Direct evidence of primary afferent sprouting in distant segments following spinal cord injury in the rat: colocalization of GAP-43 and CGRP

Mechanical and thermal allodynia develops after spinal cord injury in three areas relative to the lesion: below level, at level, and above level. The present study tests colocalization of CGRP, associated with nociceptive neurons, with growth-associated protein (GAP-43), expressed in growing neurites, to test for neurite sprouting as a mechanism for reorganization of pain pathways at the level of the lesion and distant segments. Male Sprague-Dawley rats were divided into three groups: sham control (N = 10), hemisected at T13 and sacrificed at 3 days (N = 5) and at 30 days (N = 5) following surgery, the spinal cord tissue was prepared for standard fluorescent immunocytochemistry using mouse monoclonal anti-GAP-43 (1:200) and/or rabbit polyclonal anti-CGRP (1:200), density of immunoreaction product (IR) was quantified using the Bioquant software and values from the hemisected group were compared to similar regions from the sham control. We report significant increases at C8 and L5, in CGRP-IR in lamina III compared to control tissue (P < 0.05). We report significant bilateral increases in GAP-43-IR at C8, T13, and L5 segments in lamina I through IV, at 3 days post hemisection, compared to control tissue (P < 0.05), some of which is colocalized with alpha-CGRP. The increased area and density of GAP-43-IR is consistent with neurite sprouting, and the colocalization with alpha-CGRP indicates that some of the sprouting neurites are nociceptive primary afferents. These data are consistent with endogenous regenerative neurite growth mechanisms that occur near and several segments from a spinal lesion, that provide one of many substrates for the development and maintenance of the dysfunctional state of allodynia after spinal cord injury.     

Differentiation and tropic/trophic effects of exogenous neural precursors in the adult spinal cord

The fate of exogenous neural stem cells (NSCs) in the environment of the adult nervous system continues to be a matter of debate. In the present study, we report that cells of the murine NSC clone C17.2, when grafted into the lumbar segments of the spinal cord of adult rats, survive and undergo partial differentiation. C17.2 cells migrate avidly toward axonal tracts and nerve roots and differentiate into nonmyelinating ensheathing cells. Notably, C17.2 cells induce the de novo formation of host axon tracts aiming at graft innervation. Differentiation and inductive properties of C17.2 cells are independent of the presence of lesions in the spinal cord. The tropic/trophic interactions of C17.2 NSCs with host axons, the avid C17.2 cell-host axon contacts, and the ensheathing properties of these cells are related to their complex molecular profile, which includes the expression of trophic cytokines and neurotrophins such as glial cell line-derived neurotrophic factor and brain-derived neurotrophic factor, glial growth factor receptors such as ErbB-2; and PASK, the mammalian homologue of the fray gene that is involved in axon ensheathment. These results show that NSCs might not only play a critical supportive role in repairing axonal injury in the adult spinal cord but also can be used as probes for exploring the molecular underpinnings of the regenerative potential of the mature nervous system after injury.     

Reducing host aldose reductase activity promotes neuronal differentiation of transplanted neural stem cells at spinal cord injury sites and facilitates locomotion recovery

Neural stem cell(NSC)transplantation is a promising strategy for replacing lost neurons following spinal cord injury.However,the survival and differentiation of transplanted NSCs is limited,possibly owing to the neurotoxic inflammatory microenvironment.Because of the important role of glucose metabolism in M1/M2 polarization of microglia/macrophages,we hypothesized that altering the phenotype of microglia/macrophages by regulating the activity of aldose reductase(AR),a key enzyme in the polyol pathway of glucose metabolism,would provide a more beneficial microenvironment for NSC survival and differentiation.Here,we reveal that inhibition of host AR promoted the polarization of microglia/macrophages toward the M2 phenotype in lesioned spinal cord injuries.M2 macrophages promoted the differentiation of NSCs into neurons in vitro.Transplantation of NSCs into injured spinal cords either deficient in AR or treated with the AR inhibitor sorbinil promoted the survival and neuronal differentiation of NSCs at the injured spinal cord site and contributed to locomotor functional recovery.Our findings suggest that inhibition of host AR activity is beneficial in enhancing the survival and neuronal differentiation of transplanted NSCs and shows potential as a treatment of spinal cord injury.     

Intraspinal sprouting of calcitonin gene-related peptide containing primary afferents after deafferentation in the rat.

The occurrence of sprouting in the spinal cord in response to denervation has been a subject of debate. To test for sprouting of primary afferent fibers after denervation, rats were unilaterally deafferented for 35 days (chronic side) by dorsal rhizotomies performed from T2 to T8 and T10 to L5, thus isolating or sparing the T9 root. The contralateral T9 root was spared by a similar surgery 5 days (acute side) prior to sacrifice. The survival time on the chronic side presumably allows intraspinal sprouting of T9 primary afferents to occur whereas the time on the acute side does not. To test for sprouting of primary afferents, it is necessary to identify these nerve processes. Calcitonin gene-related peptide (CGRP) immunoreactivity has been localized to a subpopulation of primary afferent nerve processes and their terminals within the dorsal horn. Therefore, immunohistochemical methods were used to determine the distribution of CGRP immunoreactivity in laminae I and II on both sides of the spinal cord. Using image analysis, there was an increase of 153 to 704% in the density of CGRP immunoreaction product on the chronic side compared to the acute side in the spared segment. This difference is statistically significant. Furthermore, the increased density on the chronic side extended two segments cranial and two segments caudal to the spared root segment. No difference was found in the laminar distribution between sides. These data support the hypothesis of primary afferent sprouting following spinal cord denervation.     

胚胎小鼠脊髓源性与纹状体源性神经干细胞的培养及分化特点

目的 探讨小鼠脊髓源性神经干细胞与纹状体源性神经干细胞的分离培养方法 及增殖特点,比较两种来源的神经干细胞发育时期上的异同,寻找更有利于脊髓损伤修复的种子细胞.方法 利用显微解剖、无血清培养和单细胞克隆技术在孕14 d小鼠的胎鼠的脊髓及纹状体中分离培养具有单细胞克隆能力的细胞,免疫荧光染色检测克隆细胞的神经巢蛋白(nestin)抗原和诱导分化后特异性成熟神经细胞抗原的表达,并比较两种来源的干细胞在培养及分化方向上的异同点.结果从胎鼠的脊髓和纹状体中成功分离出神经干细胞.两种来源的干细胞均具有连续克隆能力可传代培养,表达nestin.脊髓血清诱导分化后脊髓源性神经干细胞β-tubulinⅢ阳性细胞(13.5±0.8)较纹状体源性神经干细胞(17.4±1.1)减少,而nestin、GFAP阳性细胞明显增多(45.7±0.3vs 39.2±1.2;25.2±1.3 vs 18.8±0.9),差异均有统计学意义(P<0.05). 结论 依据细胞增殖特点和分化结果的区别,证实纹状体源性神经干细胞更适合用于移植修复脊髓损伤.     

Neural stem cells constitutively secrete neurotrophic factors and promote extensive host axonal growth after spinal cord injury

Neural stem cells (NSCs) offer the potential to replace lost tissue after nervous system injury. This study investigated whether grafts of NSCs (mouse clone C17.2) could also specifically support host axonal regeneration after spinal cord injury and sought to identify mechanisms underlying such growth. In vitro, prior to grafting, C17.2 NSCs were found for the first time to naturally constitutively secrete significant quantities of several neurotrophic factors by specific ELISA, including nerve growth factor, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor. When grafted to cystic dorsal column lesions in the cervical spinal cord of adult rats, C17.2 NSCs supported extensive growth of host axons of known sensitivity to these growth factors when examined 2 weeks later. Quantitative real-time RT-PCR confirmed that grafted stem cells expressed neurotrophic factor genes in vivo. In addition, NSCs were genetically modified to produce neurotrophin-3, which significantly expanded NSC effects on host axons. Notably, overexpression of one growth factor had a reciprocal effect on expression of another factor. Thus, stem cells can promote host neural repair in part by secreting growth factors, and their regeneration-promoting activities can be modified by gene delivery.     

Transplantation of neural stem cells for spinal cord injury]

Neural progenitor cells, including neural stem cells (NSCs), are an important potential graft material for cell therapeutics of damaged spinal cord. Here we used as a source of graft material a NSC-enriched population derived from human fetal spinal cord (Embryonic week 8-9) and expanded in vitro by neurosphere formation. NSCs labeled with BrdU (TP) or culture medium (CON) were transplanted into the adult marmoset spinal cord after contusion injury at C5 level. Grafted NSCs survived and migrated up to 7 mm far from the lesion epicenter. Double-staining with TuJ1 for neuron, GFAP for astrocyte, or CNPase for oligodendrocyte and BrdU revealed that grafted NSCs differentiated into neurons and oligodendrocytes 8 weeks after transplantation. More neurofilaments were observed in TP than those of CON. Furthermore, behavioral assessment of forelimb muscle strength using bar grip test and amount of spontaneous motor activity using infrared-rays monitoring revealed that the grafted NSCs significantly increased both of them compared to those of CON. These results indicate that in vitro expanded NSCs derived from human fetal spinal cord are useful sources for the therapeutics of spinal cord injury in primates.     

Spinally upregulated noggin suppresses axonal and dendritic plasticity following dorsal rhizotomy

Bone morphogenetic proteins (BMPs) and their antagonists, including noggin, are required for nervous system development, but their potential roles in the reactions of the adult central nervous system to injury are unknown. Here we have examined the expression of noggin and BMPs in the spinal cord following dorsal rhizotomy. Through the use of a function-blocking antibody, we have also investigated the role of endogenous noggin in the neuritic plasticity which follows rhizotomy. Dorsal rhizotomy resulted in the upregulation of BMPs 2/4, 7 and noggin in the superficial white matter and in the dorsal neuropil of the spinal cord. These co-localized with glial fibrillary acidic protein, indicating their expression by astrocytes. Because BMPs induce dendritic sprouting and synaptogenesis in some neuronal populations in vitro, we hypothesized that administration of a noggin function-blocking antibody (FbAb) in vivo would augment rhizotomy-induced sprouting in the spinal cord. Topical application of noggin-FbAb to the dorsal surface of the spinal cord following rhizotomy resulted in significant increases in the density of microtubule-associated protein 2 (MAP-2) and substance P (SP)-positive processes within the lateral spinal nucleus. In the deafferented dorsal horn, noggin-FbAb treatment induced significant increases in the density of SP, calcitonin gene-related peptide (CGRP)- and 5-hydroxytryptamine (5-HT)-positive axons. These results suggest a novel mechanism by which endogenous plasticity of spared axons is suppressed following dorsal rhizotomy, and which might be exploited to improve the outcome of spinal cord injury and other CNS trauma.     

Glial cell line-derived neurotrophic factor increases calcitonin gene-related peptide immunoreactivity in sensory and motoneurons in vivo

Calcitonin gene-related peptide (CGRP) is expressed at high levels in roughly 50% of spinal sensory neurons and plays a role in peripheral vasodilation as well as nociceptive signalling in the spinal cord. Spinal motoneurons express low levels of CGRP; motoneuronal CGRP is thought to be involved in end-plate plasticity and to have trophic effects on target muscle cells. As both sensory and motoneurons express receptors for glial cell line-derived neurotrophic factor (GDNF) we sought to determine whether CGRP was regulated by GDNF. Rats were treated intrathecally for 1-3 weeks with recombinant human GDNF or nerve growth factor (NGF) (12 microg/day) and dorsal root ganglia and spinal cords were stained for CGRP. The GDNF treatment not only increased CGRP immunoreactivity in both sensory and motoneurons but also resulted in hypertrophy of both populations. By combined in situ hybridization and immunohistochemistry we found that, in the dorsal root ganglia, CGRP was up-regulated specifically in neurons expressing GDNF but not NGF receptors following GDNF treatment. Despite the increase in CGRP in GDNF-treated rats, there was no increase in thermal or mechanical pain sensitivity, while NGF-treated animals showed significant decreases in pain thresholds. In motoneurons, GDNF increased the overall intensity of CGRP immunoreactivity but did not increase the number of immunopositive cells. As GDNF has been shown to promote the regeneration of both sensory and motor axons, and as CGRP appears to be involved in motoneuronal plasticity, we reason that at least some of the regenerative effects of GDNF are mediated through CGRP up-regulation.     

Nogo-6受体基因沉默神经干细胞立体定向移植治疗重型脑损伤

Inhibition of neurite growth, which is mediated by the Nogo-66 receptor (NgR), affects nerve regeneration following neural stem cell (NSC) transplantation. The present study utilized RNA interference to silence NgR gene expression in NSCs, which were subsequently transplanted into rats with traumatic brain injury. Following transplantation of NSCs transfected with small interfering RNA, typical neural cell-like morphology was detected in injured brain tissues, and was accompanied by absence of brain tissue cavity, increased growth-associated protein 43 mRNA and protein expression, and improved neurological function compared with NSC transplantation alone. Results demonstrated that NSC transplantation with silenced NgR gene promoted functional recovery following brain injury.     

Migration and differentiation of neural progenitor cells from two different regions of embryonic central nervous system after transplantation into the intact spinal cord

Transplantation of in vitro-expanded neural stem cells (NSCs) is a potentially powerful tool to repair functions of the injured spinal cord. A prerequisite for the successful transplantation therapy is identification of optimized experimental parameters that can promote maximal survival, extensive migration and selective differentiation of the transplanted NSC population in the spinal cord. To this end, we evaluated the basic characteristics of NSC-like cells from two different donor sources, the embryonic hippocampus and spinal cord, after transplantation into the neonatal spinal cord. Proliferation and differentiation phenotypes of both NSC-like cells can be controlled by the concentration of fibroblast growth factor-2 (FGF-2) in vitro. Both NSC-like cells can survive within the environment of the intact neonatal spinal cord and showed extensive migratory behaviour shortly after transplantation. However, quantitative analysis revealed preferential migration of hippocampus-derived cells in the dorsal white matter. Both NSC-like cells showed restricted phenotype toward the oligodendroglial lineage after transplantation. Transplantation of the mixture of two cell types revealed selective survival of hippocampus-derived NSC-like cells. This study indicates the possibility of transplanting hippocampus-derived NSCs to supply the cell source for immature oligodendrocytes, which are thought to be essential for both the myelination and trophic support of regenerating axons in the dorsal white matter of the spinal cord.     

Hypoxia-specific VEGF-expressing neural stem cells in spinal cord injury model

We established three stable neural stem cell (NSC) lines to explore the possibility of using hypoxia-specific vascular endothelial growth factor (VEGF) expressing NSC lines (EpoSV-VEGF NSCs) to treat spinal cord injury. The application of EpoSV-VEGF NSCs into the injured spinal cord after clip compression injury not only showed therapeutic effects such as extended survival and angiogenesis, but also displayed its safety profile as it did not cause unwanted cell proliferation or angiogenesis in normal spinal cord tissue, as EpoSV-VEGF NSCs consistently showed hypoxia-specific VEGF expression patterns. This suggests that our EpoSV-VEGF NSCs are both safe and therapeutically efficacious for the treatment of spinal cord injury. Furthermore, this hypoxia-inducible gene expression system may represent a safe tool suitable for gene therapy.     

Mechanisms underlying the pathogenesis of urinary bladder instability - new perspectives for the treatment of reflex incontinence

The urine storage ability of the urinary bladder is markedly impaired following inflammation of the urinary bladder and spinal cord injury because of a hyperexcitability of micturition reflexes. Using two rat models of inflammation-induced bladder overactivity and detrusor hyper-reflexia following spinal cord injury we investigated changes in the neuronal pathways to the urinary bladder which may underlie the development of this instability. Our results suggest that among the factors involved in inflammation-induced bladder instability are significant changes in the expression of the neuropeptides substance P, calcitonin gene-related peptide and galanin at the primary afferent level, as well as of the enzyme neuronal nitric oxide synthase (nNOS) at the afferent and postganglionic efferent level. In the lumbar and sacral spinal cord nNOS-immunoreactivity was depleted from dorsal horn neurones in both cystitis and spinal cord injured rats and from preganglionic parasympathetic neurones after spinal cord injury. Distension of the bladder in chronically spinalized rats elicited c-Fos expression in a significantly greater number of neurones throughout the lumbar and sacral segments than in rats with an intact neuraxis. Thus, under pathological conditions rather complicated changes in the synthesis of neuropeptides and nNOS occur at the primary afferent, spinal cord and postganglionic efferent level that together control the activity of the urinary bladder. Further mechanisms like unmasking of silent synapses and axonal sprouting in the spinal cord might further contribute to an increase in activity in micturition reflex pathways. Local cooling of the dorsal spinal cord at the level L6/S1 with temperatures between 14 and 20 °C proved a simple technique to control the unstable bladder and restore continence in both inflammation-induced detrusor overactivity and detrusor hyperreflexia following spinal cord injury. The effects of cooling are probably the result of a blockade of synaptic transmission within the dorsal cord which eliminates neuronal overactivity. Thus, local spinal cord cooling could offer a new method to treat bladder instability and reflex incontinence.     

HIF-1α基因修饰神经干细胞移植对大鼠损伤脊髓NF200和GFAP表达的影响

【摘要】目的研究低氧诱导因子-1α（HI-1α）基因修饰的神经干细胞移植对大鼠脊髓损伤后神经丝蛋白200（NF200）和胶质纤维酸性蛋白（GFAP）表达的影响及意义。方法采用电控脊髓损伤打击装置制作大鼠脊髓损伤模型。按随机数字表将120只SD大鼠平均分为4组：假手术组（Sham组）,单纯损伤组（SCI组）,神经干细胞组（NSC组）和HIF-1α基因修饰NSC组（HIF—NSC组）。应用免疫组化法检测受伤脊髓中HIF-1α、NF200和GFAP的表达。结果HIF-NSC组中HIF-1αt免疫阳性细胞平均光密度值比其他各组各时间点均高（P〈O．01）,且表达高峰延迟至移植后14d;除第1天外,HIF—NSC组NF200表达比SCI组和NSC组明显增高（P〈0．05）,移植后28dNF200免疫阳性轴突数目也比SCI组和NSC组明显增多（P〈0．01）;移植后7d、14d、28dGFAP免疫阳性细胞面积均比SCI组和NSC组明显减少（P〈0．01）。结论HIF-1α基因修饰NSC移植可引起HIF-1α在损伤脊髓内有效表达,且能明显的促进NF200的表达,并能在脊髓损伤的后期抑制GFAP的表达。这提示HIF-1α基因修饰的NSC移植可减少受伤脊髓中胶质细胞的增生和胶质疤痕的形成,促进轴突再生。     

Combined NgR vaccination and neural stem cell transplantation promote functional recovery after spinal cord injury in adult rats

C‐J. Xu, L. Xu, L‐D. Huang, Y. Li, P‐P. Yu, Q. Hang, X‐M. Xu and P‐H. Lu (2011) Neuropathology and Applied Neurobiology 37, 135–155
Combined NgR vaccination and neural stem cell transplantation promote functional recovery after spinal cord injury in adult rats Aims: After spinal cord injury (SCI), there are many adverse factors at the lesion site such as glial scar, myelin‐derived inhibitors, cell loss and deficiency of neurotrophins that impair axonal regeneration. Therefore, combination therapeutic strategies might be more effective than a single strategy for promoting functional recovery after SCI. In the present study, we investigated whether a Nogo66 receptor (NgR) vaccine, combined with neural stem cell (NSC) transplantation, could promote better functional recovery than when NgR vaccine or NSCs were used alone. Methods: Adult rats were immunized with NgR vaccine at 1 week after a contusive SCI at the thoracic level, and the NSCs, obtained from green fluorescent protein transgenic rats, were transplanted into the injury site at 8 weeks post injury. The functional recovery of the animals under various treatments was evaluated by three independent behavioural tests, that is, Basso, Beattie and Bresnahan locomotor rating scale, footprint analysis and grid walking. Results: The combined therapy with NgR vaccination and NSC transplantation protected more ventral horn motor neurones in the injured spinal cord and greater functional recovery than when they were used alone. Furthermore, NgR vaccination promoted migration of engrafted NSCs along the rostral‐caudal axis of the injured spinal cords, and induced their differentiation into neurones and oligodendrocytes in vivo. Conclusions: The combination therapy of NgR vaccine and NSC transplantation exhibited significant advantages over any single therapy alone in this study. It may represent a potential new therapy for SCI.     

Neurotrophin-3 antisense oligonucleotide attenuates nerve injury-induced Abeta-fibre sprouting

It is proposed that following peripheral nerve injury abnormal sprouting of Abeta-fibre primary afferent neurons in the spinal cord contributes to the allodynia that often occurs with such injury. Allodynia is characterized as pain due to a stimulus which is normally non-noxious. Our recent in vivo experiments show that intrathecal administration of neurotrophin-3 (NT-3), in normal animals, induces allodynia and sprouting of Abeta-fibres. In this study, we examine whether intrathecal administration of NT-3 antisense oligonucleotides (50 microM), via an osmotic pump for 14 days, attenuates nerve injury-induced sprouting and allodynia. The oligonucleotides used in this study were phosphorothioate modified and control experiments, using an ELISA, confirm that intrathecal administration of the antisense induces a significant decrease in NT-3 levels in the spinal cord. All surgery was conducted on anaesthetized Wistar rats (sodium pentobarbitone, i.p. 50 mg/kg). Consistent with previous studies, transganglionic labelling of Abeta-fibres with choleragenoid-horseradish peroxidase (C-HRP) shows that complete transection of the sciatic nerve induces an expansion of C-HRP label into lamina II of the spinal dorsal horn. Using image analysis, we find that intrathecal administration of NT-3 antisense attenuates the density of C-HRP labelling in lamina II in nerve injured animals. A NT-3 sense oligonucleotide (50 microM) has no effect. To test the effect of NT-3 antisense on allodynia, the nociceptive flexion reflex is examined, using an Ugo Basile Analgesymeter, in animals with partial sciatic nerve ligation. Intrathecal administration of 50 microM NT-3 antisense significantly attenuates nerve injury-induced allodynia, whereas the sense oligonucleotide has no effect. These results provide further evidence that endogenous NT-3 contributes to both nerve injury-induced Abeta-fibre sprouting and allodynia and demonstrates the potential of neurotrophin-3 antisense oligonucleotides as therapeutic agents for neuropathic pain.     

神经生长因子联合神经干细胞移植治疗大鼠脊髓损伤

背景：单纯的神经干细胞移植对受损脊髓组织的修复作用并不理想,研究证实神经生长因子兼有神经元营养和促突起生长双重作用,可以有效的促进脊髓损伤后神经功能的恢复。 目的：观察神经干细胞移植联合应用神经生长因子对脊髓损伤后大鼠运动功能恢复的影响。 方法：SD大鼠42只,建立急性脊髓损伤模型后随机分成3组,伤后1周于损伤处分别注入培养液、单纯神经干细胞或神经干细胞联合神经生长因子。于伤后1,2,4,6,8周进行BBB评分和斜板实验等运动功能检测。伤后4周取材行病理切片苏木精-伊红染色及BrdU免疫组化染色,伤后8周取材行辣根过氧化物酶示踪观察及体感诱发电位观察神经电生理恢复情况。 结果与结论：伤后4周单纯神经干细胞组、神经干细胞联合神经生长因子组大鼠后肢运动功能均有较明显恢复,神经干细胞联合神经生长因子组较单纯神经干细胞组快,差异有显著性意义(P < 0.05)。培养液组亦有所恢复,但程度较轻。病理切片显示培养液组未见神经轴索通过。单纯神经干细胞组可见少量神经轴索样结构,神经干细胞联合神经生长因子组可见较多神经轴索样结构。BrdU的阳性细胞数及HRP阳性神经纤维数：神经干细胞联合神经生长因子组>单纯神经干细胞组>培养液组且各组之间差异有显著性意义(P < 0.01)。神经干细胞联合神经生长因子组大鼠体感诱发电位的潜伏期、波幅优于单纯神经干细胞组(P < 0.05),明显优于培养液组(P < 0.01)。结果提示神经干细胞移植对于后肢功能的恢复有促进作用,联合应用神经生长因子有协同效果。     

Spinal cord compression injury in adult rats initiates changes in dorsal horn remodeling that may correlate with development of neuropathic pain

Spinal cord injury commonly causes chronic, neuropathic pain. The mechanisms are poorly understood but may include structural plasticity within spinal and supraspinal circuits. Our aim was to determine whether structural remodeling within the dorsal horn rostral to an incomplete injury differs from a complete spinal cord transection. Four immunohistochemical populations of primary afferent C‐fibers, and descending catecholamine and serotonergic projections, were examined in segments T9–T12 at 2 and 12 weeks after a T13 clip‐compression injury in adult male rats. Dorsal root ganglia were also examined. Two weeks after injury, fibers immunoreactive for calcitonin gene‐related peptide (CGRP) or GDNF‐family receptors (GFRα1, GFRα2, GFRα3) showed distinct injury responses within the superficial dorsal horn. CGRP fibers decreased, but GFRα1, GFRα2 and GFRα3 fibers did not change. In contrast, all groups were decreased by 12 weeks after injury. Catecholamine fibers showed a decrease at 2 weeks followed by an increase in density at 12 weeks, whereas serotonergic fibers showed a decrease (restricted to deep dorsal horn) at 12 weeks. These results show that the dorsal horn of the spinal cord undergoes substantial structural plasticity rostral to a compression injury, with the most profound effect being a prolonged and possibly permanent loss of primary afferent fibers. This loss was more extensive and more prolonged than the loss that follows spinal cord transection. Our results provide further evidence that anatomical reorganization of sensory and nociceptive dorsal horn circuits rostral to an injury could factor in the development or maintenance of spinal cord injury pain. J. Comp. Neurol. 513:668–684, 2009. © 2009 Wiley‐Liss, Inc.     

Cortical and subcortical plasticity in the brains of humans, primates, and rats after damage to sensory afferents in the dorsal columns of the spinal cord

The failure of injured axons to regenerate following spinal cord injury deprives brain neurons of their normal sources of activation. These injuries also result in the reorganization of affected areas of the central nervous system that is thought to drive both the ensuing recovery of function and the formation of maladaptive neuronal circuitry. Better understanding of the physiological consequences of novel synaptic connections produced by injury and the mechanisms that control their formation are important to the development of new successful strategies for the treatment of patients with spinal cord injuries. Here we discuss the anatomical, physiological and behavioral changes that take place in response to injury-induced plasticity after damage to the dorsal column pathway in rats and monkeys. Complete section of the dorsal columns of the spinal cord at a high cervical level in monkeys and rats interrupts the ascending axon branches of low threshold mechanoreceptor afferents subserving the forelimb and the rest of the lower body. Such lesions render the corresponding part of the somatotopic representation of primary somatosensory cortex totally unresponsive to tactile stimuli. There are also behavioral consequences of the sensory loss, including an impaired use of the hand/forelimb in manipulating small objects. In monkeys, if some of the afferents from the hand remain intact after dorsal column lesions, these remaining afferents extensively reactivate portions of somatosensory cortex formerly representing the hand. This functional reorganization develops over a postoperative period of 1 month, during which hand use rapidly improves. These recoveries appear to be mediated, at least in part, by the sprouting of preserved afferents within the cuneate nucleus of the dorsal column-trigeminal complex. In rats, such functional collateral sprouting has been promoted by the post-lesion digestion of the perineuronal net in the cuneate nucleus. Thus, this and other therapeutic strategies have the potential of enhancing sensorimotor recoveries after spinal cord injuries in humans.