Co-treatment with riluzole and GDNF is necessary for functional recovery after ventral root avulsion injury

Restoration of injured motoneurons reduces microglial proliferation in the adult rat facial nucleus

In the axotomized facial nucleus (axotFN), the levels of choline acetyltransferase, vesicular acetylcholine transporter, and gamma amino butyric acid A receptor α1 are decreased, after which the microglia begin to proliferate around injured motoneuron cell bodies. We conjectured that an injury signal released from the injured motoneurons triggers the microglial proliferation in the axotFN. However, it is unclear whether the level of microglial proliferation is dependent on the degree of motoneuronal insult. In this study, we investigated the relationship between the extents of motoneuronal injury and microglial proliferation in a rat axotFN model. Administration of glial cell line-derived neurotrophic factor, N-acetyl L-cysteine, or salubrinal at the transection site ameliorated the increase in c-Jun and the reductions in levels of phosphorylated cAMP response element binding protein (p-CREB) and functional molecules in the injured motoneurons. Concurrently, the levels of the microglial marker ionized calcium-binding adapter molecule 1 and of macrophage colony-stimulating factor (cFms), proliferating cell nuclear antigen, and p-p38/p38 were significantly downregulated in microglia. These results demonstrate that the recovery of motoneuron function resulted in the reduction in microglial proliferation. We conclude that the degree of neuronal injury regulates the levels of microglial proliferation in the axotFN.

A new anesthetic protocol to medullary nerve roots access in rats

Purpose:

To describe a new anesthetic protocol medullary and nerve roots access and in Rattus norvegicus.

Methods:

Seventy female Wistar rats (n=70) were used. The animals were randomly divided into two laminectomy groups: cervical (n=40) and thoracic (n=30). In cervical group, a right posterior hemilaminectomy was performed to access the nerve roots. In thoracic group, a laminectomy of the eighth thoracic vertebra was accomplished. Thirty-five rats (20 cervical and 15 thoracic) were submitted to old anesthetic protocol (ketamine 70 mg/kg plus xylazine 10 mg/kg); and the 35 other animals (20 cervical and 15 thoracic) were submitted to a new anesthetic protocol (ketamine 60 mg/kg,xylazine 8 mg/kg and fentanyl 0.03 mg/kg).

Results:

The time to complete induction was 4.15 ±1.20 minin ketamine, xylazine and fentanyl group, and it was 4.09 ±1.47 min in the ketamine and xylazine group. There was no correlation in the time required to perform the cervical laminectomy in the old anesthetic protocol. In all groups, the animals submitted to the old anesthetic protocol had a higher level of pain on the first and third postoperative days than the animals submitted to the new anesthetic protocol.

Conclusions:

The new anesthetic protocol reduces the surgical time, allows better maintenance of the anesthetic plan, and brings more satisfactory postoperative recovery.

Long-Term Suppression of c-Jun and nNOS Preserves Ultrastructural Features of Lower Motor Neurons and Forelimb Function after Brachial Plexus Roots Avulsion

Brachial plexus root avulsions cause debilitating upper limb paralysis. Short-term neuroprotective treatments have reported preservation of motor neurons and function in model animals while reports of long-term benefits of such treatments are scarce, especially the morphological sequelae. This morphological study investigated the long-term suppression of c-Jun- and neuronal nitric oxide synthase (nNOS) (neuroprotective treatments for one month) on the motor neuron survival, ultrastructural features of lower motor neurons, and forelimb function at six months after brachial plexus roots avulsion. Neuroprotective treatments reduced oxidative stress and preserved ventral horn motor neurons at the end of the 28-day treatment period relative to vehicle treated ones. Motor neuron sparing was associated with suppression of c-Jun, nNOS, and pro-apoptotic proteins Bim and caspases at this time point. Following 6 months of survival, neutral red staining revealed a significant loss of most of the motor neurons and ventral horn atrophy in the avulsed C6, 7, and 8 cervical segments among the vehicle-treated rats (n = 4). However, rats that received neuroprotective treatments c-Jun JNK inhibitor, SP600125 (n = 4) and a selective inhibitor of nNOS, 7-nitroindazole (n = 4), retained over half of their motor neurons in the ipsilateral avulsed side compared. Myelinated axons in the avulsed ventral horns of vehicle-treated rats were smaller but numerous compared to the intact contralateral ventral horns or neuroprotective-treated groups. In the neuroprotective treatment groups, there was the preservation of myelin thickness around large-caliber axons. Ultrastructural evaluation also confirmed the preservation of organelles including mitochondria and synapses in the two groups that received neuroprotective treatments compared with vehicle controls. Also, forelimb functional evaluation demonstrated that neuroprotective treatments improved functional abilities in the rats. In conclusion, neuroprotective treatments aimed at suppressing degenerative c-Jun and nNOS attenuated apoptosis, provided long-term preservation of motor neurons, their organelles, ventral horn size, and forelimb function.

GDNF Gene Therapy to Repair the Injured Peripheral Nerve

A spinal root avulsion is the most severe proximal peripheral nerve lesion possible. Avulsion of ventral root filaments disconnects spinal motoneurons from their target muscles, resulting in complete paralysis. In patients that undergo brachial plexus nerve repair, axonal regeneration is a slow process. It takes months or even years to bridge the distance from the lesion site to the distal targets located in the forearm. Following ventral root avulsion, without additional pharmacological or surgical treatments, progressive death of motoneurons occurs within 2 weeks (Koliatsos et al., 1994). Reimplantation of the avulsed ventral root or peripheral nerve graft can act as a conduit for regenerating axons and increases motoneuron survival (Chai et al., 2000). However, this beneficial effect is transient. Combined with protracted and poor long-distance axonal regeneration, this results in permanent function loss. To overcome motoneuron death and improve functional recovery, several promising intervention strategies are being developed. Here, we focus on GDNF gene-therapy. We first introduce the experimental ventral root avulsion model and discuss its value as a proxy to study clinical neurotmetic nerve lesions. Second, we discuss our recent studies showing that GDNF gene-therapy is a powerful strategy to promote long-term motoneuron survival and improve function when target muscle reinnervation occurs within a critical post-lesion period. Based upon these observations, we discuss the influence of timing of the intervention, and of the duration, concentration and location of GDNF delivery on functional outcome. Finally, we provide a perspective on future research directions to realize functional recovery using gene therapy.

Exercise promotes recovery after motoneuron injury via hormonal mechanisms

Injuries to spinal motoneurons manifest in a variety of forms, including damage to peripheral axons, neurodegenerative disease, or direct insult centrally. Such injuries produce a variety of negative structural and functional changes in both the directly affected and neighboring motoneurons. Exercise is a relatively simple behavioral intervention that has been demonstrated to protect against, and accelerate recovery from, these negative changes. In this article, we describe how exercise is neuroprotective for motoneurons, accelerating axon regeneration following axotomy and attenuating dendritic atrophy following the death of neighboring motoneurons. In both of these injury models, the positive effects of exercise have been found to be dependent on gonadal hormone action. Here we describe a model in which exercise, hormones, and brain-derived neurotrophic factor might all interact to produce neuroprotective effects on motoneuron structure following neural injury.

Combining timed GDNF and ChABC gene therapy to promote long-distance regeneration following ventral root avulsion and repair

Ventral root avulsion leads to severe motoneuron degeneration and prolonged distal nerve denervation. After a critical period, a state of chronic denervation develops as repair Schwann cells lose their pro-regenerative properties and inhibitory factors such as CSPGs accumulate in the denervated nerve. In rats with ventral root avulsion injuries, we combined timed GDNF gene therapy delivered to the proximal nerve roots with the digestion of inhibitory CSPGs in the distal denervated nerve using sustained lentiviral-mediated chondroitinase ABC (ChABC) enzyme expression. Following reimplantation of lumbar ventral roots, timed GDNF-gene therapy enhanced motoneuron survival up to 45 weeks and improved axonal outgrowth, electrophysiological recovery, and muscle reinnervation. Despite a timed GDNF expression period, a subset of animals displayed axonal coils. Lentiviral delivery of ChABC enabled digestion of inhibitory CSPGs for up to 45 weeks in the chronically denervated nerve. ChABC gene therapy alone did not enhance motoneuron survival, but led to improved muscle reinnervation and modest electrophysiological recovery during later stages of the regeneration process. Combining GDNF treatment with digestion of inhibitory CSPGs did not have a significant synergistic effect. This study suggests a delicate balance exists between treatment duration and concentration in order to achieve therapeutic effects.

Bionic Upper Limb Reconstruction: A Valuable Alternative in Global Brachial Plexus Avulsion Injuries-A Case Series

Global brachial plexopathies including multiple nerve root avulsions may result in complete upper limb paralysis despite surgical treatment. Bionic reconstruction, which includes the elective amputation of the functionless hand and its replacement with a mechatronic device, has been described for the transradial level. Here, we present for the first time that patients with global brachial plexus avulsion injuries and lack of biological shoulder and elbow function benefit from above-elbow amputation and prosthetic rehabilitation. Between 2012 and 2017, forty-five patients with global brachial plexus injuries approached our centre, of which nineteen (42.2%) were treated with bionic reconstruction. While fourteen patients were amputated at the transradial level, the entire upper limb was replaced with a prosthetic arm in a total of five patients. Global upper extremity function before and after bionic arm substitution was assessed using two objective hand function tests, the action research arm test (ARAT), and the Southampton hand assessment procedure (SHAP). Other outcome measures included the DASH questionnaire, VAS to assess deafferentation pain and the SF-36 health survey to evaluate changes in quality of life. Using a hybrid prosthetic arm mean ARAT scores improved from 0.6 ± 1.3 to 11.0 ± 6.7 (p = 0.042) and mean SHAP scores increased from 4.0 ± 3.7 to 13.8 ± 9.2 (p = 0.058). After prosthetic arm replacement mean DASH scores improved from 52.5 ± 9.4 to 31.2 ± 9.8 (p = 0.003). Deafferentation pain decreased from mean VAS 8.5 ± 1.0 to 6.7 ± 2.1 (p = 0.055), while the physical and mental component summary scale as part of the SF-36 health survey improved from 32.9 ± 6.4 to 40.4 ± 9.4 (p = 0.058) and 43.6 ± 8.9 to 57.3 ± 5.5 (p = 0.021), respectively. Bionic reconstruction can restore simple but robust arm and hand function in longstanding brachial plexus patients with lack of treatment alternatives.

Enhanced regeneration and reinnervation following timed GDNF gene therapy in a cervical ventral root avulsion

Avulsion of spinal nerve roots is a severe proximal peripheral nerve lesion. Despite neurosurgical repair, recovery of function in human patients is disappointing, because spinal motor neurons degenerate progressively, axons grow slowly and the distal Schwann cells which are instrumental to supporting axon extension lose their pro-regenerative properties. We have recently shown that timed GDNF gene therapy (dox-i-GDNF) in a lumbar plexus injury model promotes axon regeneration and improves electrophysiological recovery but fails to stimulate voluntary hind paw function. Here we report that dox-i-GDNF treatment following avulsion and re-implantation of cervical ventral roots leads to sustained motoneuron survival and recovery of voluntary function. These improvements were associated with a twofold increase in motor axon regeneration and enhanced reinnervation of the hand musculature. In this cervical model the distal hand muscles are located 6,5 cm from the reimplantation site, whereas following a lumber lesion this distance is twice as long. Since the first signs of muscle reinnervation are observed 6 weeks after the lesion, this suggests that regenerating axons reached the hand musculature before a critical state of chronic denervation has developed. These results demonstrate that the beneficial effects of timed GDNF-gene therapy are more robust following spinal nerve avulsion lesions that allow reinnervation of target muscles within a relatively short time window after the lesion. This study is an important step in demonstrating the potential of timed GDNF-gene therapy to enhance axon regeneration after neurosurgical repair of a severe proximal nerve lesion.

Network-centric medicine for peripheral nerve injury: Treating the whole to boost endogenous mechanisms of neuroprotection and regeneration

Peripheral nerve injuries caused by accidents may lead to paralysis, sensory disturbances, anaesthesia, and lack of autonomic functions. Functional recovery after disconnection of the motoneuronal soma from target tissue with proximal rupture of axons is determined by several factors: motoneuronal soma viability, proper axonal sprouting across inhibitory zones and elongation toward specific muscle, effective synapse contact rebuilding, and prevention of muscle atrophy. Therapies, such as adjuvant drugs with pleiotropic effects, that promote functional recovery after peripheral nerve injury are needed. Toward this aim, we designed a drug discovery workflow based on a network-centric molecular vision using unbiased proteomic data and neural artificial computational tools. Our focus is on boosting intrinsic capabilities of neurons for neuroprotection; this is in contrast to the common approach based on suppression of a pathobiological pathway known to be associated with disease condition. Using our workflow, we discovered neuroheal, a combination of two repurposed drugs that promotes motoneuronal soma neuroprotection, is anti-inflammatory, enhances axonal regeneration after axotomy, and reduces muscle atrophy. This drug discovery workflow has thus yielded a therapy that is close to its clinical application.

Pretreatment of nerve grafts with resveratrol improves axonal regeneration following replantation surgery for nerve root avulsion injury in rats

BACKGROUND

Replantation of the avulsed nerve root has been proposed for the treatment of severe brachial plexus injury for several decades. However, due to the complexity of the technique and limited functional improvement, practical applications are yet to be implemented.

OBJECTIVE

In the present study, we investigated the effect of pretreatment with resveratrol on nerve autografts used for replantation surgery in a rat model of nerve root avulsion.

METHODS

Resveratrol pretreatment was performed using an explant culture technique. Two surgical procedures were performed. During the first surgery, Sprague-Dawley rats were subjected to left C6 nerve root avulsion, and nerves were harvested for autografting. The harvested grafts were explant-cultured for 1 week. A second procedure was performed to replant the C6 nerve root using the explant-cultured nerve graft 1 week after the first procedure. Histological and immunohistochemical analyses were performed 8 weeks after the second procedure. We first compared findings between explant-cultured nerve grafts and fresh nerve grafts, following which we compared findings between explant-cultured grafts pretreated with and without resveratrol. Changes induced within nerve grafts by 1 week of explant culture with or without resveratrol were investigated in vitro.

RESULTS

There was no significant difference in outcomes between 1 week-explant-cultured and fresh nerve grafts. Addition of resveratrol to the explant culture medium resulted in a significant increase in the number and myelin thickness of regenerated axons, and in the number of regenerating motor neurons in the C6 spinal cord segment. In vitro analyses revealed that nerve grafts pretreated with resveratrol exhibited significant increases in glial cell line-derived neurotrophic factor (GDNF) expression and the number of dedifferentiated Schwann cells.

CONCLUSIONS

Resveratrol may promote axonal regeneration following replantation surgery for the treatment of nerve root avulsion injury; however, further studies are required to verify these findings in humans.

Neuroprotection and immunomodulation following intraspinal axotomy of motoneurons by treatment with adult mesenchymal stem cells

BACKGROUND

Treatment of spinal cord injury is dependent on neuronal survival, appropriate synaptic circuit preservation, and inflammatory environment management. In this sense, mesenchymal stem cell (MSC) therapy is a promising tool that can reduce glial reaction and provide trophic factors to lesioned neurons.

METHODS

Lewis adult female rats were submitted to a unilateral ventral funiculus cut at the spinal levels L4, L5, and L6. The animals were divided into the following groups: IA (intramedullary axotomy), IA + DMEM (Dulbecco's modified Eagle's medium), IA + FS (fibrin sealant), IA + MSC (106 cells), and IA + FS + MSC (106 cells). Seven days after injury, qPCR (n = 5) was performed to assess gene expression of VEGF, BDNF, iNOS2, arginase-1, TNF-α, IL-1β, IL-6, IL-10, IL-4, IL-13, and TGF-β. The cellular infiltrate at the lesion site was analyzed by hematoxylin-eosin (HE) staining and immunohistochemistry (IH) for Iba1 (microglia and macrophage marker) and arginase-1. Fourteen days after injury, spinal alpha motor neurons (MNs), evidenced by Nissl staining (n = 5), were counted. For the analysis of astrogliosis in spinal lamina IX and synaptic detachment around lesioned motor neurons (GAP-43-positive cells), anti-GFAP and anti-synaptophysin immunohistochemistry (n = 5) was performed, respectively. Twenty-eight days after IA, the gait of the animals was evaluated by the walking track test (CatWalk; n = 7).

RESULTS

The site of injury displayed strong monocyte infiltration, containing arginase-1-expressing macrophages. The FS-treated group showed upregulation of iNOS2, arginase-1, proinflammatory cytokine (TNF-α and IL-1β), and antiinflammatory cytokine (IL-10, IL-4, and IL-13) expression. Thus, FS enhanced early macrophage recruitment and proinflammatory cytokine expression, which accelerated inflammation. Rats treated with MSCs displayed high BDNF-positive immunolabeling, suggesting local delivery of this neurotrophin to lesioned motoneurons. This BDNF expression may have contributed to the increased neuronal survival and synapse preservation and decreased astrogliosis observed 14 days after injury. At 28 days after lesion, gait recovery was significantly improved in MSC-treated animals compared to that in the other groups.

CONCLUSIONS

Overall, the present data demonstrate that MSC therapy is neuroprotective and, when associated with a FS, shifts the immune response to a proinflammatory profile.

The Place of PET to Assess New Therapeutic Effectiveness in Neurodegenerative Diseases

In vivo exploration of neurodegenerative diseases by positron emission tomography (PET) imaging has matured over the last 20 years, using dedicated radiopharmaceuticals targeting cellular metabolism, neurotransmission, neuroinflammation, or abnormal protein aggregates (beta-amyloid and intracellular microtubule inclusions containing hyperphosphorylated tau). The ability of PET to characterize biological processes at the cellular and molecular levels enables early detection and identification of molecular mechanisms associated with disease progression, by providing accurate, reliable, and longitudinally reproducible quantitative biomarkers. Thus, PET imaging has become a relevant imaging method for monitoring response to therapy, approved as an outcome measure in bioclinical trials. The aim of this paper is to review and discuss the current inputs of PET in the assessment of therapeutic effectiveness in neurodegenerative diseases connected by common pathophysiological mechanisms, including Parkinson's disease, Huntington's disease, dementia, amyotrophic lateral sclerosis, multiple sclerosis, and also in psychiatric disorders. We also discuss opportunities for PET imaging to drive more personalized neuroprotective and therapeutic strategies, taking into account individual variability, within the growing framework of precision medicine.

Surgical reconstruction of spinal cord circuit provides functional return in humans

This mini review describes the current surgical strategy for restoring function after traumatic spinal nerve root avulsion in brachial or lumbosacral plexus injury in man. As this lesion is a spinal cord or central nervous injury functional return depends on spinal cord nerve cell growth within the central nervous system. Basic science, clinical research and human application has demonstrated good and useful motor function after ventral root avulsion followed by spinal cord reimplantation. Recently, sensory return could be demonstrated following spinal cord surgery bypassing the injured primary sensory neuron. Experimental data showed that most of the recovery depended on new growth reinnervating peripheral receptors. Restored sensory function and the return of spinal reflex was demonstrated by electrophysiology and functional magnetic resonance imaging of human cortex. This spinal cord surgery is a unique treatment of central nervous system injury resulting in useful functional return. Further improvements will not depend on surgical improvements. Adjuvant therapy aiming at ameliorating the activity in retinoic acid elements in dorsal root ganglion neurons could be a new therapeutic avenue in restoring spinal cord circuits after nerve root avulsion injury.

Lack of riluzole efficacy in the progression of the neurodegenerative phenotype in a new conditional mouse model of striatal degeneration

BACKGROUND

Huntington's disease (HD) is a rare familial autosomal dominant neurodegenerative disorder characterized by progressive degeneration of medium spiny neurons (MSNs) located in the striatum. Currently available treatments of HD are only limited to alleviating symptoms; therefore, high expectations for an effective therapy are associated with potential replacement of lost neurons through stimulation of postnatal neurogenesis. One of the drugs of potential interest for the treatment of HD is riluzole, which may act as a positive modulator of adult neurogenesis, promoting replacement of damaged MSNs. The aim of this study was to evaluate the effects of chronic riluzole treatment on a novel HD-like transgenic mouse model, based on the genetic ablation of the transcription factor TIF-IA. This model is characterized by selective and progressive degeneration of MSNs.

METHODS

Selective ablation of TIF-IA in MSNs (TIF-IA^D1RCre mice) was achieved by Cre-based recombination driven by the dopamine 1 receptor (D1R) promoter in the C57Bl/6N mouse strain. Riluzole was administered for 14 consecutive days (5 mg/kg, i.p.; 1× daily) starting at six weeks of age. Behavioral analysis included a motor coordination test performed on 13-week-old animals on an accelerated rotarod (4-40 r.p.m.; 5 min). To visualize the potential effects of riluzole treatment, the striata of the animals were stained by immunohistochemistry (IHC) and/or immunofluorescence (IF) with Ki67 (marker of proliferating cells), neuronal markers (NeuN, MAP2, DCX), and markers associated with neurodegeneration (GFAP, 8OHdG, FluoroJade C). Additionally, the morphology of dendritic spines of neurons was assessed by a commercially available FD Rapid Golgi Stain™ Kit.

RESULTS

A comparative analysis of IHC staining patterns with chosen markers for the neurodegeneration process in MSNs did not show an effect of riluzole on delaying the progression of MSN cell death despite an observed enhancement of cell proliferation as visualized by the Ki67 marker. A lack of a riluzole effect was also reflected by the behavioral phenotype associated with MSN degeneration. Moreover, the analysis of dendritic spine morphology did not show differences between mutant and control animals.

DISCUSSION

Despite the observed increase in newborn cells in the subventricular zone (SVZ) after riluzole administration, our study did not show any differences between riluzole-treated and non-treated mutants, revealing a similar extent of the neurodegenerative phenotype evaluated in 13-week-old TIF-IA^D1RCre animals. This could be due to either the treatment paradigm (relatively low dose of riluzole used for this study) or the possibility that the effects were simply too weak to have any functional meaning. Nevertheless, this study is in line with others that question the effectiveness of riluzole in animal models and raise concerns about the utility of this drug due to its rather modest clinical efficacy.

Transgenic human embryonic stem cells overexpressing FGF2 stimulate neuroprotection following spinal cord ventral root avulsion

Ventral root avulsion (VRA) triggers a strong glial reaction which contributes to neuronal loss, as well as to synaptic detachment. To overcome the degenerative effects of VRA, treatments with neurotrophic factors and stem cells have been proposed. Thus, we investigated neuroprotection elicited by human embryonic stem cells (hESC), modified to overexpress a human fibroblast growth factor 2 (FGF-2), on motoneurons subjected to VRA. Lewis rats were submitted to VRA (L4-L6) and hESC/FGF-2 were applied to the injury site using a fibrin scaffold. The spinal cords were processed to evaluate neuronal survival, synaptic stability, and glial reactivity two weeks post lesion. Then, qRT-PCR was used to assess gene expression of β2-microglobulin (β2m), TNFα, IL1β, IL6 and IL10 in the spinal cord in vivo and FGF2 mRNA levels in hESC in vitro. The results indicate that hESC overexpressing FGF2 significantly rescued avulsed motoneurons, preserving synaptic covering and reducing astroglial reactivity. The cells were also shown to express BDNF and GDNF at the site of injury. Additionally, engraftment of hESC led to a significant reduction in mRNA levels of TNFα at the spinal cord ventral horn, indicating their immunomodulatory properties. Overall, the present data suggest that hESC overexpressing FGF2 are neuroprotective and can shift gene expression towards an anti-inflammatory environment.

Treatment with Riluzole Restores Normal Control of Soleus and Extensor Digitorum Longus Muscles during Locomotion in Adult Rats after Sciatic Nerve Crush at Birth

The effects of sciatic nerve crush (SNC) and treatment with Riluzole on muscle activity during unrestrained locomotion were identified in an animal model by analysis of the EMG activity recorded from soleus (Sol) and extensor digitorum longus (EDL) muscles of both hindlimbs; in intact rats (IN) and in groups of rats treated for 14 days with saline (S) or Riluzole (R) after right limb nerve crush at the 1st (1S and 1R) or 2nd (2S and 2R) day after birth. Changes in the locomotor pattern of EMG activity were correlated with the numbers of survived motor units (MUs) identified in investigated muscles. S rats with 2-8 and 10-28 MUs that survived in Sol and EDL muscles respectively showed increases in the duration and duty factor of muscle EMG activity and a loss of correlation between the duty factors of muscle activity, and abnormal flexor-extensor co-activation 3 months after SNC. R rats with 5, 6 (Sol) and 15-29 MUs (EDL) developed almost normal EMG activity of both Sol and control EDL muscles, whereas EDL muscles with SNC showed a lack of recovery. R rats with 8 (Sol) and 23-33 (EDL) MUs developed almost normal EMG activities of all four muscles. A subgroup of S rats with a lack of recovery and R rats with almost complete recovery that had similar number of MUs (8 and 24-28 vs 8 and 23-26), showed that the number of MUs was not the only determinant of treatment effectiveness. The results demonstrated that rats with SNC failed to develop normal muscle activity due to malfunction of neuronal circuits attenuating EDL muscle activity during the stance phase, whereas treatment with Riluzole enabled almost normal EMG activity of Sol and EDL muscles during locomotor movement.

New Treatments for Spinal Nerve Root Avulsion Injury

Further progress in the treatment of the longitudinal spinal cord injury has been made. In an inverted translational study, it has been demonstrated that return of sensory function can be achieved by bypassing the avulsed dorsal root ganglion neurons. Dendritic growth from spinal cord sensory neurons could replace dorsal root ganglion axons and re-establish a reflex arch. Another research avenue has led to the development of adjuvant therapy for regeneration following dorsal root to spinal cord implantation in root avulsion injury. A small, lipophilic molecule that can be given orally acts on the retinoic acid receptor system as an agonist. Upregulation of dorsal root ganglion regenerative ability and organization of glia reaction to injury were demonstrated in treated animals. The dual effect of this substance may open new avenues for the treatment of root avulsion and spinal cord injuries.

Lithium accelerates functional motor recovery by improving remyelination of regenerating axons following ventral root avulsion and reimplantation

Brachial plexus injury (BPI) often involves the complete or partial avulsion of one or more of the cervical nerve roots, which leads to permanent paralysis of the innervated muscles. Reimplantation surgery has been attempted as a clinical treatment for brachial plexus root avulsion but has failed to achieve complete functional recovery. Lithium is a mood stabilizer drug that is used to treat bipolar disorder; however, its effects on spinal cord or peripheral nerve injuries have also been reported. The purpose of this study was to investigate whether lithium can improve functional motor recovery after ventral root avulsion and reimplantation in a rat model of BPI. The results showed that systemic treatment with a clinical dose of lithium promoted motor neuron outgrowth and increased the efficiency of motor unit regeneration through enhanced remyelination. An analysis of myelin-associated genes showed that the effects of lithium started during the early phase of remyelination and persisted through the late stage of the process. Efficient remyelination of the regenerated axons in the lithium-treated rats led to an earlier functional recovery. Therefore, we demonstrated that lithium might be a potential clinical treatment for BPI in combination with reimplantation surgery.

Clinical and neurobiological advances in promoting regeneration of the ventral root avulsion lesion

Root avulsions due to traction to the brachial plexus causes complete and permanent loss of function. Until fairly recent, such lesions were considered impossible to repair. Here we review clinical repair strategies and current progress in experimental ventral root avulsion lesions. The current gold standard in patients with a root avulsion is nerve transfer, whereas reimplantation of the avulsed root into the spinal cord has been performed in a limited number of cases. These neurosurgical repair strategies have significant benefit for the patient but functional recovery remains incomplete. Developing new ways to improve the functional outcome of neurosurgical repair is therefore essential. In the laboratory, the molecular and cellular changes following ventral root avulsion and the efficacy of intervention strategies have been studied at the level of spinal motoneurons, the ventral spinal root and peripheral nerve, and the skeletal muscle. We present an overview of cell-based pharmacological and neurotrophic factor treatment approaches that have been applied in combination with surgical reimplantation. These interventions all demonstrate neuroprotective effects on avulsed motoneurons, often accompanied with various degrees of axonal regeneration. However, effects on survival are usually transient and robust axon regeneration over long distances has as yet not been achieved. Key future areas of research include finding ways to further extend the post-lesion survival period of motoneurons, the identification of neuron-intrinsic factors which can promote persistent and long-distance axon regeneration, and finally prolonging the pro-regenerative state of Schwann cells in the distal nerve.

Chronic inhibitory effect of riluzole on trophic factor production

Riluzole is the only FDA approved drug for the treatment of amyotrophic lateral sclerosis (ALS). However, the drug affords moderate protection to ALS patients, extending life for a few months by a mechanism that remains controversial. In the presence of riluzole, astrocytes increase the production of factors protective to motor neurons. The stimulation of trophic factor production by motor neuron associated cells may contribute to riluzole's protective effect in ALS. Here, we investigated the effects of media conditioned by astrocytes and Schwann cells acutely or chronically incubated with riluzole on trophic factor-deprived motor neuron survival. While acute riluzole incubation induced CT-1 secretion by astrocytes and Schwann cells, chronic treatment stimulated a significant decrease in trophic factor production compared to untreated cultures. Accordingly, conditioned media from astrocytes and Schwann cells acutely treated with riluzole protected motor neurons from trophic factor deprivation-induced cell death. Motor neuron protection was prevented by incubation with CT-1 neutralizing antibodies. In contrast, conditioned media from astrocytes and Schwann cells chronically treated with riluzole was not protective. Acute and chronic treatment of mice with riluzole showed opposite effects on trophic factor production in spinal cord, sciatic nerve and brain. There was an increase in the production of CT-1 and GDNF in the spinal cord and CT-1 in the sciatic nerve during the first days of treatment with riluzole, but the levels dropped significantly after chronic treatment with the drug. Similar results were observed in brain for CT-1 and BDNF while there was no change in GDNF levels after riluzole treatment. Our results reveal that riluzole regulates long-lasting processes involving protein synthesis, which may be relevant for riluzole therapeutic effects. Changing the regimen of riluzole administration to favor the acute effect of the drug on trophic factor production by discontinuous long-term treatment may improve the outcome of ALS patient therapy.

Vascular changes associated with spinal root avulsion injury

This paper has investigated the hypothesis that spinal root avulsion (SRA) injury produces alterations in blood flow that contribute to avulsion injury induced pain-like behaviour in rodents. Photoplethysmography (PPG) is an established way of assessing blood flow in the central nervous system (CNS) and laser Doppler flowmetry (LDF) is the most widely used technique for measuring tissue perfusion. Using an established model of SRA injury that produces mechanical hypersensitivity, the PPG and LDF signals were recorded in animals 2 weeks post-injury and compared to naive recordings. PPG and LDF measurements were assessed on the ipsilateral and contralateral sides of the spinal cord rostral and caudal to the avulsion injury and at the level of the injury. Two weeks after injury, a time when vascular blood vessel endothelial markers are known to be decreased, no significant changes were seen in the spinal cord blood flow (SCBF) above, at, or below the injury site or when comparing the ipsilateral vs. contralateral side. Assessment of oxygenation levels again revealed no significant differences between naive and spinal root injured animals along the rostrocaudal axis (i.e., above, at, and below the site of injury or its equivalent on the contralateral side). From these experiments it is concluded that SRA does not significantly alter blood flow or tissue oxygen levels and so ischemia may play a less prominent role in avulsion injury induced pain.

Erythropoietin Attenuates the Apoptosis of Adult Neurons After Brachial Plexus Root Avulsion by Downregulating JNK Phosphorylation and c-Jun Expression and Inhibiting c-PARP Cleavage

In the present study, the effects of erythropoietin (EPO) on preventing adult neurons from apoptosis (introduced by brachial plexus avulsion) were examined, and the mechanism was analyzed. Fifty injury rat models were established in this study by using micro-hemostat forceps to pull out brachial plexus root from the intervertebral foramen in supine position. These models were divided into EPO group (avulsion + 1000 U/kg subcutaneously on alternate days) and control group (avulsion + normal saline). C5-T1 spinal cord was harvested at days 1, 2, 4, 7, and 14. Compared with the control group, the apoptosis of spinal motoneurons was significantly decreased on days 4 and 7 in the EPO group, which was also approved by TUNEL examination results. The detection of p-JNK and expression of c-Jun and cleavage of cleaved PARP (c-PARP) were also examined by immunohistochemistry and were increased immediately at day 1, and peaked at day 2, day 2, and day 4 in control group, respectively. However, the amounts were decreased and delayed by EPO treatment significantly at the same time points. In conclusion, the apoptosis of adult spinal motorneurons was associated with JNK phosphorylation, c-Jun expression, and caspase activity, and EPO-mediated neuronal protective effect is proved by downregulating the JNK phosphorylation and c-Jun expression and inhibiting of c-PARP cleavage.

Grafted murine induced pluripotent stem cells prevent death of injured rat motoneurons otherwise destined to die

Human plexus injuries often include the avulsion of one or more ventral roots, resulting in debilitating conditions. In this study the effects of undifferentiated murine iPSCs on damaged motoneurons were investigated following avulsion of the lumbar 4 (L4) ventral root, an injury known to induce the death of the majority of the affected motoneurons. Avulsion and reimplantation of the L4 ventral root (AR procedure) were accompanied by the transplantation of murine iPSCs into the injured spinal cord segment in rats. Control animals underwent ventral root avulsion and reimplantation, but did not receive iPSCs. The grafted iPSCs induced an improved reinnervation of the reimplanted ventral root by the host motoneurons as compared with the controls (number of retrogradely labeled motoneurons: 503 ± 38 [AR+iPSCs group] vs 48 ± 6 [controls, AR group]). Morphological reinnervation resulted in a functional recovery, i.e. the grafted animals exhibited more motor units in their reinnervated hind limb muscles, which produced a greater force than that in the controls (50 ± 2.1% vs 11.9 ± 4.2% maximal tetanic tension [% ratio of operated/intact side]). Grafting of undifferentiated iPSCs downregulated the astroglial activation within the L4 segment. The grafted cells differentiated into neurons and astrocytes in the injured cord. The grafted iPSCs, host neurons and glia were found to produce the cytokines and neurotrophic factors MIP-1a, IL-10, GDNF and NT-4. These findings suggest that, following ventral root avulsion injury, iPSCs are able to induce motoneuron survival and regeneration through combined neurotrophic and cytokine modulatory effects.

Restoration and protection of brachial plexus injury: hot topics in the last decade

Brachial plexus injury is frequently induced by injuries, accidents or birth trauma. Upper limb function may be partially or totally lost after injury, or left permanently disabled. With the development of various medical technologies, different types of interventions are used, but their effectiveness is wide ranging. Many repair methods have phasic characteristics, i.e., repairs are done in different phases. This study explored research progress and hot topic methods for protection after brachial plexus injury, by analyzing 1,797 articles concerning the repair of brachial plexus injuries, published between 2004 and 2013 and indexed by the Science Citation Index database. Results revealed that there are many methods used to repair brachial plexus injury, and their effects are varied. Intervention methods include nerve transfer surgery, electrical stimulation, cell transplantation, neurotrophic factor therapy and drug treatment. Therapeutic methods in this field change according to the hot topic of research.

Preconditioning crush increases the survival rate of motor neurons after spinal root avulsion

In a previous study, heat shock protein 27 was persistently upregulated in ventral motor neurons following nerve root avulsion or crush. Here, we examined whether the upregulation of heat shock protein 27 would increase the survival rate of motor neurons. Rats were divided into two groups: an avulsion-only group (avulsion of the L4 lumbar nerve root only) and a crush-avulsion group (the L4 lumbar nerve root was crushed 1 week prior to the avulsion). Immunofluorescent staining revealed that the survival rate of motor neurons was significantly greater in the crush-avulsion group than in the avulsion-only group, and this difference remained for at least 5 weeks after avulsion. The higher neuronal survival rate may be explained by the upregulation of heat shock protein 27 expression in motor neurons in the crush-avulsion group. Furthermore, preconditioning crush greatly attenuated the expression of nitric oxide synthase in the motor neurons. Our findings indicate that the neuroprotective action of preconditioning crush is mediated through the upregulation of heat shock protein 27 expression and the attenuation of neuronal nitric oxide synthase upregulation following avulsion.

Lithium enhances survival and regrowth of spinal motoneurons after ventral root avulsion

Background

During the clinical treatment of the brachial plexus root avulsion (BPRA), reimplantation surgery can not completely repair the motor function of the hand because the axonal growth velocity of the spinal motoneurons (MNs) is too slow to re-innervate the intrinsic hand muscles before muscle atrophy. Here, we investigated whether lithium can enhance the regenerative capacity of the spinal MNs in a rat model of BPRA.

Results

The avulsion and immediate reimplantation of the C7 and C8 ventral roots were performed and followed with daily intraperitoneal administration of a therapeutic concentrationof LiCl. After a 20 week long-term rehabilitation, the motor function recovery of the injured forepaw was studied by a grasping test. The survival and regeneration of MNs were checked by choline acetyltransferase (ChAT) immunofluorescence and by Fluoro-Gold (FG) retrograde labeling through the median and ulnar nerves of the ventral horn MNs. The number and diameter of the nerve fibers in the median nerve were assessed by toluidine blue staining. Our results showed that lithium plus reimplantation therapy resulted in a significantly higher grasping strength of the digits of the injured forepaw. Lithium plus reimplantation allowed 45.1% ± 8.11% of ChAT-positive MNs to survive the injury and increased the number and diameter of nerve fibers in the median nerve. The number of FG-labeled regenerative MNs was significantly elevated in all of the reimplantation animals. Our present data proved that lithium can enhance the regenerative capacity of spinal MNs.

Conclusions

These results suggest that immediate administration of lithium could be used to assist reimplantation surgery in repairing BPRA injuries in clinical treatment.

Lithium enhances axonal regeneration in peripheral nerve by inhibiting glycogen synthase kinase 3β activation

Brachial plexus injury often involves traumatic root avulsion resulting in permanent paralysis of the innervated muscles. The lack of sufficient regeneration from spinal motoneurons to the peripheral nerve (PN) is considered to be one of the major causes of the unsatisfactory outcome of various surgical interventions for repair of the devastating injury. The present study was undertaken to investigate potential inhibitory signals which influence axonal regeneration after root avulsion injury. The results of the study showed that root avulsion triggered GSK-3β activation in the injured motoneurons and remaining axons in the ventral funiculus. Systemic application of a clinical dose of lithium suppressed activated GSK-3β in the lesioned spinal cord to the normal level and induced extensive axonal regeneration into replanted ventral roots. Our study suggests that GSK-3β activity is involved in negative regulation for axonal elongation and regeneration and lithium, the specific GSK-3β inhibitor, enhances motoneuron regeneration from CNS to PNS.

The effects of minocycline or riluzole treatment on spinal root avulsion-induced pain in adult rats

Spinal root avulsion produces tactile and thermal hypersensitivity, neurodegeneration, and microglial and astrocyte activation in both the deafferented and the adjacent intact spinal cord segments. Following avulsion of the fifth lumbar spinal root, immediate and prolonged treatment with riluzole or minocycline for 2 weeks altered the development of behavioral hypersensitivity. Riluzole delayed the onset of thermal and tactile hypersensitivity and partially reversed established pain behavior. Minocycline effectively prevented and reversed both types of behavioral change. Histologic analysis revealed that both drugs reduced microglial staining in the spinal cord, with minocycline being more effective than riluzole. Astrocyte activation was ameliorated to a lesser extent. Surprisingly, neither drug provided a neuroprotective effect on avulsed motoneurons.

PERSPECTIVE

Immediate treatment of spinal root avulsion injuries with minocycline or riluzole prevents the onset of evoked pain hypersensitivity by reducing microglial cell activation. When treatment is delayed, minocycline, but not riluzole, reverses pre-established hypersensitivity. Thus, these drugs may provide a new translational treatment option for chronic avulsion injury pain.

A new cervical nerve root avulsion model using a posterior extra-vertebral approach in rats

BACKGROUND

The nerve root avulsion injury causes decrease of motor neurons in the spinal ventral horn. To investigate the motoneuron death after avulsion injury in rats, the intradural root avulsion procedure is usually used, although it is technically demanding and associated with a risk of unexpected spinal cord damage. We have developed a new cervical nerve root avulsion procedure in rats and investigated the validity of our procedure.

METHODS

Our procedure is using a posterior approach and pulling the C6 nerve root outside the vertebral foramen without intradural procedures. The lateral third of the lateral mass is needed to be resected before pulling the nerve root. The accomplishment of our procedure is judged by confirmation of the bifurcated stump of the avulsed nerve root and the leakage of the spinal fluid from vertebral foramen. At first, four Sprague-Dawley (SD) rats were used for the examination of C6 motor neuron distribution in the normal spinal cord. Then, 40 SD rats were divided into following four groups and the survival rate of motor neuron was examined. (A) an intradural avulsion group, (B) an intradural rhizotomy group, (C) our extravertebral avulsion group, and (D) an extravertebral rupture group. Another 26 SD rats were used for the examination of histomorphorogic changes in the spinal cord after our extra-vertebral avulsion procedure.

RESULTS

At 28 days after injury, the percentage of surviving motor neurons in groups A (39.0 ± 2.1%) and C (47.5 ± 7.1%) were significantly lower than those in groups B (77.1 ± 12.3%) and D (98.9 ± 9.9%). Compared with other groups, our procedure was easier and associated with less unexpected spinal cord damage. Although the length of the distal stump of the extravertebrally avulsed ventral rootlets was varied between 1.5 and 3.2 mm, this difference did not affect motoneuron death. The extravertebral avulsion injury showed intraspinal bleeding along the motoneuron axons, glial reaction and macrophage infiltration in the lesioned side of the ventral horn.

CONCLUSIONS

Our extravertebral avulsion procedure is simple and reproducible. It would become a useful tool for the study of cervical nerve root avulsion injury.

Valproic acid protection against the brachial plexus root avulsion-induced death of motoneurons in rats

In this study, the role of valproic acid (VPA) in protecting motoneuron after brachial plexus root avulsion was investigated in adult rats. Sixty rats were used in this study, and underwent the brachial plexus root avulsion injury, which was created by using a micro-hemostat forceps to pull out brachial plexus root from the intervertebral foramen. The animals were divided into two groups, VPA group administered with VPA dissolved in drinking water (300 mg/kg) daily, and control group had drinking water every day. The spinal cords (C5-T1) were harvested at day 1, 2, 3, 7, 14, and 28 for immunohistochemistry analysis, TUNEL staining, Nissl staining, and electron microscopy, respectively. The results showed that with VPA administration, the survival of motoneurons was promoted and the cell apoptosis was inhibited. The number of c-Jun and Bcl-2 positive motoneurons was increased immediately after avulsion both in control and VPA group, however, the percent of c-Jun positive motoneurons was decreased and the percent of Bcl-2 positive motoneurons was increased by VPA treatment significantly. Our results indicated that motoneurons were protected by VPA against cell death induced by brachial plexus root avulsion through c-Jun inhibition and Bcl-2 induction.

Neuroprotection and axonal regeneration after lumbar ventral root avulsion by re-implantation and mesenchymal stem cells transplant combined therapy

Ventral spinal root avulsion causes complete denervation of muscles in the limb and also progressive death of segmental motoneurons (MN) leading to permanent paralysis. The chances for functional recovery after ventral root avulsion are very poor owing to the loss of avulsed neurons and the long distance that surviving neurons have to re-grow axons from the spinal cord to the corresponding targets. Following unilateral avulsion of L4, L5 and L6 spinal roots in adult rats, we performed an intraspinal transplant of mesenchymal stem cells (MSC) and surgical re-implantation of the avulsed roots. Four weeks after avulsion the survival of MN in the MSC-treated animals was significantly higher than in vehicle-injected rats (45% vs. 28%). Re-implantation of the avulsed roots in the injured spinal cord allowed the regeneration of motor axons. By combining root re-implantation and MSC transplant the number of surviving MN at 28 days post-injury was higher (60%) than in re-implantation alone animals (46%). Electromyographic tests showed evidence of functional re-innervation of anterior tibialis and gastrocnemius muscles by the regenerated motor axons only in rats with the combined treatment. These results indicate that MSC are helpful in enhancing neuronal survival and increased the regenerative growth of injured axons. Surgical re-implantation and MSC grafting combined had a synergic neuroprotective effect on MN and on axonal regeneration and muscle re-innervation after spinal root avulsion.

Segmental spinal root avulsion in the adult rat: a model to study avulsion injury pain

Road traffic accidents are the most common cause of avulsion injury, in which spinal roots are torn from the spinal cord. Patients suffer from a loss of sensorimotor function, intractable spontaneous pain, and border-zone hypersensitivity. The neuropathic pains are particularly difficult to treat because the lack of a well-established animal model of avulsion injury prevents identifying the underlying mechanisms and hinders the development of efficacious drugs. This article describes a hindlimb model of avulsion injury in adult rats where the L5 dorsal and ventral spinal root are unilaterally avulsed (spinal root avulsion [SRA]), leaving the adjacent L4 spinal root intact. SRA produced a significant ipsilateral hypersensitivity to mechanical and thermal stimulation by 5 days compared with sham-operated or naïve rats. This hypersensitivity is maintained for up to 60 days. No autotomy was observed and locomotor deficits were minimal. The hypersensitivity to peripheral stimuli could be temporarily ameliorated by administration of amitriptyline and carbamazepine, drugs that are currently prescribed to avulsion patients. Histological assessment of the L4 ganglion cells revealed no significant alterations in calcitonin gene-related peptide (CGRP), IB4, transient receptor potential cation channel subfamily V member 1 (TrpV1), or N52 staining across groups. Immunohistochemistry of the spinal cord revealed a localized glial response, phagocyte infiltration, and neuronal loss within the ipsilateral avulsed segment. A comparable response from glia and phagocytes was also found in the intact L4 spinal cord, supporting the role for central mechanisms within the L4-5 spinal cord in contributing to the generation of the pain-related behavior. The SRA model provides a platform to investigate possible new pharmacological treatments for avulsion injuries.

Translational potential of preclinical trials of neuroprotection through pharmacotherapy for spinal cord injury

There is a need to enhance the pipeline of discovery and evaluation of neuroprotective pharmacological agents for patients with spinal cord injury (SCI). Although much effort and money has been expended on discovering effective agents for acute and subacute SCI, no agents that produce major benefit have been proven to date. The deficiencies of all aspects of the pipeline, including the basic science input and the clinical testing output, require examination to determine remedial strategies. Where has the neuroprotective/pharmacotherapy preclinical process failed and what needs to be done to achieve success? These are the questions raised in the present review, which has 2 objectives: 1) identification of articles that address issues related to the translational readiness of preclinical SCI pharmacological therapies; and 2) examination of the preclinical studies of 5 selected agents evaluated in animal models of SCI (including blunt force trauma, penetrating trauma, or ischemia). The 5 agents were riluzole, glyburide, magnesium sulfate, nimodipine, and minocycline, and these were selected because of their promise of translational readiness as determined by the North American Clinical Trials Network Consortium.

The authors found that there are major deficiencies in the effort that has been extended to coordinate and conduct preclinical neuroprotection/pharmacotherapy trials in the SCI field. Apart from a few notable exceptions such as the NIH effort to replicate promising strategies, this field has been poorly coordinated. Only a small number of articles have even attempted an overall evaluation of the neuroprotective/pharmacotherapy agents used in preclinical SCI trials. There is no consensus about how to select the agents for translation to humans on the basis of their preclinical performance and according to agreed-upon preclinical performance criteria.

In the absence of such a system and to select the next agent for translation, the Consortium has developed a Treatment Strategy Selection Committee, and this committee selected the most promising 5 agents for potential translation. The results show that the preclinical work on these 5 agents has left numerous gaps in knowledge about their preclinical performance and confirm the need for significant changes in preclinical neuroprotection/pharmacotherapy trials in SCI. A recommendation is made for the development and validation of a preclinical scoring system involving worldwide experts in preclinical and clinical SCI.

The longitudinal spinal cord injury: lessons from intraspinal plexus, cauda equina and medullary conus lesions

Spinal nerve root avulsion injury interrupts the transverse segmental spinal cord nerve fibers. There is degeneration of sensory, motor, and autonomic axons, loss of synapses, deterioration of local segmental connections, nerve cell death, and reactions among non neuronal cells with central nerve system (CNS) scar formation, i.e., a cascade of events similar to those known to occur in any injury to the spinal cord. This is the longitudinal spinal cord injury (SCI). For function to be restored, nerve cells must survive and there must be regrowth of new nerve fibers along a trajectory consisting of CNS growth-inhibitory tissue in the spinal cord as well as peripheral nervous system (PNS) growth-promoting tissue in nerves. Basic science results have been translated into a successful surgical strategy to treat root avulsion injuries in man. In humans, this technique is currently the most promising treatment of any spinal cord injury, with return of useful muscle function together with pain alleviation. Experimental studies have also identified potential candidates for adjunctive therapies that, together with surgical replantation of avulsed roots after brachial plexus and cauda equina injuries, can restore not only motor but also autonomic and sensory trajectories to augment the recovery of neurological function. This is the first example of a spinal cord lesion that can be treated surgically, leading to restoration of somatic and autonomic activity and alleviation of pain.

Activating transcription factor 3, a useful marker for regenerative response after nerve root injury

Activating transcription factor 3 (ATF3) is induced in various tissues in response to stress. In this experiment, ATF3 expression was studied in adult rats subjected either to a dorsal or ventral root avulsion (VRA; L4-6), or sciatic nerve transection (SNT). Post-operative survival times varied between 1.5 h and 3 weeks. In additional experiments an avulsed ventral root was directly replanted to the spinal cord. Dorsal root ganglias (DRGs) from humans exposed to traumatic dorsal root avulsions were also examined. After SNT ATF3 immunoreactivity (ATF3 IR) was detected in a few DRG neurons already 6 h after the lesion. After 24 h the number had clearly increased and still at 3 weeks DRG neurons remained labeled. In the ventral horn, ATF3 IR in motoneurons (MN) was first detected 24 h after the SNT, and still 3 weeks post-operatively lesioned MN showed ATF3 labeling. After a VRA many spinal MN showed ATF3 IR already after 3 h, and after 6 h all MN were labeled. At 3 weeks a majority of the lesioned MN had died, but all the remaining ones were labeled. When an avulsed ventral root was directly replanted, MN survived and were still labeled at 5 weeks. In DRG, a few neurons were labeled already at 1.5 h after a dorsal root avulsion. At 24 h the number had increased but still only a minority of the neurons were labeled. At 3 days the number of labeled neurons was reduced, and a further reduction was at hand at 7 days and 3 weeks. In parallel, in humans, 3 days after a traumatic dorsal root avulsion, only a few DRG neurons showed ATF3 IR. At 6 weeks no labeled neurons could be detected. These facts imply that ATF3 response to axotomy involves a distance-dependent mechanism. ATF3 also appears to be a useful and reliable neuronal marker of nerve lesions even in humans. In addition, ATF3 up-regulation in both motor and sensory neurons seems to be linked to regenerative competence.

Increased survival and reinnervation of cervical motoneurons by riluzole after avulsion of the C7 ventral root

Although adult motoneurons do not die if their axons are injured at some distance from the cell body, they are unable to survive injury caused by ventral root avulsion. Some of the injured motoneurons can be rescued if the ventral root is re-inserted into the spinal cord. Brachial plexus injuries that involve the complete or partial avulsion of one or more cervical ventral roots can be treated successfully only if satisfactory numbers of motoneurons remain alive following such an injury at the time of reconstructive surgery. Here we investigated the various strategies that could be used to rescue injured rat cervical motoneurons. The seventh cervical ventral root (C7) was avulsed and various therapeutic approaches were applied to induce motoneuronal survival and regeneration. Avulsion of the root without reimplantation resulted in very low numbers of surviving motoneurons (65 ± 8 SEM), while treatment of the injured motoneurons with riluzole resulted in high numbers of surviving motoneurons (637 ± 26 SEM). When the C7 ventral root was reimplanted or a peripheral nerve implant was used to guide the regenerating axons to a muscle, considerable numbers of motoneurons regenerated their axons (211 ± 15 SEM and 274 ± 28 SEM, respectively). Much greater numbers of axons regenerated when reimplantation was followed by riluzole treatment (573 ± 9 SEM). These results show that injured adult motoneurons can be rescued by riluzole treatment, even if they cannot regenerate their axons. Reinnervation of the peripheral targets can also be further improved with riluzole treatment.

Repair and rehabilitation of plexus and root avulsions in animal models and patients

PURPOSE OF REVIEW

This review will discuss recent progress in experimental and translational research related to surgical repair of proximal nerve root injuries, and emerging potential therapies, which may be combined with replantation surgeries to augment functional outcomes after brachial plexus and cauda equina injuries.

RECENT FINDINGS

Progress in experimental studies of root and peripheral nerve injuries has identified potential candidates for adjunctive therapies, which may be combined with surgical replantation of avulsed roots after brachial plexus and cauda equina injuries. We will discuss recent advances related to adjunctive neuroprotective strategies, neurotrophic factor delivery, and emerging cellular treatment strategies after extensive nerve root trauma. We will also provide an update on electrical stimulation to promote regenerative axonal growth and new insights on the recovery of sensory functions after root injury and repair.

SUMMARY

In the light of recent advances in experimental studies, we envision that future repair of brachial plexus and cauda equina injuries will include spinal cord surgery to restore motor and sensory trajectories and a variety of adjunctive therapies to augment the recovery of neurological function.

Cauda equina repair in the rat: part 1. Stimulus-evoked EMG for identifying spinal nerves innervating intrinsic tail muscles

Cauda equina injuries may produce severe leg and pelvic floor dysfunction, for which no effective treatments exist. We are developing a rat cauda equina injury model to allow nerve root identification and surgical repair. One possible difficulty in implementing any repair strategy after trauma in humans involves the correct identification of proximal and distal ends of nerve roots separated by the injury. Two series of studies were carried out. In Series 1, we electrically stimulated segmental contributors to the dorsal and ventral caudales nerves in order to characterize the recruitment patterns of muscles controlling rat tail movements. In Series 2, we attempted to identify individual nerve roots forming the cauda equina by both level of origin and function (i.e., dorsal or ventral), based solely upon the recruitment patterns in response to electrical stimulation. For Series 1 studies, electrical stimulation of the segmental contributors showed that all nerve roots-from the sixth lumbar to the first coccygeal-contributed to recruitment of muscles found at the base of the tail. Intrinsic tail muscles lying more distally in the tail showed a more root-specific pattern of innervation. For Series 2, the rate of successful identification of an unknown nerve root as being ventral was very high (>95%), and only somewhat lower (approximately 80%) for dorsal roots. Correctly identifying the level of origin of that root was more difficult, but for ventral roots this rate still exceeded 90%. Using the rat cauda equina model, we have shown that stimulus-evoked EMG can be used to identify ventral nerve roots innervating tail muscles with a high degree of accuracy. These findings support the feasibility of using this conceptual approach for identifying and repairing damaged human cauda equina nerve roots based on stimulus-evoked recruitment of muscles in the leg and pelvic floor.

Perspectives on the treatment of the longitudinal spinal cord injury

The current technique for surgical treatment of the longitudinal spinal cord injury has proven to be successful for restoration of some motor function and alleviation of pain. This has been the first step in finding a cure for spinal cord injuries, but so far there are many obstacles still to be overcome. In this particular injury return of function from spinal cord surgery is only partial. Some of the main remaining problems are related to injury-induced neuronal death, direction and specificity of regeneration and muscle, and receptor disintegration from long time denervation. Currently this is a surgical procedure without any adjuvant treatments. In order to gain further functional improvement combinational therapies developed in basic science experiments are essential.

Cortical activity and hand function restoration in a patient after spinal cord surgery

BACKGROUND

Following a motorcycle accident, a 9-year-old boy experienced a complete right-sided (dominant) arm and hand paralysis with total sensory loss, Horner syndrome and severe constant pain. This study assessed the long-term outcome of spinal cord surgery undertaken on the patient, focusing on the restored hand function and related cortical activity. The study follows on from previous reports on the same patient.

INVESTIGATIONS

Clinical functional and electrophysiological examinations. Functional MRI of cortical activity.

DIAGNOSIS

Complete brachial plexus (C5-T1) avulsion from the spinal cord.

MANAGEMENT

Spinal cord surgery to restore motor trajectories.

GAP-43 expression correlates with spinal motoneuron regeneration following root avulsion

BACKGROUND

The growth-associated protein GAP-43 plays a crucial role in axonal regeneration in injured neurons.

METHODS

We have used immunohistochemistry to investigate the expression of GAP-43 in spinal motoneurons during nerve reconstruction following root avulsion in the neonatal and adult rats.

RESULTS

Following the injury, GAP-43-immunoreactivity (IR) could be found in adult avulsed motoneurons as early as 1 day, increased from 3 to 7 days and reached a maximal level at 2 weeks post-injury. The up-regulation of GAP-43 in adult avulsed motoneurons was accompanied with the axonal regeneration indicated by numerous regenerating motor axons entering the reimplanted ventral root and nerve. In contrast, GAP-43-IR could not be found in the neonatal avulsed motoneurons at any examined post-injury time points. This failure of up-regulation of GAP-43 was coincident with no axonal regeneration in the reimplanted nerve in the neonatal rats.

CONCLUSION

Close association of GAP-43 expression and capacity of regeneration in reimplanted spinal nerve of avulsed motoneurons suggests that GAP-43 is a potential therapeutic target for treatment of root avulsion of brachial plexus.