Relationship between residual hindlimb-assisted locomotion and surviving axons after incomplete spinal cord injuries

A Scoping Review of Epidural Spinal Cord Stimulation for Improving Motor and Voiding Function Following Spinal Cord Injury

Objectives

To identify and synthesize the existing evidence on the effectiveness and safety of epidural spinal cord stimulation (SCS) for improving motor and voiding function and reducing spasticity following spinal cord injury (SCI).

Methods

This scoping review was performed according to the framework of Arksey and O'Malley. Comprehensive serial searches in multiple databases (MEDLINE, Embase, Cochrane Central, Cochrane Database of Systematic Reviews, LILACS, PubMed, Web of Science, and Scopus) were performed to identify relevant publications that focused on epidural SCS for improving motor function, including spasticity, and voiding deficits in individuals with SCI.

Results

Data from 13 case series including 88 individuals with complete or incomplete SCI (American Spinal Injury Association Impairment Scale [AIS] grade A to D) were included. In 12 studies of individuals with SCI, the majority (83 out of 88) demonstrated a variable degree of improvement in volitional motor function with epidural SCS. Two studies, incorporating 27 participants, demonstrated a significant reduction in spasticity with SCS. Two small studies consisting of five and two participants, respectively, demonstrated improved supraspinal control of volitional micturition with SCS.

Conclusion

Epidural SCS can enhance central pattern generator activity and lower motor neuron excitability in individuals with SCI. The observed effects of epidural SCS following SCI suggest that the preservation of supraspinal transmission is sufficient for the recovery of volitional motor and voiding function, even in patients with complete SCI. Further research is warranted to evaluate and optimize the parameters for epidural SCS and their impact on individuals with differing degrees of severity of SCI.

Differences in sensorimotor and functional recovery between the dominant and non-dominant upper extremity following cervical spinal cord injury

STUDY DESIGN

Post hoc analysis of prospective multi-national, multi-centre cohort study.

OBJECTIVE

Determine whether cerebral dominance influences upper extremity recovery following cervical spinal cord injury (SCI).

SETTING

A multi-national subset of the longitudinal GRASSP dataset (n = 127).

METHODS

Secondary analysis of prospective, longitudinal multicenter study of individuals with cervical SCI (n = 73). Study participants were followed for up to 12 months after a cervical SCI, and the following outcome measures were serially assessed - the Graded Redefined Assessment of Strength, Sensibility, and Prehension (GRASSP) and the International Standards for the Neurological Classification of SCI (ISNCSCI), including upper extremity motor and sensory scores. Observed recovery and relative (percent) recovery were then determined for both the GRASSP and ISNCSCI, based on change from initial to last available assessment.

RESULTS

With the exception of prehension performance (quantitative grasping) following complete cervical SCI, there were no significant differences (p < 0.05) for observed and relative (percent) recovery, between the dominant and non-dominant upper extremities, as measured using GRASSP subtests, ISNCSCI motor scores and ISNCSCI sensory scores.

CONCLUSION

Despite well documented differences between the cerebral hemispheres, cerebral dominance appears to play a limited role in upper extremity recovery following acute cervical SCI.

Enhancing Functional Recovery Through Intralesional Application of Extracellular Vesicles in a Rat Model of Traumatic Spinal Cord Injury

Local inflammation plays a pivotal role in the process of secondary damage after spinal cord injury. We recently reported that acute intravenous application of extracellular vesicles (EVs) secreted by human umbilical cord mesenchymal stromal cells dampens the induction of inflammatory processes following traumatic spinal cord injury. However, systemic application of EVs is associated with delayed delivery to the site of injury and the necessity for high doses to reach therapeutic levels locally. To resolve these two constraints, we injected EVs directly at the lesion site acutely after spinal cord injury. We report here that intralesional application of EVs resulted in a more robust improvement of motor recovery, assessed with the BBB score and sub-score, as compared to the intravenous delivery. Moreover, the intralesional application was more potent in reducing inflammation and scarring after spinal cord injury than intravenous administration. Hence, the development of EV-based therapy for spinal cord injury should aim at an early application of vesicles close to the lesion.

Role of Baclofen in Modulating Spasticity and Neuroprotection in Spinal Cord Injury

Spinal cord injury (SCI) affects an estimated three million persons worldwide, with ∼180,000 new cases reported each year leading to severe motor and sensory functional impairments that affect personal and social behaviors. To date, no effective treatment has been made available to promote neurological recovery after SCI. Deficits in motor function is the most visible consequence of SCI; however, other secondary complications produce a significant impact on the welfare of patients with SCI. Spasticity is a neurological impairment that affects the control of muscle tone as a consequence of an insult, trauma, or injury to the central nervous system, such as SCI. The management of spasticity can be achieved through the combination of both nonpharmacological and pharmacological approaches. Baclofen is the most effective drug for spasticity treatment, and it can be administered both orally and intrathecally, depending on spasticity location and severity. Interestingly, recent data are revealing that baclofen can also play a role in neuroprotection after SCI. This new function of baclofen in the SCI scope is promising for the prospect of developing new pharmacological strategies to promote functional recovery in patients with SCI.

Adenovirus vector‑mediated in vivo gene transfer of nuclear factor erythroid‑2p45‑related factor 2 promotes functional recovery following spinal cord contusion

The aim of the present study was to investigate whether nuclear factor erythroid 2p45‑related factor 2 (Nrf2) overexpression by gene transfer may protect neurons/glial cells and the association between neurons/glial cells and axons in spinal cord injury (SCI). In the present study, Nrf2 recombinant adenovirus (Ad) vectors were constructed. The protein levels of Nrf2 in the nucleus and of the Nrf2‑regulated gene products heme oxygenase‑1 (HO‑1) and NAD (P)H‑quinone oxidoreductase‑1 (NQO1), were detected using western blot analysis in PC12 cells following 48 h of transfection. Furthermore, the expression of Nrf2 was localized using an immunofluorescence experiment, and the expression of Nrf2, HO‑1 and NQO1 were detected using an immunohistochemical experiment in the grey matter of spinal cord in rats. Post‑injury motor behavior was assessed via the Basso, Beattie and Bresnahan (BBB) locomotor scale method. In PC12 cells, subsequent to Ad‑Nrf2 transfection, nuclear Nrf2, HO‑1 and NQO1 levels were significantly increased compared with the control (P<0.01). There was statistically significant changes in the PC12‑Ad‑Nrf2 group [Nrf2 (1.146±0.095), HO‑1 (1.816±0.095) and NQO1 (1.421±0.138)] compared with the PC12‑control group [Nrf2 (0.717±0.055), HO‑1 (1.264±0.081) and NQO1 (0.921±0.088)] and PC12‑Ad‑green fluorescent protein group [Nrf2 (0.714±0.111), HO‑1 (1.238±0.053) and NQO1 (0.987±0.045); P<0.01]. The BBB scores of the rats indicated that they had improved functional recovery following the local injection of Ad‑Nrf2. On the third day following the operation, BBB scores in the adenovirus groups (0.167±0.408) were significantly decreased compared with the SCI group (1±0.894; P<0.05). In the injured section of the spinal cord in the rats, the number of positive cells expressing Nrf2, HO‑1 and NQO1 were raised compared with the control and SCI groups, indicating that the adenovirus vector‑mediated gene transfer of Nrf2 promotes functional recovery following spinal cord contusion in rats.

Neuroprotective effect of local hypothermia in a computer-controlled compression model in minipig: Correlation of tissue sparing along the rostro-caudal axis with neurological outcome

This study investigated the neuroprotective efficacy of local hypothermia in a minipig model of spinal cord injury (SCI) induced by a computer-controlled impactor device. The tissue integrity observed at the injury epicenter, and up to 3 cm cranially and caudally from the lesion site correlated with motor function. A computer-controlled device produced contusion lesions at L3 level with two different degrees of tissue sparing, depending upon pre-set impact parameters (8N- and 15N-force impact). Hypothermia with cold (4°C) saline or Dulbecco's modified Eagle's medium (DMEM)/F12 culture medium was applied 30 min after SCI (for 5 h) via a perfusion chamber (flow 2 ml/min). After saline hypothermia, the 8N-SCI group achieved faster recovery of hind limb function and the ability to walk from one to three steps at nine weeks in comparison with non-treated animals. Such improvements were not observed in saline-treated animals subjected to more severe 15N-SCI or in the group treated with DMEM/F12 medium. It was demonstrated that the tissue preservation in the cranial and caudal segments immediately adjacent to the lesion, and neurofilament protection in the lateral columns may be essential for modulation of the key spinal microcircuits leading to a functional outcome. Tissue sparing observed only in the caudal sections, even though significant, was not sufficient for functional improvement in the 15N-SCI model.

Degeneration, Trophic Interactions, and Repair of Severed Axons: A Reconsideration of Some Common Assumptions

We suggest that several interrelated properties of severed axons (degeneration, trophic dependencies, initial repair, and eventual repair) differ in important ways from commonly held assumptions about those properties. Specifically, (1) axotomy does not necessarily produce rapid degeneration of distal axonal segments because (2) the trophic maintenance of nerve axons does not necessarily depend entirely on proteins transported from the perikaryon—but instead axonal proteins can be trophically maintained by slowing their degradation and/or by acquiring new proteins via axonal synthesis or transfer from adjacent cells (e.g., glia). (3) The initial repair of severed distal or proximal segments occurs by barriers (seals) formed amid accumulations of vesicles and/or myelin delaminations induced by calcium influx at cut axonal ends—rather than by collapse and fusion of cut axolemmal leaflets. (4) The eventual repair of severed mammalian CNS axons does not necessarily have to occur by neuritic outgrowths, which slowly extend from cut proximal ends to possibly reestablish lost functions weeks to years after axotomy—but instead complete repair can be induced within minutes by polyethylene glycol to rejoin (fuse) the cut ends of surviving proximal and distal stumps. Strategies to repair CNS lesions based on fusion techniques combined with rehabilitative training and induced axonal outgrowth may soon provide therapies that can at least partially restore lost CNS functions.

Valproic acid-mediated neuroprotection and neurogenesis after spinal cord injury: from mechanism to clinical potential

Spinal cord injury (SCI) is difficult to treat because of secondary injury. Valproic acid (VPA) is clinically approved for mood stabilization, but also counteracts secondary damage to functionally rescue SCI in animal models by improving neuroprotection and neurogenesis via inhibition of HDAC and GSK-3. However, a comprehensive review summarizing the therapeutic benefits and mechanisms of VPA for SCI and the issues affecting clinical trials is lacking, limiting future research on VPA and impeding its translation into clinical therapy for SCI. This article presents the current status of VPA treatment for SCI, emphasizing interactions between enhanced neuroprotection and neurogenesis. Crucial issues are discussed to optimize its clinical potential as a safe and effective treatment for SCI.

A characterization of white matter pathology following spinal cord compression injury in the rat

Our laboratory has previously described the characteristics of neuronal injury in a rat compression model of spinal cord injury (SCI), focussing on the impact of this injury on the gray matter. However, white matter damage is known to play a critical role in functional outcome following injury. Therefore, in the present study, we used immunohistochemistry and electron microscopy to examine the alterations to the white matter that are initiated by compression SCI applied at T12 vertebral level. A significant loss of axonal and dendritic cytoskeletal proteins was observed at the injury epicenter within 1day of injury. This was accompanied by axonal dysfunction, as demonstrated by the accumulation of β-amyloid precursor protein (β-APP), with a peak at 3days post-SCI. A similar, acute loss of cytoskeletal proteins was observed up to 5mm away from the injury epicenter and was particularly evident rostral to the lesion site, whereas β-APP accumulation was prominent in tracts proximal to the injury. Early myelin loss was confirmed by myelin basic protein (MBP) immunostaining and by electron microscopy, which also highlighted the infiltration of inflammatory and red blood cells. However, 6weeks after injury, areas of new Schwann cell and oligodendrocyte myelination were observed. This study demonstrates that substantial white matter damage occurs following compression SCI in the rat. Moreover, the loss of cytoskeletal proteins and accumulation of β-APP up to 5mm away from the lesion site within 1day of injury indicates the rapid manner in which the axonal damage extends in the rostro-caudal axis. This is likely due to both Wallerian degeneration and spread of secondary cell death, with the latter affecting axons both proximal and distal to the injury.

Blocking the P2X7 receptor improves outcomes after axonal fusion

BACKGROUND

Activation of the P2X7 receptor on peripheral neurons causes the formation of pannexin pores, which allows the influx of calcium across the cell membrane. Polyethylene glycol (PEG) and methylene blue have previously been shown to delay Wallerian degeneration if applied during microsuture repair of the severed nerve. Our hypothesis is that by modulating calcium influx via the P2X7 receptor pathway, we could improve PEG-based axonal repair. The P2X7 receptor can be stimulated or inhibited using bz adenosine triphosphate (bzATP) or brilliant blue (FCF), respectively.

METHODS

A single incision rat sciatic nerve injury model was used. The defect was repaired using a previously described PEG methylene blue fusion protocol. Experimental animals were treated with 100 μL of 100 μM FCF solution (n = 8) or 100 μL of a 30 μM bzATP solution (n = 6). Control animals received no FCF, bzATP, or PEG. Compound action potentials were recorded prior to transection (baseline), immediately after repair, and 21 d postoperatively. Animals underwent behavioral testing 3, 7, 14, and 21 d postoperatively. After sacrifice, nerves were fixed, sectioned, and immunostained to allow for counting of total axons.

RESULTS

Rats treated with FCF showed an improvement compared with control at all time points (n = 8) (P = 0.047, 0.044, 0.014, and 0.0059, respectively). A statistical difference was also shown between FCF and bzATP at d 7 (P < 0.05), but not shown with d 3, 14, and 21 (P > 0.05).

CONCLUSIONS

Blocking the P2X7 receptor improves functional outcomes after PEG-mediated axonal fusion.

Locomotor recovery after spinal cord hemisection/contusion injures in bonnet monkeys: footprint testing--a minireview

Spinal cord injuries usually produce loss or impairment of sensory, motor and reflex function below the level of damage. In the absence of functional regeneration or manipulations that promote regeneration, spontaneous improvements in motor functions occur due to the activation of multiple compensatory mechanisms in animals and humans following the partial spinal cord injury. Many studies were performed on quantitative evaluation of locomotor recovery after induced spinal cord injury in animals using behavioral tests and scoring techniques. Although few studies on rodents have led to clinical trials, it would appear imperative to use nonhuman primates such as macaque monkeys in order to relate the research outcomes to recovery of functions in humans. In this review, we will discuss some of our research evidences concerning the degree of spontaneous recovery in bipedal locomotor functions of bonnet monkeys that underwent spinal cord hemisection/contusion lesions. To our knowledge, this is the first report to discuss on the extent of spontaneous recovery in bipedal locomotion of macaque monkeys through the application of footprint analyzing technique. In addition, the results obtained were compared with the published data on recovery of quadrupedal locomotion of spinally injured rodents. We propose that the mechanisms underlying spontaneous recovery of functions in spinal cord lesioned monkeys may be correlated to the mature function of spinal pattern generator for locomotion under the impact of residual descending and afferent connections. Moreover, based on analysis of motor functions observed in locomotion in these subjected monkeys, we understand that spinal automatism and development of responses by afferent stimuli from outside the cord could possibly contribute to recovery of paralyzed hindlimbs. This report also emphasizes the functional contribution of progressive strengthening of undamaged nerve fibers through a collateral sprouts/synaptic plasticity formed in partially lesioned cord of monkeys.

Hydrophilic polymers enhance early functional outcomes after nerve autografting

BACKGROUND

Approximately 12% of operations for traumatic neuropathy are for patients with segmental nerve loss, and less than 50% of these injuries obtain meaningful functional recovery. Polyethylene glycol (PEG) therapy has been shown to improve functional outcomes after nerve severance, and we hypothesized this therapy could also benefit nerve autografting.

METHODS

We used a segmental rat sciatic nerve injury model in which we repaired a 0.5-cm defect with an autograft using microsurgery. We treated experimental animals with solutions containing methylene blue (MB) and PEG; control animals did not receive PEG. We recorded compound action potentials (CAPs) before nerve transection, after solution therapy, and at 72 h postoperatively. The animals underwent behavioral testing at 24 and 72 h postoperatively. After we euthanized the animals, we fixed the nerves, sectioned and immunostained them to allow for quantitative morphometric analysis.

RESULTS

The introduction of hydrophilic polymers greatly improved morphological and functional recovery of rat sciatic axons at 1-3 d after nerve autografting. Polyethylene glycol therapy restored CAPs in all animals, and CAPs were still present 72 h postoperatively. No CAPS were detectable in control animals. Foot Fault asymmetry scores and sciatic functional index scores were significantly improved for PEG therapy group at all time points (P < 0.05 and P < 0.001; P < 0.001 and P < 0.01). Sensory and motor axon counts were increased distally in nerves treated with PEG compared with control (P = 0.019 and P = 0.003).

CONCLUSIONS

Polyethylene glycol therapy improves early physiologic function, behavioral outcomes, and distal axonal density after nerve autografting.

Delayed granulocyte colony-stimulating factor treatment promotes functional recovery in rats with severe contusive spinal cord injury

STUDY DESIGN

We used a severe contusive spinal cord injury (SCI) model and electrophysiologic, motor functional, immunohistochemical, and electron microscopic examinations to analyze the neuroprotective effects of delayed granulocyte colony-stimulating factor (G-CSF) treatment.

OBJECTIVE

To determine the neuroprotective effects of delayed G-CSF treatment using multimodality evaluations after severe contusive SCI in rats.

SUMMARY OF BACKGROUND DATA

Despite some reports that G-CSF treatment in the acute stage of different central nervous system injury models was neuroprotective, it has not been determined whether delayed G-CSF treatment can promote neural recovery in severe contusive SCI.

METHODS

Rats with severe contusive SCI were divided into 2 groups: G-CSF group rats were given serial subcutaneous injections of G-CSF, and control group rats (controls) were given only saline injections on postcontusion days 9 to 13. Using the Basso-Beattie-Bresnahan scale and cortical somatosensory evoked potentials, we recorded functional evaluations weekly. The spinal cords were harvested for protein and immunohistochemical analysis, and for electron microscopy examination.

RESULTS

The preserved spinal cord area was larger in G-CSF group rats than in control group rats. Both sensory and motor functions improved after G-CSF treatment. Detachment and disruption of the myelin sheets in the myelinated axons were significantly decreased, and axons sprouted and regenerated. There were fewer microglia and macrophages in the G-CSF group than in the control group. The levels of brain-derived neurotrophic factor were comparable between the 2 groups.

CONCLUSION

Delayed G-CSF treatment at the subacute stage of severe contusive SCI promoted spinal cord preservation and improved functional outcomes. The mechanism of G-CSF's protection may be related in part to attenuating the infiltration of microglia and macrophages.

Docosahexaenoic acid prevents white matter damage after spinal cord injury

We have previously shown that the omega-3 fatty acid docosahexaenoic acid (DHA) significantly improves several histological and behavioral measures after spinal cord injury (SCI). White matter damage plays a key role in neurological outcome following SCI. Therefore, we examined the effects of the acute intravenous (IV) administration of DHA (250 nmol/kg) 30 min after thoracic compression SCI in rats, alone or in combination with a DHA-enriched diet (400 mg/kg/d, administered for 6 weeks post-injury), on white matter pathology. By 1 week post-injury, the acute IV DHA injection led to significantly reduced axonal dysfunction, as indicated by accumulation of β-amyloid precursor protein (-55% compared to vehicle-injected controls) in the dorsal columns. The loss of cytoskeletal proteins following SCI was also significantly reduced. There were 43% and 73% more axons immunoreactive for non-phosphorylated 200-kD neurofilament in the ventral white matter and ventrolateral white matter, respectively, in animals receiving DHA injections than vehicle-injected rats. The acute DHA treatment also led to a significant improvement in microtubule-associated protein-2 immunoreactivity. By 6 weeks, damage to myelin and serotonergic fibers was also reduced. For some of the parameters measured, the combination of DHA injection and DHA-enriched diet led to greater neuroprotection than DHA injection alone. These findings demonstrate the therapeutic potential of DHA in SCI, and clearly indicate that this fatty acid confers significant protection to the white matter.

Effects of dantrolene on apoptosis and immunohistochemical expression of NeuN in the spinal cord after traumatic injury in rats

Dantrolene has been shown to be neuroprotective by reducing neuronal apoptosis after brain injury in several animal models of neurological disorders. In this study, we investigated the effects of dantrolene on experimental spinal cord injury (SCI). Forty-six male Wistar rats were laminectomized at T13 and divided in six groups: GI (n = 7) underwent SCI with placebo and was euthanized after 32 h; GII (n = 7) underwent laminectomy alone with placebo and was euthanized after 32 h; GIII (n = 8) underwent SCI with dantrolene and was euthanized after 32 h; GIV (n = 8) underwent SCI with placebo and was euthanized after 8 days; GV (n = 8) underwent laminectomy alone with placebo and was euthanized after 8 days; and GVI (n = 8) underwent SCI with dantrolene and was euthanized after 8 days. A compressive trauma was performed to induce SCI. After euthanasia, the spinal cord was evaluated using light microscopy, TUNEL staining and immunochemistry with anti-Caspase-3 and anti-NeuN. Animals treated with dantrolene showed a smaller number of TUNEL-positive and caspase-3-positive cells and a larger number of NeuN-positive neurons, both at 32 h and 8 days (P ≤ 0.05). These results showed that dantrolene protects spinal cord tissue after traumatic SCI by decreasing apoptotic cell death.

Acute rolipram/thalidomide treatment improves tissue sparing and locomotion after experimental spinal cord injury

Traumatic spinal cord injury (SCI) causes severe and permanent functional deficits due to the primary mechanical insult followed by secondary tissue degeneration. The cascade of secondary degenerative events constitutes a range of therapeutic targets which, if successfully treated, could significantly ameliorate functional loss after traumatic SCI. During the early hours after injury, potent pro-inflammatory cytokines, including tumor necrosis factor alpha (TNF-alpha) and interleukin-1 beta (IL-1beta) are synthesized and released, playing key roles in secondary tissue degeneration. In the present investigation, the ability of rolipram and thalidomide (FDA approved drugs) to reduce secondary tissue degeneration and improve motor function was assessed in an experimental model of spinal cord contusion injury. The combined acute single intraperitoneal administration of both drugs attenuated TNF-alpha and IL-1beta production and improved white matter sparing at the lesion epicenter. This was accompanied by a significant (2.6 point) improvement in the BBB locomotor score by 6 weeks. There is, at present, no widely accepted intervention strategy that is appropriate for the early treatment of human SCI. The present data suggest that clinical trials for the acute combined application of rolipram and thalidomide may be warranted. The use of such "established drugs" could facilitate the early initiation of trials.

Comparison of inflammation in the brain and spinal cord following mechanical injury

Inflammation in the CNS predominantly involves microglia and macrophages, and is believed to be a significant cause of secondary injury following trauma. This study compares the microglial and macrophage response in the rat brain and spinal cord following discrete mechanical injury to better appreciate the degree to which these cells could contribute to secondary damage in these areas. We find that, 1 week after injury, the microglial and macrophage response is significantly greater in the spinal cord compared to the brain. This is the case for injuries to both gray and white matter. In addition, we observed a greater inflammatory response in white matter compared to gray matter within both the brain and spinal cord. Because activated microglia and macrophages appear to be effectors of secondary damage, a greater degree of inflammation in the spinal cord is likely to result in more extensive secondary damage. Tissue saving strategies utilizing anti-inflammatory treatments may therefore be more useful in traumatic spinal cord than brain injury.

Recovery of bipedal locomotion in bonnet macaques after spinal cord injury: footprint analysis

Analysis of the recovery of gait after spinal cord injury has been widely demonstrated in rat and cat models using different behavioral tests and scoring systems. The present investigation was aimed to quantitatively analyze the degree of functional recovery in bipedal locomotion of bonnet macaques after inflicting spinal cord hemisection lesion. To measure the degree of locomotor recovery, we recorded four gait variables, viz., tip of opposite foot (TOF), print length (PL), toe spread (TS), and intermediary toes (IT) using a footprint analyzing technique. Monkeys were trained preoperatively to perform the monopedal hop or bipedal locomotion on runways. Footprints of trained monkeys were recorded using the nontoxic ink and white paper before and after surgery. Surgical hemisection was induced unilaterally in the right side of spinal cord at T12-L1 level of trained monkeys. In hemiplegic monkeys, initially there was a substantial decrease in TOF and PL variables of the paretic limb, which then gradually increased for longer duration and reached the near presurgical values by the 7th and 5th postoperative month, respectively. In contrast to TOF and PL, the recovery of TS and IT variables was quicker, which dramatically increased at first and then slowly recovered to levels not significantly different from the corresponding preoperative values by the 4th postoperative month. The nonparetic limb has also showed mild alterations in all footprint variables but reached the normal values much faster compared to the paretic limb. The alterations in footprint variables of hemiplegic monkeys were examined for a postoperative period of up to 1 year. The findings of this study suggest that the mechanisms underlying locomotor recovery of lesioned macaques may be correlated to the mature function of spinal pattern generator for locomotion under the impact of residual descending and afferent connections. Further, this study also indicates the functional contribution of progressive strengthening of undamaged nerve fibers through a collateral sprouts/synaptic plasticity formed in partially lesioned cord of macaques.

Effects of polyethylene glycol and magnesium sulfate administration on clinically relevant neurological outcomes after spinal cord injury in the rat

The purpose of this study was to determine the long-term effects of polyethylene glycol (PEG) and magnesium sulfate (MgSO(4)) on clinically relevant motor, sensory, and autonomic outcomes after spinal cord injury (SCI). Rats were injured by clip compression (50 g; T4) and treated 15 min and 6 hr postinjury intravenously (tail vein) with PEG (1 g/kg, 30% w/w in saline; n = 11), MgSO(4) (300 mg/kg; n = 5), PEG + MgSO(4) (n = 6), or saline (n = 10). Behavioral testing lasted for 6 weeks, followed by histological analysis of the spinal cord. Both PEG and MgSO(4) resulted in enhanced locomotor recovery and lower susceptibility to neuropathic pain (mechanical allodynia) compared with saline. At 6 weeks, BBB scores were 7.3 +/- 0.2, 7.7 +/- 0.4, and 6.4 +/- 0.6 in PEG-treated, MgSO(4)-treated, and saline-treated control groups, respectively. Likewise, at 6 weeks PEG-, MgSO(4)-, and saline-treated control animals showed 3.5 +/- 0.4, 2.8 +/- 0.9, and 5.0 +/- 0.5 avoidance responses to at-level touch, respectively. PEG + MgSO(4) improved locomotor recovery and reduced pain but did not provide additional benefit compared with either treatment alone. Neither treatment, nor their combination, attenuated mean arterial pressure (MAP) increases during autonomic dysreflexia. However, saline-treated controls had significantly lower resting MAP than PEG-treated rats and tended to have lower resting MAP than MgSO(4)-treated rats 6 weeks postinjury. MgSO(4) treatment and PEG + MgSO(4) treatment resulted in significant increases in dorsal myelin sparing, and the latter resulted in significant reductions in lesion volume, compared with saline-treated controls. Furthermore, mean lesion volumes correlated negatively with the corresponding mean BBB scores and positively with the corresponding mean pain scores. In conclusion, both PEG and MgSO(4) enhanced long-term clinical outcomes after SCI.

Regeneration following spinal cord injury, from experimental models to humans: where are we?

Regeneration in the adult CNS following injury is extremely limited. Traumatic spinal cord injury causes a permanent neurological deficit followed by a very limited recovery due to failed regeneration attempts. In fact, it is now clear that the spinal cord intrinsically has the potential to regenerate, but cellular loss and the presence of an inhibitory environment strongly limit tissue regeneration and functional recovery. The molecular mechanisms responsible for failed regeneration are starting to be unveiled. This gain in knowledge led to the design of therapeutic strategies aimed to limit the tissue scar, to enhance the proregeneration versus the inhibitory environment, and to replace tissue loss, including the use of stem cells. They have been very successful in several animal models, although results are still controversial in humans. Nonetheless, novel experimental approaches hold great promise for use in humans.

Strategies to promote neural repair and regeneration after spinal cord injury

STUDY DESIGN

Retrospective review of current literature regarding neuroprotection and axonal regeneration therapies for acute spinal cord injury.

OBJECTIVES

To provide an update for spine clinicians of the emerging therapeutic strategies for promoting neural repair and regeneration after spinal cord injury.

SUMMARY OF BACKGROUND DATA

The neuroscientific community has generated a number of novel potential treatments for spinal injuries, some of which have entered clinical trials. Clinicians who manage spinal cord trauma are likely to encounter patients and their families who have questions or wish to be involved in these emerging treatments.

METHODS

Literature review, with particular focus on currently used medications that may have neuroprotective potential in spinal cord injury, and axonal regeneration strategies that are emerging in preliminary human clinical trials.

RESULTS

A number of medications such as erythropoietin and minocycline have demonstrated neuroprotective properties in animal models of spinal cord injury, and their long-established safety in humans make them appealing candidates for clinical trials. Human experience with novel neuroprotective and axonal regeneration strategies is growing around the world, and the peer-reviewed reporting of this is anxiously awaited.

CONCLUSIONS

The initiation of human clinical trials for spinal cord-injured patients heralds great hope that effective therapies will be forthcoming, although a great deal remains to be learned. Clinicians must provide leadership in the epidemiologic design and rigor of these initial forays into human evaluation.

From Animal Models to Humans

There are currently no fully restorative therapies for human spinal cord injury (SCI). Here,we briefly review the different types of human SCI pathology as well as the most commonly used rodent and nonhuman primate models of SCI that are used to simulate these pathologies and to test potential therapies. We then discuss various high profile (sometimes controversial) experimental strategies that have reported CNS axon regeneration and functional recovery of limb movement using these animal models of SCI. We particularly focus upon strategies that have been tested both in rodents and in nonhuman primates, and highlight those which are currently transitioning to clinical tests or trials in humans. Finally we discuss ways in which animal studies might be improved and what the future may hold for physical therapists involved in rehabilitation of humans with SCI.

Differential vulnerability of propriospinal tract neurons to spinal cord contusion injury

The propriospinal system is important in mediating reflex control and in coordination during locomotion. Propriospinal neurons (PNs) present varied patterns of projections with ascending and/or descending fibers. Following spinal cord contusion injury (SCI) in the rat, certain supraspinal pathways, such as the corticospinal tract, appear to be completely abolished, whereas others, such as the rubrospinal and vestibuospinal tracts, are only partially damaged. The amount of damage to propriospinal axons following different severities of SCI is not fully known. In the present study retrograde and anterograde tracing techniques were used to assess the projection patterns of propriospinal neurons in order to determine how this system is affected following SCI. Our findings reveal that PNs have differential vulnerabilities to SCI. While short thoracic propriospinal axons are severely damaged after injury, 5-7% of long descending propriospinal tract (LDPT) projections survive following 50 and 12.5-mm weight drop contusion lesions, respectively, albeit with a reduced intensity of retrograde label. Even though the axons of short thoracic propriospinal cells are damaged, their cell bodies of origin remain intact 2 weeks after injury, indicating that they have not undergone postaxotomy retrograde cell death at this time point. Thus, short PNs may constitute a very attractive population of cells to study regenerative approaches, whereas LDPT neurons with spared axons could be targeted with therapeutic interventions, seeking to enhance recovery of function following incomplete lesions to the spinal cord.

Immediate plasticity in the motor pathways after spinal cord hemisection: implications for transcranial magnetic motor-evoked potentials

The present study evaluates motor functional recovery after C2 spinal cord hemisection with or without contralateral brachial root transection, which causes a condition that is similar to the crossed phrenic phenomenon on rats. Descending motor pathways, including the reticulospinal extrapyramidal tract and corticospinal pyramidal tracts, were evaluated by transcranial magnetic motor-evoked potentials (mMEPs) and direct cortical electrical motor-evoked potentials (eMEP), respectively. All MEPs recorded from the left forelimb were abolished immediately after the left C2 hemisection. Left mMEPs recovered dramatically immediately after contralateral right brachial root transection. Corticospinal eMEPs never recovered, regardless of transection. The facilitation of mMEPs in animals that had undergone combined contralateral root transection was well correlated with open-field behavioral motor performance. Both electrophysiological and neurological facilitations were significantly attenuated by the selective serotonin synthesis inhibitor para-chlorophenylalanine (p-CPA). These results suggest that serotonergic reticulospinal fibers located contralateral to hemisection contribute to the behavioral and electrophysiological improvement that immediately follows spinal cord injury (SCI).

Behavioral Testing After Spinal Cord Injury: Congruities, Complexities, and Controversies

Selection and implementation of behavioral tests in spinal cord injury research is an important process, and yet few papers have focused on these issues. The critical component of any behavioral experiment is the ability to produce reliable, reproducible, and worthwhile data. Unfortunately, the difference between worthwhile and worthless data is often subtle. This paper describes factors that must be considered in order to select the most sensitive behavioral tests to match the hypothesis of the experiment and apply any test in a standardized, consistent manner. Classifications of behavioral tests, their strengths and limitations, as well as methods to overcome these limitations are discussed. Recent work in translating behavioral tests from rats to mice is also provided. The purpose of this article is to provide a framework by which behavioral testing can be standardized within and across spinal cord injury labs.

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.

CNS regeneration: clinical possibility or basic science fantasy?

Following injury to the CNS, severed axons undergo a phase of abortive sprouting in the vicinity of the wound, but do not spontaneously re-grow or regenerate. From a long history of attempts to stimulate regeneraion, a major strategy that has been developed clinically is the implantation of tissue into denervated target regions. Unfortunately trials have so far not borne out the promise that this would prove a useful therapy for disorders such as Parkinson's disease. Many strategies have also been developed to stimulate the regeneration of axons across sites of injury, particularly in the spinal cord. Animal data have demonstrated that some of these approaches hold promise and that the spinal cord has a remarkable degree of intrinsic plasticity. Attempts are now being made to utilize experimental techniques in spinal patients.

Increasing plasticity and functional recovery of the lesioned spinal cord

In vitro assays have shown that adult CNS tissue, in particular oligodendrocytes and myelin, contains several molecular constituents (Nogo-A/NI-220, MAG, several proteoglycans) which exert neurite growth inhibitory activity. Elimination of oligodendrocytes or myelin, or application of antibodies against some of these constituents enhance regenerative growth and compensatory sprouting of lesioned and unlesioned fiber tracts in spinal cord and brain. Enhanced growth is paralleled by various degrees of functional recovery.

Preservation of neurologic function during inflammatory demyelination correlates with axon sparing in a mouse model of multiple sclerosis

Axonal injury has been proposed as the basis of permanent deficits in the inflammatory, demyelinating disease, multiple sclerosis. However, reports on the degree of injury are highly variable, and the responsible mechanisms are poorly understood. We examined the relationships among long-term demyelination, inflammation, axonal injury, and motor function in a model of multiple sclerosis, in which mice develop chronic, immune-mediated demyelination of the spinal cord resulting from persistent infection with Theiler's virus. We studied two strains of mice, inbred SJL/J and C57BL/6x129 mice deficient in beta(2)-microglobulin and therefore CD8 lymphocytes. After 8 months of disease, SJL mice had considerably worse motor function than beta(2)-microglobulin-deficient mice. Motor dysfunction correlated linearly with the extent of demyelinated lesions in the spinal cord (lesion load) within each strain, but no difference in lesion load was present between strains. Also, the extent of remyelination did not differ between strains. Instead, the disparity in motor deficits reflected differences in the integrity of descending neurons. That is, retrograde labeling of reticulospinal, vestibulospinal, and rubrospinal neurons, although reduced in all chronically diseased mice, was two to seven times higher in beta(2)-microglobulin-deficient mice. The labeling was superior in beta(2)-microglobulin-deficient mice despite the fact that lesion expanse and therefore the number of axons traversing lesions were similar in both strains. Thus, by all criteria axons were equivalently demyelinated in SJL and beta(2)-microglobulin-deficient mice, but the extent of axonal injury differed significantly. These results indicate that mechanisms of demyelination and axonal injury are at least partly separable, and are consistent with the hypothesis that cytotoxic CD8 lymphocytes may selectively injure demyelinated axons. Additionally, the data suggest that axonal injury obligatorily results from chronic inflammatory demyelination and significantly contributes to neurological deficits.

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.

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.

Behavioural assessment of functional recovery after spinal cord hemisection in the bonnet monkey (Macaca radiata)

In spinal cord research, current approaches to behavioural assessment often fail in defining the exact nature of motor deficits or in evaluating the return of motor behaviour from lost functions following spinal cord injury. In addition to the assessment of gross motor behaviour, it is often appropriate to use complex tests for locomotion to evaluate the masked deficits in the evaluation of functional recovery after spinal cord injury. We designed a series of sensitive quantitative tests for reflex responses and complex locomotor behaviour in the form of a combined behavioural score (CBS) to assess the recovery of function in the Bonnet monkey (Macaca radiata). Monkeys were tested for various motor/reflex components, trained to cross different complex runways, and to walk on a treadmill bipedally. The overall performance of animal's motor behaviour and the functional status of individual limb movement during bipedal locomotion was graded and scored by the CBS. Surgical hemisection was then performed on the right side of the spinal cord at the T12-L1 level. Spinal cord hemisected animals showed a significant alteration in certain reflex responses such as grasping, extension withdrawal, and placing reflexes, which persisted through 1 year of follow-up. The spinal cord hemisected animals traversed the complex locomotor runways (Narrow beam and Grid runway) with more steps and few errors, at similar levels to control animals. These observations indicate that the various motor/reflex components and bipedal locomotor behaviour of spinal cord hemisected monkeys return to control levels gradually. These results are similar to those obtained in rat models by other investigators. These results demonstrate that the basic motor strategy and the spinal pattern generator for locomotion (SPGL) in adult monkeys for the accomplishment of complex motor tasks is similar, but not identical, to that in adult rats. This suggests that the mechanisms underlying recovery are probably similar in rats and monkeys, but that primates may take a longer duration to achieve the same functional end point.

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.

Functional reconnection of severed mammalian spinal cord axons with polyethylene glycol

We describe a technique using the water-soluble polymer polyethylene glycol (PEG) to reconnect the two segments of completely transected mammalian spinal axons within minutes. This was accomplished by fusing completely severed strips of isolated guinea pig thoracic white matter maintained in vitro in a double sucrose gap recording chamber. The faces of the severed segments were pressed together, and PEG (MW 1,400-3,500 d; approximately 50% by weight in distilled water) was applied directly to this region through a micropipette and removed by aspiration within 2 min. Successful fusion was documented by the immediate restored conduction of compound action potentials through the original transection and by the variable numbers of fused axons in which anatomical continuity was shown to be restored by high-resolution light microscopy and by the diffusion of intracellular fluorescent dyes through fused axons. These data support the conclusion that some severed and subsequently PEG-fused spinal axons both demonstrate restored anatomical continuity and also are physiologically competent to conduct action potentials. This work adds to our previous demonstration that PEG application can immediately repair severely crushed, rather than cut, spinal cord white matter, and may lead to novel treatments for acute trauma to the central and peripheral nervous systems.

Depletion of hematogenous macrophages promotes partial hindlimb recovery and neuroanatomical repair after experimental spinal cord injury

Traumatic injury to the spinal cord initiates a series of destructive cellular processes which accentuate tissue damage at and beyond the original site of trauma. The cellular inflammatory response has been implicated as one mechanism of secondary degeneration. Of the various leukocytes present in the spinal cord after injury, macrophages predominate. Through the release of chemicals and enzymes involved in host defense, macrophages can damage neurons and glia. However, macrophages are also essential for the reconstruction of injured tissues. This apparent dichotomy in macrophage function is further complicated by the overlapping influences of resident microglial-derived macrophages and those phagocytes that are derived from peripheral sources. To clarify the role macrophages play in posttraumatic secondary degeneration, we selectively depleted peripheral macrophages in spinal-injured rats during a time when inflammation has been shown to be maximal. Standardized behavioral and neuropathological analyses (open-field locomotor function, morphometric analysis of the injured spinal cord) were used to evaluate the efficacy of this treatment. Beginning 24 h after injury and then again at days 3 and 6 postinjury, spinal cord-injured rats received intravenous injections of liposome-encapsulated clodronate to deplete peripheral macrophages. Within the spinal cords of rats treated in this fashion, macrophage infiltration was significantly reduced at the site of impact. These animals showed marked improvement in hindlimb usage during overground locomotion. Behavioral recovery was paralleled by a significant preservation of myelinated axons, decreased cavitation in the rostrocaudal axis of the spinal cord, and enhanced sprouting and/or regeneration of axons at the site of injury. These data implicate hematogenous (blood-derived) macrophages as effectors of acute secondary injury. Furthermore, given the selective nature of the depletion regimen and its proven efficacy when administered after injury, cell-specific immunomodulation may prove useful as an adjunct therapy after spinal cord injury.

Rapid induction of functional and morphological continuity between severed ends of mammalian or earthworm myelinated axons

The inability to rapidly restore the loss of function that results from severance (cutting or crushing) of PNS and CNS axons is a severe clinical problem. As a novel strategy to help alleviate this problem, we have developed in vitro procedures using Ca2+-free solutions of polyethylene glycol (PEG solutions), which within minutes induce functional and morphological continuity (PEG-induced fusion) between the cut or crushed ends of myelinated sciatic or spinal axons in rats. Using a PEG-based hydrogel that binds to connective tissue to provide mechanical strength at the lesion site and is nontoxic to nerve tissues in earthworms and mammals, we have also developed in vivo procedures that permanently maintain earthworm myelinated medial giant axons whose functional and morphological integrity has been restored by PEG-induced fusion after axonal severance. In all these in vitro or in vivo procedures, the success of PEG-induced fusion of sciatic or spinal axons and myelinated medial giant axons is measured by the restored conduction of action potentials through the lesion site, the presence of intact axonal profiles in electron micrographs taken at the lesion site, and/or the intra-axonal diffusion of fluorescent dyes across the lesion site. These and other data suggest that the application of polymeric fusiogens (such as our PEG solutions), possibly combined with a tissue adherent (such as our PEG hydrogels), could lead to in vivo treatments that rapidly and permanently repair cut or crushed axons in the PNS and CNS of adult mammals, including humans.

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.

Myelin gene expression after experimental contusive spinal cord injury

After incomplete traumatic spinal cord injury (SCI), the spared tissue exhibits abnormal myelination that is associated with reduced or blocked axonal conductance. To examine the molecular basis of the abnormal myelination, we used a standardized rat model of incomplete SCI and compared normal uninjured tissue with that after contusion injury. We evaluated expression of mRNA for myelin proteins using in situ hybridization with oligonucleotide probes to proteolipid protein (PLP), the major protein in central myelin; myelin basic protein (MBP), a major component of central myelin and a minor component of peripheral myelin; and protein zero (P0), the major structural protein of peripheral myelin, as well as myelin transcription factor 1 (MYT1). We found reduced expression of PLP and MBP chronically after SCI in the dorsal, lateral, and ventral white matter both rostral and caudal to the injury epicenter. Detailed studies of PLP at 2 months after injury indicated that the density of expressing cells was normal but mRNA per cell was reduced. In addition, P0, normally restricted to the peripheral nervous system, was expressed both at the epicenter and in lesioned areas at least 4 mm rostral and caudal to it. Thus, after SCI, abnormal myelination of residual axons may be caused, at least in part, by changes in the transcriptional regulation of genes for myelin proteins and by altered distribution of myelin-producing cells. In addition, the expression of MYT1 mRNA and protein seemed to be upregulated after SCI in a pattern suggesting the presence of undifferentiated progenitor cells in the chronically injured cord.

Mechanisms of motor recovery after subtotal spinal cord injury: insights from the study of mice carrying a mutation (WldS) that delays cellular responses to injury

Partial lesions of the mammalian spinal cord result in an immediate motor impairment that recovers gradually over time; however, the cellular mechanisms responsible for the transient nature of this paralysis have not been defined. A unique opportunity to identify those injury-induced cellular responses that mediate the recovery of function has arisen from the discovery of a unique mutant strain of mice in which the onset of Wallerian degeneration is dramatically delayed. In this strain of mice (designated WldS for Wallerian degeneration, slow), many of the cellular responses to spinal cord injury are also delayed. We have used this experimental animal model to evaluate possible causal relationships between these delayed cellular responses and the onset of functional recovery. For this purpose, we have compared the time course of locomotor recovery in C57BL/6 (control) mice and in WldS (mutant) mice by hemisecting the spinal cord at T8 and evaluating locomotor function at daily postoperative intervals. The time course of locomotor recovery (as determined by the Tarlov open-field walking procedure) was substantially delayed in mice carrying the WldS mutation: C57BL/6 control mice began to stand and walk within 6 days (mean Tarlov score of 4), whereas mutant mice did not exhibit comparable locomotor function until 16 days postoperatively.

INTERPRETATION AND CONCLUSION

(a) The rapid return of locomotor function in the C57BL/6 mice suggests that the recovery resulted from processes of functional plasticity rather than from regeneration or collateral sprouting of nerve fibers. (b) The marked delay in the return of locomotor function in WldS mice indicates that the processes of neuroplasticity are induced by degenerative changes in the damaged neurons. (c) These strains of mice can be effectively used in future studies to elucidate the specific biochemical and physiological alterations responsible for inducing functional plasticity and restoring locomotor function after spinal cord injury.

Axonal regrowth after spinal cord transection in adult zebrafish

Using axonal tracers, we characterized the neurons projecting from the brain to the spinal cord as well as the terminal fields of ascending spinal projections in the brain of adult zebrafish with unlesioned or transected spinal cords. Twenty distinct brain nuclei were found to project to the spinal cord. These nuclei were similar to those found in the closely related goldfish, except that additionally the parvocellular preoptic nucleus, the medial octavolateralis nucleus, and the nucleus tangentialis, but not the facial lobe, projected to the spinal cord in zebrafish. Terminal fields of axons, visualized by anterograde tracing, were seen in the telencephalon, the diencephalon, the torus semicircularis, the optic tectum, the eminentia granularis, and throughout the ventral brainstem in unlesioned animals. Following spinal cord transection at a level approximately 3.5 mm caudal to the brainstem/spinal cord transition zone, neurons in most brain nuclei grew axons beyond the transection site into the distal spinal cord to the level of retrograde tracer application within 6 weeks. However, the individually identifiable Mauthner cells were never seen to do so up to 15 weeks after spinal cord transection. Nearly all neurons survived axotomy, and the vast majority of axons that had grown beyond the transection site belonged to previously axotomized neurons as shown by double tracing. Terminal fields were not re-established in the torus semicircularis and the eminentia granularis following spinal cord transection.

Recovery from spinal cord injury mediated by antibodies to neurite growth inhibitors

There is little axonal growth after central nervous system (CNS) injury in adult mammals. The administration of antibodies (IN-1) to neutralize the myelin-associated neurite growth inhibitory proteins leads to long-distance regrowth of a proportion of CNS axons after injury. Our aim was: to determine if spinal cord lesion in adult rats, followed by treatment with antibodies to neurite growth inhibitors, can lead to regeneration and anatomical plasticity of other spinally projecting pathways; to determine if the anatomical projections persist at long survival intervals; and to determine whether this fibre growth is associated with recovery of function. We report here that brain stem-spinal as well as corticospinal axons undergo regeneration and anatomical plasticity after application of IN-1 antibodies. There is a recovery of specific reflex and locomotor functions after spinal cord injury in these adult rats. Removal of the sensorimotor cortex in IN-1-treated rats 2-3 months later abolished the recovered contact-placing responses, suggesting that the recovery was dependent upon the regrowth of these pathways.

Detrusor-sphincteric dyssynergia in humans with spinal cord lesions may be caused by a loss of stable phase relations between and within oscillatory firing neuronal networks of the sacral micturition center

(1) Single-fibre action potentials (APs) were recorded with 2 pairs of wire electrodes from lower sacral nerve roots during surgery in patients with spinal cord lesions and in a brain-dead human. Conduction velocity distribution histograms were constructed for afferent and efferent fibres, nerve fibre groups were identified and simultaneous impulse patterns of alpha and gamma-motoneurons and secondary muscle spindle afferents (SP2) were constructed. Temporal relations between afferent and efferent APs were analysed by interspike interval (II) and phase relation changes. (2) In a paraplegic with hyperreflexia of the bladder, urinary bladder stretch (S1) and tension receptor afferents (ST) fired already when the bladder was empty, and showed a several times higher bladder afferent activity increase upon retrograde bladder filling than observed in the brain-dead individual. Two alpha 2-motoneurons (FR) innervating the external bladder sphincter were already oscillatory firing to generate high activity levels when the bladder was empty. They showed activity levels with no bladder filling, comparable to those measured at a bladder filling of 600 ml in the brain-dead individual. A bladder storage volume of 600 ml was thus lost in the paraplegic, due to a too high bladder afferent input to the sacral micturition center, secondary to inflammation and hypertrophy of the detrusor. (3) In a brain-dead human, 2 phase relations existed per oscillation period of 160 ms between the APs of a sphincteric oscillatory firing alpha 2-motoneuron, a dynamic fusimotor and a secondary muscle spindle afferent fibre. Following stimulation of mainly somatic afferent fibres, the phase relations changed only little. (4) In a paraplegic with dyssynergia of the urinary bladder also 2 phase relations existed per oscillation period of 110 ms in a functional unit between the APs of a sphincteric alpha-motoneuron, a fusimotor and a secondary spindle afferent fibre. The phase relations changed with time following stimulation of mainly somatic afferents. A second functional unit organized by phase-related interactions was phase related to the first functional unit. (5) Following painful bladder catheter pulling, the parasympathetic division was transiently activated several times in the paraplegic. At times of activation of the parasympathetic division, 3 broad phase relations occurred within and between the two functional units, indicating that the parasympathetic division in the sacral micturition and defecation center channeled an additional input to the somatic oscillatory firing neuronal networks driving motoneurons which innervate the external bladder and/or anal sphincters.