晚期周围神经损伤后感觉功能恢复中:脊髓后角P物质及降钙素基因相关肽的变化

背景晚期周围神经损伤有无修复价值?如果脊髓神经元中P物质和降钙素基因相关肽的变化发生了不可逆的变化,其修复后也预示着感觉功能的缺失. 目的定量研究周围神经损伤24周后,脊髓后角中P物质和降钙素基因相关肽的变化.设计建立以大鼠坐骨神经损伤为研究对象的实验模型,损伤后24周为最远期观察点,自身对照(对侧空白组),定量化研究.单位第四军医大学骨科研究所.材料实验于2002-10/2003-05在第四军医大学骨科研究所完成.SD大鼠55只,分成11组,即坐骨神经切断1,2,3,4,6,8,10,12,16,20,24周各组.干预切断大鼠一侧坐骨神经并结扎其近端的方法建立周围神经损伤模型;另一侧为对照侧.应用计算机图像分析技术测试P物质和降钙素基因相关肽免疫反应区的面积.主要观察指标各组大鼠脊髓后角中P物质和降钙素基因相关肽阳性纤维的终末分布面积的变化.结果55只大鼠均进入结果分析.①P物质时间序列表示周围神经损伤后2～6周,P物质在脊髓后角免疫反应区面积下降至最低,随之回升,至16周恢复正常,20,24周无明显的进一步变化.②脊髓后角降钙素基因相关肽阳性纤维和终末分布面积损伤与自身对照侧的比值1周时1.14,6周时1.13,24周时0.29,各时间点基本相似(P＞0.05)结论周围神经损伤至晚期,脊髓后角及后根神经节细胞合成和分泌P物质及降钙素基因相关肽的功能尚未受到破坏,脊髓后角已处于一种稳定的平衡状态,仍有恢复感觉功能的神经学基础.     

Evoked bursting in injured Aβ dorsal root ganglion neurons: a mechanism underlying tactile allodynia

Chronic compression of rat dorsal root ganglion (CCD) produced tactile allodynia accompanied with hyperexcitability of the myelinated Aβ dorsal root ganglion (DRG) neurons. The Aβ DRG neuron hyperexcitability exhibits as bursting discharges in response to peripherally evoked action potentials (evoked bursting [EB]). The incidence of EB was significantly increased after chronic compression of DRG (CCD) (43.3%) vs control (13.3%). EB was maintained by oscillation of the membrane potential, and its duration was increased when the membrane potential was depolarized. EB was found to coexist in some neurons with spontaneous bursting (SB), but EB always occurred at a more negative membrane potential than SB. Afterdischarges of the wide dynamic range neurons of the dorsal horn in the spinal cord in response to electrical stimulation of Aβ afferent nerve fibers were suppressed by blocking EB of the DRG neurons. CCD neurons with EB exhibited increased current density of persistent sodium current (I(Nap)) and hyperpolarization-activated cation current (I(h)) and decreased α-dendrotoxin (α-DTX) sensitive current (I(DTX)). The increased I(h) activated by afterhyperpolarization of peripheral afferent action potential was necessary for EB generation and a balance between I(DTX) and I(Nap) might be necessary for EB maintenance. This study may suggest a role of EB of myelinated DRG neurons in development of allodynia after nerve injury and a potential pharmaceutical therapy in treating neuropathic allodynia.     

肢体负压对周围动脉闭塞犬脊髓及背根神经节降钙素基因相关肽免疫反应性神经的影响

背景伤害性刺激可引起脊髓及背根神经节降钙素基因相关肽分泌的增多,及其微血管的强烈扩张.应用肢体负压治疗周围动脉闭塞性病变时,其扩张血管,减轻肢体疼痛症状的作用是否伴随着降钙素基因相关肽合成增多.目的对周围动脉闭塞性病变犬行肢体负压干预后,检测脊髓及背根神经节中降钙素基因相关肽免疫反应阳性神经纤维的变化.设计随机分组,实验组及空白组对照的验证性研究.单位一所军医大学医院普外科.材料实验于2003-01/08在第四军医大学西京医院完成.成年健康杂种犬17只,体质量(12～18)kg,雌雄不限.干预犬17只,随机分为3组.①治疗组10只将动物制作左后肢缺血模型,制作后14 d,开始行患肢负压治疗10 d,结束后,取L1～5的脊髓及背根神经节,行免疫组化染色,检测降钙素基因相关肽免疫反应阳性纤维.②单纯造模组5只造模后不进行患肢负压治疗,处理、检查均同治疗组.③正常对照组2只不行缺血模型制作及负压治疗,仅行免疫组化染色检测.主要观察指标3组犬脊髓及背根神经节中降钙素基因相关肽免疫反应阳性纤维分布.结果17只犬均进入结果分析.①脊髓及背根神经节中降钙素基因相关肽免疫反应阳性纤维单纯造模组明显高于治疗组和正常对照组[(75.00±4.30)%,(68.20±2.60)%;(58.20±5.10)%,(52.20±6.20)%;(37.00±4 20)%,(34.00±1.40)%,P＜0.01].②阳性神经纤维检测结果治疗组比单纯造模组染色变浅,但仍较正常对照组加深,3组比较差异意义显著(P均＜0.01).结论肢体负压疗法可以减少周围动脉闭塞性病变后脊髓及背根神经节中降钙素基因相关肽免疫反应阳性纤维的合成与痛觉的传递,即减少伤害性刺激的传入,从而达到缓解肢体疼痛的效果.     

Increased excitability and spontaneous activity of rat sensory neurons following in vitro stimulation of sympathetic fiber sprouts in the isolated dorsal root ganglion

Many chronic pain conditions including complex regional pain syndrome are exacerbated by sympathetic activity. In animal models, sympathetic fibers sprout into the dorsal root ganglia (DRG) after peripheral nerve injury, forming abnormal connections with sensory neurons. However, functional studies of sympathetic-sensory connections have been limited largely to in vivo studies. This study describes a new method for studying sympathetic-sensory connections in an isolated whole DRG preparation in the rat spinal nerve ligation (SNL) model. Three days after ligation of the ventral ramus of the spinal nerve (SNL), sympathetic fibers sprouting into the DRG were observed to originate largely in the intact dorsal ramus of the spinal nerve, which at the lumbar level is a small branch of the spinal nerve separating from the ventral ramus near the intervertebral foramen. In whole DRG isolated 3 days after SNL, microelectrode recordings of sensory neurons showed that repeated stimulation of the dorsal ramus enhanced spontaneous activity in large and medium diameter neurons and reduced rheobase in large neurons. These effects, which were slow and long lasting, were attributed to stimulation of the sympathetic sprouts because: stimulation had no effect in uninjured DRG; and effects could be reduced or eliminated by a “cocktail” of antagonists of norepinephrine and ATP receptors, by pretreatment with the sympathetic release blocker bretylium, or by pre-cutting the grey ramus through which sympathetic fibers coursed to the ligated DRG. The latter treatment, a relatively minimal form of sympathectomy, was also highly effective in reducing mechanical pain ipsilateral to the SNL.     

Differential distribution of PI3K isoforms in spinal cord and dorsal root ganglia: Potential roles in acute inflammatory pain

PI3-kinases (PI3Ks) participate in nociception within spinal cord, dorsal root ganglion (DRG), and peripheral nerves. To extend our knowledge, we immunohistochemically stained for each of the 4 class I PI3K isoforms along with several cell-specific markers within the lumbar spinal cord, DRG, and sciatic nerve of naive rats. Intrathecal and intraplantar isoform specific antagonists were given as pretreatments before intraplantar carrageenan; pain behavior was then assessed over time. The α-isoform was localized to central terminals of primary afferent fibers in spinal cord laminae IIi to IV as well as to neurons in ventral horn and DRG. The PI3Kβ isoform was the only class I isoform seen in dorsal horn neurons; it was also observed in DRG, Schwann cells, and axonal paranodes. The δ-isoform was found in spinal cord white matter oligodendrocytes and radial astrocytes, and the γ-isoform was seen in a subpopulation of IB4-positive DRG neurons. No isoform co-localized with microglial markers or satellite cells in naive tissue. Only the PI3Kβ antagonist, but none of the other antagonists, had anti-allodynic effects when administered intrathecally; coincident with reduced pain behavior, this agent completely blocked paw carrageenan-induced dorsal horn 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl) propanoic acid (AMPA) receptor trafficking to plasma membranes. Intraplantar administration of the γ-antagonist prominently reduced pain behavior. These data suggest that each isoform displays specificity with regard to neuronal type as well as to specific tissues. Furthermore, each PI3K isoform has a unique role in development of nociception and tissue inflammation.     

Sensory neurons and fibers from multiple spinal cord levels innervate the rabbit lumbar disc

OBJECTIVE: To establish the neurotransmission pathway from the lumbar L5/6 intervertebral disc (IVD) to the spinal cord in the rabbit. DESIGN: Fluorogold particles injected into the posterior portion of the rabbit L5/6 IVD were traced by examining gold-positive neurons and fibers in the dorsal root ganglion (DRG) and spinal cord at various root levels. RESULTS: Fluorogold-labeled neurons were observed bilaterally in primary afferent DRG neurons from the L3 through L5 segments; a small number of gold-labeled neurons were found at the L1 level. Fluorogold-labeled neurons were predominantly present in the ipsilateral DRG (the side of the injection) at the L5 level, but they were more equally distributed (on both sides) at the L4 and L3 levels. In the posterior horn of the spinal cord, Fluorogold particles were found in nerve fibers as rostral as the T12 level. CONCLUSIONS: Our study has shown that Fluorogold particles injected into the rabbit L5/6 IVD are taken up by primary sensory neurons in the DRGs and primary sensory fibers in the posterior horn of the spinal cord at multiple levels. This diffuse innervation pattern of the lumbar disc may help explain why discogenic back pain in humans is often poorly localized.     

EphrinB-EphB receptor signaling contributes to neuropathic pain by regulating neural excitability and spinal synaptic plasticity in rats

Bidirectional signaling between ephrins and Eph receptor tyrosine kinases was first found to play important roles during development, but recently has been implicated in synaptic plasticity and pain processing in the matured nervous system. We show that ephrinB-EphB receptor signaling plays a critical role is induction and maintenance of neuropathic pain by regulating neural excitability and synaptic plasticity in the dorsal root ganglion (DRG) and the spinal dorsal horn (DH). Intrathecal application of blocking reagents for EphB-receptors, EphB1-Fc and EphB2-Fc chimeras inhibits the induction and maintenance of nerve injury-induced thermal hyperalgesia and mechanical allodynia. These blockers also prevent and suppress the nerve injury-induced hyperexcitability of nociceptive small DRG neurons, sensitization of DH neurons and long-term potentiation (LTP) of synapses between C fibers and DH neurons. In naïve, uninjured animals intrathecal administration of EphB-receptor activators ephrinB1-Fc and ephrinB2-Fc, respectively, induces thermal hypersensitivity and lowers the threshold for LTP, while EphB1-Fc prevents induction of the LTP. Western Blot analysis shows that nerve injury triggers an upregulation of the ephrinB1 and EphB1 receptor proteins in DRG and the spinal cord. These results indicate that, by regulating excitability of nociceptive-related neurons in DRG and DH and the synaptic plasticity at the spinal level, ephrinB-EphB receptor signaling contributes to neuropathic pain. This novel role for ephrinB-EphB receptor signaling suggests that these molecules may be useful therapeutic targets for treating pain after nerve injury.     

多节段背根节慢性压迫大鼠的机械触刺激和冷刺激诱发痛行为

目的:脊椎间盘突出、椎间孔狭窄、脊髓损伤以及肿瘤造成的背根节(dorsal root ganglion,DRG)及其邻近神经根的机械性压迫可能是引起腰背痛与坐骨神经痛的重要原因.临床上多节段神经根性痛比单一神经根性痛更常见,患者表现出多节段神经根压迫和多节段椎间孔狭窄.为此,本实验观察了多节段DRG慢性压迫大鼠的痛行为.方法:实验在本室创建的大鼠背根节慢性压迫(chronic compression of DRG,CCD)模型基础上采用单侧L3-5多节段DRG慢性压迫模型,应用von Frey细丝和丙酮分别检测机械触刺激诱发痛阚值和冷刺激诱发痛反应级别及反应百分数.结果:多节段DRG慢性压迫大鼠表现明显双侧机械触刺激诱发痛和冷刺激诱发痛行为,伴随明显延迟的对侧机械触刺激和冷刺激诱发痛的镜像痛行为.组织学观察显示多节段DRG慢性压迫同侧DRG内部及其神经根有明显炎症反应.结论:机械性压迫和炎症共同作用神经根和DRG导致多节段DRG慢性压迫大鼠明显的机械触刺激诱发痛和冷刺激诱发痛行为.     

A novel neurotransmitter, DAN, mediates pain sensation in the spinal dorsal horn

Differential screening-selected gene aberrative in neuroblastoma(DAN) belongs to a novel gene family(DAN family) that includes the head-inducing factor, Cerberus, and dorsaling factor, Gremlin. It has been suggested that DAN family members control diverse processes in growth, development and the cell cycle. Here, we demonstrate that DAN is produced in the small neurons of the dorsal root ganglion(DRG) and transported to the nerve terminals in the spinal dorsal horn in adult rats. Furthermore, intrathecal injection of an antibody to DAN suppressed pain sensations induced by the application of complete Freund's adjuvant and carageenan into the rat hindpaw, and the amount of DAN mRNA in the DRG neurons and of DAN in the spinal dorsal horn were increased in the inflammatory models. These data suggest that DAN in a novel neurotransmitter and/or modulator in the primary sensory nerve fibers for pain sensation.     

Nerve injury-induced tactile allodynia is present in the absence of FOS labeling in retrogradely labeled post-synaptic dorsal column neurons

The dorsal column pathway consists of direct projections from primary afferents and of ascending fibers of the post-synaptic dorsal column (PSDC) cells. This pathway mediates touch but may also mediate allodynia after nerve injury. The role of PSDC neurons in nerve injury-induced mechanical allodynia is unknown. Repetitive gentle, tactile stimulus or noxious pinch was applied to the ipsilateral hindpaw of rats with spinal nerve ligation (SNL) or sham surgery that had previously received tetramethylrhodamine dextran in the ipsilateral n. gracilis. Both touch and noxious stimuli produced marked increases in FOS expression in other cells throughout all laminae of the ipsilateral dorsal horn after nerve injury. However, virtually none of the identified PSDC cells expressed FOS immunofluorescence in response to repetitive touch or pinch in either the nerve-injured or sham groups. In contrast, labeled PSDC cells expressed FOS in response to ureter ligation and labeled spinothalamic tract (STT) cells expressed FOS in response to noxious pinch. Identified PSDC neurons from either sham-operated or SNL rats did not express immunoreactivity to substance P, CGRP, NPY, PKCY, MOR, the NK1 and the NPY-Y1 receptor. Retrogradely labeled DRG cells of nerve injured rats were large diameter neurons, which expressed NPY, but no detectable CGRP or substance P. Spinal nerve injury sensitizes neurons in the spinal dorsal horn to repetitive light touch but PSDC neurons apparently do not participate in touch-evoked allodynia. Sensitization of these non-PSDC neurons may result in activation of projections integral to the spinal/supraspinal processing of enhanced pain states and of descending facilitation, thus priming the central nervous system to interpret tactile stimuli as being aversive.     

脑源性神经生长因子抗体对小鼠坐骨神经损伤后脊髓与背根节内Synaptophysin表达的影响

目的探查小鼠坐骨神经压榨损伤后内源性脑源性神经营养因子(brainderivedneuroliophicfactor,BDNF)对Synaptophysin(SYN)在相应脊髓前角运动细胞与背根节神经元内表达的影响。方法在小鼠一侧坐骨神经压榨损伤后腹腔注射BDNF抗体,中和内源性BDNF,然后用免疫组织化学方法观察SYN在与坐骨神经相连的脊髓前角运动细胞与背根节神经元的表达。结果实验组SYN免疫反应阳性神经元的数目较对照组明显减少,阳性细胞的平均光密度也显著下降(P<0.01)。结论小鼠坐骨神经压榨损伤后内源性BDNF可能参与脊髓前角运动细胞与背根节神经元内SYN的表达。     

Artemin induced functional recovery and reinnervation after partial nerve injury

Systemic artemin promotes regeneration of dorsal roots to the spinal cord after crush injury. However, it is unclear whether systemic artemin can also promote peripheral nerve regeneration, and functional recovery after partial lesions distal to the dorsal root ganglion (DRG) remains unknown. In the present investigation, male Sprague Dawley rats received axotomy, ligation, or crush of the L5 spinal nerve or sham surgery. Starting the day of injury, animals received intermittent subcutaneous artemin or vehicle across 2 weeks. Sensory thresholds to tactile or thermal stimuli were monitored for 6 weeks after injury. Immunohistochemical analyses of the DRG and nerve regeneration were performed at the 6-week time point. Artemin transiently reversed tactile and thermal hypersensitivity after axotomy, ligation, or crush injury. Thermal and tactile hypersensitivity reemerged within 1 week of treatment termination. However, artemin-treated rats with nerve crush, but not axotomy or ligation, subsequently showed gradual return of sensory thresholds to preinjury baseline levels by 6 weeks after injury. Artemin normalized labeling for NF200, IB4, and CGRP in nerve fibers distal to the crush injury, suggesting persistent normalization of nerve crush-induced neurochemical changes. Sciatic and intradermal administration of dextran or cholera toxin B distal to the crush injury site resulted in labeling of neuronal profiles in the L5 DRG, suggesting regeneration functional restoration of nonmyelinated and myelinated fibers across the injury site into cutaneous tissue. Artemin also diminished ATF3 and caspase 3 expression in the L5 DRG, suggesting persistent neuroprotective actions. A limited period of artemin treatment elicits disease modification by promoting sensory reinnervation of distal territories and restoring preinjury sensory thresholds.     

Spinal modulation of calcitonin gene-related peptide by endocannabinoids in the development of opioid physical dependence

Studies implicate endocannabinoids in the acute and chronic actions of opioid drugs, including the genesis of physical dependence. Previous evidence suggests that spinal release of calcitonin gene-related peptide (CGRP) and activation of its receptors contribute to opioid physical dependence. The release of CGRP at the spinal level is modulated by cannabinoid (CB1)-receptors. Thus, this study examined whether CB1-receptor activity mediates changes in CGRP underlying development of opioid physical dependence. Systemic morphine administration for 5-days elevated CGRP-immunoreactivity in the rat spinal dorsal horn. In situ hybridization of dorsal root ganglion (DRG) neurons revealed an increase in CGRP mRNA during initial (day 1-3) but not later phase (day 4-5) of morphine treatment. CGRP-immunoreactivity in DRG neurons, however, was increased in the later phase of morphine treatment. Naloxone challenge to morphine-treated animals precipitated an intense withdrawal syndrome that depleted CGRP-immunoreactivity and increased Fos expression in the dorsal horn. The Fos-response primarily occurred in neurons that expressed CGRP receptor component protein (RCP) suggesting CGRP activity contributes to neuronal activation during precipitated withdrawal. Spinal slices obtained from morphine-treated animals showed higher levels of CGRP release than from saline controls. Intrathecal co-administration of CB1-receptor antagonists, AM-251 or SR141716A, with daily morphine attenuated the behavioral manifestations of withdrawal. Treatment with AM-251 also reduced the depletion of CGRP, suppressed Fos-induction, and prevented the increase in capsaicin-evoked spinal CGRP release. Altogether, this study suggests that endocannabinoid activity, expressed via CB1-receptors, contributes to the induction of opioid physical dependence through spinal modulation of CGRP.     

Injury discharges regulate calcium channel alpha-2-delta-1 subunit upregulation in the dorsal horn that contributes to initiation of neuropathic pain

Previous studies have shown that peripheral nerve injury in rats induces increased expression of the voltage gated calcium channel (VGCC) alpha-2-delta-1 subunit (Ca v alpha2 delta1) in spinal dorsal horn and sensory neurons in dorsal root ganglia (DRG) that correlates to established neuropathic pain states. To determine if injury discharges trigger Ca v alpha2 delta1 induction that contributes to neuropathic pain initiation, we examined allodynia onset and Ca v alpha2 delta1 levels in DRG and spinal dorsal horn of spinal nerve ligated rats after blocking injury induced neural activity with a local brief application of lidocaine on spinal nerves before the ligation. The lidocaine pretreatment blocked ligation-induced discharges in a dose-dependent manner. Similar pretreatment with the effective concentration of lidocaine diminished injury-induced increases of the Ca v alpha2 delta1 in DRG and abolished that in spinal dorsal horn specifically, and resulted in a delayed onset of tactile allodynia post-injury. Both dorsal horn Ca v alpha2 delta1 upregulation and tactile allodynia in the lidocaine pretreated rats returned to levels similar to that in saline pretreated controls 2 weeks post the ligation injury. In addition, preemptive intrathecal Ca v alpha2 delta1 antisense treatments blocked concurrently injury-induced allodynia onset and Ca v alpha2 delta1 upregulation in dorsal spinal cord. These findings indicate that injury induced discharges regulate Ca v alpha2 delta1 expression in the spinal dorsal horn that is critical for neuropathic allodynia initiation. Thus, preemptive blockade of injury-induced neural activity or Ca v alpha2 delta1 upregulation may be a beneficial option in neuropathic pain management.     

The role of tumor necrosis factor-alpha in the neuropathic pain induced by Lumbar 5 ventral root transection in rat

Accumulating evidence has demonstrated that tumor necrosis factor-alpha (TNF-alpha) plays an important role in neuropathic pain. Recently, it has been shown that Lumbar 5 ventral root transection (L5 VRT) induces persistent mechanical allodynia and thermal hyperalgesia in bilateral hind paws. In the present study, the role of TNF-alpha in the L5 VRT model was investigated. We found that immunoreactivity (IR) of TNF-alpha and TNF receptor 1 (TNFR1) in ipsilateral (but not in contralateral) L4 and L5 dorsal root ganglion (DRG) was increased following L5 VRT, started 1 day after the lesion and persisted for 2 weeks. Double immunofluorescence staining revealed that the increased TNF-alpha-IR in DRG was in satellite glial cells, immune cells and neuronal cells, while TNFR1-IR was almost restricted at DRG neuronal cells. L5 VRT increased TNF-alpha-IR and TNFR1-IR in bilateral L5 spinal dorsal horn, started 1 day after lesion and persisted for 2 weeks. The increased TNF-alpha-IR in spinal dorsal horn was observed in astrocytes, microglias and neurons, but the upregulation of TNFR1 was mainly in neurons. Intraperitoneal injection of thalidomide, an inhibitor of TNF-alpha synthesis, started at 2h before surgery, blocked mechanical allodynia and thermal hyperalgesia. However, the drug failed to reverse the abnormal pain behaviors, when it was applied at day 7 after surgery. These data suggest that the upregulation of TNF-alpha and TNFR1 in DRG and spinal dorsal horn is essential for the initiation but not for maintenance of the neuropathic pain induced by L5 VRT.     

改良高选择性脊神经后根部分切断术中前后根神经分束的应用解剖

背景:高选择性脊神经后根部分切断术中前后根的神经分束应达到神经小束水平,分束越多越利于电刺激选择,利于准确地切断阈值低的引起痉挛的Ia类神经纤维,也越可能最大限度地保留后根中的感觉神经纤维.目的:根据限制性和高选择性脊神经后根切断术的要求,对脊神经前后根进行显微解剖,确定神经小束的分束标准和数目,为临床手术提供可靠的依据和新的手术标准.设计:以成人尸体标本为观察对象,单一样本实验.单位:锦州医学院附属第一医院骨科和锦州医学院解剖教研室.对象:实验于1999-12在锦州医学院解剖学实验室进行.以志愿捐献的15具成人尸体标本为观察对象,男11具,女4具,生前均签署志愿捐献书.方法:①在15具(30侧)成人脊柱标本上,对L1～S2节段的脊神经前后根进行形态学观察和显微测量.②取新鲜尸体的L5脊神经前后根进行免疫组化染色,将脊神经后根起始部、中间部和椎间孔外部3个部位切片,分别测定神经纤维总数、引起痉挛的Ia类神经纤维的数目及其占神经纤维总数的百分率,比较3个部位Ia类神经纤维的分布规律和数量.主要观察指标:①脊神经根神经分束情况及神经小束的直径.②脊神经后根起始部、中间部和椎间孔外部计数100 μm2神经纤维总数及Ia类神经纤维占神经纤维总数的百分率.结果:①脊髓圆锥部脊神经根是由根丝逐步汇合而成.应用显微外科技术,后根一般可分为10～18小束,前根一般分为6～11小束,其小束的直径是基本一样,数值较为恒定.②脊神经后根起始部、中间部和椎间孔外部计数100μm2总的神经纤维数为(3 243±143)根,Ia类神经纤维为(1 702±85)根,占总神经纤维数的52.5%.Ia类神经纤维在后根内呈均匀分布,没有集中分布区.结论:改良脊神经后根部分切断术的最大特点即脊神经前后根的分束标准应尽量细,这样有利于准确切断Ia类神经纤维,一般前根达到6～11小束,后根达到10～18小束,切断最大比例应不超过后根神经纤维总数的1/2.     

兔腰神经根慢性压迫和炎症刺激后背根神经节的形态学变化研究

目的 分别经光镜和电镜观察兔腰神经根经慢性压迫和炎症刺激后背根神经节(dorsalrootganglion，DRG)的形态学变化。方法 纯种新西兰大白兔20只，随机分为对照组(5只)和实验组(15只)，实验组又分为损伤后10d、30d和90d组。取兔尾部的自体髓核组织放入内径1．5mm、外径2．5mm、管壁带孔的硅胶管内，压迫左侧L，神经根，实验组各亚组分别于造模后10d、30d、90d取材，作光镜及电镜观察。结果 10d组中，经压迫和炎症刺激后神经根与DRG胞膜水肿，内膜间隙明显充血、水肿，大量炎性细胞浸润，出现变性、坏死及小胶质细胞“嗜神经”现象；DRG胞质内粗面内质网及线粒体等细胞器含量减少，粗面内质网核糖体脱落，线粒体肿胀；细胞核常染色质淡染且分布不均匀，核膜皱褶。30d组DRG胞膜稍增厚，节细胞染色不均，部分神经元出现变性、坏死，DRG溶酶体与滑面内质网含量增多，线粒体肿胀，嵴部分消失，核仁浓缩偏向一侧。90d组DRG胞膜明显增厚，节细胞内纤维样改变：溶酶体及滑面内质网含量增多，线粒体肿胀、嵴消失，核仁浓缩居中。结论 神经根慢性压迫和自体髓核刺激可导致神经组织出现水肿、炎性细胞浸润以及神经纤维增生等神经变性改变。     

Upregulation and redistribution of ephrinB and EphB receptor in dorsal root ganglion and spinal dorsal horn neurons after peripheral nerve injury and dorsal rhizotomy

EphrinB–EphB receptor signaling plays diverse roles during development, but recently has been implicated in synaptic plasticity in the matured nervous system and in pain processes. The present study investigated the correlation between expression of ephrinB and EphB receptor proteins and chronic constriction injury (CCI) of the sciatic nerve and dorsal rhizotomy (DR) in dorsal root ganglion (DRG) and spinal cord (SC); and interaction of CCI and DR on expression of these signals. Adult, male Sprague–Dawley rats were employed and thermal sensitivity was determined in the sham operated CCI and DR rats. Western blot and immunobiochemistry analysis and immunofluorescence staining techniques were used to detect the expression and location of the ephrinB–EphB receptor proteins in DRG and SC. The results showed that expression of ephrinB1 and EphB1 receptor proteins was significantly upregulated in DRG and SC in a time‐dependent manner corresponding to the development of thermal hyperalgesia after CCI. The increased expression is predominately located in the medium‐ and small‐sized DRG neurons, the superficial layers of spinal dorsal horn (DH) neurons, and the IB4 positive nociceptive terminals. DR increases ephrinB1 in DRG, not SC and EphB receptor in SC, not DRG. DR suppressed CCI‐induced upregulation of ephrinB1 in SC and EphB1 receptor in DRG and SC. These findings indicate that ephrinB–EphB receptor activation and redistribution in DRG and DH neurons after nerve injury could contribute to neuropathic pain. This study may also provide a new mechanism underlying DR‐induced analgesia in clinic.     

Basic Science (30)

Sympathetic‐sensory coupling after L5 spinal nerve lesion in the rat and its relation to changes in dorsal root ganglion blood flow. (Christian‐Albrechts‐Universität, Kiel, Germany) Pain 2000;87:335–345. In rats 3‐56 days after L5 spinal nerve lesion, the authors of this study tested the responses of axotomized afferent fibers recorded in the dorsal root of the lesioned segment to norepinephrine (NE, 0.5 μg/kg) injected intravenously and to selective electrical stimulation of the lumbar sympathetic trunk (LST). In some experiments, blood flow was measured in the dorsal root ganglion (DRG) by laser Doppler flowmetry. The majority of lesioned afferent fibers with spontaneous activity responded to neither LST stimulation (82.4%) nor NE (71.4%). In those that did react to LST stimulation, responses occurred only at high stimulation frequencies and they could be mimicked by nonadrenergic vasoconstrictor drugs (angiotensin II, vasopressin). Excitatory responses to LST stimulation were closely correlated with the stimulation‐induced phasic vasoconstrictions in the DRG. Therefore, the activation of lesioned afferents might be brought about indirectly by an impaired blood supply to the DRG. To test this hypothesis, a strong and sustained baseline vasoconstriction in the DRG was induced by blocking endothelial nitric oxide synthesis with N^G‐nitro‐L‐arginine methyl ester (L‐NAME) applied systemically. L‐NAME enhanced baseline vascular resistance in the DRG about threefold and also increased stimulation‐induced vasoconstrictions. After L‐NAME, the majority of axotomized neurons with spontaneous activity were activated by LST stimulation (76%) or NE (75%). Again, activations closely followed stimulation‐induced phasic vasoconstrictions in the DRG provided that a critical level of vasoconstriction was exceeded. Inhibitory responses to LST stimulation were generally rare and could be reversed to activation by prolonged stimulation or after L‐NAME. These results show that sympathetic‐sensory coupling occurs only in a minority of axotomized afferents after L5 spinal nerve injury. Like previous studies, they cast doubt on the notion that L5 spinal nerve lesion is a good model for sympathetically maintained pain. Since responses of lesioned afferent neurons to LST stimulation and NE could be provoked with high reliability after inducing vasoconstriction in the DRG, and since they mirrored stimulation‐induced vasoconstrictions in the DRG, it appears that in this model the association of sympathetic activity with afferent discharge occurs mainly when perfusion of the DRG is impaired. Comments by Marshall Devor, PhD. Animal research has revealed that massive ectopic afferent discharge is generated in the dorsal root ganglion (DRG) following nerve injury. This source of ectopic firing is in addition to activity that may be generated at the nerve injury site (Tinel sign). The combined impulse barrage is almost certainly an important cause of neuropathic pain. It has been discovered recently that the intensity of the ectopic DRG barrage is modulated by sympathetic efferent activity. This is a potential link between sympathetic activity and symptomatology in sympathetic related pain conditions such as complex regional pain syndrome/reflex sympathetic dystrophy. But what is the mechanism of the sympathetic‐sensory coupling? Considerable evidence indicates that axotomized DRG neurons become abnormally adrenosensitivity. Habler et al now point out an additional, indirect, coupling mechanism … modulation of intrinsic DRG blood flow. That is, sympathetic activity may reduce DRG blood flow inducing partial ischemia, with the ischemia causing neural excitation. This finding may also have broader implications as spinal pathology can also compromise DRG blood flow. Might low back pain and sciatica, for example, derive from this same process? It is surprising that ectopic firing in the DRG has played so little part in clinical thinking and practice in patients with neuropathic pain. So far.