals, to 59.2 +/- 3.0%, 70.0 +/- 3.0%, 80.2 +/- 1.1% and 88.6 +/- 3.6% of the conditioning pulse amplitudes, respectively. At both 100 microM and 1 mM concentrations, GABA significantly prolonged the latencies of test responses. Treatment with 100 microM GABA prolonged the latencies of test responses at 3-, 4- and 5-ms interpulse intervals, to 119.3 +/- 3.1%, 107.3 +/- 2.8% and 105.5 +/- 2.5% of conditioning pulse latencies, respectively. The addition of 100 microM bicuculline methochloride, a GABAA antagonist, eliminated the effects of 100 microM GABA. The combined application of GABA and bicuculline (both 100 microM) did not affect amplitudes or latencies of test responses. These results suggest that GABA(A) receptor subtypes are present on the spinal dorsal column axons of adult rat, and that they modulate the excitability of the axons. The randomized double pulse methods reveal that GABA increases refractoriness of adult rat dorsal column axons.

Abnormal axonal physiology is associated with altered expression and distribution of Kv1.1 and Kv1.2 K+ channels after chronic spinal cord injury

Dysfunction of surviving axons which traverse the site of spinal cord injury (SCI) has been linked to altered sensitivity to the K+ channel blocker 4-aminopyridine (4-AP) and appears to contribute to post-traumatic neurological deficits although the underlying mechanisms remain unclear. In this study, sucrose gap electrophysiology in isolated dorsal column strips, Western blotting and confocal immunofluorescence microscopy were used to identify the K+ channels associated with axonal dysfunction after chronic (6-8 weeks postinjury) clip compresssion SCI of the thoracic cord at T7 in rats. The K+ channel blockers 4-AP (200 microM, 1 mM and 10 mM) and alpha-dendrotoxin (alpha-DTX, 500 nM) resulted in a significant relative increase in the amplitude and area of compound action potentials (CAP) recorded from chronically injured dorsal column axons in comparison with control noninjured preparations. In contrast, TEA (10 mM) and CsCl (2 mM) had similar effects on injured and control spinal cord axons. Western blotting and quantitative immunofluorescence microscopy showed increased expression of Kv1.1 and Kv1.2 K+ channel proteins on spinal cord axons following injury. In addition, Kv1.1 and Kv1.2 showed a dispersed staining pattern along injured axons in contrast to a paired juxtaparanodal localization in uninjured spinal cord axons. Furthermore, labelled alpha-DTX colocalized with Kv1.1 and Kv1.2 along axons. These findings suggest a novel mechanism of axonal dysfunction after SCI whereby an increased 4-AP- and alpha-DTX-sensitive K+ conductance, mediated in part by increased Kv1.1 and Kv1.2 K+ channel expression, contributes to abnormal axonal physiology in surviving axons.

Resealing of transected myelinated mammalian axons in vivo: evidence for involvement of calpain

The mechanisms underlying resealing of transected myelinated rat dorsal root axons were investigated in vivo using an assay based on exclusion of a hydrophilic dye (Lucifer Yellow-biocytin conjugate). Smaller caliber axons (<5 microm outer diameter) resealed faster than larger axons. Resealing was Ca2+ dependent, requiring micromolar levels of extracellular [Ca2+] to proceed, and further accelerated in 1 mM Ca2+. Two hours after transection, 84% of axons had resealed in saline containing 2 mM Ca2+, 28% had resealed in saline containing no added Ca2+ and only 3% had resealed in the Ca2+ buffer BAPTA (3 mM). The enhancing effect of Ca2+ could be overcome by both non-specific cysteine protease inhibitors (e.g., leupeptin) and inhibitors specific for the calpain family of Ca2+ -activated proteases. Resealing in 2 mM Ca2+ was not inhibited by an inhibitor of phospholipase A2. Resealing in low [Ca2+] was not enhanced by agents which disrupt microtubules, but was enhanced by dimethylsulfoxide (0.5-5%). These results suggest that activation of endogenous calpain-like proteases by elevated intra-axonal [Ca2+] contributes importantly to membrane resealing in transected myelinated mammalian axons in vivo.

Spinal cord injury in small animals 2. Current and future options for therapy

Although there can be substantial spontaneous improvements in functional status after a spinal cord injury, therapeutic intervention is desirable in many patients to improve the degree of recovery. At present only decompressive surgery and the neuroprotective drug methylprednisolone sodium succinate are effective and in widespread clinical use. There are limitations to the efficacy of these therapies in some clinical cases and they cannot restore satisfactory functional status to all patients. Many drugs have been investigated experimentally to assess their potential to preserve injured tissue and promote functional recovery in clinically relevant settings, and several of them would be suitable for assessment in future veterinary clinical trials. In addition, experimental techniques designed to mould the response of the CNS to injury, by the promotion of axonal regeneration across the lesion and the encouragement of local sprouting of undamaged axons, have recently been successful, suggesting that effective therapy for even very severe spinal cord injury may soon be available.

Effects of the sodium channel blocker tetrodotoxin on acute white matter pathology after experimental contusive spinal cord injury

Focal microinjection of tetrodotoxin (TTX), a potent voltage-gated sodium channel blocker, reduces neurological deficits and tissue loss after spinal cord injury (SCI). Significant sparing of white matter (WM) is seen at 8 weeks after injury and is correlated to a reduction in functional deficits. To determine whether TTX exerts an acute effect on WM pathology, Sprague Dawley rats were subjected to a standardized weight-drop contusion at T8 (10 gm x 2.5 cm). TTX (0. 15 nmol) or vehicle solution was injected into the injury site 5 or 15 min later. At 4 and 24 hr, ventromedial WM from the injury epicenter was compared by light and electron microscopy and immunohistochemistry. By 4 hr after SCI, axonal counts revealed reduced numbers of axons and significant loss of large (>/=5 micrometer)-diameter axons. TTX treatment significantly reduced the loss of large-diameter axons. In addition, TTX significantly attenuated axoplasmic pathology at both 4 and 24 hr after injury. In particular, the development of extensive periaxonal spaces in the large-diameter axons was reduced with TTX treatment. In contrast, there was no significant effect of TTX on the loss of WM glia after SCI. Thus, the long-term effects of TTX in reducing WM loss after spinal cord injury appear to be caused by the reduction of acute axonal pathology. These results support the hypothesis that TTX-sensitive sodium channels at axonal nodes of Ranvier play a significant role in the secondary injury of WM after SCI.

Behavioural consequences of oligodendrocyte progenitor cell transplantation into experimental demyelinating lesions in the rat spinal cord

Glial cell transplantation has the potential to be developed into a clinical treatment for human demyelinating diseases because of its demonstrated efficacy in remyelinating experimentally demyelinated axons. As a step towards clinical application it is necessary to demonstrate that the procedure is safe and efficacious in promoting behavioural recovery. In this study we transplanted glial cell progenitors into demyelinating lesions induced by intraspinal injection of ethidium bromide in the rat. Locomotor function after transplantation was assessed using a beam-walking test that has previously been shown able to detect deficits associated with demyelination in the dorsal funiculus of the rat spinal cord. Two groups of animals with transplants were examined. In one group, spontaneous remyelination was prevented by exposure of the lesion to 40 Gy of X-irradiation; in the other, male glial cells were transplanted into nonirradiated female recipients, permitting their identification by use of a probe specific to the rat Y chromosome. Following transplantation, there was severe axon loss in a large proportion of the irradiated animals and those affected did not recover normal behavioural function. In contrast, both the small proportion of the irradiated group that sustained only mild axon loss and the nonirradiated recipients of transplants recovered normal function on our behavioural test. We conclude that glial cell transplantation is able to reverse the functional deficits associated with demyelination, provided axonal loss is minimal.

Spinal cord injury in small animals. 1. Mechanisms of spontaneous recovery

Spinal cord injury causes obvious clinical deficits early in the course of lesion evolution, but it is commonly observed that recovery can occur spontaneously during a period of days, weeks or even months afterwards. Spinal cord dysfunction arises after injury because of a combination of reversible alterations in the concentration of intra- and extracellular ionic constituents and irreversible tissue destruction. Recovery can therefore occur through re-establishment of the normal microenvironment of the spinal cord, which occurs soon after injury induction, and also by formation of new patterns of central nervous system circuitry. Alterations in circuitry, termed 'plasticity', can occur during the immediate period after injury but apparently continue for many weeks or months. There are differences in the extent and nature of recovery between complete and incomplete experimental spinal cord injuries that illustrate the roles played by reorganisation of intra- and suprasegmental circuitry. Information that is available on mechanisms of spontaneous recovery may aid development of novel therapies for clinical spinal cord injury.

Operant conditioning of H-reflex increase in spinal cord--injured rats

Operant conditioning of the spinal stretch reflex or its electrical analog, the H-reflex, is a new model for exploring the mechanisms of long-term supraspinal control over spinal cord function. Primates and rats can gradually increase (HRup conditioning mode) or decrease (HRdown conditioning mode) the H-reflex when reward is based on H-reflex amplitude. An earlier study indicated that HRdown conditioning of the soleus H-reflex in rats is impaired following contusion injury to thoracic spinal cord. The extent of impairment was correlated with the percent of white matter lost at the injury site. The present study investigated the effects of spinal cord injury on HRup conditioning. Soleus H-reflexes were elicited and recorded with chronically implanted electrodes from 14 rats that had been subjected to calibrated contusion injuries to the spinal cord at T8. At the lesion epicenter, 12-39% of the white matter remained. After control-mode data were collected, each rat was exposed to the HRup conditioning mode for 50 days. Final H-reflex amplitudes after HRup conditioning averaged 112% (+/-22% SD) of control. This value was significantly smaller than that for 13 normal rats exposed to HRup conditioning, in which final amplitude averaged 153% (+/-51%) SD of control. As previously reported for HRdown conditioning after spinal cord injury, success was inversely correlated with the severity of the injury as assessed by white matter preservation and by time to return of bladder function. HRup and HRdown conditioning are similarly sensitive to injury. These results further demonstrate that H-reflex conditioning is a sensitive measure of the long-term effects of injury on supraspinal control over spinal cord functions and could prove a valuable measure of therapeutic efficacy.