一氧化氮在神经根性疼痛中的作用

目的：探索一氧化氮(NO)在髓核突出所致的神经根性疼痛中的作用。方法：取大鼠自体尾椎髓核无压迫下放置在L4和L5神经根表面，分别在术后3d及1、2、3、4周时观察大鼠后足机械刺激和热刺激敏感性的变化，并用免疫组化方法对移植髓核中的一氧化氮合酶(NOS)进行检测．探索NO在疼痛中的作用：结果：在无明显机械压迫情况下，大鼠腰神经根上放置自体髓核可产生痛觉过敏，移植髓核组织中NOS染色阳性一结论：髓核自身是引起腰腿痛的重要原因，NO可能参与疼痛的产生.     

Mechanical compression of the lumbar nerve root alters pain-related behaviors induced by the nucleus pulposus in the rat.

The purpose of this study was to refine a method of nerve-root injury in the rat to produce hyperalgesia, a pain-related behavior, and to determine if there were any relationships between the histological extent of nerve-root injury and the magnitude of hyperalgesia. Three methods were used to produce hyperalgesia: irritation of a nerve root by ectopic nucleus pulposus, silk loop alone, or both silk loop and ectopic nucleus pulposus. Autologous nucleus pulposus obtained from coccygeal intervertebral discs was relocated on the lumbar nerve roots after laminectomy. Two loops of 4-0 silk were placed around the exposed nerve roots. Hyperalgesia was measured preoperatively and postoperatively. The distribution of myelinated axons in the dorsal nerve roots was evaluated histologically. Mechanical hyperalgesia was detected in rats in which autologous nucleus pulposus was applied to the nerve root but not in those in which silk loops were used. Silk loops around the nerve root resulted in thermal hyperalgesia only in rats in which autologous nucleus pulposus was applied to the nerve root. Fewer large myelinated fibers were seen in the rats in which silk loops were used. Although a silk loop around the nerve root was not sufficient to produce hyperalgesia, supplemental application of autologous nucleus pulposus to the nerve root produced thermal hyperalgesia. It is possible that mechanical constriction of the nerve root alters the pain-related behavior elicited by chemical factors from the nucleus pulposus.     

Effect of nucleus pulposus on the neural activity of dorsal root ganglion

STUDY DESIGN: This study was designed to investigate, using neurophysiologic techniques in an in vivo rat model, the effect of application of nucleus pulposus to the nerve root on the neural activity of the dorsal root ganglion and the corresponding receptive fields. OBJECTIVES: To assess a further role of the dorsal root ganglion in mechanisms of radicular pain in lumbar disc herniation. SUMMARY OF BACKGROUND DATA: It has been suggested that the epidural application of autologous nucleus pulposus without mechanical compression causes nerve root inflammation and related radicular pain in lumbar disc herniation. Concerning the dorsal root ganglion, its mechanical hypersensitivity and potential for generating ectopic discharges have been reported. However, the effect of autologous nucleus pulposus on the dorsal root ganglion is uncertain. METHODS: In adult Sprague-Dawley rats spontaneous neural activity was recorded from the surgically exposed L5 dorsal root using electrophysiologic techniques, and the mechanosensitivity of L5 dorsal root ganglia and corresponding receptive fields on the hind paw were measured using calibrated nylon filaments. Autologous nucleus pulposus from the tail or fat was implanted at the L5 nerve root. Neural activity was monitored for 6 hours. RESULTS: Spontaneous neural activity in the nucleus pulposus group gradually increased and showed significant differences compared with the fat group from 2.5 to 6 hours after exposure. The mechanosensitivity of the dorsal root ganglia showed significant increases compared with the fat group. CONCLUSIONS: After application of nucleus pulposus to the nerve root, the dorsal root ganglion demonstrated increased excitability and mechanical hypersensitivity. These results suggest that nucleus pulposus causes excitatory changes in the dorsal root ganglion.     

髓核对背根节神经元GDNF表达影响及其与痛觉过敏的关系

目的:探讨腰神经根周围髓核组织移植对背根节胶质细胞源性神经营养因子(glialcellline-derivedneurotrophicfactor,GDNF)表达的影响及其与痛觉过敏之间的关系。方法:从鼠尾椎间盘取髓核组织移植到腰神经根周围,采用神经行为学观察痛觉过敏的出现规律,免疫荧光染色的方法计数背根节内GDNF免疫反应阳性神经元百分比,分析其与痛觉过敏之间的关系。结果:在髓核组织刺激下,背根节内GDNF免疫反应阳性细胞明显增多(P<0.01),这种变化与痛觉过敏有显著的正相关性(P<0.05)。结论:内源性GDNF很可能参与了痛觉过敏的调控。     

A Rat Model of Radicular Pain Induced by Chronic Compression of Lumbar Dorsal Root Ganglion with SURGIFLO (TM)

Background: Radicular pain is a common and debilitating clinical pain condition. To date, the mechanisms of radicular pain remain unclear, partly because of the lack of suitable preclinical models. The authors report a modified rat model of radicular pain that could mimic a subset of clinical radicular pain conditions induced by the soft tissue compression on dorsal root ganglion.

Methods: A rat model of radicular pain was produced by infiltrating the L5 intervertebral foramen with 60 [mu]l of a hemostatic matrix (SURGIFLO (TM); Johnson & Johnson, Somerville, NJ) resulting in chronic compression of lumbar dorsal root ganglion. Thermal hyperalgesia and mechanical allodynia were measured with or without epidural treatment with triamcinolone. Western blot was used to assess the expression of the NR1 subunit of the N-methyl-d-aspartate receptor and inhibitory factor [kappa][beta]-[alpha], an inflammatory marker, within the affected L5 dorsal root ganglion and spinal cord dorsal horn.

Results: Chronic compression of lumbar dorsal root ganglion resulted in: (1) persistent mechanical allodynia and thermal hyperalgesia up to 4 or 5 postoperative weeks and (2) up-regulation of the N-methyl-d-aspartate receptor and inhibitory factor [kappa][beta]-[alpha] within the ipsilateral L5 dorsal root ganglion and spinal cord dorsal horn. Epidural administration of triamcinolone (6.25-100 [mu]g) on postoperative day 3 dose-dependently attenuated both thermal hyperalgesia and mechanical allodynia in rats with chronic compression of lumbar dorsal root ganglion.     

Nitric oxide as a mediator of nucleus pulposus-induced effects on spinal nerve roots.

Nerve root dysfunction and sciatic pain in disc herniation are considered to be caused by mechanical compression and related to the presence of nucleus pulposus in the epidural space. Autologous nucleus pulposus has been shown to induce endoneural edema and to decrease nerve-conduction velocity in spinal nerve roots in experimental disc herniation models, and inflammatory mediators have been suggested to be involved in these mechanisms. Nitric oxide, a potent inflammatory mediator, is implicated in vasoregulation, neurotransmission, and neuropathic pain. Nitric oxide synthesis can be induced by different cytokines, e.g., tumor necrosis factor-alpha, which recently was shown to be of pathophysiological importance in experimental disc herniation. The enzyme nitric oxide synthase mediates the production of nitric oxide. Three series of experiments were performed in rat and pig disc herniation models to (a) investigate nitric oxide synthase activity in spinal nerve roots after exposure to autologous nucleus pulposus and (b) evaluate the effects of systemic treatment with aminoguanidine, a nitric oxide synthase inhibitor, on vascular permeability and nerve-conduction velocity. In a disc herniation model in the rat, calcium-independent nitric oxide synthase activity was measured in nerve roots exposed to nucleus pulposus; however, no nitric oxide synthase activity was detected in nerve roots from animals that underwent a sham operation, reflecting increased inducible nitric oxide synthase activity. In nucleus pulposus-exposed spinal nerve roots in the pig, the edema was less severe after systemic aminoguanidine administration than without aminoguanidine treatment. Aminoguanidine treatment also significantly reduced the negative effect of nucleus pulposus on nerve-conduction velocity in spinal nerve roots in the pig. These results demonstrate that nucleus pulposus increases inducible nitric oxide synthase activity in spinal nerve roots and that nitric oxide synthase inhibition reduces nucleus pulposus-induced edema and prevents reduction of nerve-conduction velocity. Furthermore, the results suggest that nitric oxide is involved in the pathophysiological effects of nucleus pulposus in disc herniation.     

Application of nucleus pulposus to the nerve root simultaneously reduces blood flow in dorsal root ganglion and corresponding hindpaw in the rat

STUDY DESIGN: An experimental study to clarify the effects of nucleus pulposus on blood flow in the dorsal root ganglion and hindpaws. OBJECTIVES: To investigate the effects of application of nucleus pulposus to nerve root on blood flow in the dorsal root ganglion and the corresponding hindpaw. SUMMARY OF BACKGROUND DATA: It has been reported experimentally that application of nucleus pulposus into the epidural space induces morphologic and functional changes in the nerve roots and induces compartment syndrome in the dorsal root ganglia. However, it has not been clarified which of these changes induces symptoms in the lower limbs. METHODS: Sixteen adult, female Sprague-Dawley rats had the left L5 nerve root and associated dorsal root ganglions exposed. Autologous nucleus pulposus was applied to the L5 nerve root, just proximal to the dorsal root ganglion (NP group). For control, the same volume of muscle tissue was applied similarly to the neural tissue (control group). Blood flow in the dorsal root ganglion, corresponding hindpaw, and the contralateral hindpaw was continuously monitored by two-channel laser Doppler flowmeter for 3 hours. After measurement of blood flow, the nerve root and dorsal root ganglion were processed for histology and evaluated by light microscope. RESULTS: Blood flow in the NP group was reduced, not only in the dorsal root ganglion, but also in the corresponding hindpaw. These reductions were statistically significant compared with the control group (P < 0.01). Edema was the principal pathologic finding seen consistently in the nerve roots and in many of the associated dorsal root ganglia from nucleus pulposus-treated animals. CONCLUSION: Application of nucleus pulposus to nerve root decreased blood flow in the dorsal root ganglion and corresponding hindpaw. These basic pathophysiologic changes are associated with compression injuries caused by herniated discs and are accepted neuropathologic mechanisms of injury associated with painful neuropathies. These acute observations in the dorsal root ganglion and the hindpaw may be important initial factors in the pathogenesis of radicular leg pain (sciatica) due to disc herniation.     

Protein kinase Cbeta selective inhibitor LY333531 attenuates diabetic hyperalgesia through ameliorating cGMP level of dorsal root ganglion neurons

Streptozocin (STZ)-induced diabetic rats show hyperalgesia that is partially attributed to altered protein kinase C (PKC) activity. Both attenuated neuronal nitric oxide synthase (nNOS)-cGMP system and tetrodotoxin-resistant (TTX-R) Na channels in dorsal root ganglion neurons may be involved in diabetic hyperalgesia. We examined whether PKCbeta inhibition ameliorates diabetic hyperalgesia and, if so, whether the effect is obtained through action on neurons by testing nociceptive threshold in normal and STZ-induced diabetic rats treated with or without PKCbeta-selective inhibitor LY333531 (LY) and by assessing the implication of LY in either nNOS-cGMP system or TTX-R Na channels of isolated dorsal root ganglion neurons. The decreased nociceptive threshold in diabetic rats was improved either after 4 weeks of LY treatment or with a single intradermal injection into the footpads. The treatment of LY for 6 weeks significantly decreased p-PKCbeta and ameliorated a decrease in cGMP content in dorsal root ganglia of diabetic rats. The latter effect was confirmed in ex vivo condition. The treatment with NO donor for 4 weeks also normalized both diabetic hyperalgesia and decreased cGMP content in dorsal root ganglions. The expressions of nNOS and TTX-R Na channels were not changed with LY treatment. These results suggest that LY is effective for treating diabetic hyperalgesia through ameliorating the decrease in the nNOS-cGMP system.     

Comparison of neuropathic pain induced by the application of normal and mechanically compressed nucleus pulposus to lumbar nerve roots in the rat.

We studied whether applying nucleus pulposus tissue, obtained from tail intervertebral discs that had been subjected to chronic mechanical compression, to the lumbar nerve roots produces hyperalgesia, which is thought to be a pain-related behavior in the rat. An Ilizarov-type apparatus was used for immobilization and chronically applied compression of the rat tail for eight weeks. Three weeks after application of extracted nucleus pulposus tissue on the lumbar nerve roots, motor function, sensitivity to noxious mechanical stimuli was measured. Eight weeks after application of the apparatus, the instrumented vertebrae were resected and sections were stained with hematoxylin and eosin to evaluate degeneration of the intervertebral disc. Mechanical hyperalgesia observed in rats treated with the compressed nucleus pulposus tissue was greater and of longer duration than in the rats treated with normal and non-compressed discs. The nucleus pulposus in the instrumented vertebrae showed some histological degeneration. In conclusion, chronic mechanical compression of nucleus pulposus, which resulted in degeneration to some extent, enhanced mechanical hyperalgesia, which was induced by application of nucleus pulposus on the nerve root in the rat. Degenerative intervertebral discs might induce more significant pain than normal intervertebral discs.     

Dorsal root ganglia morphologic features in patients with herniation of the nucleus pulposus: assessment using magnetic resonance myelography and clinical correlation.

STUDY DESIGN: Morphologic features of the dorsal root ganglia were investigated in patients with herniation of the nucleus pulposus by means of magnetic resonance myelography. OBJECTIVES: This study was undertaken to assess morphologic changes of the dorsal root ganglia in patients with herniation of the nucleus pulposus and to determine the relations between the morphologic features of the dorsal root ganglia and clinical features. SUMMARY OF BACKGROUND DATA: It has recently been reported that application of the nucleus pulposus to a nerve root induces edema in the rat dorsal root ganglion. Edema in the human dorsal root ganglion resulting from lumbar disc herniation has not been discussed in the literature, to the authors' knowledge. METHODS: Eighty-three consecutive patients (average age 42.1 years; range 17 to 77 years) with monoradicular symptoms were examined. Dorsal root ganglion morphologic features, i.e., indentations and swelling, were evaluated by magnetic resonance myelography. The dorsal root ganglion swelling at each level was quantitatively expressed as a ratio of the dorsal root ganglion width on the involved side to that of the contralateral side and was termed dorsal root ganglion ratio. Eighty-three uninvolved levels were chosen as controls in a randomized manner. Factors possibly contributing to the morphologic changes in the dorsal root ganglion were investigated. Neurologic symptoms, evaluated by the Japan Orthopaedic Association scoring system, were correlated to the morphologic changes. The morphologic features were followed up for 1 year after treatment in a small group of patients. RESULTS: Dorsal root ganglion indentations were always found in the narrowed intervertebral foramens. The incidence of indentations was significantly higher at the involved nerve roots (10.8%) than at the uninvolved nerve roots (4.0%) (P = 0.026). Patients with dorsal root ganglion indentations were significantly older (P = 0.0008). Leg pain scores in patients with indentations were significantly poor (P = 0.007). The dorsal root ganglion ratios were significantly higher at the involved levels than at the uninvolved levels (P = 0.001); the means +/- SD were 1.19 +/- 0.25 and 1.08 +/- 0.13, respectively. Patients with lateral herniated nucleus pulposus had significantly higher dorsal root ganglion ratios than those with central herniated nucleus pulposus (P = 0.0001); the mean ratios +/- SD were 1.48 +/- 0.32 and 1.10 +/- 0.12, respectively. A moderate positive correlation was found between dorsal root ganglion ratio and age (Pearson's correlation coefficient = 0.313). There was moderate negative correlation between the dorsal root ganglion ratio and leg pain, gait, motor, and total Japan Orthopaedic Association score (correlation coefficients were = -0.385, -0.350, -0.422, and -0.358, respectively). The dorsal root ganglion ratios were significantly diminished at 1-year follow-up (P = 0.001); the means +/- SD were 1.22 +/- 0.22 and 1.09 +/- 0.07, respectively. Indentations observed before treatment disappeared after treatment. CONCLUSIONS: Swelling and impingement in the involved dorsal root ganglion were clearly visualized by magnetic resonance myelography. The swelling and indentations were well correlated with severity of leg pain. These findings have important value in understanding the pathophysiology of the nerve roots in herniated nucleus pulposus.     

Epidural injection of cyclooxygenase-2 inhibitor attenuates pain-related behavior following application of nucleus pulposus to the nerve root in the rat.

Cyclooxygenase-2 (COX-2), the inducible isoform of COX, has been identified as the key enzyme to regulate prostaglandin E2 synthesis in inflammatory conditions. Although it has been reported that COX-2 is present in herniated disc samples obtained from patients, little is known concerning the relationships between COX-2 and painful radiculopathy. The purpose of this study was to evaluate whether epidural injection of COX-2 inhibitor abolishes hyperalgesia induced by nucleus pulposus, which is a pain-related behavior in the rat. Rats, in which nucleus pulposus was relocated on the nerve root, exhibited evidence of mechanical hyperalgesia. Epidural injection of COX-2 inhibitor resulted in decrease in mechanical hyperalgesia 1 h, 3 and 7 days after the epidural injection of COX-2 inhibitor (0.1 mg/kg SC-'236 dissolved in the vehicle). There were no significant differences in sensitivity to thermal noxious stimuli after either application of the nucleus pulposus or epidural injections. These results suggest that prostaglandins and thromboxane, which are produced by COX-2 in inflammatory cells, appear to be related to the inflammatory process produced by application of nucleus pulposus to the nerve root. It is possible that COX-2 plays a significant role in painful radiculopathy following herniated nucleus pulposus.     

大鼠正常与退变性髓核突出导致神经根性疼痛的对比研究

目的探讨正常与退变髓核突出对大鼠疼痛阈值以及背根神经节中TNF-α表达的影响,研究椎间盘退变与神经根性疼痛之间的关系。方法72只大鼠随机分为4组:正常对照组(n=18)、假手术组(n=19)、正常髓核(N-NP)组(n=16)和退变髓核(P-NP)组(n=19)。对P-NP组大鼠利用尾椎椎间盘纤维环穿刺的方法建立椎间盘退变模型。分别取出N-NP组和P-NP组大鼠自体的正常髓核与退变髓核组织,置于手术显露后的腰5左侧神经根处,建立髓核突出致神经根性疼痛动物模型。采用行为学测试的方法分别观察各组大鼠术前1天,术后1、4、7、10、14、21天机械刺激阈值与热刺激阈值的变化;采用免疫组化方法分别检测术后第4、14天各组大鼠背根神经节中TNF-α的表达。结果行尾椎间盘纤维环穿刺后2周,组织学与MRI检查均证实椎间盘组织发生明显退变。对照组和假手术组动物未出现明显的痛觉过敏现象,N-NP组和P-NP组大鼠机械性刺激阈值均显著下降,该痛觉过敏现象持续至术后2周消失;与正常髓核组织相比,退变髓核所致机械性刺激阈值下降程度更为严重。各实验组均未发生热刺激阈值的规律性变化。术后第4、14天对照组和假手术组背根神经节中未见TNF-α明显表达,而正常及退变髓核组TNF-α表达量均显著升高。结论大鼠尾椎纤维环穿刺是建立大鼠椎间盘退变模型的一种有效方法。与正常髓核组织相比,发生退变的髓核组织可导致神经根性疼痛的加重,提示椎间盘退变过程中释放的炎症因子在疼痛的发生机制中可能起到了重要作用。     

Spinal glial activation and cytokine expression after lumbar root injury in the rat

STUDY DESIGN: This study was designed to examine the behaviorial immunohistochemical changes of spinal glial cells and spinal Interleukin (IL)-1beta expression after various nerve root injuries used as models of lumbar radiculopathy. OBJECTIVES: In order to better understand the role of central inflammation in the pathophysiologic mechanisms that give rise to pain associated with lumbar radiculopathy, this research studied the relationship between pain-related behavior associated with spinal glial activation and IL-1beta expression generated by three types of nerve root injury: loose ligation with chromic gut, loose ligation with silk, and tight ligation with silk. SUMMARY OF BACKGROUND DATA: An animal model of lumbar radiculopathy originally described by Kawakami and Weinstein involved loose ligation of unilateral L4-L6 nerve roots with chromic gut. Characterization and establishment of such an animal model of low back pain enables further investigation of the nature of the pathophysiologic mechanisms associated with lumbar radiculopathy in humans. METHODS: Seventy-three rats were divided into four treatment groups. Chromic group (n = 25): The L5 nerve roots (dorsal and ventral) were exposed by hemilaminectomy and loosely ligated with chromic gut. Tight silk group (n = 18): The exposed L5 nerve roots were tightly ligated extradurally with 5-0 silk suture. Loose silk group (n = 15): two loose ligatures of 5-0 silk were placed around the exposed L5 nerve roots. Sham group (n = 15): the rats were subjected to laminectomy alone for exposing nerve roots. Following surgery, thermal hyperalgesia and mechanical allodynia was assessed time-dependently up to 42 days post operatively. At 1, 3, 7, 14, and 42 days postoperatively, the rats in each group were perfused with fixative. The L5 spinal cord segments was harvested and cryosectioned for glial and cytokine immunohistochemistry. RESULTS: In the chromic and the tight silk group, an immediate and sustained mechanical allodynia was observed in the ipsilateral hind paw up to 35 days postoperatively. The loose silk group also showed an immediate mechanical allodynia that subsided by 14 days postoperatively. Sham-treated animals exhibited mild mechanicalallodynia for the initial 7 days after the surgery. Thermalhyperalgesia was evident in the three primary treatment groups, but not in the sham-treated rats. OX-42 expression was elevated in the gray matter of the L5 spinal section by 3 days in the chromic, the tight silk, and the loose silk groups as compared to the sham group. Astrocytic activation increased over time in all groups except the sham group. There was no direct correlation between degree of microglial response and severity of pain behaviors. In contrast, astrocytic activation demonstrated a direct relationship with the elevation of mechanical allodynia for the first 7 days. In addition, spinal IL-1beta protein expression was increased bilaterally in the superficial layer of the dorsal horn and cell nuclei of the ventral horns in the ligature treated groups as compared with the sham group. CONCLUSION: Direct mechanical and/or chemical injury to lumbar roots in the rat gives rise to pain behavior suggestive of lumbar radiculopathy. The finding that glial activation and enhanced IL-1beta expression are observed in the spinal cord after root injury supports a central, neuroimmune component in the generation of lumbar radiculopathy. A further understanding of the immunologic consequences of root injury may lead to further development and the novel use of selective cytokine-inflammatory inhibitors for the treatment of low back pain associated with radiculopathy.     

Pathology of lumbar nerve root compression. Part 2: morphological and immunohistochemical changes of dorsal root ganglion.

STUDY DESIGN: This study is to investigate the changes of dorsal root ganglion (DRG) induced by mechanical compression using in vivo model. OBJECTIVES: The effect of axonal flow disturbance induced by nerve root compression was determined in DRG. SUMMARY OF BACKGROUND DATA: The dorsal root ganglion should not be overlooked when considering the mechanism of low back pain and sciatica, so it is important to understand the morphologic and functional changes that occur in primary sensory neurons of the dorsal root ganglion as a result of nerve root compression. However, few studies have looked at changes of neurons within the dorsal root ganglion caused by disturbance of axonal flow and the axon reaction as a result of mechanical compression of the dorsal root through which the central branches of the primary sensory nerves pass. METHODS: In mongrel dogs, the seventh lumbar nerve root was compressed for 24 h, one week, or three weeks using a clip with a pressure of 7.5 gf. Morphologic changes of the primary sensory neurons in the dorsal root ganglion secondary to the axon reaction were examined by light and electron microscopy. Changes of immunostaining for substance P (SP), calcitonin gene-related peptide (CGRP), and somatostatin (SOM) in the primary sensory neurons affected by central chromatolysis after nerve root compression were also examined. RESULTS: Light microscopy showed central chromatolysis of neurons in the dorsal root ganglion from one week after the start of compression. Electron microscopy of the affected neurons revealed movement of the nucleus to the cell periphery and the loss of rough endo-plasmic reticulum and mitochondria from the central region. Immunohistochemical studies showed a marked decrease of SP, CGRP, and SOM staining in small ganglion cells with central chromatolysis when compared with cells from control ganglia. CONCLUSION: It is important to be aware that in patients with nerve root compression due to lumbar disc herniation or lumbar canal stenosis, dysfunction is not confined to degeneration at the site of compression, but also extends to the primary sensory neurons within the dorsal root ganglion as a result of the axon reaction. Patients with sensory disturbance should therefore be fully informed of the fact that these symptoms will not resolve immediately after surgery.     

2000 Volvo Award winner in basic science studies: Exogenous tumor necrosis factor-alpha mimics nucleus pulposus-induced neuropathology. Molecular, histologic, and behavioral comparisons in rats

STUDY DESIGN: This study tested the hypothesis that the 17-kDa form of tumor necrosis factor-alpha is the pathophysiologic agent expressed by herniated nucleus pulposus in vivo that is primarily responsible for the histologic and behavioral manifestations of experimental sciatica associated with herniated lumbar discs. OBJECTIVE: The authors determined the molecular weight and concentration of active tumor necrosis factor-alpha in rat herniated disc and used exogenous tumor necrosis factor-alpha at the same molecular weight to study its neuropathologic effect on rat nerve root and dorsal root ganglion preparations in vivo. SUMMARY OF BACKGROUND DATA: Expressed by herniated nucleus pulposus in culture, tumor necrosis factor-alpha causes neuropathologic injury in nerve roots and neuropathic pain states in which mechanical allodynia is seen in response to peripheral stimuli. METHODS: Western blotting was used to identify the molecular weight of the operative tumor necrosis factor-alpha protein form, and measures of optical density were used for semiquantitative determination of concentration. Plastic-embedded nerve roots and dorsal root ganglion were used for neuropathologic evaluation, and von Frey stimulation was used to quantify mechanical allodynia. RESULTS: The 17-kDa form of tumor necrosis factor-alpha is expressed by herniated nucleus pulposus at a concentration of approximately 0.48 ng per herniated rat lumbar disc. Exogenous tumor necrosis factor-alpha applied in vivo to rat nerve roots produced neuropathologic changes and behavior deficits that mimicked experimental studies with herniated nucleus pulposus applied to nerve roots. CONCLUSIONS: The data reinforce other evidence that tumor necrosis factor-alpha is involved in mechanisms of neuropathic pain.     

Role of leukocytes in radicular pain secondary to herniated nucleus pulposus

Some studies have assessed inflammatory cells such as macrophages, lymphocytes, and neutrophils in herniated lumbar disc tissues using histologic analysis. However, there is no consensus regarding the relationships between clinical symptoms, including radicular pain and the presence of inflammatory cells. It has been shown that autologous nucleus pulposus relocated on the lumbar nerve root in rats produces time dependent and reversible mechanical hyperalgesia, which is thought to be a pain related behavior in peripheral neuropathic pain models. The purpose of this study was to determine whether leukocytes play a role in the mechanical hyperalgesia induced by the nucleus pulposus and to characterize the role of leukocytes in radicular pain attributable to lumbar disc herniation. Nitrogen mustard was used to induce and evaluate leukocytopenia in rats. Sensitivity to mechanical noxious stimuli was measured quantitatively, and inflammatory cells in granulation tissue around the nerve root were examined histologically. The nucleus pulposus produced neither mechanical hyperalgesia nor abundant inflammatory cells in rats with nitrogen mustard induced leukocytopenia. Neuropathic pain produced by the nucleus pulposus, when placed on the nerve root, may be related to inflammatory cell infiltration induced by relocation of the nucleus pulposus, rather than the nucleus pulposus itself.     

Effect of mechanical compression on the vascular permeability of the dorsal root ganglion.

The dorsal root ganglion contains primary sensory neurons and is closely related to low back pain and sciatia. The present study investigated whether endoneurial edema, which is involved in the onset of pain and nerve dysfunction, was increased in the dorsal root ganglion by compression. The influence of mechanical compression on the vascular permeability of the lumbar dorsal root ganglion was determined. The dorsal root ganglion is reported to have a higher vascular permeability compared with other nerve tissues as well as lacking a blood-nerve barrier. However, only a few studies have assessed the influence of mechanical compression on the dorsal root ganglion. especially its vascular permeability. In dogs, laminectomy was performed at L7 and the dorsal root ganglion of the seventh lumbar spinal nerve was compressed for 1 h using four kinds of clips with various strengths. After clip removal, Evans blue albumin (EBA) or horseradish peroxidase (HRP) was administered intravenously as a tracer. After sacrifice, the EBA-injected specimens were observed by fluorescence microscopy and the HRP-injected specimens were observed by light and transmission electron microscopy. After compression of the dorsal root ganglion at 15 gf or more, leakage of tracer into the endoneurial space was markedly increased compared with the sham-operated group and severe edema was noted. Extravascular leakage of tracer was obvious around venules and capillaries. Electron microscopy showed an increase of extravascular HRP in the gap junctions and fenestrae between endothelial cells due to increased vascular permeability. However, the dorsal root ganglion was covered with a thick perineurium and HRP that leaked from the blood vessels did not enter the epineurium even after compression at 60 gf. It was proven that the increased vascular permeability occurred as well as in leakage of dye within the dorsal root ganglion after a single hour of compression of the dorsal root ganglion.     

皮层躯体感觉诱发电位在监测腰神经根损伤中作用的研究

目的：利用大鼠髓核突出动物模型。探索皮层躯体感觉诱发电位（CSEP）的波幅和潜伏期变化是否与神经根性疼痛有关系。方法：取大鼠自体尾部的髓核无压迫下放置在L4和L5神经根上，制成髓核突出动物模型。分别在术后3d,1,2及4周观察大鼠术侧肢体机械刺激敏感性和热刺激敏感性和热刺激敏感性的变化，并引出大鼠后肢CSEP，观察术侧肢体CSEP的变化。结果：在无明显机械压迫的情况下，大鼠腰神经根上植入自体髓核可产生痛觉过敏，CSEP波幅增高。结论：髓核自身是引起腰腿痛的重要原因，CSEP波幅的增高与神经根性疼痛有一定相关性。     

Prevention of compartment syndrome in dorsal root ganglia caused by exposure to nucleus pulposus

STUDY DESIGN: An experimental study to clarify the effects of pentoxifylline, as an anti-tumor necrosis factor-alpha therapy on endoneurial fluid pressure in the dorsal root ganglion using an animal model of herniated nucleus pulposus. OBJECTIVES: To investigate the effects of anti-tumor necrosis factor-alpha therapy to nucleus pulposus-induced nerve root/dorsal root ganglion changes. SUMMARY OF BACKGROUND DATA: It has been reported experimentally that application of nucleus pulposus into epidural space induces morphologic and functional changes in the nerve roots and induces compartment syndrome in the dorsal root ganglia. Tumor necrosis factor-alpha has been considered a key pathogenic factor in the initiation and maintenance of neuropathic pain states. METHODS: A total of 11 adult, female Sprague-Dawley rats had their left L5 nerve roots and associated dorsal root ganglions exposed. Autologous nucleus pulposus was applied to the L5 nerve root just proximal to the dorsal root ganglion. A piece of Spongel (Yamanouchi Pharmaceutical Co., Tokyo) containing 20 microL of 1000 microg/mL pentoxifylline was applied with the nucleus pulposus (NP+PTX group). In control animals nucleus pulposus was applied with a piece of Spongel containing 20 microL of physiologic saline solution in a similar fashion (NP+PS group). Endoneurial fluid pressure was recorded with a servo-null micropipette system using glass micropipettes with tip diameters of 4 microm. Endoneurial fluid pressure in the dorsal root ganglion was measured before and 3 hours after application of test substances. After measurement of endoneurial fluid pressure, the nerve root and dorsal root ganglion were processed for histology and evaluated by light microscope. RESULTS: Values of endoneurial fluid pressure before application of test substances were as follows: 2.4 +/- 1.2 cm H2O in the NP+PS (control) group and 1.8 +/- 0.4 cm H2O in the NP+PTX group. There was no statistically significant difference between these two pretreatment measurements. However, values of endoneurial fluid pressure after application were as follows: 8.6 +/- 1.8 cm H2O in the NP+PS group and 2.9 +/- 0.8 cm H2O in the NP+PTX group. Values of endoneurial fluid pressure in the NP+PTX group were significantly lower compared with the NP+PS group. Histologic examination consistently showed only a slight degree of edema evident in the NP+PTX group compared with the NP+PS group. CONCLUSION: Pentoxifylline, an anti-tumor necrosis factor-alpha drug, prevented the dorsal root ganglion compartment syndrome caused by topical application of nucleus pulposus. Anti-inflammatory cytokine therapy may become an effective treatment of sciatica due to disc herniation.     

Opioid-induced Hyperalgesia in a Murine Model of Postoperative Pain: Role of Nitric Oxide Generated from the Inducible Nitric Oxide Synthase

Background: Opioid-induced delayed hyperalgesia and allodynia have been reported in human and animal models. The authors evaluated the influence of different opioids used during clinical anesthesia on nociceptive sensitivity and incisional pain in mice. The role of the inducible nitric oxide synthase on surgical pain and opioid-induced pronociception also was investigated.

Methods: CD1 mice were used to study the efficacy of opioids inducing pronociception and enhancing incisional pain. The implication of nitric oxide generated from the inducible nitric oxide synthase was investigated using knockout mice (C57/BL6) for its gene. Mice underwent right hind paw surgery under sevoflurane anesthesia combined with subcutaneous administration of saline or the opioids fentanyl (0.05 mg/kg), alfentanil (1 mg/kg), and remifentanil (0.04 mg/kg). Nociception was evaluated daily for 7 days using paw-pressure, plantar, and von Frey tests.

Results: The antinociceptive effect of opioids was followed by long-lasting thermal hyperalgesia and mechanical allodynia (each lasting between 2 and 7 days), but not mechanical hyperalgesia. Intraoperative infusion of opioids significantly enhanced incisional pain in all tests. The most prominent effects were observed with remifentanil. The inducible nitric oxide synthase gene deletion attenuated both remifentanil- and incision-induced pronociceptive effects. In mutant mice for the inducible nitric oxide synthase gene, remifentanil was still efficient in enhancing incisional pain, but the global pronociceptive effect was attenuated significantly as compared with wild-type mice.