C3 Peptide Promotes Axonal Regeneration and Functional Motor Recovery after Peripheral Nerve Injury

Peripheral nerve injuries are frequently seen in trauma patients and due to delayed nerve repair, lifelong disabilities often follow this type of injury. Innovative therapies are needed to facilitate and expedite peripheral nerve regeneration. The purpose of this study was to determine the effects of a 1-time topical application of a 26-amino-acid fragment (C3^156-181), derived from the Clostridium botulinum C3-exoenzyme, on peripheral nerve regeneration in 2 models of nerve injury and repair in adult rats. After sciatic nerve crush, different dosages of C3^156-181 dissolved in buffer or reference solutions (nerve growth factor or C3^bot-wild-type protein) or vehicle-only were injected through an epineurial opening into the lesion sites. After 10-mm nerve autotransplantation, either 8.0 nmol/kg C3^156-181 or vehicle were injected into the proximal and distal suture sites. For a period of 3 to 10 postoperative weeks, C3^156-181-treated animals showed a faster motor recovery than control animals. After crush injury, axonal outgrowth and elongation were activated and consequently resulted in faster motor recovery. The nerve autotransplantation model further elucidated that C3^156-181 treatment accounts for better axonal elongation into motor targets and reduced axonal sprouting, which are followed by enhanced axonal maturation and better axonal functionality. The effects of C3^156-181 are likely caused by a nonenzymatic down-regulation of active RhoA. Our results indicate the potential of C3^156-181 as a therapeutic agent for the topical treatment of peripheral nerve repair sites.     

Peripheral Nerve Grafts Support Regeneration after Spinal Cord Injury

Traumatic insults to the spinal cord induce both immediate mechanical damage and subsequent tissue degeneration leading to a substantial physiological, biochemical, and functional reorganization of the spinal cord. Various spinal cord injury (SCI) models have shown the adaptive potential of the spinal cord and its limitations in the case of total or partial absence of supraspinal influence. Meaningful recovery of function after SCI will most likely result from a combination of therapeutic strategies, including neural tissue transplants, exogenous neurotrophic factors, elimination of inhibitory molecules, functional sensorimotor training, and/or electrical stimulation of paralyzed muscles or spinal circuits. Peripheral nerve grafts provide a growth-permissive substratum and local neurotrophic factors to enhance the regenerative effort of axotomized neurons when grafted into the site of injury. Regenerating axons can be directed via the peripheral nerve graft toward an appropriate target, but they fail to extend beyond the distal graft–host interface because of the deposition of growth inhibitors at the site of SCI. One method to facilitate the emergence of axons from a graft into the spinal cord is to digest the chondroitin sulfate proteoglycans that are associated with a glial scar. Importantly, regenerating axons that do exit the graft are capable of forming functional synaptic contacts. These results have been demonstrated in acute injury models in rats and cats and after a chronic injury in rats and have important implications for our continuing efforts to promote structural and functional repair after SCI.     

Neural Regeneration Research Regeneration Following Spinal Cord Injury

<正>HTTP://WWW.NRRONLINE.ORGReorganization of spinal neural circuitry and functional recovery after spinal cord injury Autophagy in degenerating axons following spinal cord injury:evidence for autophagosome biogenesis in retraction bulbsBad regeneratorsdie after spinal cord injury:insights from lampreys Induced pluripotent stem cell-derived neural stem cell therapies for spinal cord injury Electroacupuncture improves microcirculation and neuronal morphology in the spinal cord of a rat model of intervertebral disc extrusion     

Serotonergic Facilitation of Forelimb Functional Recovery in Rats with Cervical Spinal Cord Injury

Serotonergic agents can improve the recovery of motor ability after a spinal cord injury. Herein, we compare the effects of buspirone, a 5-HT_1A receptor partial agonist, to fluoxetine, a selective serotonin reuptake inhibitor, on forelimb motor function recovery after a C4 bilateral dorsal funiculi crush in adult female rats. After injury, single pellet reaching performance and forelimb muscle activity decreased in all rats. From 1 to 6 weeks after injury, rats were tested on these tasks with and without buspirone (1–2 mg/kg) or fluoxetine (1–5 mg/kg). Reaching and grasping success rates of buspirone-treated rats improved rapidly within 2 weeks after injury and plateaued over the next 4 weeks of testing. Electromyography (EMG) from selected muscles in the dominant forelimb showed that buspirone-treated animals used new reaching strategies to achieve success after the injury. However, forelimb performance dramatically decreased within 2 weeks of buspirone withdrawal. In contrast, fluoxetine treatment resulted in a more progressive rate of improvement in forelimb performance over 8 weeks after injury. Neither buspirone nor fluoxetine significantly improved quadrupedal locomotion on the horizontal ladder test. The improved accuracy of reaching and grasping, patterns of muscle activity, and increased excitability of spinal motor–evoked potentials after buspirone administration reflect extensive reorganization of connectivity within and between supraspinal and spinal sensory-motor netxcopy works. Thus, both serotonergic drugs, buspirone and fluoxetine, neuromodulated these networks to physiological states that enabled markedly improved forelimb function after cervical spinal cord injury.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13311-020-00974-8.Key Words: Serotonin, Spinal cord injury, Buspirone, Fluoxetine, Forelimb     

蛛网膜下腔移植自体激活许旺细胞治疗大鼠脊髓损伤***

背景：许旺细胞能够分泌多种神经营养因子,促进脊髓损伤功能的恢复。但异体许旺细胞移植可引发自身免疫反应,且在移植方式上,局部移植无法避免二次损伤,静脉移植虽可以透过血脊髓屏障到达损伤局部,但不能达到有效的治疗浓度。 目的：探讨经蛛网膜下腔移植自体激活许旺细胞对脊髓损伤大鼠功能恢复的影响。 方法：66只大鼠均建立脊髓损伤模型,造模后随机分为3组,自体激活许旺细胞组通过结扎单侧隐神经从而激活许旺细胞,自体未激活许旺细胞组、模型对照组仅在相同部位手术但不结扎神经。切除各组手术远端1 cm神经,采用组织块法进行许旺细胞的体外分离培养及纯化。1周后,自体激活许旺细胞组、自体未激活许旺细胞组分别通过蛛网膜下腔注入经Hoechst33342标记的对应许旺细胞悬液,模型对照组仅注入等量DMEM。对脊髓损伤后肢体功能的恢复进行BBB运动功能评分及脚印分析,通过苏木精-伊红染色和GFAP染色从组织学角度评价脊髓损伤恢复情况。 结果与结论：从术后第4周开始,自体激活许旺细胞组BBB后肢功能评分明显优于另两组(P < 0.05)。移植后2周,可见迁移至大鼠脊髓损伤局部的许旺细胞。与自体未激活许旺细胞组比较,移植后5周自体激活许旺细胞组的前后足中心距离、后肢第3足趾外旋角度均显著减小(P < 0.05),移植后13周损伤区胶质瘢痕面积明显减小(P < 0.05),损伤区空洞面积明显减小(P < 0.05)。证实经蛛网膜下腔移植自体激活许旺细胞可以促进脊髓损伤的恢复。     

Epidural Spinal Cord Stimulation Promotes Motor Functional Recovery by Enhancing Oligodendrocyte Survival and Differentiation and by Protecting Myelin after Spinal Cord Injury in Rats

Epidural spinal cord stimulation (ESCS) markedly improves motor and sensory function after spinal cord injury (SCI), but the underlying mechanisms are unclear.Here, we investigated whether ESCS affects oligodendrocyte differentiation and its cellular and molecular mechanisms in rats with SCI. ESCS improved hindlimb motor function at 7 days, 14 days, 21 days, and 28 days after SCI.ESCS also significantly increased the myelinated area at 28days, and reduced the number of apoptotic cells in the spinal white matter at 7 days. SCI decreased the expression of 20,30-cyclic-nucleotide 30-phosphodiesterase (CNPase,an oligodendrocyte marker) at 7 days and that of myelin basic protein at 28 days. ESCS significantly upregulated these markers and increased the percentage of Sox2/CNPase/DAPI-positive cells (newly differentiated oligodendrocytes) at 7 days. Recombinant human bone morphogenetic protein 4 (rh BMP4) markedly downregulated these factors after ESCS. Furthermore, ESCS significantly decreased BMP4 and p-Smad1/5/9 expression after SCI,and rh BMP4 reduced this effect of ESCS. These findings indicate that ESCS enhances the survival and differentiation of oligodendrocytes, protects myelin, and promotes motor functional recovery by inhibiting the BMP4-Smad1/5/9 signaling pathway after SCI.     

Neurotrophic Factors Increase Axonal Growth after Spinal Cord Injury and Transplantation in the Adult Rat

The capacity of CNS neurons for axonal regrowth after injury decreases as the age of the animal at time of injury increases. After spinal cord lesions at birth, there is extensive regenerative growth into and beyond a transplant of fetal spinal cord tissue placed at the injury site. After injury in the adult, however, although host corticospinal and brainstem-spinal axons project into the transplant, their distribution is restricted to within 200 μm of the host/transplant border. The aim of this study was to determine if the administration of neurotrophic factors could increase the capacity of mature CNS neurons for regrowth after injury. Spinal cord hemisection lesions were made at cervical or thoracic levels in adult rats. Transplants of E14 fetal spinal cord tissue were placed into the lesion site. The following neurotrophic factors were administered at the site of injury and transplantation: brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), ciliary-derived neurotrophic factor (CNTF), or vehicle alone. After 1–2 months survival, neuroanatomical tracing and immunocytochemical methods were used to examine the growth of host axons within the transplants. The neurotrophin administration led to increases in the extent of serotonergic, noradrenergic, and corticospinal axonal ingrowth within the transplants. The influence of the administration of the neurotrophins on the growth of injured CNS axons was not a generalized effect of growth factors per se, since the administration of CNTF had no effect on the growth of any of the descending CNS axons tested. These results indicate that in addition to influencing the survival of developing CNS and PNS neurons, neurotrophic factors are able to exert aneurotropicinfluence on injured mature CNS neurons by increasing their axonal growth within a transplant.     

Oligodendrocyte Fate after Spinal Cord Injury

Oligodendrocytes (OLs) are particularly susceptible to the toxicity of the acute lesion environment after spinal cord injury (SCI). They undergo both necrosis and apoptosis acutely, with apoptosis continuing at chronic time points. Loss of OLs causes demyelination and impairs axon function and survival. In parallel, a rapid and protracted OL progenitor cell proliferative response occurs, especially at the lesion borders. Proliferating and migrating OL progenitor cells differentiate into myelinating OLs, which remyelinate demyelinated axons starting at 2 weeks post-injury. The progression of OL lineage cells into mature OLs in the adult after injury recapitulates development to some degree, owing to the plethora of factors within the injury milieu. Although robust, this endogenous oligogenic response is insufficient against OL loss and demyelination. First, in this review we analyze the major spatial–temporal mechanisms of OL loss, replacement, and myelination, with the purpose of highlighting potential areas of intervention after SCI. We then discuss studies on OL protection and replacement. Growth factors have been used both to boost the endogenous progenitor response, and in conjunction with progenitor transplantation to facilitate survival and OL fate. Considerable progress has been made with embryonic stem cell-derived cells and adult neural progenitor cells. For therapies targeting oligogenesis to be successful, endogenous responses and the effects of the acute and chronic lesion environment on OL lineage cells must be understood in detail, and in relation, the optimal therapeutic window for such strategies must also be determined.     

Noninvasive Neuroprosthesis Promotes Cardiovascular Recovery After Spinal Cord Injury

Spinal cord injury (SCI) leads to severe impairment in cardiovascular control, commonly manifested as a rapid, uncontrolled rise in blood pressure triggered by peripheral stimuli—a condition called autonomic dysreflexia. The objective was to demonstrate the translational potential of noninvasive transcutaneous stimulation (TCS) in mitigating autonomic dysreflexia following SCI, using pre-clinical evidence and a clinical case report. In rats with SCI, we show that TCS not only prevents the instigation of autonomic dysreflexia, but also mitigates its severity when delivered during an already-triggered episode. Furthermore, when TCS was delivered as a multisession therapy for 6 weeks post-SCI, the severity of autonomic dysreflexia was significantly reduced when tested in the absence of concurrent TCS. This treatment effect persisted for at least 1 week after the end of therapy. More importantly, we demonstrate the clinical applicability of TCS in treatment of autonomic dysreflexia in an individual with cervical, motor-complete, chronic SCI. We anticipate that TCS will offer significant therapeutic advantages, such as obviating the need for surgery resulting in reduced risk and medical expenses. Furthermore, this study provides a framework for testing the potential of TCS in improving recovery of other autonomic functions such lower urinary tract, bowel, and sexual dysfunction following SCI.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13311-021-01034-5.Key Words: Spinal cord injuries, Cardiovascular dysfunction, Blood pressure, Autonomic dysreflexia, Transcutaneous stimulation, Noninvasive neuromodulation     

A Quantifiable Model of Axonal Regeneration in the Demyelinated Adult Rat Spinal Cord

Strategies to increase the extent of axonal regeneration in the adult CNS must address an array of intrinsic and environmental factors which influence neuritic outgrowth. In order to develop anin vivomodel of axonal regeneration in which potential therapies may be assessed, we have quantified growth cones within demyelinated regions in the dorsal funiculus of the spinal cord, following a discrete axotomy. Demyelinated lesions were produced by the intraspinal injection of galactocerebroside antibodies plus serum complement proteins. Axonal integrity was not compromised by the demyelination protocol. Axonal injury was induced at the caudal extent of the demyelinated region using a micromanipulator-controlled Scouten knife. The severity of axonal injury was varied in different animals at the time of surgery and was quantified 8 days later by counting degenerate axons in transverse 1-μm resin sections. Evidence of axonal regeneration within these animals was assessed by an electron microscopic analysis of growth cone frequency and position relative to the site of axotomy. Growth cones were identified within the region of demyelination only; no growth cones were identified within the dorsal column white matter adjacent to the demyelinated region, or rostral or caudal to the region of demyelination, or in animals with an injury but no demyelination. Quantification of growth cones within regions of demyelination indicated a strong linear relationship (P< 0.001) between the number of growth cones and the number of axons severed. These findings indicate that demyelination facilitates axonal regeneration in the adult rat CNS and illustrate a quantifiable method of assessing axonal regeneration.     

Inhibition of Autophagy by Estradiol Promotes Locomotor Recovery after Spinal Cord Injury in Rats

17β-estradiol(E2) has been shown to have neuroprotective effects in different central nervous system diseases. The mechanisms underlying estrogen neuroprotection in spinal cord injury(SCI) remain unclear. Previous studies have shown that autophagy plays a crucial role in the course of nerve injury. In this study, we showed that E2 treatment improved the restoration of locomotor function and decreased the loss of motor neurons in SCI rats. Realtime PCR and western blot analysis revealed that the protective function of E2 was related to the suppression of LC3 II and beclin-1 expression. Immunohistochemical study further confirmed that the immunoreactivity of LC3 in the motor neurons was down-regulated when treated with E2. In vitro studies demonstrated similar results that E2 pretreatment decreased the autophagic activity induced by rapamycin(autophagy sensitizer) and increased viability in a PC12 cell model. These results indicated that the neuroprotective effects of E2 in SCI are partly related to the suppression of excessive autophagy.     

Tacrolimus (FK506) Increases Neuronal Expression of GAP-43 and Improves Functional Recovery after Spinal Cord Injury in Rats

Tacrolimus (FK506), a widely used immunosuppressant drug, has neurite-promoting activity in cultured PC12 cells and peripheral neurons. The present study investigated whether tacrolimus affects the expression of the neuronal growth-associated protein, GAP-43, as well as functional recovery after photothrombotic spinal cord injury in the rat. In injured animals receiving tacrolimus, the number of neurons expressing GAP-43 mRNA and protein approximately doubled compared to that in injured animals receiving vehicle alone. This increase in GAP-43-positive cells was paralleled by a significant improvement in neurological function evaluated by open-field and inclined plane tests. Another FKBP-12 ligand (V-10,367) had similar effects on GAP-43 expression and functional outcome, indicating that the observed effects of tacrolimus do not involve inhibition of the phosphatase calcineurin. Thus, tacrolimus, a drug which is already approved for use in humans, as well as other FKBP-12 ligands which do not inhibit calcineurin, could potentially enhance functional outcome after CNS injury in humans.     

Crocetin Potentiates Neurite Growth in Hippocampal Neurons and Facilitates Functional Recovery in Rats with Spinal Cord Injury

Crocetin is an ingredient of traditional Chinese medicine and has therapeutic potential in various diseases due to its pharmacological properties, such as neuroprotection, anti-oxidative stress, and anti-inflammation. These properties might benefit the treatment of spinal cord injury.In the present study, we tested the effect of crocetin on neurite growth and sensorimotor dysfunction in a rat model of spinal cord injury. We evaluated the viability of cultured hippocampal neurons with tetrazolium dye and lactate dehydrogenase assays, visualized neurites and axons with antibody staining, and monitored motor and sensorimotor functions in rats with spinal cord injury using the Basso,Beattie, and Bresnahan assay and the contact plantar placement test, respectively, and measured cytokine expression using enzyme-linked immuno-absorbent assays.We found that crocetin(1) did not alter the viability of cultured hippocampal neurons;(2) accelerated neurite growth with preference for the longest process in individual hippocampal neurons;(3) reversed the inhibition of neurite growth by chondroitin sulfate proteoglycan and Nogo A;(4) facilitated the recovery of motor and sensorimotor functions after spinal cord injury; and(5) did not inhibit pro-inflammatory responses, but restored the innervation of the descending 5-HT system in injured spinalcord. Crocetin promotes neurite growth and facilitates the recovery of motor and sensorimotor functions after spinal cord injury, likely through repairing neuronal connections.     

神经干细胞移植修复鼠脊髓损伤的实验研究

目的 :观察神经干细胞移植治疗对鼠脊髓损伤后神经结构修复和功能恢复的作用并探讨其作用机制。方法 :制备鼠T10 脊髓损伤模型 ,体外培养、诱导鼠神经干细胞 ,定量评价神经干细胞移植对脊髓损伤后神经结构修复和功能恢复的影响。结果 :与对照组相比 ,神经干细胞移植组明显的增强了GAP 43mRNA的表达 ,促进了脊髓ChAT阳性的运动神经元的再生、结构的修复和下肢运动功能的恢复。结论 :神经干细胞移植促进了脊髓损伤后神经结构的修复和功能的恢复 ,是急性脊髓损伤一种有效的治疗方案     

Depletion of Hematogenous Macrophages Promotes Partial Hindlimb Recovery and Neuroanatomical Repair after Experimental Spinal Cord Injury

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

Expression of CAPON after Spinal Cord Injury in Rats

The adaptor protein, carboxy-terminal PDZ ligand of nNOS (CAPON), regulates the distribution of neuronal nitric oxide synthase (nNOS) that increased after spinal cord injury (SCI) and produces the key signaling molecule nitric oxide (NO). But little is known about the role of CAPON in the pathological process of SCI. The main objective of the present study was to investigate expression of CAPON and nNOS in a spinal cord contusion model in adult rats. Real time-polymerase chain reaction (PCR) and Western blot analysis revealed that mRNA and protein for CAPON increased at 2 h after SCI and reached the peak at 8 h, gradually recovered to the baseline level at 14 days. The expression of nNOS mRNA and protein was similar to that of CAPON. During the peak expression, CAPON mRNA was found in the ventral horn, mediate zone, dorsal horn, and white matter by in situ hybridization. Immunofluorescence showed that CAPON was colocalized with nNOS in neurons, oligodendrocytes, and some astrocytes of spinal cord tissues within 5 mm from the epicenter. Interaction between CAPON and nNOS was also detected by co-immunoprecipitation. Thus, the transient expression of high levels of CAPON may provide new insight into the secondary response after SCI. Chun Cheng and Xin Li contributed equally to this work.     

Spinal Cord Injury Induced by a Cervical Spinal Cord Stimulator

Objective: The use of cervical spinal cord stimulators for the treatment of refractory neck and upper extremity pain is widely accepted and growing in use as a treatment modality. This case highlights a previously unreported potential complication of spinal cord stimulators. Methods: Analysis of a patient with a cervical spinal cord stimulator presenting with a spinal cord injury. Patient was followed from presentation in the emergency room until 1‐year follow‐up in the office. Results: The patient in this case presented after a fall and sustained a cervical spinal cord injury induced by the electrodes of her spinal cord stimulator working as a space occupying mass. Conclusion: As more patients are undergoing implantation of spinal cord stimulators we must be aware of the long‐term risks that can be encountered.     

Spinal Cord Stimulation for Pain Treatment After Spinal Cord Injury

In addition to restoration of bladder, bowel, and motor functions, alleviating the accompanying debilitating pain is equally important for improving the quality of life of patients with spinal cord injury(SCI). Currently,however, the treatment of chronic pain after SCI remains a largely unmet need. Electrical spinal cord stimulation(SCS) has been used to manage a variety of chronic pain conditions that are refractory to pharmacotherapy. Yet, its efficacy, benefit profiles, and mechanisms of action in SCI pain remain elusive, due to limited research, methodological weaknesses in previous clinical studies, and a lack of mechanistic exploration of SCS for SCI pain control. We aim to review recent studies and outline the therapeutic potential of different SCS paradigms for traumatic SCI pain. We begin with an overview of its manifestations,classification, potential underlying etiology, and currentchallenges for its treatment. The clinical evidence for using SCS in SCI pain is then reviewed. Finally, future perspectives of pre-clinical research and clinical study of SCS for SCI pain treatment are discussed.     

Methylprednisolone Administration Improves Axonal Regeneration into Schwann Cell Grafts in Transected Adult Rat Thoracic Spinal Cord

Schwann cell (SC) grafts support the regeneration of axons of numerous spinal cord neurons when placed into transected adult rat midthoracic spinal cord. Clinically, methylprednisolone (MP) has been shown to be neuroprotective if administered within 8 h after spinal cord injury. We investigated whether axonal regrowth into SC grafts is enhanced when MP is administered at the time of spinal cord transection and SC implantation. SCs from adult rat sciatic nerves were purified in culture, suspended in Matrigel, and drawn into semipermeable polymeric channels. MP (30 mg/kg) or vehicle (control) was administered intravenously at 5 min, 2 h, and 4 h to adult Fischer rats after transection at T8 and removal of the next three caudal segments. The rostral cord stump was inserted 1 mm into the channel; the distal end of the channel was capped. Thirty to forty-five days later, the SC/MP group showed large tissue cables in the channels and host cord tissue retained in the rostral end of the channels. Significantly more myelinated axons (1159 ± 308) were present at the 5-mm level in SC/MP grafts (n = 6) than in SC/vehicle cables (355 ± 108,n = 5). More unmyelinated than myelinated axons (approximately 4:1,n = 3) were resolved in the cables by electron microscopy. In the SC/MP group, unlike the SC/vehicle group, serotonergic and noradrenergic fibers were detected immunocytochemically 2.5 and 2.0 mm, respectively, into the graft; astrocytes were also identified at similar distances from the interface. Fast Blue retrograde tracing (SC/MP,n = 4; SC/vehicle,n = 3) showed that more spinal cord neurons (1116 ± 113 vs 284 ± 88, respectively) and spinal cord neurons more distant from the graft (C8 vs C5) responded by extending axons into the graft in the presence of MP. Also, very significantly, supraspinal brain stem neurons extended axons into the graft only when MP was administered (mean 46 vs 0,n = 3). These results indicate that MP improves axonal regeneration from both spinal cord and brain stem neurons into thoracic SC grafts, possibly by reducing secondary host tissue loss adjacent to the graft.