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.     

Cyclooxygenase-2 inhibitor SC-236 attenuates mechanical allodynia following nerve root injury in rats.

Low back pain is a common problem, affecting approximately two-thirds of the adult population. Of these individuals, a significant percentage will exhibit symptoms of radicular pain or sciatica. The purpose of this study was to determine the effect of one systemic (2 mg/kg) or intrathecal (0.2 mg/kg) dose of a selective cyclooxygenase-2 inhibitor (SC-236) in decreasing existing mechanical allodynia in a rat model of radiculopathy. Gait disturbance and mechanical allodynia (increased response to non-noxious von Frey monofilament stimuli) were assessed daily until the rats were killed 7 days after surgery. Robust mechanical allodynia developed in the rats in all groups except for those in the sham group by day 1 after surgery. Mechanical allodynia was significantly lower in the rats that received the systemic or the intrathecal dose of SC-236 than in those in the vehicle control group (analysis of variance followed by Bonferroni multiple comparison test, p = 0.002). The intrathecal drug route of administration produced greater attenuation in allodynia than the systemic dose, supporting a central mechanism of action of the cyclooxygenase-2 inhibitor (p = 0.002). The hypothesis that cyclooxygenase-2 is involved in spinal nociceptive processing after a nerve root injury was supported by this study. In addition, these data support continued basic science research to further elucidate central inflammatory processes that follow nerve root injury.     

Chronic pain and neuroinflammation

In rheumatology, chronic pain most often sets in after a musculoskeletal injury. Its persistence is not always due to the progression of the initial injury, but in some cases to the onset of central sensitization. Much scientific data suggests that this central sensitization is caused by multiple complex interactions between the nervous system and immune system. Afferent nerve fibers carrying pain information are responsible for peripheral sensitization partly linked to inflammation molecules. These afferent fibers release neurotransmitters in the dorsal root ganglion and dorsal horn of the spinal cord, capable of activating microglia, which are the local immune cells. The activated microglia will produce pro-inflammatory cytokines, chemokines and neuropeptides capable of interacting with the second-order neuron, but also segmental and descending inhibitory neurons. This is referred to as neuroinflammation, which will amplify the hypersensitivity of second-order neurons, otherwise called central sensitization. This neuroinflammation will be able to reach the higher brain structures, which are involved in pain modulation and the emotional and cognitive aspects of pain. The aim of this update is to describe the pathophysiology of chronic pain, incorporating the latest scientific data on neuroplasticity and neuroinflammation.     

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.     

Chronic compression of the cervical myelon as complication of anterior interbody fusion (AIF): neurological improvement after late anterior decompression. Case report

Severe neurological deficits directly related to intraoperative injury of the spinal cord and the nerve roots is rare complication of anterior interbody fusion (AIF) in cervical spondylosis. A case of radiculopathy and Brown-Séquard Syndrome caused by a bone fragment following AIF in which a late anterior decompression and fusion of the cervical spine was performed four years after the initial operation is presented. Immediate relief of the radicular pain, improvement of the spasticity, and better spincter control could be achieved. Therefore, patients with chronic anterior compression of an incomplete spinal cord injury after AIF may benefit from a late anterior decompression and fusion.     

Activation of glial cells in the spinal cord of a model of lumbar radiculopathy

Purpose  

Glial cells in the spinal cord of a lumbar radiculopathy model were investigated using immunohistochemical methods. Neuropathic pain is a consequence of neural plasticity. In models of neuropathic pain models, roles for glial cells in the development of pain behaviors have been reported. Accumulating evidence suggests that activation of p38 mitogen-activated protein kinase (p38) in glial cells contributes to the pathogenesis of neuropathic pain. We examined whether activation of glial cells is involved in the development of neuropathic pain-like behavior observed in a model of lumbar radicular pain that we developed. However, the pathogenesis of lumbar radiculopathy and in particular the effect of spinal glial activation on pain transmission in the dorsal horn of the spinal cord are still not fully known.     

加巴喷丁对神经病理性痛大鼠脊髓胶质细胞活化的影响

目的 评价加巴喷丁对神经病理性痛大鼠脊髓胶质细胞活化的影响.方法 雄性SD大鼠24只,体重180～220 g,随机分为3组(n=8):假手术组(S组)、坐骨神经慢性压迫性损伤组(CCI组)和加巴喷丁组(G组).CCI组和G组采用坐骨神经慢性压迫性损伤法建立大鼠神经病理性痛模型;S组只暴露坐骨神经,不结扎.G组于术后8 d时开始胃内灌注加巴喷丁50mg/kg(溶于5 ml生理盐水中),2次/d,持续5 d;CCI组胃内灌注0.9%生理盐水5 ml,2次/d,持续5 d;S组不给予任何药物.分别于术前1 d、术后7、15 d时测定机械痛阈,并于术后15 d时断头处死大鼠,取L4.5脊髓组织,采用免疫组化法检测星形胶质细胞和小胶质细胞的活化水平.结果 与S组比较,CCI组术后7、15 d时机械痛阈降低,脊髓星型胶质细胞和小胶质细胞活化水平升高,G组术后7 d时机械痛阈降低(P＜0.05);与CCI组比较,G组术后15 d时机械痛阈升高,脊髓星形胶质细胞和小胶质细胞活化水平降低(P＜0.05).结论 加巴喷丁可抑制大鼠脊髓星形胶质细胞和小胶质细胞的活化,从而减轻神经病理性痛.     

Drug sensitivities of the primary afferents and their changes after inflammation

This study explored the possibility that altered sensitivities of the dorsal root and dorsal root ganglion to neuroactive substances released in inflamed tissue may be involved in radicular pain. The chemical sensitivities of the dorsal root and ganglion of rats were examined by monitoring nerve membrane potential. Endogenous pain inducing substances such as bradykinin, serotonin, acetylcholine, and histamine caused depolarizations of the dorsal root and the ganglion. Application of bradykinin or capsaicin to the dorsal root and ganglion on the isolated spinal cord preparation evoked spinal reflex activities in the lumbar ventral root. These results suggest that, when pain inducing substances are released at the dorsal root or its ganglion, they may initiate action potentials and cause pain. As an inflammation model, chromic gut was tied loosely around the lower lumbar nerve root. The dorsal root of the surgically treated rats showed an increased sensitivity to bradykinin when compared with sham operated rats. In contrast, the sensitivity of the dorsal root to gamma-aminobutyric acid, a major inhibitory transmitter in the spinal cord, was decreased. This result suggests that these reciprocal changes in the sensitivities of the dorsal root may play an important role in the pathogenesis of chemical radiculitis.     

Injury to dorsal root ganglia alters innervation of spinal cord dorsal horn lamina involved in nociception

STUDY DESIGN: A study of the relation between the development of mechanical allodynia and the reorganization of primary afferent terminals in the sensory lamina of the rat spinal cord dorsal horn after partial dorsal root ganglion injury in rats. OBJECTIVES: To investigate the pathologic mechanisms of mechanical allodynia after partial dorsal root ganglion injury. SUMMARY OF BACKGROUND DATA: After experimental peripheral nerve injury causing neuropathic pain, myelinated afferent fibers sprout into lamina II of the dorsal horn. This lamina is associated with nociceptive-specific neurons that generally are not stimulated by myelinated fiber input from mechanical receptors. These morphologic changes are suggested to have significance in the pathogenesis of chronic mechanical allodynia, although it is not known whether this kind of morphologic change occurs after dorsal root ganglion injury. METHODS: After partial dorsal root ganglion crush injury, the mechanical force causing footpad withdrawal was measured with von Frey hairs, and myelinated primary afferents were labeled with cholera toxin B subunit horseradish peroxidase, a selective myelinated fiber tracer that identifies transganglionic synapses. RESULTS: After partial dorsal root ganglion injury, mechanical allodynia developed in the corresponding footpad within 3 days and persisted throughout the experimental period. At 2 and 4 weeks after the injury, B subunit horseradish peroxidase-positive fibers, presumably myelinated afferents, were observed to be sprouting into lamina II of the dorsal horn on the injured side, but not on the contralateral control side. CONCLUSIONS: Morphologic change in spinal cord dorsal horn lamina II occurs after partial dorsal root ganglion injury. This change may have significance in the pathogenesis of chronic mechanical allodynia after partial dorsal root ganglion injury.     

Marked enhancement of anti-allodynic effect by combined intrathecal administration of the adenosine A1-receptor agonist R-phenylisopropyladenosine and morphine in a rat model of central pain

BACKGROUND: There is often no satisfactory treatment for chronic pain after spinal cord injury. We have previously reported that intrathecal (i.t.) administration of the adenosine A1-receptor agonist R-phenylisopropyl-adenosine (R-PIA) or the opioid morphine has anti-allodynic effects in a model of presumed chronic central pain after photochemically induced spinal cord injury in rats. In the present study, we set out to investigate the possible interaction between i.t. R-PIA and morphine in spinally injured rats. METHODS: Sprague-Dawley rats displaying allodynia-like behaviors to mechanical and cold stimuli after photochemically induced spinal cord injury with minor motor deficits were used. R-PIA and morphine, either alone or in combination, were administered i.t. through an implanted catheter to lumbar spinal cord. RESULTS: Cumulative doses of R-PIA or morphine dose-dependently reduced the mechanical allodynia-like behavior, with a threshold of 1 nmol and 1.5 nmol, respectively. When co-administrated, R-PIA and morphine produced marked suppression of mechanical allodynia at doses of 5 pmol and 7.5 pmol, respectively. The effect of i.t. co-administration of R-PIA and morphine on cold allodynia was comparable to i.t. R-PIA alone. The combination of R-PIA and morphine did not increase adverse effects such as motor deficits in comparison to either drug alone. CONCLUSION: These results demonstrate a supra-additive interaction between the adenosine A1-receptor agonist R-PIA and morphine to reduce mechanical allodynia-like behavior in rats with chronic spinal cord injury. The combination of R-PIA and morphine administered spinally may be superior to R-PIA or morphine alone for treating such pain.     

Spinal prostaglandins facilitate exaggerated A- and C-fiber-mediated reflex responses and are critical to the development of allodynia early after L5-L6 spinal nerve ligation

BACKGROUND: Spinal prostaglandins are important in the early pathogenesis of spinal nerve ligation (SNL)-induced allodynia. This study examined the effect of SNL on the expression of cyclooxygenase (COX)-1, COX-2, and prostaglandin E2 receptors in the rat lumbar spinal cord, and the temporal and pharmacologic relation of these changes to the exaggerated A- and C-fiber-mediated reflex responses and allodynia, 24 h after injury. METHODS: Male Sprague-Dawley rats, fitted with intrathecal catheters, underwent SNL or sham surgery. Paw withdrawal threshold, electromyographic analysis of the biceps femoris flexor reflex, and immunoblotting of the spinal cord were used. RESULTS: Both allodynia (paw withdrawal threshold of < or = 4 g) and exaggerated A- and C-fiber-mediated reflex responses (i.e., decrease in activation threshold, increase in evoked activity, including windup; P < 0.05) were evident 24 h after SNL but not sham surgery. Allodynic animals exhibited significant increases in prostaglandin E2 receptor (subtypes 1-3) and COX-1 (but not COX-2) expression in the ipsilateral lumbar dorsal horn. The corresponding ventral horns and contralateral dorsal horn were unchanged from sham controls. Exaggerated A- and C-fiber-mediated reflex responses were significantly attenuated by intrathecal SC-560 or SC-51322, but not SC-236, given 24 h after SNL. CONCLUSION: These results provide further evidence that spinal prostaglandins, derived primarily from COX-1, are critical in the exaggeration of A- and C-fiber input and allodynia, 24 h after SNL.     

Perineural alpha(2A)-adrenoceptor activation inhibits spinal cord neuroplasticity and tactile allodynia after nerve injury

BACKGROUND: Nerve injury in animals increases alpha(2)-adrenoceptor expression in dorsal root ganglion cells and results in novel excitatory responses to their activation, perhaps leading to the phenomenon of sympathetically maintained pain. In contrast to this notion, peripheral alpha(2)-adrenoceptor stimulation fails to induce pain in patients with chronic pain. We hypothesized that alpha(2) adrenoceptors at the site of nerve injury play an inhibitory, not excitatory role. METHODS: Partial sciatic nerve ligation was performed on rats, resulting in a reduction in withdrawal threshold to tactile stimulation. Animals received perineural injection at the injury site of clonidine, saline, or clonidine plus an alpha(2)-adrenergic antagonist, and withdrawal threshold was monitored. Immunohistochemistry was performed on the sciatic nerve ipsi- and contralateral to injury and on the spinal cord. RESULTS: Clonidine reduced this hypersensitivity in a dose-dependent manner, and this was blocked by an alpha(2A)-preferring antagonist. Perineural clonidine injection had a slow onset (days) and prolonged duration (weeks). Systemic or intrathecal clonidine, or transient neural blockade with ropivacaine, had short lasting or no effect on hypersensitivity. alpha(2A)-adrenoceptor immunostaining was increased near the site of peripheral nerve injury, both in neurons and in immune cells (macrophages and T lymphocytes). Phosphorylated cAMP response element binding protein (pCREB) in lumbar spinal cord was increased ipsilateral to nerve injury, and this was reduced 1 week after perineural clonidine injection. CONCLUSIONS: These data suggest that peripheral alpha(2) adrenoceptors are concentrated at the site of peripheral nerve injury, and their activation receptors produce long-lasting reductions in abnormal spinal cord gene activation and mechanical hypersensitivity.     

脊髓神经元型一氧化氮合酶在大鼠神经病理性痛中的作用

目的 探讨脊髓神经元型一氧化氮合酶(nNOS)在大鼠神经病理性痛中的作用.方法 健康雄性SD大鼠40只,体重220～280 g,采用结扎坐骨神经干的方法建立坐骨神经慢性压迫性损伤(CCI)模型.随机分为4组(n=10),Ⅰ组及Ⅱ组暴露坐骨神经干,分别于术后1 d开始鞘内注射选择性nNOS抑制剂7-NI 60 μg[溶于20%二甲基亚砜(DMSO)]10μl)、20%DMSO 10μl,1次/d,连续6d;Ⅲ组及Ⅳ组制备CCI模型,分别于术后1 d开始鞘内注射7-NI 60μg(溶于20%DMSO 10μl)、20%DMSO 10 μl,1次/d,连续6 d.分别于CCI前1 d、CCI后1、3、5、7 d时测定大鼠机械痛阈和热痛阈.于CCI后7 d,各组分别取5只大鼠,取术侧L_(4～6)背根神经节,分别采用实时定量PCR和Western blot法测定nNOS mRNA及蛋白的表达水平.结果 与Ⅰ组和Ⅱ组比较,T_(1～4)时Ⅲ组和Ⅳ组术侧后肢机械痛阈和热痛阈降低(P＜0.05),背根神经节nNOS蛋白及mRNA的表达上调(P＜0.05);与Ⅲ组比较,T_(1～4)时Ⅳ组机械痛阈和热痛阈降低,背根神经节nNOS蛋白及mRNA的表达上调(P＜0.05).结论 脊髓nNOS参与了大鼠神经病理性痛的形成.     

Surgical experience of gas-containing disk herniation

Disk herniation with gas or gas-containing disk herniation (GCDH) is rare, although epidural gas is associated with the vacuum phenomenon. The clinical, radiologic, and surgical findings were retrospectively analyzed of 18 patients with GCDH. The demographic, clinical, and radiologic findings including computed tomography and magnetic resonance imaging, as well as operative methods were examined. The mean age was 64.4 years (range 51-84 years). All patients presented with acute radiculopathy or exacerbation of chronic pain associated with GCDH of the lumbar spine. All lumbar GCDHs were related to the vacuum phenomenon. Ruptured disks predominantly compressed the nerve root with gas in 17 cases, except in one with only compressed nerve root by gas without disk herniation. All patients had confirmed GCDH at surgery. All patients underwent removal of GCDH and five with another level of spinal stenosis or disk herniation underwent selective decompression. The six patients with instability underwent fusion. Visual analogue scale score of radicular pain was improved from 7.4 ± 0.9 before surgery to 3.2 ± 0.7 at the 3-month follow-up examination. No recurrence occurred after surgery. GCDH can occur as a space-occupying lesion in epidural space as well as a cause of radiculopathy. GCDH may indicate the source of clinical symptoms in the degenerative spine, especially combined with spinal stenosis or multiple spinal disk herniations.     

Age-dependent responses to nerve injury-induced mechanical allodynia

BACKGROUND: Developmental differences in responses to acute and chronic nerve injury have received minimal attention. This study examines developmental differences in behavioral responses to a proximal (closer to the spinal cord) (L5 and L6 spinal nerve root ligation) or to a more distal (closer to peripheral innervation) (partial sciatic nerve ligation) nerve injury in rats paralleling the infant to young adult human. METHODS: Withdrawal thresholds to von Frey filament testing in the hind paw were determined before and various times after either spinal nerve root ligation or partial sciatic nerve ligation in rats aged 2, 4, and 16 weeks. Control rats of these ages were observed serially without surgery. Times for withdrawal thresholds to mechanical stimuli to return to 80% of that of the hind paw in the control animals were compared among the different ages in the two models. RESULTS: Baseline withdrawal thresholds in younger rats were lower (P < 0.05). In the 2-week-old animals, distal injury partial sciatic nerve ligation did not cause a reduction in withdrawal threshold from baseline. This was different from the spinal nerve root ligation group and the older animals in the partial sciatic nerve ligation group. However, when compared with age-matched control animals, both nerve injuries resulted in reduced withdrawal thresholds (P < 0.05). The resolution of hypersensitivity to mechanical stimulation, as measured by return of threshold to 80% of controls, occurred more quickly in 2-week-old than in 4- and 16-week-old animals in both injury models (P < 0.05). CONCLUSION: These data suggest that resolution of sensitization to A-fiber input occurs more rapidly in young animals. In addition, distal injury has less of a sensitizing effect on A-fiber input than proximal injury in the younger animals. The authors speculate that neuroimmune responses, especially at the site of injury, are developmentally regulated and less likely to produce chronic pain when injury occurs at a young age.     

Paraplegia after intracord injection during attempted epidural steroid injection in an awake-patient

Epidural steroid injection is recommended in patients with back ache from spinal and radicular pain or pain suggestive of radiculopathy. During needle placement and injections, clinicians often rely on the patient's complaint of paresthesia or shooting pain along the nerve root, dura, or cord in case a needle pierces these areas. We report the accidental intracord injection of steroid solution during epidural block using fluoroscopy in a conscious patient, which caused paraplegia. This case suggests failure of undue reliance on a patient reporting pain in the vicinity of needle puncturing the spinal cord structures. IMPLICATIONS: Intracord injection of triamcinolone acetate and local anesthetic, resulting in permanent paraplegia, may occur in conscious patients.     

Lumbar radiculopathy after zygapophyseal joint injection

We report a case of lumbar radiculopathy after zygapophysealjoint injections for chronic low back pain. The management ofthe patient and potential causes for the radiculopathy are discussed.The case acts as a reminder that the spinal nerve roots shouldbe considered when performing intra-articular facet joint injectionsand demonstrates the importance of including nerve injury inthe patient consent process as a rare, but significant complication.     

Sterile, benign radiculitis associated with lumbosacral lateral recess spinal canal stenosis: evaluation with enhanced magnetic resonance imaging

Two cases of symptomatic lumbar lateral recess stenosis are described in which the compressed nerve root became focally enhanced on magnetic resonance imaging (MRI) studies performed with gadolinium DTPA. Two men with low back pain and lumbar radiculopathy were examined with contrast-enhanced MRI studies, which showed intradural enhancement of the symptomatic nerve roots. In selected cases of lateral recess stenosis, focal radicular injury may be visualized on enhanced MRI as a result of a breakdown of the blood-brain barrier.