Motor Recovery and Anatomical Evidence of Axonal Regrowth in Spinal Cord-Repaired Adult Rats

Monkey Recovery from Spinal Cord Hemisection: Nerve Repair Strategies for Rhesus Macaques

OBJECTIVE

Repair of spinal cord injury (SCI) using peripheral nerve graft (PNG) and acidic fibroblast growth factor (aFGF) has shown promising results in rats and a few human patients, but not in nonhuman primates. The aim of this study was to verify the effective use of PNG and aFGF for repairing incomplete SCI in nonhuman primates.

METHODS

Six adult rhesus macaques received spinal cord hemisection at T8 level and were grouped into repair and control groups (n = 3 in each). Animals in the repair group underwent nerve repair with autologous PNG plus aFGF immediately after lesioning. The control group received exactly the same operation for lesioning but no treatment. Postoperative behavioral evaluations, electrophysiologic tests (including motor and somatosensory evoked potentials), and magnetic resonance imaging were performed and compared between the 2 groups as well as histologic examination of the spinal cord cephalic to, at, and caudal to the lesion site after sacrifice.

RESULTS

Animals in the repair group had better motor function in the lower limbs at every observed time point and demonstrated more improvement on electrophysiologic examinations than the control group. The repair group had smaller areas of myelomalacia on magnetic resonance imaging around the lesion compared with the control group, suggesting diminished inflammatory responses with the repair strategy.

CONCLUSIONS

PNG plus aFGF for SCI in nonhuman primates yielded improvements in clinical behavior, electrophysiologic tests, and magnetic resonance imaging. This study suggests that the repair strategy is feasible and effective for nonhuman primate SCI. Further investigations are warranted to corroborate its effectiveness for clinical application.

Diversity of reticulospinal systems in mammals

Reticulospinal (RS) neurons provide the spinal cord with the executive signals for a large repertoire of motor and autonomic functions, ensuring at the same time that these functions are adapted to the different behavioral contexts. This requires the coordinated action of many RS neurons. In this mini-review, we examine how the RS neurons that carry out specific functions distribute across the three parts of the brain stem. Extensive overlap between populations suggests a need to explore multi-functionality at the single cell-level. We next contrast functional diversity and homogeneity in transmitter phenotype. Then, we examine the molecular genetic mechanisms that specify brain stem development and likely contribute to RS neurons identities. We advocate that a better knowledge of the developmental lineage of the RS neurons and a better knowledge of RS neuron activity across multiple behaviors will help uncover the fundamental principles behind the diversity of RS systems in mammals.

Acidic Fibroblast Growth Factor in Spinal Cord Injury

Spinal cord injury (SCI), with an incidence rate of 246 per million person-years among adults in Taiwan, remains a devastating disease in the modern day. Elderly men with lower socioeconomic status have an even higher risk for SCI. Despite advances made in medicine and technology to date, there are few effective treatments for SCI due to limitations in the regenerative capacity of the adult central nervous system. Experiments and clinical trials have explored neuro-regeneration in human SCI, encompassing cell- and molecule-based therapies. Furthermore, strategies have aimed at restoring connections, including autologous peripheral nerve grafts and biomaterial scaffolds that theoretically promote axonal growth. Most molecule-based therapies target the modulation of inhibitory molecules to promote axonal growth, degrade glial scarring obstacles, and stimulate intrinsic regenerative capacity. Among them, acidic fibroblast growth factor (aFGF) has been investigated for nerve repair; it is mitogenic and pluripotent in nature and could enhance axonal growth and mitigate glial scarring. For more than 2 decades, the authors have conducted multiple trials, including human and animal experiments, using aFGF to repair nerve injuries, including central and peripheral nerves. In these trials, aFGF has shown promise for neural regeneration, and in the future, more trials and applications should investigate aFGF as a neurotrophic factor. Focusing on aFGF, the current review aimed to summarize the historical evolution of the utilization of aFGF in SCI and nerve injuries, to present applications and trials, to summarize briefly its possible mechanisms, and to provide future perspectives.

hucMSC derived exosomes promote functional recovery in spinal cord injury mice via attenuating inflammation

The exploration of effective spinal cord injury (SCI) healing still remain a great challenge due to the high morbidity, complex pathology and unclear targets. Human umbilical cord mesenchymal stem cells (hucMSC) play an important role in tissue regeneration. However, transplanting stem cells has a potential risk of teratogenicity. Recent studies have suggested that exosomes secreted by stem cells may contribute to tissue injury repair. We hypothesized that the application of hucMSC derived exosomes may be a potential way for SCI treatment. Our studies showed the hucMSC derived exosomes with a mean particle size of 70 nm could effectively trigger the bone marrow derived macrophage (BMDM) polarization from M1 to a M2 phenotype. In vivo studies demonstrated that the hucMSC derived exosomes could improve the functional recovery after SCI through down-regulation of the inflammatory cytokines, such as TNF-α, MIP-1α, IL-6 and IFN-γ. Collectively, our findings indicated that hucMSC derived exosomes could facilitate spinal cord injury healing via attenuating the inflammation of the injury region. Our results provided a new perspective and therapeutic strategy for the use of hucMSC derived exosomes in soft tissue repair.

Local inhibition of matrix metalloproteinases reduced M2 macrophage activity and impeded recovery in spinal cord transected rats after treatment with fibroblast growth factor-1 and nerve grafts

Alternatively activated macrophages (M2 macrophages) promote central nervous system regeneration. Our previous study demonstrated that treatment with peripheral nerve grafts and fibroblast growth factor-1 recruited more M2 macrophages and improved partial functional recovery in spinal cord transected rats. The migration of macrophages is matrix metalloproteinase (MMP) dependent. We used a general inhibitor of MMPs to influence macrophage migration, and we examined the migration of macrophage populations and changes in spinal function. Rat spinal cords were completely transected at T₈, and 5 mm of spinal cord was removed (group T). In group R, spinal cord-transected rats received treatment with fibroblast growth factor-1 and peripheral nerve grafts. In group RG, rats received the same treatment as group R with the addition of 200 μM GM6001 (an MMP inhibitor) to the fibrin mix. We found that MMP-9, but not MMP-2, was upregulated in the graft area of rats in group R. Local application of the MMP inhibitor resulted in a reduction in the ratio of arginase-1 (M2 macrophage subset)/inducible nitric oxide synthase-postive cells. When the MMP inhibitor was applied at 8 weeks postoperation, the partial functional recovery observed in group R was lost. This effect was accompanied by a decrease in brain-derived neurotrophic factor levels in the nerve graft. These results suggested that the arginase-1 positive population in spinal cord transected rats is a migratory cell population rather than the phenotypic conversion of early iNOS⁺ cells and that the migration of the arginase-1⁺ population could be regulated locally. Simultaneous application of MMP inhibitors or promotion of MMP activity for spinal cord injury needs to be considered if the coadministered treatment involves M2 recruitment.

The Principle of the Micro-Electronic Neural Bridge and a Prototype System Design

The micro-electronic neural bridge (MENB) aims to rebuild lost motor function of paralyzed humans by routing movement-related signals from the brain, around the damage part in the spinal cord, to the external effectors. This study focused on the prototype system design of the MENB, including the principle of the MENB, the neural signal detecting circuit and the functional electrical stimulation (FES) circuit design, and the spike detecting and sorting algorithm. In this study, we developed a novel improved amplitude threshold spike detecting method based on variable forward difference threshold for both training and bridging phase. The discrete wavelet transform (DWT), a new level feature coefficient selection method based on Lilliefors test, and the k-means clustering method based on Mahalanobis distance were used for spike sorting. A real-time online spike detecting and sorting algorithm based on DWT and Euclidean distance was also implemented for the bridging phase. Tested by the data sets available at Caltech, in the training phase, the average sensitivity, specificity, and clustering accuracies are 99.43%, 97.83%, and 95.45%, respectively. Validated by the three-fold cross-validation method, the average sensitivity, specificity, and classification accuracy are 99.43%, 97.70%, and 96.46%, respectively.

Expression of suppressor of cytokine signaling-3 (SOCS3) and its role in neuronal death after complete spinal cord injury

The present study investigates the endogenous expression of Suppressor of Cytokine Signaling-3 (SOCS3) after spinal cord injury (SCI) and its effect on SCI-induced cell death in vivo. In addition, we determined whether a reduction of SOCS3 expression induced by microinjection of short hairpin RNA (shSOCS3) carried by lentivirus into spinal cord provides cellular protection after SCI. We demonstrated that complete transection of rat T8 spinal cord induced SOCS3 expression at the mRNA and protein levels as early as 2days post-injury, which was maintained up to 14days. SOCS3 immunoreactivity was detected in neurons and activated microglia after SCI. We also demonstrated that SCI induces phosphorylation of proteins that are involved in signal transduction and transcription-3 (STAT3) in neurons, which induced SOCS3 expression. Western blot analyses and double-immunofluorescent staining showed significant up-regulation of the pro-apoptotic protein Bax, increases in the ratio of Bax to the anti-apoptotic protein Bcl-2, and up-regulation of cleaved caspase-3 in neurons. Treatment with shSOCS3 inhibited SCI-induced mRNA expression of SOCS3 2days post-injury and suppressed SCI-induced Bax expression 7days after SCI, both rostral and caudal to the lesion. Moreover, treatment with shSOCS3 inhibited SCI-induced neuronal death and protected neuronal morphology both rostral and caudal to the injury site 7days post-injury. Our results suggest that the STAT3/SOCS3 signaling pathway plays an important role in regulating neuronal death after SCI.

Recovery after brain injury: mechanisms and principles

The past 20 years have represented an important period in the development of principles underlying neuroplasticity, especially as they apply to recovery from neurological injury. It is now generally accepted that acquired brain injuries, such as occur in stroke or trauma, initiate a cascade of regenerative events that last for at least several weeks, if not months. Many investigators have pointed out striking parallels between post-injury plasticity and the molecular and cellular events that take place during normal brain development. As evidence for the principles and mechanisms underlying post-injury neuroplasticity has been gleaned from both animal models and human populations, novel approaches to therapeutic intervention have been proposed. One important theme has persisted as the sophistication of clinicians and scientists in their knowledge of neuroplasticity mechanisms has grown: behavioral experience is the most potent modulator of brain plasticity. While there is substantial evidence for this principle in normal, healthy brains, the injured brain is particularly malleable. Based on the quantity and quality of motor experience, the brain can be reshaped after injury in either adaptive or maladaptive ways. This paper reviews selected studies that have demonstrated the neurophysiological and neuroanatomical changes that are triggered by motor experience, by injury, and the interaction of these processes. In addition, recent studies using new and elegant techniques are providing novel perspectives on the events that take place in the injured brain, providing a real-time window into post-injury plasticity. These new approaches are likely to accelerate the pace of basic research, and provide a wealth of opportunities to translate basic principles into therapeutic methodologies.

Effects of bone marrow stromal cell transplantation through CSF on the subacute and chronic spinal cord injury in rats

It has been demonstrated that the infusion of bone marrow stromal cells (BMSCs) through the cerebrospinal fluid (CSF) has beneficial effects on acute spinal cord injury (SCI) in rats. The present study examined whether BMSC infusion into the CSF is effective for subacute (1- and 2-week post-injury), and/or chronic (4-week post-injury) SCI in rats. The spinal cord was contused by dropping a weight at the thoracic 8-9 levels. BMSCs cultured from GFP-transgenic rats of the same strain were injected three times (once weekly) into the CSF through the fourth ventricle, beginning at 1, 2 and 4 weeks post-injury. At 4 weeks after initial injection, the average BBB score for locomotor assessment increased from 1.0–3.5 points before injection to 9.0-10.9 points in the BMSC-injection subgroups, while, in the PBS (vehicle)-injection subgroups, it increased only from 0.5–4.0 points before injection to 3.0-5.1 points. Numerous axons associated with Schwann cells extended longitudinally through the connective tissue matrices in the astrocyte-devoid lesion without being blocked at either the rostral or the caudal borders in the BMSC-injection subgroups. A small number of BMSCs were found to survive within the spinal cord lesion in SCI of the 1-week post-injury at 2 days of injection, but none at 7 days. No BMSCs were found in the spinal cord lesion at 2 days or at 7 days in the SCI of the 2-week and the 4-week post-injury groups. In an in vitro experiment, BMSC-injected CSF promoted the survival and the neurite extension of cultured neurons more effectively than did the PBS-injected CSF. These results indicate that BMSCs had beneficial effects on locomotor improvement as well as on axonal regeneration in both subacute and chronic SCI rats, and the results also suggest that BMSCs might function as neurotrophic sources via the CSF.

Contrasting neuropathology and functional recovery after spinal cord injury in developing and adult rats

Conflicting findings exist regarding the link between functional recovery and the regrowth of spinal tracts across the lesion leading to the restoration of functional contacts. In the present study, we investigated whether functional locomotor recovery was attributable to anatomical regeneration at postnatal day 1 (PN1), PN7, PN14 and in adult rats two months after transection injury at the tenth thoracic segment of the spinal cord. The Basso, Beattie, and Bresnahan scores showed that transection led to a failure of hindlimb locomotor function in PN14 and adult rats. However, PN1 and PN7 rats showed a significant level of stepping function after complete spinal cord transection. Unexpectedly, unlike the transected PN14 and adult rats in which the spinal cord underwent limited secondary degeneration and showed a scar at the lesion site, the rats transected at PN1 and PN7 showed massive secondary degeneration both anterograde and retrograde, leaving a >5-mm gap between the two stumps. Furthermore, retrograde tracing with fluorogold (FG) also showed that FG did not cross the transection site in PN1 and PN7 rats as in PN14 and adult rats, and re-transection of the cord caused no apparent loss in locomotor performance in the rats transected at PN1. Thus, these three lines of evidence strongly indicated that the functional recovery after transection in neonatal rats is independent of regrowth of spinal tracts across the lesion site. Our results support the notion that the recovery of locomotor function in developing rats may be due to intrinsic adaptations in the spinal circuitry below the lesion that control hindlimb locomotor activity rather than the regrowth of spinal tracts across the lesion. The difference in secondary degeneration between neonatal and adult rats remains to be explored.

Axon regeneration and exercise-dependent plasticity after spinal cord injury

Current dogma states that meaningful recovery of function after spinal cord injury (SCI) will likely require a combination of therapeutic interventions comprised of regenerative/neuroprotective transplants, addition of neurotrophic factors, elimination of inhibitory molecules, functional sensorimotor training, and/or stimulation of paralyzed muscles or spinal circuits. We routinely use (1) peripheral nerve grafts to support and direct axonal regeneration across an incomplete cervical or complete thoracic transection injury, (2) matrix modulation with chondroitinase (ChABC) to facilitate axonal extension beyond the distal graft-spinal cord interface, and (3) exercise, such as forced wheel walking, bicycling, or step training on a treadmill. We and others have demonstrated an increase in spinal cord levels of endogenous neurotrophic factors with exercise, which may be useful in facilitating elongation and/or synaptic activity of regenerating axons and plasticity of spinal neurons below the level of injury.

Bench to bedside of neural stem cell in traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of major disability and death worldwide. Neural stem cells (NSCs) have recently been shown to contribute to the cellular remodelling that occurs following TBI and attention has been drawn to the area of neural stem cell as possible therapy for TBI. The NSCs may play an important role in the treatment of TBI by replacing the damaged cells and eventual remyelination. This paper summarized a critical assessment of recent data and developed a view comprising of six points to possible quality translation of NSCs in TBI.

The effect of minocycline on the masticatory movements following the inferior alveolar nerve transection in freely moving rats

Background

To determine the effects of inferior alveolar nerve transection (IAN-X) on masticatory movements in freely moving rats and to test if microglial cells in the trigeminal principal sensory nucleus (prV) or motor nucleus (motV) may be involved in modulation of mastication, the effects of microglial cell inhibitor minocycline (MC) on masticatory jaw movements, microglia (Iba1) immunohistochemistry and the masticatory jaw movements and related masticatory muscle EMG activities were studied in IAN-X rats.

Results

The number of Iba1-immunoreactive (IR) cells both in prV and motV was significantly larger in IAN-X rats compared with sham rats on day 3 after IAN-X. The intraperitoneal (i.p.) administration of MC caused a significant reduction of the number of Iba1-IR cells both in prV and motV that was evident on day 14 after IAN-X. Furthermore, a significant reduction of the number of Iba1-IR cells could be observed in motV but not in prV after microinjection (m.i.) of MC into the motV of IAN-X rats. The rats also exhibited a significant decrease in the head-withdrawal threshold on the side ipsilateral to the IAN-X compared to the threshold before IAN-X and it lasted to day 14. In addition, IAN-X markedly affected the ability to rat to carry out mastication. The number of complete masticatory sequences was significantly decreased. Furthermore, the total masticatory sequence time and food preparatory (PP) period duration was significantly elongated in compared to sham rats. Although IAN-X significantly affected the total number of chewing cycles within the RC period of a masticatory sequence, it had no effect on the duration of the chewing cycles. On the other hand, systemic administration of MC (both i.p. and m.i.) in IAN-X rats significantly improved decreased head-withdrawal threshold and the impaired masticatory jaw movements.

Conclusions

The present findings reveal that the strong modulation of masticatory jaw movements occurs following microglial cell activation after IAN-X, and the modulation recovers after inhibition of the microglial cell activation by MC, suggesting that microglial cell activation in the motV as well as in the prV has a pivotal role in modulating mastication following trigeminal nerve injury associated with orofacial neuropathic pain.

Regulation of chondroitin sulphate proteoglycan and reactive gliosis after spinal cord transection: effects of peripheral nerve graft and fibroblast growth factor 1

AIMS

The combined treatment of peripheral nerve (PN) graft and fibroblast growth factor (FGF)-1 for spinal cord injury produces functional recovery, but how it affects injury events is still unknown. This project studied the effect of PN graft and FGF-1 on white matter degeneration following spinal cord injury.

METHODS

Rats were divided into four groups: (i) complete spinal cord transection and T8 segment removed; the remaining three groups underwent transection followed by (ii) PN grafting; (iii) supply of exogenous FGF-1; and (iv) PN grafting plus FGF-1 treatment. Chondroitin sulphate proteoglycan (CSPG) deposition, astrocytes and macrophage activation, cavity size, and calcitonin gene-related peptide and synaptophysin immunoreactivity were compared.

RESULTS

Peripheral nerve grafting increased CSPG levels compared to transection surgery alone. This CSPG was associated with the proximity to the PN graft. FGF-1 reduced CSPG deposition in grafted animals regardless of the proximity to the graft. The CSPG reduction was accompanied by reduced GFAP expression and macrophage activation. The amount of CSPG with dissociated glycosaminoglycan did not differ between groups. FGF-1 in Schwann cell-astrocyte coculture did not reduce CSPG deposition. Furthermore, the PN graft increased the calcitonin gene-related peptide immunoreactivity and altered the distribution of synaptophysin-positive axons.

CONCLUSION

Peripheral nerve graft supported sensory re-innervation and partial protection of the grey matter, but up-regulated CSPG in the graft-stump junction compared to non-grafted rats. The reduction of CSPG was caused by FGF-1-PN synergy, and did not involve dissociation of CSPG or the suppression of a general immune response.

Frontiers of spinal cord and spine repair: experimental approaches for repair of spinal cord injury

Regeneration of injured CNS neurons was once thought to be an unachievable goal. Most patients with significant damage to the spinal cord suffer from permanently impaired neurological function. A century of research, however, has led to an understanding of multiple factors that limit CNS regeneration and from this knowledge experimental strategies have emerged for enhancing CNS repair. Some of these approaches have undergone human translation. Nevertheless, translating experimental findings to human trials has been more challenging than anticipated. In this chapter, we will review the current state of knowledge regarding central axonal growth failure after injury, and approaches taken to enhance recovery after SCI.

Adeno-associated virus-mediated human acidic fibroblast growth factor expression promotes functional recovery of spinal cord-contused rats

BACKGROUND

Following spinal cord injury, the delivery of neurotrophic factors to the injured spinal cord has been shown to promote axonal regeneration and functional recovery. In previous studies, we showed that acidic fibroblast growth factor (aFGF) is a potent neurotrophic factor that promotes the regeneration of axotomized spinal cord or dorsal root ganglion neurones.

METHODS

We constructed a recombinant adeno-associated virus (AAV) vector to express human aFGF and evaluated aFGF expression and function in AAV-aFGF-infected PC12 cells. We analyzed AAV-green fluorescent protein (GFP) tropism and AAV-mediated aFGF expression in contused spinal cords. Animals received behavioural testing to evaluate the functional recovery.

RESULTS

Overexpression of aFGF was shown in AAV-aFGF-infected PC12 cells in a dose-dependent manner. Concurrently, neurite extension and cell number were significantly increased in AAV-aFGF infected cells. AAV-mediated GFP expression persisted for at least 5 weeks in contused spinal cords, and the most prominently transduced cells were neurones. Contusive injury reduced endogenous aFGF expression in spinal cords. Overexpression of aFGF was demonstrated in AAV-aFGF transduced spinal cords compared to AAV-GFP transduced spinal cords at 3 and 14 days post-injury. Evaluation of motor function revealed that the improvement of AAV-aFGF-treated rats was prominent. Both AAV-aFGF- and recombinant human aFGF-treated rats revealed significantly better recovery at 5 weeks post-injury, compared to vehicle- and AAV-GFP-treated rats.

CONCLUSIONS

These data suggest that supplement of aFGF improve the functional recovery of spinal cord-contused rats and that AAV-aFGF-mediated gene transfer could be a clinically feasible therapeutic approach for patients after nervous system injuries.

Acid fibroblast growth factor and peripheral nerve grafts regulate Th2 cytokine expression, macrophage activation, polyamine synthesis, and neurotrophin expression in transected rat spinal cords

Spinal cord injury elicits an inflammatory response that recruits macrophages to the injured spinal cord. Quantitative real-time PCR results have shown that a repair strategy combining peripheral nerve grafts with acidic fibroblast growth factor (aFGF) induced higher interleukin-4 (IL-4), IL-10, and IL-13 levels in the graft areas of rat spinal cords compared with transected spinal cords at 10 and 14 d. This led to higher arginase I-positive alternatively activated macrophage (M2 macrophage) responses. The gene expression of several enzymes involved in polyamine biosynthesis pathways was also upregulated in the graft areas of repaired spinal cords. The treatment induced a twofold upregulation of polyamine levels at 14 d, as confirmed by HPLC. Polyamines are important for the repair process, as demonstrated by the observation that treatment with inhibitors of arginase I and ornithine decarboxylase attenuates the functional recoveries of repaired rats. After 14 d, the treatment also induced the expression of neurotrophin nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), as well as M2 macrophages within grafted nerves expressing BDNF. IL-4 was upregulated in the injury sites of transected rats that received aFGF alone compared with those that received nerve grafts alone at 10 d. Conversely, nerve graft treatment induced NGF and BDNF expression at 14 d. Macrophages expressing polyamines and BDNF may benefit axonal regeneration at 14 d. These results indicate that aFGF and nerve grafts regulate different macrophage responses, and M2 macrophages may play an important role in axonal regeneration after spinal cord injury in rats.

Cellular and paracellular transplants for spinal cord injury: a review of the literature

BACKGROUND

Experimental approaches to limit the spinal cord injury and to promote neurite outgrowth and improved function from a spinal cord injury have exploded in recent decades. Due to the cavitation resulting after a spinal cord injury, newer important treatment strategies have consisted of implanting scaffolds with or without cellular transplants. There are various scaffolds, as well as various different cellular transplants including stem cells at different levels of differentiation, Schwann cells and peripheral nerve implants, that have been reviewed. Also, attention has been given to different re-implantation techniques in avulsion injuries.

METHODS

Using standard search engines, this literature is reviewed.

CONCLUSION

Cellular and paracellular transplantation for application to spinal cord injury offers promising results for those patients with spinal cord pathology.

Effect of repeatedly given CDP-choline on cardiovascular and tissue injury in spinal shock conditions: investigation of the acute phase

OBJECTIVES

The protective effect of CDP-choline in spinal cord transection and the mediation of its cardiovascular effects were investigated.

METHODS

Spinal cords of rats were transected at the T1-T2 levels. CDP-choline (250 mg/kg; intravenous) was administered 2 h and/or 24 h after the injury.

KEY FINDINGS

Spinal cord transection caused severe tissue damage, decreased mean arterial pressure, heart rate, plasma adrenaline, and noradrenaline but increased plasma vasopressin levels. Repeated CDP-choline treatment attenuated the degree of tissue injury. Administration of CDP-choline at 2 h after transection transiently increased blood pressure and decreased heart rate, while it produced a small decrease in blood pressure and heart rate when it was given at 24 h. Plasma adrenaline levels were higher in the group where CDP-choline was given repeatedly. Plasma noradrenaline and vasopressin levels did not change additionally after CDP-choline injections in all groups. In order to determine if CDP-choline attenuates the oxidative injury induced by transection, we measured blood superoxide dismutase, glutathione peroxidase activity and malondialdehyde levels. Repeated CDP-choline administration decreased blood superoxide dismutase and glutathione peroxidase activity without any effect on malondialdehyde levels.

CONCLUSIONS

Data indicate that repeated intravenous CDP-choline treatment prevents tissue damage in spinal shock conditions in the acute phase. The cardiovascular effects of the drug do not seem to be responsible for this protection but the drug-induced attenuation of the oxidative stress may play a role.

Potassium channels as a potential therapeutic target for trigeminal neuropathic and inflammatory pain

Previous studies in several different trigeminal nerve injury/inflammation models indicated that the hyperexcitability of primary afferent neurons contributes to the pain pathway underlying mechanical allodynia. Although multiple types of voltage-gated ion channels are associated with neuronal hyperexcitability, voltage-gated K⁺ channels (Kv) are one of the important physiological regulators of membrane potentials in excitable tissues, including nociceptive sensory neurons. Since the opening of K⁺ channels leads to hyperpolarization of cell membrane and a consequent decrease in cell excitability, several Kv channels have been proposed as potential target candidates for pain therapy. In this review, we focus on common changes measured in the Kv channels of several different trigeminal neuropathic/inflammatory pain animal models, particularly the relationship between changes in Kv channels and the excitability of trigeminal ganglion (TRG) neurons. We also discuss the potential of Kv channel openers as therapeutic agents for trigeminal neuropathic/inflammatory pain, such as mechanical allodynia.

Improvement of gait patterns in step-trained, complete spinal cord-transected rats treated with a peripheral nerve graft and acidic fibroblast growth factor

The effects of peripheral nerve grafts (PNG) and acidic fibroblast growth factor (alpha FGF) combined with step training on the locomotor performance of complete spinal cord-transected (ST, T8) adult rats were studied. Rats were assigned randomly to five groups (N=10 per group): sham control (laminectomy only), ST only, ST-step-trained, repaired (ST with PNG and alpha FGF treatment), or repaired-step-trained. Step-trained rats were stepped bipedally on a treadmill 20 min/day, 5 days/week for 6 months. Bipolar intramuscular EMG electrodes were implanted in the soleus and tibialis anterior (TA) muscles of ST-step-trained (n=3) and repaired-step-trained (n=2) rats. Gait analysis was conducted at 3 and 6 months after surgery. Stepping analysis was completed on the best continuous 10-s period of stepping performed in a 2-min trial. Significantly better stepping (number of steps, stance duration, swing duration, maximum step length, and maximum step height) was observed in the repaired and repaired-step-trained than in the ST and ST-step-trained rats. Mean EMG amplitudes in both the soleus and TA were significantly higher and the patterns of activation of flexors and extensors more reciprocal in the repaired-step-trained than ST-step-trained rats. 5-HT fibers were present in the lumbar area of repaired but not ST rats. Thus, PNG plus alpha FGF treatment resulted in a clear improvement in locomotor performance with or without step training. Furthermore, the number of 5-HT fibers observed below the lesion was related directly to stepping performance. These observations indicate that the improved stepping performance in Repaired rats may be due to newly formed supraspinal control via regeneration.

Functional recovery of stepping in rats after a complete neonatal spinal cord transection is not due to regrowth across the lesion site

Rats receiving a complete spinal cord transection (ST) at a neonatal stage spontaneously can recover significant stepping ability, whereas minimal recovery is attained in rats transected as adults. In addition, neonatally spinal cord transected rats trained to step more readily improve their locomotor ability. We hypothesized that recovery of stepping in rats receiving a complete spinal cord transection at postnatal day 5 (P5) is attributable to changes in the lumbosacral neural circuitry and not to regeneration of axons across the lesion. As expected, stepping performance measured by several kinematics parameters was significantly better in ST (at P5) trained (treadmill stepping for 8 weeks) than age-matched non-trained spinal rats. Anterograde tracing with biotinylated dextran amine showed an absence of labeling of corticospinal or rubrospinal tract axons below the transection. Retrograde tracing with Fast Blue from the spinal cord below the transection showed no labeled neurons in the somatosensory motor cortex of the hindlimb area, red nucleus, spinal vestibular nucleus, and medullary reticular nucleus. Retrograde labeling transsynaptically via injection of pseudorabies virus (Bartha) into the soleus and tibialis anterior muscles showed no labeling in the same brain nuclei. Furthermore, re-transection of the spinal cord at or rostral to the original transection did not affect stepping ability. Combined, these results clearly indicate that there was no regeneration across the lesion after a complete spinal cord transection in neonatal rats and suggest that this is an important model to understand the higher level of locomotor recovery in rats attributable to lumbosacral mechanisms after receiving a complete ST at a neonatal compared to an adult stage.

Alteration of primary afferent activity following inferior alveolar nerve transection in rats

Background

In order to evaluate the neural mechanisms underlying the abnormal facial pain that may develop following regeneration of the injured inferior alveolar nerve (IAN), the properties of the IAN innervated in the mental region were analyzed.

Results

Fluorogold (FG) injection into the mental region 14 days after IAN transection showed massive labeling of trigeminal ganglion (TG). The escape threshold to mechanical stimulation of the mental skin was significantly lower (i.e. mechanical allodynia) at 11-14 days after IAN transection than before surgery. The background activity, mechanically evoked responses and afterdischarges of IAN Aδ-fibers were significantly higher in IAN-transected rats than naive. The small/medium diameter TG neurons showed an increase in both tetrodotoxin (TTX)-resistant (TTX-R) and -sensitive (TTX-S) sodium currents (I_Na) and decrease in total potassium current, transient current (I_A) and sustained current (I_K) in IAN-transected rats. The amplitude, overshoot amplitude and number of action potentials evoked by the depolarizing pulses after 1 μM TTX administration in TG neurons were significantly higher, whereas the threshold current to elicit spikes was smaller in IAN-transected rats than naive. Resting membrane potential was significantly smaller in IAN-transected rats than that of naive.

Conclusions

These data suggest that the increase in both TTX-S I_Na and TTX-R I_Na and the decrease in I_A and I_k in small/medium TG neurons in IAN-transected rats are involved in the activation of spike generation, resulting in hyperexcitability of Aδ-IAN fibers innervating the mental region after IAN transection.

A neural repair treatment with gait training improves motor function recovery after spinal cord injury

Aimed to develop an effective approach for treating spinal cord injury (SCI), we investigated the effectiveness of a treatment strategy that combined peripheral nerve grafting, nerve growth factors and functional task based physical therapy on non-human primate models. SCI was by unilateral surgical hemi-section at the T8 spine level (approximately 4 mm gap). Two of the 4 subjects as treatment received the transplants of sural nerve segments as well as infused acidic fibroblast growth factor (aFGF) to the injured spinal cord. All four subjects received physical therapy and bipedal walking training on a treadmill to promote motor function recovery. A comprehensive evaluation system including general observation in the home cage, behavioral test and clinic score system was used to assess the effect of the treatment. The recovery of functional mobility in treated group is much faster than the control group. The treated group started to move around in their cages within a week and continued to improve in walking performance as measured by gait symmetry, while the control group developed spasticity and rigidity with a much slower and less functional recovery of mobility. All these results suggest that the treatment strategy of peripheral nerve grafting with aFGF combined with physical therapy is effective to treat SCI.

A novel strategy for repairing preganglionic cervical root avulsion in brachial plexus injury by sural nerve grafting

OBJECT

In this study, the authors evaluated the efficacy of a new surgical strategy for reconnecting the injured brachial plexus with the spinal cord using fibrin glue containing acidic fibroblast growth factor as an adhesive and neurotrophic agent.

METHODS

Eighteen patients with preganglionic brachial plexus injuries, each with varying degrees of upper limb dysfunction, underwent cervical laminectomy with or without sural nerve grafting. The treatment of each avulsed root varied according to the severity of the injury. Some patients also underwent a second-stage operation involving supraclavicular brachial plexus exploration for reconnection with the corresponding segment of cervical spinal cord at the trunk level. Muscle strength was graded both pre- and postoperatively with the British Medical Research Council scale, and the results were analyzed with the Friedman and Wilcoxon signed-rank tests.

RESULTS

Muscle strength improvements were observed in 16 of the 18 patients after 24 months of follow-up. Significant improvements in mean muscle strength were observed in patients from all repair method groups at 12 and 24 months postoperatively (p < 0.05). Statistical significance was not reached in the groups with insufficient numbers of cases.

CONCLUSIONS

The authors' new surgical strategy yielded clinical improvement in muscle strength after preganglionic brachial plexus injury, such that nerve regeneration may have taken place. Reconnection of the brachial plexus to the cervical spinal cord is possible. Functional motor recovery, observed through increases in Medical Research Council-rated muscle strength in the affected arm, is likewise possible.

Delayed implantation of intramedullary chitosan channels containing nerve grafts promotes extensive axonal regeneration after spinal cord injury

OBJECTIVE

We describe a new strategy to promote axonal regeneration after subacute or chronic spinal cord injury consisting of intramedullary implantation of chitosan guidance channels containing peripheral nerve (PN) grafts.

METHODS

Chitosan channels filled with PN grafts harvested from green fluorescent protein rats were implanted in the cavity 1 week (subacute) or 4 weeks (chronic) after 50-g clip injury at T8 and were compared with similarly injured animals implanted with either unfilled channels or no channels. Functional recovery was measured weekly for 12 weeks by open-field locomotion, after which histological examination was performed.

RESULTS

The implanted channels with PN grafts contained a thick tissue bridge containing as many as 35,000 myelinated axons in both the subacute and chronic spinal cord injury groups, with the greatest number of axons in the channels containing PN grafts implanted subacutely. There were numerous green fluorescent protein-positive donor Schwann cells in the tissue bridges in all animals with PN grafts. Moreover, these Schwann cells had high functional capacity in terms of myelination of the axons in the channels. In addition, PN-filled chitosan channels showed excellent biocompatibility with the adjacent neural tissue and no obvious signs of degradation and minimal tissue reaction at 14 weeks after implantation. In control animals that had unfilled chitosan channels implanted, there was minimal axonal regeneration in the channels; in control animals without channels, there were large cavities in the spinal cords, and the bridges contained only a small number of axons and Schwann cells. Despite the large numbers of axons in the chitosan channel-PN graft group, there was no significant difference in functional recovery between treatment and control groups.

CONCLUSION

Intramedullary implantation of chitosan guidance channels containing PN grafts in the cavity after subacute spinal cord injury resulted in a thicker bridge containing a larger number of myelinated axons compared with chitosan channels alone. A chitosan channel containing PN grafts is a promising strategy for spinal cord repair.

Nerve repair using acidic fibroblast growth factor in human cervical spinal cord injury: a preliminary Phase I clinical study

Object

The aim of this study was to assess functional outcomes of nerve repair using acidic fibroblast growth factor (FGF) in patients with cervical spinal cord injury (SCI).

Methods

Nine patients who had cervical SCI for longer than 5 months were included in pre- and postoperative assessments of their neurological function. The assessments included evaluating activities of daily living, associated functional ability, and degree of spasticity, motor power, sensation, and pain perception. After the first set of assessments, the authors repaired the injured segment of the spinal cord using a total laminectomy followed by the application of fibrin glue containing acidic FGF. Clinical evaluations were conducted 1, 2, 3, 4, 5, and 6 months after the surgery. Preoperative versus postoperative differences in injury severity and grading of key muscle power and sensory points were calculated using the Wilcoxon signed-rank test.

Results

The preoperative degree of injury severity, as measured using the American Spinal Injury Association (ASIA) scoring system, showed that preoperative motor (52.4 ± 25.9 vs 68.6 ± 21.5), pinprick (61.0 ± 34.9 vs 71.6 ± 31.0), and light touch scores (57.3 ± 33.9 vs 71.9 ± 30.2) were significantly lower than the respective postoperative scores measured 6 months after surgery (p = 0.005, 0.012, and 0.008, respectively).

Conclusions

Based on the significant difference in ASIA motor and sensory scale scores between the preoperative status and the 6-month postoperative follow-up, this novel nerve repair strategy of using acidic FGF may have a role in the repair of human cervical SCI. Modest nerve regeneration occurred in all 9 patients after this procedure without any observed adverse effects. This repair strategy thus deserves further investigation, clinical consideration, and refinement.

Combined treatment using peripheral nerve graft and FGF-1: changes to the glial environment and differential macrophage reaction in a complete transected spinal cord

We used a complete spinal cord transection model in which the T8 spinal segment was removed to study the effect of combined treatment of peripheral nerve graft and application of FGF-1 on the glial environment. The combined treatment resulted in reduced astrocytic glial scarring, reactive macrophage gliosis, and inhibitory proteoglycan in the back-degenerated white matter tract. While the macrophage activities in the back-degenerative tract were down-regulated, those in the grafted peripheral nerves and in the distal Wallerian degenerative tracts were not. We concluded that the combined treatment changed the glial environment in the back-degenerative tract, and differentially regulated the macrophage activities in the system, in favor of CNS regeneration.

Repair of spinal cord transection and its effects on muscle mass and myosin heavy chain isoform phenotype

A number of significant advances have been developed for treating spinal cord injury during the past two decades. The combination of peripheral nerve grafts and acidic fibroblast growth factor (hereafter referred to as PNG) has been shown to partially restore hindlimb function. However, very little is known about the effects of such treatments in restoring normal muscle phenotype. The primary goal of the current study was to test the hypothesis that PNG would completely or partially restore 1) muscle mass and muscle fiber cross-sectional area and 2) the slow myosin heavy chain phenotype of the soleus muscle. To test this hypothesis, we assigned female Sprague-Dawley rats to three groups: 1) sham control, 2) spinal cord transection (Tx), and 3) spinal cord transection plus PNG (Tx+PNG). Six months following spinal cord transection, the open-field test was performed to assess locomotor function, and then the soleus muscles were harvested and analyzed. SDS-PAGE for single muscle fiber was used to evaluate the myosin heavy chain (MHC) isoform expression pattern following the injury and treatment. Immunohistochemistry was used to identify serotonin (5-HT) fibers in the spinal cord. Compared with the Tx group, the Tx+PNG group showed 1) significantly improved Basso, Beattie, and Bresnahan scores (hindlimb locomotion test), 2) less muscle atrophy, 3) a higher percentage of slow type I fibers, and 4) 5-HT fibers distal to the lesion site. We conclude that the combined treatment of PNG is partially effective in restoring the muscle mass and slow phenotype of the soleus muscle in a T-8 spinal cord-transected rat model.

Transplantation of porous tubes following spinal cord transection improves hindlimb function in the rat

STUDY DESIGN

Experimental.

OBJECTIVE

To determine the effects of a porous tube transplant in spinal cord transected rats.

SETTING

Acadia University, Wolfville, Nova Scotia, Canada.

METHODS

Female rats were randomly assigned to three experimental groups: control (Con, n=8), spinal cord transected (Tx, n=5) and spinal cord transected with transplant (TxTp, n=7). The rats in the TxTp and Tx groups received a complete spinal cord transection at the T10 level and the TxTp group immediately received a porous tube transplant.

RESULTS

Locomotor activity rated on the Basso, Beattie, Bresnahan scale improved significantly in the TxTp animals over the 4 weeks such that final scores were 21, 1.4 and 7.1 for the Con, Tx and TxTp groups, respectively. As expected, the muscle to body mass ratios of the hindlimb skeletal muscles of the Tx group were decreased (soleus 35%, plantaris 29% and gastrocnemius 29%) and this was also observed in the TxTp group (soleus 33%, plantaris 23% and gastrocnemius 30%). Cytochrome c oxidase (CYTOX) activity in the plantaris was decreased by Tx but maintained in the TxTp group (Con=82.2, Tx=44.8 and TxTp=72.8 U/min/g).

CONCLUSION

Four weeks after the spinal cord transection, plantaris CYTOX activity and locomotor function improved with porous tube implantation.

SPONSORSHIP

Natural Sciences and Engineering Research Council.

Plasticity of functional connectivity in the adult spinal cord

This paper emphasizes several characteristics of the neural control of locomotion that provide opportunities for developing strategies to maximize the recovery of postural and locomotor functions after a spinal cord injury (SCI). The major points of this paper are: (i) the circuitry that controls standing and stepping is extremely malleable and reflects a continuously varying combination of neurons that are activated when executing stereotypical movements; (ii) the connectivity between neurons is more accurately perceived as a functional rather than as an anatomical phenomenon; (iii) the functional connectivity that controls standing and stepping reflects the physiological state of a given assembly of synapses, where the probability of these synaptic events is not deterministic; (iv) rather, this probability can be modulated by other factors such as pharmacological agents, epidural stimulation and/or motor training; (v) the variability observed in the kinematics of consecutive steps reflects a fundamental feature of the neural control system and (vi) machine-learning theories elucidate the need to accommodate variability in developing strategies designed to enhance motor performance by motor training using robotic devices after an SCI.

The combination of peripheral nerve grafts and acidic fibroblast growth factor enhances arginase I and polyamine spermine expression in transected rat spinal cords

Treatment with a combination of peripheral nerve grafts and acidic fibroblast growth factor improves hind limb locomotor function after spinal cord transection. This study examined the effect of treatment on expression of arginase I (Arg I) and polyamines. Arg I expression was low in the spinal cords of normal rats but increased following spinal injury. Only fully repaired spinal cords expressed higher Arg I levels 6-14 days following repair. In 10-day repaired spinal cords, high Arg I immunoreactivity was detected in motoneurons and alternatively activated macrophages in the graft area and graft-stump edges, and high levels of the polyamine spermine were expressed by macrophages within the intercostal nerve graft. Thus, in addition to enhancing the expression of Arg I and spermine in repaired spinal cords, our treatment may recruit activated macrophages and create a more favorable environment for axonal regrowth.

Therapeutic interventions after spinal cord injury

Spinal cord injury (SCI) can lead to paraplegia or quadriplegia. Although there are no fully restorative treatments for SCI, various rehabilitative, cellular and molecular therapies have been tested in animal models. Many of these have reached, or are approaching, clinical trials. Here, we review these potential therapies, with an emphasis on the need for reproducible evidence of safety and efficacy. Individual therapies are unlikely to provide a panacea. Rather, we predict that combinations of strategies will lead to improvements in outcome after SCI. Basic scientific research should provide a rational basis for tailoring specific combinations of clinical therapies to different types of SCI.

Complete Spinal Cord Transection Treatedby Implantation of a Reinforced Synthetic Hydrogel Channel Results in Syringomyelia and Caudal Migration of the Rostral Stump

OBJECTIVE

Previously, we reported that synthetic poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (PHEMA-MMA) channels promoted regeneration of a small number of axons from brainstem motor nuclei yet provided limited functional recovery after complete spinal cord transection at T8 in rats. However, we found that these modulus channels partially collapsed over time. Therefore, we synthesized coil-reinforced PHEMA or PHEMA-MMA channels with greater elastic moduli and introduced a new spinal fixation technique to prevent collapse. We also assessed axonal regeneration within the new channels containing a cocktail of autologous peripheral nerve grafts, fibrin matrix, and acidic fibroblast growth factor.

METHODS

After spinal cord transection, rats were divided into six groups: Groups 1 and 2 had either a PHEMA or PHEMA-MMA reinforced channel implanted between the stumps of the transected spinal cord with the cocktail; Groups 3 and 4 had either an unfilled reinforced PHEMA or PHEMA-MMA channel similarly implanted; Group 5 had an spinal cord transection without channel implanted, and Group 6 underwent the identical procedure to Group 1, but rats were sacrificed by 8 weeks for early histological assessment. Groups 1 to 5 were sacrificed at 18 weeks.

RESULTS

There was no channel collapse at any time. However, there was no improvement in axonal regeneration or functional recovery among Groups 1 to 4 because of the unexpected development of syringomyelia and caudal migration of the rostral stump. Functional recovery was better in Groups 1 to 4 compared with Group 5 (P < 0.05).

CONCLUSION

The use of channels to enhance regeneration of axons is promising; however, improvement of the design of the channels is required.

Schwann cell transplantation for repair of the adult spinal cord

The Schwann cell is one of the most widely studied cell types for repair of the spinal cord. These cells play a crucial role in endogenous repair of peripheral nerves due to their ability to dedifferentiate, migrate, proliferate, express growth promoting factors, and myelinate regenerating axons. Following trauma to the spinal cord, Schwann cells migrate from the periphery into the injury site, where they apparently participate in endogenous repair processes. For transplantation into the spinal cord, large numbers of Schwann cells are necessary to fill injury-induced cystic cavities. Several culture systems have been developed that provide large, highly purified populations of Schwann cells. Importantly, the development of in vitro systems to harvest human Schwann cells presents a unique opportunity for autologous transplantation in the clinic. In animal models of spinal cord injury (SCI), grafting Schwann cells or peripheral nerve into the lesion site has been shown to promote axonal regeneration and myelination. However, axons do not regenerate beyond the transplant due to the inhibitory nature of the glial scar surrounding the injury. To overcome the glial scar inhibition, additional approaches such as increasing the intrinsic capacity of axons to regenerate and/or removal of the inhibitory molecules associated with reactive astrocytes and/or oligodendrocyte myelin should be incorporated. Clearly, Schwann cells have great potential for repair of the injured spinal cord, but they need to be combined with other interventions to maximize axonal regeneration and functional recovery.

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

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

Bioengineered Strategies for Spinal Cord Repair

This article reviews bioengineered strategies for spinal cord repair using tissue engineered scaffolds and drug delivery systems. The pathophysiology of spinal cord injury (SCI) is multifactorial and multiphasic, and therefore, it is likely that effective treatments will require combinations of strategies such as neuroprotection to counteract secondary injury, provision of scaffolds to replace lost tissue, and methods to enhance axonal regrowth, synaptic plasticity, and inhibition of astrocytosis. Biomaterials have major advantages for spinal cord repair because of their structural and chemical versatility. To date, various degradable or non-degradable biomaterial polymers have been tested as guidance channels or delivery systems for cellular and non-cellular neuroprotective or neuroregenerative agents in experimental SCI. There is promise that bioengineering technology utilizing cellular treatment strategies, including Schwann cells, olfactory ensheathing glia, or neural stem cells, can promote repair of the injured spinal cord. This review is divided into three parts: (1) degradable and non-degradable biomaterials; (2) device design; and (3) combination strategies with scaffolds. We will show that bioengineering combinations of cellular and non-cellular strategies have enhanced the potential for experimental SCI repair, although further pre-clinical work is required before this technology can be translated to humans.

Long-Term Care of Paraplegic Laboratory Mammals

Repair of spinal cord injuries (SCIs) is still a major clinical challenge. Several attempts have been made to find a cure for this condition in experimental animals that could be extrapolated to humans. A key for success seems the availability of optimum animal models for testing different therapies. Complete spinal cord lesion in mammals is considered the most accurate injury model. In addition, long-term survival of animals seems more appropriate, as this increases the efficacy of the repair strategies. However, paraplegic animals require special care and treatment for proper longterm maintenance, and to date, there are no published protocols. This lack of available information has discouraged scientists from working with this injury model. Over the past 7 years, we have tested the repair efficacy of olfactory ensheathing glia in paraplegic rats for survival periods of more than 8 months. To keep these animals healthy for this long time, we adapted and administered treatments used in people with paraplegia. These same protocols (developed for rodents in our group) are being applied to paraplegic monkeys. In this review, we provide an overview of the proper handling and care of paraplegic adult laboratory mammals for long periods. This information might help other groups to optimize the outcome obtained and to better evaluate the prospect of a given experimental repair strategy. In addition, the use of human treatments in paraplegic animals provides a more realistic model for a later transfer to the clinical arena.

Regeneration of descending axon tracts after spinal cord injury

Axons within the adult mammalian central nervous system do not regenerate spontaneously after injury. Upon injury, the balance between growth promoting and growth inhibitory factors in the central nervous system dramatically changes resulting in the absence of regeneration. Axonal responses to injury vary considerably. In central nervous system regeneration studies, the spinal cord has received a lot of attention because of its relatively easy accessibility and its clinical relevance. The present review discusses the axon-tract-specific requirements for regeneration in the rat. This knowledge is very important for the development and optimalization of therapies to repair the injured spinal cord.

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.

Corticospinal regeneration into lumbar grey matter correlates with locomotor recovery after complete spinal cord transection and repair with peripheral nerve grafts, fibroblast growth factor 1, fibrin glue, and spinal fusion

Knowledge of which tracts are essential for the recovery of locomotor function in rats after repair is unknown. To assess the mechanism of recovery, we examined the correlation between functional recovery and axonal regeneration. All rats underwent complete cord transection and repair with peripheral nerves, fibroblast growth factor 1, fibrin glue, and spinal fixation. Repaired rats recovered both motor-evoked potentials recorded at the lumbar level and locomotor function. Cord retransection rostral to the repair abolished the recovery, indicating improvement was due to long tract regeneration. To determine which long tracts correlated with recovery, a novel technique of simultaneous bidirectional axonal tracing and immunohistochemical examination of axonal type was used to quantitate the regeneration of corticospinal, rubrospinal, reticulospinal, vestibulospinal, raphespinal, propriospinal, serotonergic, and calcitonin gene-related peptide containing axons. Multiple linear regression analysis revealed recovery of function correlated only with regeneration of corticospinal axons into the gray matter of the lumbar spinal cord (R = 0.977, p < 0.02). For the first time, we show that regeneration of the corticospinal tract into the lumbar gray matter is a mechanism of functional locomotor recovery after complete cord transection and repair.