Glial phosphorylated p38 MAP kinase mediates pain in a rat model of lumbar disc herniation and induces motor dysfunction in a rat model of lumbar spinal canal stenosis

Compensatory upregulation of MT2A alleviates neurogenic intermittent claudication through inhibiting activated p38 MAPK-mediated neuronal apoptosis

Neurogenic intermittent claudication (NIC), a classic symptom of lumbar spinal stenosis (LSS), is associated with neuronal apoptosis. To explore the novel therapeutic target of NIC treatment, we constructed the rat model of NIC by cauda equina compression (CEC) method and collected dorsal root ganglion (DRG) tissues, a region responsible for sensory and motor function, for mRNA sequencing. Bioinformatic analysis of mRNA sequencing indicated that upregulated metallothionein 2A (MT2A), an apoptosis-regulating gene belonging to the metallothionein family, might participate in NIC progression. Activated p38 MAPK mediated motor dysfunction following LSS and it was also found in DRG tissues of rats with NIC. Therefore, we supposed that MT2A might affect NIC progression by regulating p38 MAPK pathway. Then the rat model of NIC was used to explore the exact role of MT2A. Rats at day 7 post-CEC exhibited poorer motor function and had two-fold MT2A expression in DRG tissues compared with rats with sham operation. Co-localization analysis showed that MT2A was highly expressed in neurons, but not in microglia or astrocytes. Subsequently, neurons isolated from DRG tissues of rats were exposed to hypoxia condition (3% O2, 92% N2, 5% CO2) to induce cell damage. Gain of MT2A function in neurons was performed by lentivirus-mediated overexpression. MT2A overexpression inhibited apoptosis by inactivating p38 MAPK in hypoxia-exposed neurons. Our findings indicated that high MT2A expression was related to NIC progression, and MT2A overexpression protected against NIC through inhibiting activated p38 MAPK-mediated neuronal apoptosis in DRG tissues.

Stress-Activated Protein Kinases in Intervertebral Disc Degeneration: Unraveling the Impact of JNK and p38 MAPK

Intervertebral disc degeneration (IDD) is a major cause of lower back pain. The pathophysiological development of IDD is closely related to the stimulation of various stressors, including proinflammatory cytokines, abnormal mechanical stress, oxidative stress, metabolic abnormalities, and DNA damage, among others. These factors prevent normal intervertebral disc (IVD) development, reduce the number of IVD cells, and induce senescence and apoptosis. Stress-activated protein kinases (SAPKs), particularly, c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK), control cell signaling in response to cellular stress. Previous studies have shown that these proteins are highly expressed in degenerated IVD tissues and are involved in complex biological signal-regulated processes. Therefore, we summarize the research reports on IDD related to JNK and p38 MAPK. Their structure, function, and signal regulation mechanisms are comprehensively and systematically described and potential therapeutic targets are proposed. This work could provide a reference for future research and help improve molecular therapeutic strategies for IDD.

Effects of the administration of Shinbaro 2 in a rat lumbar disk herniation model

The current standard for the pharmacological management of lumbar disk herniation (LDH), involving non-steroidal anti-inflammatory drugs, muscle relaxants, and opioid analgesics, often carries a risk of adverse events. The search for alternative therapeutic options remains a vital objective, given the high prevalence of LDH and the critical impact on the quality of life. Shinbaro 2 is a clinically effective herbal acupuncture against inflammation and various musculoskeletal disorders. Therefore, we explored whether Shinbaro 2 exerts protective effects in an LDH rat model. The results showed that Shinbaro 2 suppressed pro-inflammatory cytokines, interleukin-1 beta, tumor necrosis factor-alpha, disk degeneration-related factors, matrix metalloproteinase-1,−3,−9, and ADAMTS-5 in LDH rats. Shinbaro 2 administration reinstated a behavioral activity to a normal level in the windmill test. The results indicated that Shinbaro 2 administration restored spinal cord morphology and functions in the LDH model. Therefore, Shinbaro 2 exerted a protective effect in LDH via actions on inflammatory responses and disk degeneration, indicating that future research is warranted to assess the action mechanisms further and validate its effects.

Microglia and macrophages contribute to the development and maintenance of sciatica in lumbar disc herniation

ABSTRACT

Lumbar disc herniation (LDH) is a major cause of sciatica. Emerging evidence indicated that inflammation induced by the herniated nucleus pulposus (NP) tissues plays a major role in the pathogenesis of sciatica. However, the underlying mechanisms are still elusive. Although microglia and macrophages have been implicated in nerve injury-induced neuropathic pain, their roles in LDH-induced sciatica largely remain unknown. This study successfully established and modified a mouse model of LDH. We found that nerve root compression using degenerated NP tissues can initiate remarkable and persistent sciatica, with increased and prolonged macrophage infiltration in dorsal root ganglia (DRG) and significant activation of microglia in the spinal dorsal horn. Instead, compression of the nerve root with nondegenerated NP tissues only led to transient sciatica, with transient infiltration and activation of macrophages and microglia. Moreover, continuous treatment of PLX5622, a specific colony-stimulating factor 1 receptor antagonist, ablated both macrophages and microglia, which effectively alleviated LDH-induced sciatica. However, mechanical allodynia reoccurred along with the repopulation of macrophages and microglia after the withdrawal of PLX5622. Using RNA sequencing analysis, the current study depicted transcriptional profile changes of DRG after LDH and identified several macrophage-related potential target candidates. Our results suggested that microglia and macrophages may play an essential role in the development and maintenance of LDH-induced sciatica. Targeting microglia and macrophages may be a promising treatment for chronic LDH-induced sciatica.

Network Pharmacological Dissection of the Mechanisms of Eucommiae Cortex-Achyranthis Radix Combination for Intervertebral Disc Herniation Treatment

Eucommiae cortex (EC) and Achyranthis radix (AR) are herbal medicines widely used in combination for the treatment of intervertebral disc herniation (IDH). The mechanisms of action of the herbal combination have not been understood from integrative and comprehensive points of view. By adopting network pharmacological methodology, we aimed to investigate the pharmacological properties of the EC-AR combination as a therapeutic agent for IDH at a systematic molecular level. Using the pharmacokinetic information for the chemical ingredients of the EC-AR combination obtained from the comprehensive herbal drug-associated databases, we determined its 31 bioactive ingredients and 68 IDH-related therapeutic targets. By analyzing their enrichment for biological functions, we observed that the targets of the EC-AR combination were associated with the regulation of angiogenesis; cytokine and chemokine activity; oxidative and inflammatory stress responses; extracellular matrix organization; immune response; and cellular processes such as proliferation, apoptosis, autophagy, differentiation, migration, and activation. Pathway enrichment investigation revealed that the EC-AR combination may target IDH-pathology-associated signaling pathways, such as those of cellular senescence and chemokine, neurotrophin, TNF, MAPK, toll-like receptor, and VEGF signaling, to exhibit its therapeutic effects. Collectively, these data provide mechanistic insights into the pharmacological activity of herbal medicines for the treatment of musculoskeletal diseases such as IDH.

Inflammatory interactions between degenerated intervertebral discs and microglia: Implication of sphingosine-1-phosphate signaling

The etiology of intervertebral disc degeneration is largely unknown, but local neuroinflammation may exert a crucial role through activation of cells as microglia and pro-inflammatory cytokines production. We aimed to compare the effect of degenerated and normal intervertebral disc microenvironment on microglial cells and the potential role of sphingosine-1-phosphate, a pro-inflammatory sphingolipid, in their crosstalk. Human degenerated intervertebral discs (Pfirrmann grade IV) were obtained at surgery for spondylolisthesis. Normal intervertebral discs were collected from cadaveric normal lumbar spines. Normal and degenerated-intervertebral discs were kept in culture to obtain media conditioning. Then, microglial cells were cocultured with conditioned media and viability, proliferation, migration, chemotaxis, and inflammatory gene expression were evaluated. The results demonstrate that conditioned media from degenerated intervertebral discs activate microglial cells, increasing chemotaxis, migration, and pro-inflammatory mediators release to a great extent than normal discs. In addition, we show that the administration of sphingosine-1-phosphate to normal intervertebral disc/microglia coculture mimicked degenerative effects. Interestingly, sphingosine-1-phosphate content in conditioned media from degenerated discs was significantly higher than that from normal ones. In addition, FTY720, a functional antagonist of sphingosine-1-phosphate, potently inhibited the effect of degenerated intervertebral discs on microglial inflammatory factor transcription and migration. Our data report, for the first time, that sphingosine-1-phosphate is involved as signal in the microenvironment of human degenerated intervertebral discs. Sphingosine-1-phosphate signaling modulation by FTY720 may induce beneficial effects in counteracting microglial activation during intervertebral disc degeneration.

p38 mitogen-activated protein kinase and pain

Inflammatory and neuropathic pain is initiated by tissue inflammation and nerve injury, respectively. Both are characterized by increased activity in the peripheral and central nervous system, where multiple inflammatory cytokines and other active molecules activate different signaling pathways that involve in the development and/or maintenance of pain. P38 mitogen-activated protein kinase (MAPK) is one member of the MAPK family, which is activated in neurons and glia and contributes importantly to inflammatory and neuropathic pain. The aim of this review is to summarize the latest advances made about the implication of p38 MAPK signaling cascade in pain. It can deepen our understanding of the molecular mechanisms of pain and may help to offer new targets for pain treatment.

IL-33/ST2 signaling contributes to radicular pain by modulating MAPK and NF-κB activation and inflammatory mediator expression in the spinal cord in rat models of noncompressive lumber disk herniation

BACKGROUND

Immune and inflammatory responses occurring in the spinal cord play a pivotal role in the progression of radicular pain caused by intervertebral disk herniation. Interleukin-33 (IL-33) orchestrates inflammatory responses in a wide range of inflammatory and autoimmune disorders of the nervous system. Thus, the purpose of this study is to investigate the expression of IL-33 and its receptor ST2 in the dorsal spinal cord and to elucidate whether the inhibition of spinal IL-33 expression significantly attenuates pain-related behaviors in rat models of noncompressive lumbar disc herniation.

METHODS

Lentiviral vectors encoding short hairpin RNAs that target IL-33 (LV-shIL-33) were constructed for gene silencing. Rat models of noncompressive lumber disk herniation were established, and the spines of rats were injected with LV-shIL-33 (5 or 10 μl) on the first day after the operation. Mechanical thresholds were evaluated during an observation period of 21 days. Moreover, the expression levels of spinal tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and cyclooxygenase 2 (COX-2) and the activation of the mitogen-activated protein kinases (MAPK) and nuclear factor-κB (NF-κB) pathways were evaluated to gain insight into the mechanisms related to the contribution of IL-33/ST2 signaling to radicular pain.

RESULTS

The application of nucleus pulposus (NP) to the dorsal root ganglion (DRG) induced an increase in IL-33 and ST2 expression in the spinal cord, mainly in the dorsal horn neurons, astrocytes, and oligodendrocytes. Spinally delivered LV-shIL-33 knocked down the expression of IL-33 and markedly attenuated mechanical allodynia. In addition, spinal administration of LV-shIL-33 reduced the overexpression of spinal IL-1β, TNF-α, and COX-2 and attenuated the activation of C-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and NF-κB/p65 but not p38.

CONCLUSIONS

This study indicates that spinal IL-33/ST2 signaling plays an important role in the development and progression of radicular pain in rat models of noncompressive lumber disk herniation. Thus, the inhibition of spinal IL-33 expression may provide a potential treatment to manage radicular pain caused by intervertebral disk herniation.

Association Between Neurotrophic Factor Expression and Pain-Related Behavior Induced by Nucleus Pulposus Applied to Rat Nerve Root

STUDY DESIGN

An experimental animal study.

OBJECTIVE

To investigate the relationship between pain-related behavior and the expression of neurotrophic factors in the dorsal root ganglion (DRG) and spinal cord (SC) using a nucleus pulposus (NP) rat model.

SUMMARY OF BACKGROUND DATA

Neurotrophic factors are released from activated glial cells and are associated with pain-related behavior. Nerve growth factor (NGF) is a neurotrophic factor that is induced by inflammation.

METHODS

Rats were divided into an NP group (n = 94) and a sham-operated group (n = 46). NP harvested from the tail was applied to the left L5 DRG. Rats in the NP group were then divided into five subgroups: one non-treatment and four treatment groups. In the treatment groups, a dose of anti-NGF antibody or phosphate-buffered saline was administered into the DRG. Behavioral testing was performed to investigate the mechanical withdrawal threshold of the left hind paw for all groups. Immunohistochemical localization of NGF, phosphorylated p38 (p38), and brain-derived neurotrophic factor (BDNF) in the DRGs and SCs was performed, and the numbers of immunoreactive (IR) cells were counted.

RESULTS

The withdrawal threshold in the nontreatment NP group was significantly decreased for 35 days, and that of the middle- and high-dose treatment rats was significantly higher than the phosphate-buffered saline group values. In the DRG, NGF-IR, p38-IR, and BDNF-IR cells were increased for days 21. In the SC, BDNF-IR, and p38-IR cells were increased from days 7 to 21.

CONCLUSION

In the DRG, NGF expression increased, mechanical thresholds were reduced, and p38 and BDNF expression was increased in the NP group. p38 and BDNF expression was increased in SC neurons during the same period. Inhibition of NGF may be a potential treatment for neuropathic pain due to lumbar disc herniation.

LEVEL OF EVIDENCE

5.

Efficacy and safety of etanercept in the treatment of sciatica: A systematic review and meta-analysis

Etanercept might be promising to alleviate sciatica caused by lumbar disc herniation and spinal stenosis. However, the results remained controversial. We conducted a systematic review and meta-analysis to evaluate the efficacy of etanercept in patients with sciatica. PubMed, EMbase, Web of science, EBSCO, and Cochrane library databases were systematically searched. Randomized controlled trials (RCTs) and Controlled clinical trials (CCT) assessing the efficacy of etanercept on sciatica caused by lumbar disc herniation and spinal stenosis were included. Two investigators independently searched articles, extracted data, and assessed the quality of included studies. The primary outcome was leg pain scores. Meta-analysis was performed using random-effect model. Four RCTs and one CCT involving 184 patients were included in the meta-analysis. Overall, compared with placebo, etanercept could significantly reduce leg pain (Std. mean difference=-0.83; 95% CI=-1.59 to -0.06; P=0.03) and back pain (Std. mean difference=-1.89; 95% CI=-3.34 to -0.43; P=0.01). However, when comparing etanercept to steroids there was no significant difference in the relief of leg pain (Std. mean difference=-1.18; 95% CI=-3.21 to 0.84; P=0.25) and back pain (Std. mean difference=-0.29; 95% CI=-1.26 to 0.67; P=0.55). Etanercept showed no increase in Oswestry Disability Index (ODI) compared with placebo (Std. mean difference=-0.83; 95% CI=-2.03 to 0.37; P=0.18) and steroids (Std. mean difference=-0.19; 95% CI=-1.15 to 0.77; P=0.70). Etanercept treatment was associated with a significantly reduced pain in leg and back compared to placebo and may possibly improve leg pain relief compared to steroids, but failed to improve ODI. Etanercept should be recommended for sciatica with caution because of heterogeneity.

Metabolomic Changes in Rat Model of Cauda Equina Injury

BACKGROUND

To show the differences of metabolomic changes in a rat model of cauda equina injury (CEI) and find potent metabolic biomarkers of CEI.

METHODS

A total of 28 Sprague-Dawley rats were used in this study. After the rats were given anesthesia and fixed in a prone position, a piece of silicone block was placed into the epidural space below the lamina. Behavior tests including the Basso, Beattie, and Bresnahan open field locomotor scale and an inclined plane test were conducted 1 day and 2 days after surgery. The cauda equina tissue was collected 12 hours, 1 day, and 2 days after surgery. Ultraperformance liquid chromatography coupled with quadruple time-of-flight mass spectrometry was used for a quantitative analysis of cauda equine metabolic changes in rats from different groups. The differences between the metabolic profiles of the rats in 4 groups were analyzed using partial least squares discriminant analysis.

RESULTS

In behavior tests and histologic analyses given 2 days after surgery, the animals showed remarkable organ dysfunction and pathologic damage. Metabolic profiles showed remarkable differences between the control and model groups. Thirty-four potential CEI metabolite biomarkers were identified between the control group and different time-point model groups. These potential biomarkers appeared in 15 metabolic pathways.

CONCLUSIONS

Our results may improve the cause of CEI and provide a basis for clinical diagnosis and locating biomarkers in the early stages of the pathologic process of CEI.

Selective suppression of the α isoform of p38 MAPK rescues late-stage tau pathology

BACKGROUND

Hyperphosphorylation and aggregation of tau protein are the pathological hallmarks of Alzheimer's disease and related tauopathies. We previously demonstrated that the microglial activation induces tau hyperphosphorylation and cognitive impairment via activation of p38 mitogen-activated protein kinase (p38 MAPK) in the hTau mouse model of tauopathy that was deficient for microglial fractalkine receptor CX3CR1.

METHOD

We report an isoform-selective, brain-permeable, and orally bioavailable small molecule inhibitor of p38α MAPK (MW181) and its effects on tau phosphorylation in vitro and in hTau mice.

RESULTS

First, pretreatment of mouse primary cortical neurons with MW181 completely blocked inflammation-induced p38α MAPK activation and AT8 (pS199/pS202) site tau phosphorylation, with the maximum effect peaking at 60-90 min after stimulation. Second, treatment of old (~20 months of age) hTau mice with MW181 (1 mg/kg body weight; 14 days via oral gavage) significantly reduced p38α MAPK activation compared with vehicle-administered hTau mice. This also resulted in a significant reduction in AT180 (pT231) site tau phosphorylation and Sarkosyl-insoluble tau aggregates. Third, MW181 treatment significantly increased synaptophysin protein expression and resulted in improved working memory. Fourth, MW181 administration reduced phosphorylated MAPK-activated protein kinase 2 (pMK2) and phosphorylated activating transcription factor 2 (pATF2), which are known substrates of p38α MAPK. Finally, MW181 reduced the expression of interferon-γ and interleukin-1β.

CONCLUSIONS

Taken together, these studies support p38α MAPK as a valid therapeutic target for the treatment of tauopathies.

Comparative Effectivenesses of Pulsed Radiofrequency and Transforaminal Steroid Injection for Radicular Pain due to Disc Herniation: a Prospective Randomized Trial

Transforaminal Epidural steroid injections (TFESI) have been widely adopted to alleviate and control radicular pain in accord with current guidelines. However, sometimes repeated steroid injections have adverse effects, and thus, this prospective randomized trial was undertaken to compare the effectivenesses of pulsed radiofrequency (PRF) administered to a targeted dorsal root ganglion (DRG) and TFESI for the treatment of radicular pain due to disc herniation. Subjects were recruited when first proved unsuccessful (defined as a score of > 4 on a visual analogue scale (VAS; 0-10 mm) and of > 30% according to the Oswestry Disability Index (ODI) or the Neck Disability Index (NDI)). Forty-four patients that met the inclusion criteria were enrolled. The 38 subjects were randomly assigned to receive either PRF (PRF group; n = 19) or additional TFESI (TFESI group; n = 19) and were then followed for 2, 4, 8, and 12 weeks. To evaluate pain intensity were assessed by VAS. ODI and NDI were applied to evaluate functional disability. Mean VAS scores for cervical and lumbar radicular pain were significantly lower 12 weeks after treatment in both study groups. NDI and ODI scores also declined after treatment. However, no statistically significant difference was observed between the PRF and TFESI groups in terms of VAS, ODI, or NDI scores at any time during follow-up. PRF administered to a DRG might be as effective as TFESI in terms of attenuating radicular pain caused by disc herniation, and its use would avoid the adverse effects of steroid.

The Effect of GCSB-5 a New Herbal Medicine on Changes in Pain Behavior and Neuroglial Activation in a Rat Model of Lumbar Disc Herniation

Objective

Lumbar disc herniation can induce sciatica by mechanical compression and/or chemical irritation. The aim of this study was to compare the effects of GCSB-5 (Shinbaro®) and NSAIDs on pain-related behavior and on the expressions of microglia, astrocytes, CGRP, TRPV1, IL-6, and CX3CL1 in a rat model of lumbar disc herniation.

Methods

112 male Sprague-Dawley rats underwent implantation of nucleus pulposus to a dorsal root ganglion (DRG). Rats were divided into five groups as follows; a saline group (the vehicle control group) (n=27), a 10 mg/kg aceclofenac group (the aceclofenac group) (n=22), and 100, 300 or 600 mg/kg GCSB-5 groups (the GCSB-5 100, 300, or 600 groups) (n=21 for each group). Rats were tested for mechanical allodynia at 3 days after surgery and at 1 day, 3 days, 7 days, 14 days, 21 days, 28 days, 35 days, 42 days, 49 days, and 56 days after treatment commencement. Immunohistochemical staining of microglia (Iba1), astrocytes (GFAP), CGRP, and TRPV1, and PCR for IL-6 and CX3CL1 were performed on spinal dorsal horns and DRGs at 56 days after medication commencement.

Results

After 56 days of GCSB-5 300 administration, mechanical withdrawal thresholds were significantly increased (p<0.05), and immunohisto-chemical expressions of Iba1, GFAP, CGRP, and TRPV1 were reduced than other groups, but this difference was not statistically significant.

Conclusion

These results indicate GCSB-5 reduces mechanical allodynia and downregulates neuroglial activity and the expressions of CGRP and TRPV1 in the spinal segments of a rat model of lumbar disc herniation.

Changes in the Expressions of Iba1 and Calcitonin Gene-Related Peptide in Adjacent Lumbar Spinal Segments after Lumbar Disc Herniation in a Rat Model

Lumbar disc herniation is commonly encountered in clinical practice and can induce sciatica due to mechanical and/or chemical irritation and the release of proinflammatory cytokines. However, symptoms are not confined to the affected spinal cord segment. The purpose of this study was to determine whether multisegmental molecular changes exist between adjacent lumbar spinal segments using a rat model of lumbar disc herniation. Twenty-nine male Sprague-Dawley rats were randomly assigned to either a sham-operated group (n=10) or a nucleus pulposus (NP)-exposed group (n=19). Rats in the NP-exposed group were further subdivided into a significant pain subgroup (n=12) and a no significant pain subgroup (n=7) using mechanical pain thresholds determined von Frey filaments. Immunohistochemical stainings of microglia (ionized calcium-binding adapter molecule 1; Iba1), astrocytes (glial fibrillary acidic protein; GFAP), calcitonin gene-related peptide (CGRP), and transient receptor potential vanilloid 1 (TRPV1) was performed in spinal dorsal horns and dorsal root ganglions (DRGs) at 10 days after surgery. It was found immunoreactivity for Iba1-positive microglia was higher in the L5 (P=0.004) dorsal horn and in the ipsilateral L4 (P=0.009), L6 (P=0.002), and S1 (P=0.002) dorsal horns in the NP-exposed group than in the sham-operated group. The expression of CGRP was also significantly higher in ipsilateral L3, L4, L6, and S1 segments and in L5 DRGs at 10 days after surgery in the NP-exposed group than in the sham-operated group (P<0.001). Our results indicate that lumbar disc herniation upregulates microglial activity and CGRP expression in many adjacent and ipsilateral lumbar spinal segments.

Microglia in the spinal cord and neuropathic pain

In contrast to physiological pain, pathological pain is not dependent on the presence of tissue‐damaging stimuli. One type of pathological pain – neuropathic pain – is often a consequence of nerve injury or of diseases such as diabetes. Neuropathic pain can be agonizing, can persist over long periods and is often resistant to known painkillers. A growing body of evidence shows that many pathological processes within the central nervous system are mediated by complex interactions between neurons and glial cells. In the case of painful peripheral neuropathy, spinal microglia react and undergo a series of changes that directly influence the establishment of neuropathic pain states. After nerve damage, purinergic P2X4 receptors (non‐selective cation channels activated by extracellular adenosine triphosphate) are upregulated in spinal microglia in a manner that depends on the transcription factors interferon regulatory factor 8 and 5, both of which are expressed in microglia after peripheral nerve injury. P2X4 receptor expression on the cell surface of microglia is also regulated at the post‐translational level by signaling from CC chemokine receptor chemotactic cytokine receptor 2. Furthermore, spinal microglia in response to extracellular stimuli results in signal transduction through intracellular signaling cascades, such as mitogen‐activated protein kinases, p38 and extracellular signal‐regulated protein kinase. Importantly, inhibiting the function or expression of these microglial molecules suppresses the aberrant excitability of dorsal horn neurons and neuropathic pain. These findings show that spinal microglia are a central player in mechanisms for neuropathic pain, and might be a potential target for treating the chronic pain state.

Up-Regulation of Pain Behavior and Glial Activity in the Spinal Cord after Compression and Application of Nucleus Pulposus onto the Sciatic Nerve in Rats

Study Design

Experimental animal study.

Purpose

To evaluate pain-related behavior and changes in glial activity in the spinal dorsal horn after combined sciatic nerve compression and nucleus pulposus (NP) application in rats.

Overview of Literature

Mechanical compression and inflammation caused by prostaglandins and cytokines at disc herniation sites induce pain. Structural changes and pain-associated cytokines in the dorsal root ganglia and spinal dorsal horn contribute to prolonged pain. Glial cells in the spinal dorsal horn may also function in pain transmission.

Methods

The sciatic nerve was compressed with NP for 2 seconds using forceps in the NP+nerve compression group; the sham-operated group received neither compression nor NP; and the control group received no operation. Mechanical hyperalgesia was measured for 3 weeks using von Frey filaments. Glial activity in the spinal dorsal horn was examined 7 days and 14 days postsurgery using anti-glial fibrillary acidic protein and anti-Ionized calcium binding adaptor molecule-1 antibodies to detect astrocytes and microglia, respectively.

Results

Mechanical hyperalgesia was detected throughout the 14-day observation in the NP+nerve compression group, but not in control or sham-operated groups (p<0.05). Both astrocytes and microglia were significantly increased in the spinal dorsal horn of the NP+nerve compression group compared to control and sham groups on days 7 and 14 (p<0.05).

Conclusions

Nerve compression with NP application produces pain-related behavior, and up-regulates astrocytes and microglia in the spinal dorsal horn, suggesting that these glia may be related to pain transmission.

Lumbar radiculopathy and its neurobiological basis

Lumbar radiculopathy, a group of diseases in which the dorsal root ganglia (DRG) or dorsal roots are adversely affected by herniated discs or spinal stenosis, are clinically characterized by spontaneous and evoked types of pain. The pain is underpinned by various distinct pathophysiological mechanisms in the peripheral and central nervous systems. However, the diagnosis of lumbar radiculopathy is still unsatisfactory, because the association of the pain with the neurobiological basis of radiculopathy is largely unknown. Several animal models used to explore the underlying neurobiological basis of lumbar radiculopathy could be classified as mechanical, chemical, or both based on the component of injury. Mechanical injury elevates the intraneural pressure, reduces blood flow, and eventually establishes ischemia in the dorsal root and the DRG. Ischemia may induce ischemic pain and cause nerve damage or death, and the subsequent nerve damage or death may induce neuropathic pain. Chemical injury predominately induces inflammation surrounding the dorsal roots or DRG and consequent inflammatory mediators cause inflammatory pain. Furthermore, DRG neurons sensitized by inflammatory mediators are hypersensitive to innocuous mechanical force (stretch or compression) and responsible for mechanical allodynia in radiculopathy. As well, central sensitization in the spinal cord may play an important role in pain generation in lumbar radiculopathy. Increasing knowledge of pain-generating mechanisms and their translation into clinical symptoms and signs might allow for dissecting the mechanisms that operate in each patient. With precise clinical phenotypic characterization of lumbar radiculopathy and its connection to a specific underlying mechanism, we should be able to design optimal treatments for individuals. This review discusses the present knowledge of lumbar radiculopathy and proposes a novel mechanism-based classification.

Inhibition of p38 mitogen-activated protein kinase activation in the rostral anterior cingulate cortex attenuates pain-related negative emotion in rats

The emotional components of pain are far less studied than the sensory components. Previous studies have indicated that the rostral anterior cingulate cortex (rACC) is implicated in the affective response to noxious stimuli. Activation of p38 mitogen-activated protein kinase (MAPK) in the spinal cord has been documented to play an important role in diverse kinds of pathological pain states. We used formalin-induced conditioned place aversion (F-CPA) in rats, an animal model believed to reflect the emotional response to pain, to investigate the involvement of p38 MAPK in the rACC after the induction of affective pain. Intraplantar formalin injection produced a significant activation of p38 MAPK, as well as mitogen-activated kinase kinase (MKK) 3 and MKK6, its upstream activators, in the bilateral rACC. p38 MAPK was elevated in both NeuN-positive neurons and Iba1-positive microglia in the rACC, but not GFAP-positive cells. Blocking p38 MAPK activation in the bilateral rACC using its specific inhibitor SB203580 or SB239063 dose-dependently suppressed the formation of F-CPA. Inhibiting p38 MAPK activation did not affect formalin-induced two-phase spontaneous nociceptive response and low intensity electric foot-shock induced CPA. The present study demonstrated that p38 MAPK signaling pathway in the rACC contributes to pain-related negative emotion. Thus, a new pharmacological strategy targeted at the p38 MAPK cascade may be useful in treating pain-related emotional disorders.

Evaluation of pain behavior and calcitonin gene-related peptide immunoreactive sensory nerve fibers in the spinal dorsal horn after sciatic nerve compression and application of nucleus pulposus in rats

STUDY DESIGN

Animal study.

OBJECTIVE

To evaluate pain behavior and neuropeptide changes in the spinal dorsal horn after sciatic nerve compression and application of nucleus pulposus (NP) in rats.

SUMMARY OF BACKGROUND DATA

The pathomechanisms of lumbar disc herniation pain have not been fully elucidated. Pain-associated neuropeptides, including substance P and calcitonin gene-related peptide (CGRP), are produced in dorsal root ganglion neurons and transported to spinal dorsal horn nerve terminals where they function in pain transmission. However, changes in CGRP-immunoreactive (IR) sensory nerve terminals have not been reported in models of disc herniation. This study evaluated pain-related behavior and changes in CGRP-IR terminals in the spinal dorsal horn after combined sciatic nerve compression and NP application.

METHODS

Five groups of rats underwent either sciatic nerve compression with NP (n = 20), application of NP only (n = 20), nerve compression only (n = 20), and sham operation with neither compression nor NP (n = 20) or no operation (controls, n = 20). Mechanical hyperalgesia was measured every second day for 3 weeks. CGRP-IR terminals in each spinal dorsal horn lamina were examined 7 and 14 days postsurgery. Pain behavior and CGRP immunoreactivity were compared among the 5 groups.

RESULTS

Mechanical hyperalgesia was found in the NP only, nerve compression only, and the NP with nerve compression groups (P ≤ 0.05). CGRP-IR nerve terminals in the superficial laminae (I and II) and the deep laminae (III-VI) significantly increased in the NP only, nerve compression only, and NP with nerve compression groups compared with control and sham groups (P ≤ 0.05). Significant mechanical hyperalgesia and increased CGRP-IR nerve terminals were found in the NP with nerve compression group compared with the NP only and nerve compression only groups (P ≤ 0.05).

CONCLUSION

Our results indicate that nerve compression plus NP application produces the most pain-related behavior. CGRP-IR nerve terminals increased in laminae I and II that transmit pain and in laminae III to VI that transmit proprioception. Findings suggest that nerve compression plus NP application induces changes in CGRP expression in the superficial and deep laminae, and these changes are partly responsible for disc herniation pain.

Evaluation of behavior and expression of NaV1.7 in dorsal root ganglia after sciatic nerve compression and application of nucleus pulposus in rats

PURPOSE

The pathomechanisms of pain resulting from lumbar disc herniation have not been fully elucidated. Prostaglandins and cytokines generated at the inflammatory site produce associated pain; however, non-steroidal anti-inflammatory drugs and steroids are sometimes ineffective in patients. Tetrodotoxin-sensitive voltage-gated sodium (NaV) channels are related to sensory transmission in primary sensory nerves. The sodium channel NaV1.7 has emerged as an attractive analgesic target. The purpose of this study was to evaluate pain-related behavior and expression of NaV1.7 in dorsal root ganglia (DRG) after combined sciatic nerve compression and nucleus pulposus (NP) application in rats.

METHODS

Rats were divided into three groups and underwent either sciatic nerve compression with NP for 2 s using forceps (n = 20), sham operation with neither compression nor NP (n = 20), or no operation (controls, n = 20). Mechanical hyperalgesia was measured every second day for three weeks using von Frey filaments. NaV1.7 expression in L5 DRG was examined 7 and 14 days after surgery using immunohistochemistry. The number of neurons immunoreactive for NaV1.7 was compared among the three groups.

RESULTS

Mechanical hyperalgesia was found over the 14-day observation in the nerve compression plus NP application group, but not in the sham-operated or control groups (P < 0.05). NaV1.7 expression in L5 DRG was up-regulated in the nerve compression plus NP application group, compared with sham-operated and control rats (P < 0.01).

CONCLUSIONS

Our results indicate that nerve compression plus NP application produces pain-related behavior. We conclude that NaV1.7 expression in DRG neurons may play an important role in mediating pain from sciatic nerves after compression injury and exposure to NP.

A rat model for chronic spinal nerve root compression

OBJECTIVES

The pathophysiology of radiculopathy associated with lumbar spinal stenosis and lumbar disc herniation is incompletely understood. The goal of the present study was to establish a chronic spinal nerve root compression model that can mimic lumbar disc herniation or spinal stenosis using silicone tube compression. We also try to link the pathology changes of damaged nerve root with the reaction of microglia in spinal cord in same rat at different time points.

METHODS

Thirty rats were used in this study. The L5 nerve roots (dorsal and ventral) were exposed by hemilaminectomy; the diameter of the L5 nerve root was measured at the 2 mm proximal from the dorsal root ganglia. The dorsal and ventral nerve roots of L5 were compressed using a silicone tube, and the sham group was only exposed dorsal and ventral roots of L5. Five rats from the sham group were perfused at 8 days after surgery, and 25 rats from the model groups were perfused at 3, 8, 12, 45 days, and 5 months after surgery, each model group was composed of 5 rats according to the time point. The L5 spinal cord segments and nerve root that compressed by silicone tube were harvested from the same rat. Microglia and neuron in the spinal cord were stained by immunohistochemistry, and the nerve root was shown by electron microscope.

RESULTS

In sham-operated rat, the arrangement of axon and myelin sheath is normal, the ventral root is mainly composed of large axon (>6 μm) and it is composed of 46.3 % of all the axons of the ventral root; the average myelin thickness of large axon is 1.86 μm; the dorsal root is mainly composed of medium (2-3.9 or 4-5.9 μm) axons and they are composed of 79.1 % of all the axons of the dorsal root; the average myelin thickness of this category is 0.94 or 1.55 μm. The average myelin thickness of large axon in ventral root reduced to 0.97 and 1.19 μm from more than 1.86 μm after compression for 3 and 8 days separately. Most of myelin sheath disappeared after 12 days of compression; the myelin sheath was partly restored at 45 days after compression which the myelin sheath thickness of large axons in ventral root was 0.47 μm. The medium category in dorsal root reduced to 0.59 or 0.72 μm from 0.94 μm, and 1.55 μm after compression for 3 days (p < 0.05 to p < 0.0001). The medium category axon in dorsal root is also 0.47 μm after compression for 45 days (p ≤ 0.0001). The myelin sheath was almost totally restored at the 5 months of compression; the myelin sheath thickness returned to normal and the axons were intact in structure under EM. The number of Iba1-positive microglia increased by 18.69, 40.44, and 18.49 % after compression for 3, 8, and 12 days separately in the ipsilateral dorsal horn and 21.26, 32.15, 22.87 % in ventral horns, and the activation of microglia was also prominent in contralateral sides of the dorsal and ventral horn at 8 days time point. The microglia cell reconverted to resting status after compression for 45 days or 5 months.

CONCLUSION

The chronic spinal nerve root compression with silicone tube produces a recoverable damage to nerve root, which produces recoverable microglial activation in the spinal cord. These results demonstrated that the chronic spinal nerve root compression with silicone tube could mimic the pathological changes of lumbar spinal stenosis or lumbar disc herniation.

Simvastatin ameliorates cauda equina compression injury in a rat model of lumbar spinal stenosis

Lumbar spinal stenosis (LSS) is the leading cause of morbidity and mortality worldwide. LSS pathology is associated with secondary injury caused by inflammation, oxidative damage and cell death. Apart from laminectomy, pharmacological therapy targeting secondary injury is limited. Statins are FDA-approved cholesterol-lowering drug. They also show pleiotropic anti-inflammatory, antioxidant and neuroprotective effects. To investigate the therapeutic efficacy of simvastatin in restoring normal locomotor function after cauda equina compression (CEC) in a rat model of LSS, CEC injury was induced in rats by implanting silicone gels into the epidural spaces of L4 and L6. Experimental group was treated with simvastatin (5 mg/kg body weight), while the injured (vehicle) and sham operated (sham) groups received vehicle solution. Locomotor function in terms of latency on rotarod was measured for 49 days and the threshold of pain was determined for 14 days. Rats were sacrificed on day 3 and 14 and the spinal cord and cauda equina fibers were extracted and studied by histology, immunofluorescence, electron microscopy (EM) and TUNEL assay. Simvastatin aided locomotor functional recovery and enhanced the threshold of pain after the CEC. Cellular Infiltration and demyelination decreased in the spinal cord from the simvastatin group. EM revealed enhanced myelination of cauda equina in the simvastatin group. TUNEL assay showed significantly decreased number of apoptotic neurons in spinal cord from the simvastatin group compared to the vehicle group. Simvastatin hastens the locomotor functional recovery and reduces pain after CEC. These outcomes are mediated through the neuroprotective and anti-inflammatory properties of simvastatin. The data indicate that simvastatin may be a promising drug candidate for LSS treatment in humans.

The role of fluoroscopic interlaminar epidural injections in managing chronic pain of lumbar disc herniation or radiculitis: a randomized, double-blind trial

BACKGROUND

There is continued debate on the effectiveness, indications, and medical necessity of epidural injections in managing pain and disability from lumbar disc herniation, despite extensive utilization. There is paucity of literature on interlaminar epidural injections in managing lumbar disc herniation or radiculitis in contemporary interventional pain management settings utilizing fluoroscopy.

METHODS

A randomized, double-blind, active-control trial was undertaken to assess the effectiveness of lumbar interlaminar epidural injections with or without steroids for disc herniation and radiculitis. The primary outcome was defined as pain relief and functional status improvement of ≥ 50%. One hundred twenty patients were randomly assigned to 1 of the 2 groups. Group I patients received lumbar interlaminar injections containing a local anesthetic (lidocaine 0.5%, 6 mL), whereas Group II patients received lumbar interlaminar epidural injections of 0.5% lidocaine, 5 mL, mixed with 1 mL of non-particulate betamethasone.

RESULTS

In the patients who responded with initial 2 procedures with at least 3 weeks of relief, significant improvement was seen in 80% of the patients in the local anesthetic group and 86% of the patients in the local anesthetic and steroid group. The overall average procedures per year were 3.6 in the local anesthetic group and 4.1 in the local anesthetic and steroid group, with an average relief of 33.7 ± 18.1 weeks in the local anesthetic group and 39.1 ± 12.2 weeks in the local anesthetic and steroid group over a period of 52 weeks in the overall population.

CONCLUSIONS

Lumbar interlaminar epidural injections of local anesthetic with or without steroids might be effective in patients with disc herniation or radiculitis, with potential superiority of steroids compared with local anesthetic alone at 1 year follow-up.

Distinct degree of radiculopathy at different levels of peripheral nerve injury

BACKGROUND

Lumbar radiculopathy is a common clinical problem, characterized by dorsal root ganglion (DRG) injury and neural hyperactivity causing intense pain. However, the mechanisms involved in DRG injury have not been fully elucidated. Furthermore, little is known about the degree of radiculopathy at the various levels of nerve injury. The purpose of this study is to compare the degree of radiculopathy injury at the DRG and radiculopathy injury proximal or distal to the DRG.

RESULTS

The lumbar radiculopathy rat model was created by ligating the L5 nerve root 2 mm proximal to the DRG or 2 mm distal to the DRG with 6.0 silk. We examined the degree of the radiculopathy using different points of mechanical sensitivity, immunohistochemistry and in vivo patch-clamp recordings, 7 days after surgery. The rats injured distal to the DRG were more sensitive than those rats injured proximal to the DRG in the behavioral study. The number of activated microglia in laminas I-II of the L5 segmental level was significantly increased in rats injured distal to the DRG when compared with rats injured proximal to the DRG. The amplitudes and frequencies of EPSC in the rats injured distal to the DRG were higher than those injured proximal to the DRG. The results indicated that there is a different degree of radiculopathy at the distal level of nerve injury.

CONCLUSIONS

Our study examined the degree of radiculopathy at different levels of nerve injury. Severe radiculopathy occurred in rats injured distal to the DRG when compared with rats injured proximal to the DRG. This finding helps to correctly diagnose a radiculopathy.

Epidural administration of spinal nerves with the tumor necrosis factor-alpha inhibitor, etanercept, compared with dexamethasone for treatment of sciatica in patients with lumbar spinal stenosis: a prospective randomized study

STUDY DESIGN

Prospective randomized trial.

OBJECTIVE

To examine the effect of the tumor necrosis factor alpha (TNF-α) inhibitor, etanercept, on radicular pain by its epidural administration onto spinal nerves in patients with lumbar spinal stenosis.

SUMMARY OF BACKGROUND DATA

TNF-α is thought to play a crucial role in the radicular pain caused by lumbar disc herniation and spinal stenosis. Intravenous infusion of infliximab for sciatica has been examined in 2 studies; however, the results were equivocal.

METHODS

Eighty patients with low back and radicular leg pain were investigated. We diagnosed the patients by physical examination, and X-ray and magnetic resonance imaging. In 40 patients, we epidurally administered 2.0 mL of lidocaine and 10 mg of etanercept onto the affected spinal nerve, and 2.0 mL of lidocaine and 3.3 mg of dexamethasone was used in 40 patients. Low back pain, leg pain, and leg numbness were evaluated using a visual analogue scale (VAS) and Oswestry Disability Index (ODI) score before and for 1 month after epidural administration.

RESULTS

Low back pain, leg pain, and leg numbness in the 2 groups were not significantly different before epidural administration. Epidural administration of etanercept was more effective than dexamethasone for leg pain (3 days, and 1, 2, and 4 weeks: P < 0.05), low back pain (3 days, and 1 and 2 weeks: P < 0.05), and leg numbness (3 days, and 1 and 2 weeks: P < 0.05). No adverse event was observed in either group.

CONCLUSION

Our results indicate that epidural administration of a TNF-α inhibitor onto the spinal nerve produced pain relief, but no adverse event. TNF-α inhibitors may be useful tools for the treatment of radicular pain caused by spinal stenosis.

Efficacy of epidural administration of anti-interleukin-6 receptor antibody onto spinal nerve for treatment of sciatica

INTRODUCTION

Interleukin-6 (IL-6) is thought to play a crucial role in the radicular pain caused by lumbar spinal stenosis. However, efficacy of inhibition of IL-6 for sciatica in patients with lumbar spinal stenosis has not been clarified. The purpose of the current study was to examine the effect of the anti-IL-6 receptor monoclonal antibody, tocilizumab, on radicular pain by its epidural administration onto spinal nerves in patients with lumbar spinal stenosis.

METHODS

Sixty patients with low back and radicular leg pain caused by spinal stenosis were investigated. In 30 patients, we infiltrated 2.0 mL of lidocaine and 80 mg of tocilizumab onto the affected spinal nerve, and 2.0 mL of lidocaine and 3.3 mg of dexamethasone were used in 30 patients. Low back pain, leg pain, and leg numbness were evaluated during 1 month after spinal nerve infiltration.

RESULTS

Infiltration of tocilizumab was more effective than dexamethasone for leg pain (3 days, 1, 2, and 4 weeks), low back pain (3 days, 1, 2 and 4 weeks), and leg numbness (3 days, 1 and 2 weeks). No adverse event was observed in either group.

CONCLUSION

Our results indicate that the epidural administration of an anti-IL-6 receptor monoclonal antibody, tocilizumab, onto the spinal nerve produced reduction of radicular leg pain, numbness, and low back pain without adverse event. IL-6 may be one of the inducers of pain caused by spinal stenosis in humans.

Changes in expression of mRNA for interleukin-8 and effects of interleukin-8 receptor inhibitor in the spinal dorsal horn in a rat model of lumbar disc herniation

STUDY DESIGN

Autologous nucleus pulposus obtained from coccygeal intervertebral discs was grafted on the proximal of L5 dorsal root ganglion. Pain behavior, mRNA expression of Interleukin-8 (IL-8), and immunohistochemical changes were assessed.

OBJECTIVE

The purpose of this study is to investigate temporal changes of IL-8 expression in the spinal cord and dorsal root ganglion and the pain-related behaviors with time course and to elucidate whether repertaxin (IL-8 receptor inhibitor) attenuates pain-related behaviors in a rat model of lumbar disc herniation.

SUMMARY OF BACKGROUND DATA

Inflammatory mediators like cytokines and chemokines have been implicated in radicular pain because of disc herniation. IL-8, known as CXCL8, is a chemokine, which has been reported to be associated with painful degenerative disc disorders and chronic inflammatory pain states.

METHODS

Lumbar disc herniated rat model was made by implantation of the autologous nucleus pulposus, harvested from the coccygeal vertebra of each tail, on the left L5 nerve root just proximal to the dorsal root ganglion. Rats were tested for mechanical allodynia and thermal hyperalgesia at 2 days before surgery, and on days 1, 5, 10, 20, 30, 40, 50, and 60 postoperatively. Experimental group was intrathecally injected with the IL-8 receptor inhibitor at L5 level on postoperative day 10. Mechanical allodynia of the plantar surface of both hindpaw was tested on 30 minutes, 1, 3 hours, 1, 3, 5, and 10 days after administration. For the staining of astrocytes and microglia, immunohistochemical study was done 20 days after surgery.

RESULTS

Mechanical allodynia in ipsilateral hindpaw developed 1 day after surgery and lasted until 60 days and thermal withdrawal latency decreased significantly on the ipsilateral side 10 days after surgery and gradually increased through day 60. The IL-8 receptor inhibitor attenuated the mechanical allodynia caused by nucleus pulposus when it was administered on postoperative day 10 and reduced microglial activation and phosphorylated form of mitogen-activated protein kinase (pERK) expression in the spinal dorsal horn.

CONCLUSION

IL-8 might be a potential therapeutic target in chronic radicular neuropathic pain because of disc herniation, CXCL8 inhibitor could be one of its promising therapeutic agents.

Analgesic effects of prostaglandin E2 receptor subtype EP1 receptor antagonist: experimental study of application of nucleus pulposus

STUDY DESIGN

The effect of an EP1 receptor antagonist on pain-related behavior induced by nucleus pulposus (NP) applied to the dorsal root ganglion (DRG) in rats was investigated.

OBJECTIVE

We investigated pain-related behavior, the amount of prostaglandin E2 (PGE2), and neural damage to the DRG after application of NP to the DRG after administration of an EP1 receptor antagonist.

SUMMARY OF BACKGROUND DATA

PGE2 induces mechanical allodynia and hyperalgesia, which are mediated by PGE2 receptors. EP1 is one of the PGE2 receptor subtypes. An EP1 antagonist reduces hyperalgesia, allodynia, and c-fos expression in the rat chronic nerve constriction model.

METHODS

Sprague-Dawley rats (n = 103) were used. Animals receiving NP were divided into three experimental groups (n = 12 in each group): saline, high-dose (5 mg/kg) EP1 receptor antagonist (RA), and low-dose (2.5 mg/kg) EP1-RA (orally once daily for 5 days). Animals in the sham group did not receive NP. Von Frey tests were used for pain-behavior testing. The amount of PGE2 in DRG and the number of activating transcription factor-3 (ATF3) immunoreactive positive cells were compared among groups.

RESULTS

The mechanical thresholds in the three groups decreased 7 days after surgery (just before treatment). The threshold in both the high- and low-dose EP1-RA groups increased at 11 days (5 days after treatment) and continued for 14 days. The thresholds in both the low- and high-dose EP1-RA groups increased significantly compared with the saline group (P < 0.05). The amount of PGE2 was significantly increased in the NP group compared with the sham and naïve animals after application of NP. ATF3 expression was increased by NP but was not increased after administration of the EP1-RA.

CONCLUSION

An EP1 receptor antagonist improves pain-related behavior in the rat model and might be a potential agent to improve pain-related behavior in patients with lumbar disc herniation.

The red wine polyphenol resveratrol shows promising potential for the treatment of nucleus pulposus-mediated pain in vitro and in vivo

STUDY DESIGN

Descriptive and mechanistic investigation of the anti-inflammatory and anticatabolic effect of resveratrol in intervertebral discs (IVDs) in vitro and of the analgetic effect in vivo.

OBJECTIVE

To determine whether resveratrol may be useful in treating nucleus pulposus (NP)-mediated pain.

SUMMARY OF BACKGROUND DATA

Proinflammatory cytokines seem to be key mediators in the development of NP-mediated pain. Patients with discogenic or radiculopathic pain may substantially benefit from anti-inflammatory substances that could be used in a minimal-invasive treatment approach. Resveratrol, a polyphenolic phytoalexin found in red wine exhibits anti-inflammatory effects in various cell types and tissues, but no data exists so far with regards to the IVD in the context of low back and leg pain.

METHODS

In part 1, the anti-inflammatory and anticatabolic effect of resveratrol was investigated in a cell culture model on interleukin 1β (IL-1β) prestimulated human IVD cells on the gene and protein expression level. In part 2, the molecular mechanisms underlying the effects observed upon resveratrol treatment were investigated (toll-like receptors, nuclear factor κB, sirtuin 1 (SIRT1), mitogen-activated protein (MAP) kinases p38/ERK/JNK). In part 3, the analgetic effects of resveratrol were investigated in vivo using a rodent model of radiculopathy and von Frey filament testing. All quantitative data were statistically evaluated either by Mann-Whitney U test or by one-way analysis of variance and Bonferroni post hoc testing (P < 0.05).

RESULTS

In vitro, resveratrol exhibited an anti-inflammatory and anticatabolic effect on the messenger RNA and protein level for IL-6, IL-8, MMP1, MMP3 and MMP13. This effect does not seem to be mediated via the MAP kinase pathways (p38, ERK, JNK) or via the NF-κB/SIRT1 pathway, although toll-like receptor 2 was regulated to a minor extent. In vivo, resveratrol significantly reduced pain behavior triggered by application of NP tissue on the dorsal root ganglion for up to 14 days.

CONCLUSION

Resveratrol was able to reduce levels of proinflammatory cytokines in vitro and showed analgetic potential in vivo. A decrease in proinflammatory cytokines may possibly be the underlying mechanism of pain reduction observed in vivo. Resveratrol seems to have considerable potential for the treatment of NP-mediated pain and may thus be an alternative to other currently discussed (biological) treatment options.

Kinematic and dynamic gait compensations in a rat model of lumbar radiculopathy and the effects of tumor necrosis factor-alpha antagonism

Introduction

Tumor necrosis factor-α (TNFα) has received significant attention as a mediator of lumbar radiculopathy, with interest in TNF antagonism to treat radiculopathy. Prior studies have demonstrated that TNF antagonists can attenuate heightened nociception resulting from lumbar radiculopathy in the preclinical model. Less is known about the potential impact of TNF antagonism on gait compensations, despite being of clinical relevance. In this study, we expand on previous descriptions of gait compensations resulting from lumbar radiculopathy in the rat and describe the ability of local TNF antagonism to prevent the development of gait compensations, altered weight bearing, and heightened nociception.

Methods

Eighteen male Sprague-Dawley rats were investigated for mechanical sensitivity, weight-bearing, and gait pre- and post-operatively. For surgery, tail nucleus pulposus (NP) tissue was collected and the right L5 dorsal root ganglion (DRG) was exposed (Day 0). In sham animals, NP tissue was discarded (n = 6); for experimental animals, autologous NP was placed on the DRG with or without 20 μg of soluble TNF receptor type II (sTNFRII, n = 6 per group). Spatiotemporal gait characteristics (open arena) and mechanical sensitivity (von Frey filaments) were assessed on post-operative Day 5; gait dynamics (force plate arena) and weight-bearing (incapacitance meter) were assessed on post-operative Day 6.

Results

High-speed gait characterization revealed animals with NP alone had a 5% decrease in stance time on their affected limbs on Day 5 (P ≤0.032). Ground reaction force analysis on Day 6 aligned with temporal changes observed on Day 5, with vertical impulse reduced in the affected limb of animals with NP alone (area under the vertical force-time curve, P <0.02). Concordant with gait, animals with NP alone also had some evidence of affected limb mechanical allodynia on Day 5 (P = 0.08) and reduced weight-bearing on the affected limb on Day 6 (P <0.05). Delivery of sTNFRII at the time of NP placement ameliorated signs of mechanical hypersensitivity, imbalanced weight distribution, and gait compensations (P <0.1).

Conclusions

Our data indicate gait characterization has value for describing early limb dysfunctions in pre-clinical models of lumbar radiculopathy. Furthermore, TNF antagonism prevented the development of gait compensations subsequent to lumbar radiculopathy in our model.

Changes in spinal cord expression of fractalkine and its receptor in a rat model of disc herniation by autologous nucleus pulposus

STUDY DESIGN

Behavior, mRNA and immunohistochemical assessment of the expression of fractalkine (CX3CL1) and its receptor (CX3CR1) in a rat model of disc herniation by autologous nucleus pulposus (NP) implantation.

OBJECTIVE

To evaluate the changes in expression of fractalkine and its receptor in the spinal cord and their association with pain behavior in a rat model of disc herniation.

SUMMARY OF BACKGROUND DATA

Chemokines have recently been implicated in the pathophysiology of neuropathic pain. They mediate astrocytic migration and microglial proliferation, which are involved in the regulation of nociceptive transmission. Fractalkine is a chemokine, which participates in the mechanisms of neuropathic pain as a mediator of neuron-glia interactions.

METHODS

Sixty-six rats (NP-treated = 47, sham = 19) were implanted with autologous NP (approximately 3 mg) on the left L5 nerve root, just proximal to the dorsal root ganglion and tested for thermal hyperalgesia and mechanical allodynia before surgery and on days 1, 5, 10, 20, and 30 after surgery. The changes of expression of fractalkine and its receptor in the spinal cord were studied using real time PCR and immunohistochemistry.

RESULTS

Rats developed ipsilateral mechanical allodynia at day 1 and bilateral thermal hyperalgesia at day 5 after surgery, and these changes in sensitivity persisted throughout the observation period. The expression of mRNA for fractalkine in the spinal cord was increased by day 5 and remained upregulated for the duration of the experiment. The immunostaining for fractalkine increased in neurons and astrocytes and that for the fractalkine receptor increased in microglia in the dorsal horn ipsilateral to the disc herniation.

CONCLUSION

Our results indicate that autologous implantation of NP induces thermal hyperalgesia and mechanical allodynia, and leads to an upregulation of fractalkine and its receptor in spinal neurons and glia, implicating fractalkine in association with radicular pain.

The animal model of spinal cord injury as an experimental pain model

Pain, which remains largely unsolved, is one of the most crucial problems for spinal cord injury patients. Due to sensory problems, as well as motor dysfunctions, spinal cord injury research has proven to be complex and difficult. Furthermore, many types of pain are associated with spinal cord injury, such as neuropathic, visceral, and musculoskeletal pain. Many animal models of spinal cord injury exist to emulate clinical situations, which could help to determine common mechanisms of pathology. However, results can be easily misunderstood and falsely interpreted. Therefore, it is important to fully understand the symptoms of human spinal cord injury, as well as the various spinal cord injury models and the possible pathologies. The present paper summarizes results from animal models of spinal cord injury, as well as the most effective use of these models.

Effects of asialo-erythropoietin on pain-related behavior and expression of phosphorylated-p38 map kinase and tumor necrosis factor-alpha induced by application of autologous nucleus pulposus on nerve root in rat

STUDY DESIGN

this study was designed to examine the neuroprotective effects of asialo-erythropoietin (A-EPO) in a rat model of lumbar disc herniation.

OBJECTIVE

to investigate the effects of A-EPO on pain-related behavior, the expression of phosphorylated-p38 (p-p38) mitogen activated kinase, and the expression of tumor necrosis factor alpha (TNF-α) induced by nucleus pulposus (NP) application on the nerve root.

SUMMARY OF BACKGROUND DATA

erythropoietin (EPO) has neuroprotective effects in a variety of models of central and peripheral nerve injuries. However, EPO is a hematopoietic growth factor and can therefore cause significant side effects such as thicker blood and promotion of blood clotting. A-EPO is a neuroprotective derivative of EPO that is not hematopoietic.

METHODS

female Sprague-Dawley rats (n = 149) were used in this study. NP harvested from the tail was applied to the left L5 nerve root and the rats were then divided into four groups: NP + nontreatment group, no further treatment; NP + A-EPO group, 13.4 microg/kg A-EPO; NP + EPO group, 13.4 microg/kg EPO; and NP + vehicle group, received vehicle. The substances were administered subcutaneously 1 day before surgery and daily for 2 weeks. In the sham group of animals, the L5 nerve root was exposed and NP was not applied. Withdrawal thresholds were determined by the von-Frey test 28 days after surgery. The expressions of p-p38 and TNF-α were assessed by immunohistochemical and immunoblotting analysis. Data were analyzed by unpaired Student t test and Dunnett t test (significance level, P < 0.05).

RESULTS

in the NP + nontreatment and NP + vehicle groups, withdrawal thresholds were decreased significantly for 28 days compared with the sham group (P < 0.05). In the NP + A-EPO group, the thresholds were significantly increased on day 28, and in the NP + EPO group, the thresholds were significantly increased on days 21 and 28 (P < 0.05) compared with the NP + nontreatment and NP + vehicle groups. The expression of p-p38 in the NP + A-EPO group was significantly lower than that in the NP + vehicle group on day 1 (P < 0.05). The expression of TNF in the NP + A-EPO and NP + EPO groups was significantly lower than that in the NP + vehicle group on days 1 and 7 (P < 0.05).

CONCLUSIONS

A-EPO improved pain-related behavior and reduced the expression of p-p38 and TNF-α. The effect of A-EPO may be related to the inhibitory action of p-p38 and TNF-α in the dorsal root ganglion.

Proinflammatory cytokines in the cerebrospinal fluid of patients with lumbar radiculopathy

In pathologic radicular pain of lumbar spinal stenosis, cytokines such as tumor necrosis factor-alpha (TNF-α) and interleukins (ILs) play a crucial role in the pathogenesis of nerve degeneration and pain. We investigated TNF-α and IL-6 levels in the cerebrospinal fluid (CSF) of patients with radicular pain caused by lumbar spinal stenosis (LSS). A total of 30 LSS patients and 10 age-matched controls were examined. CSF samples were obtained adjacent to the level of stenosis in 30 LSS patients, and at the L4-L5 level in the 10 control patients. TNF-α and IL-6 levels in the samples were analyzed using enzyme-linked immunosorbent assays (ELISA). We compared the amounts of TNF-α and IL-6 with severity of pain (low back and leg pain), walking ability, and severity of stenosis (cross-sectional area of dural space). The concentration of IL-6 was significantly higher in LSS patients than in controls, but TNF-α levels were beneath the limit of detection. There was no correlation between IL-6 levels and severity of pain or walking ability (p > 0.05). However, there was a significant correlation between IL-6 levels and severity of stenosis (p < 0.05). The current study showed that the increased CSF IL-6 levels in LSS patients with radicular pain were not correlated with pain severity; although not proven in this study, the increase in CSF IL-6 concentration could indicate pathological nerve damage or degeneration of lumbar radiculopathy represented by the severity of stenosis.

Evaluation of behavior and neuropeptide markers of pain in a simple, sciatic nerve-pinch pain model in rats

Pathomechanisms of injured-nerve pain have not been fully elucidated. Radicular pain and chronic constriction injury models have been established; however, producing these models is complicated. A sciatic nerve-pinch injury is easy to produce but the reliability of this model for evaluating pain behavior has not been examined. The current study evaluated pain-related behavior and change in pain markers in the dorsal root ganglion (DRG) of rats in a simple, sciatic nerve-pinch injury model. In the model, the sciatic nerve was pinched for 2 s using forceps (n = 20), but not injured in sham-operated animals (n = 20). Mechanical and thermal hyperalgesia were measured every second day for 2 weeks using von Frey filaments and a Hargreaves device. Calcitonin gene-related peptide (CGRP), activating transcription factor-3 (ATF-3), phosphorylated p38 mitogen activated protein (Map) kinase (p-p38), and nuclear factor-kappa B (NF-κB; p65) expression in L5 DRGs were examined at 4 and 7 days after surgery using immunohistochemistry. The proportion of neurons immunoreactive for these markers was compared between the two groups. Mechanical (during 8 days) and thermal hyperalgesia (during 6 days) were found in the pinch group rats, but not in the sham-operated animals (p < 0.05); however, hyperalgesia was not significant from days 10 to 14. CGRP, ATF-3, p-p38, and NF-κB expression in L5 DRGs was upregulated in the nerve-injured rats compared with the sham-operated rats (p < 0.01). Our results indicate that a simple sciatic nerve pinch produced pain-related behavior. Upregulation of the pain-marker expression in the nerve-injury model suggested it could be used as a model of pain. However, it was not considered as suitable for long-term studies.

The reactions of glial cells and endoneurial macrophages in the dorsal root ganglion and their contribution to pain-related behavior after application of nucleus pulposus onto the nerve root in rats

STUDY DESIGN

Controlled, interventional, animal study.

OBJECTIVE

To observe the reaction of glial cells and endoneurial macrophages in the dorsal root ganglion (DRG) after application of nucleus pulposus (NP) and investigate whether activated DRG glial cells play a role in the pathogenesis of neuropathic pain.

SUMMARY OF BACKGROUND DATA

Peripheral nerve injury activated DRG and spinal cord glial cells and several cytokines and neurotrophins released from these activated glial cells might induce pain hypersensitivity.

METHODS

Adult male Sprague-Dawley rats were used. NP harvested from the tail was applied to the left L5 DRG. Behavioral testing was performed to investigate the mechanical withdrawal threshold. The numbers of activated satellite glial cells and endoneurial macrophages were counted, and the expressions of tumor necrosis factor-alpha (TNF-alpha) and glial cell-line derived neurotrophic factor (GDNF) were examined by double-labeled immunohistochemistry and immunoblotting.

RESULTS

The mechanical withdrawal threshold was significantly decreased for 28 days and then gradually recovered (P < 0.05). Long-term activation of endoneurial macrophages and satellite glial cells in the DRG was observed, and the reactions of these cells correlated well with pain-related behavior. TNF-alpha was expressed in both endoneurial macrophages and activated satellite glial cells, and TNF-alpha expression was significantly increased in the early stage (P < 0.05). Activated satellite glial cells also expressed GDNF, and its expression was significantly increased and persisted for 28 days (P < 0.05).

CONCLUSION

Activation of DRG glial cells and endoneurial macrophages plays an important role in the pathogenesis of the neuropathic pain state. TNF-alpha actively released from activated glial cells and endoneurial macrophages in the DRG might initiate and maintain the neuropathic pain together with TNF-alpha derived from the applied NP. In the recovery phase, persistent expression of GDNF from activated satellite glial cells might play an important role to restore the function of damaged neurons and recover from neuropathic pain.

The reactions of glial cells and endoneurial macrophages in the dorsal root ganglion and their contribution to pain-related behavior after application of nucleus pulposus onto the nerve root in rats

STUDY DESIGN

Controlled, interventional, animal study.

OBJECTIVE

To observe the reaction of glial cells and endoneurial macrophages in the dorsal root ganglion (DRG) after application of nucleus pulposus (NP) and investigate whether activated DRG glial cells play a role in the pathogenesis of neuropathic pain.

SUMMARY OF BACKGROUND DATA

Peripheral nerve injury activated DRG and spinal cord glial cells and several cytokines and neurotrophins released from these activated glial cells might induce pain hypersensitivity.

METHODS

Adult male Sprague-Dawley rats were used. NP harvested from the tail was applied to the left L5 DRG. Behavioral testing was performed to investigate the mechanical withdrawal threshold. The numbers of activated satellite glial cells and endoneurial macrophages were counted, and the expressions of tumor necrosis factor-alpha (TNF-alpha) and glial cell-line derived neurotrophic factor (GDNF) were examined by double-labeled immunohistochemistry and immunoblotting.

RESULTS

The mechanical withdrawal threshold was significantly decreased for 28 days and then gradually recovered (P < 0.05). Long-term activation of endoneurial macrophages and satellite glial cells in the DRG was observed, and the reactions of these cells correlated well with pain-related behavior. TNF-alpha was expressed in both endoneurial macrophages and activated satellite glial cells, and TNF-alpha expression was significantly increased in the early stage (P < 0.05). Activated satellite glial cells also expressed GDNF, and its expression was significantly increased and persisted for 28 days (P < 0.05).

CONCLUSION

Activation of DRG glial cells and endoneurial macrophages plays an important role in the pathogenesis of the neuropathic pain state. TNF-alpha actively released from activated glial cells and endoneurial macrophages in the DRG might initiate and maintain the neuropathic pain together with TNF-alpha derived from the applied NP. In the recovery phase, persistent expression of GDNF from activated satellite glial cells might play an important role to restore the function of damaged neurons and recover from neuropathic pain.

Direct single injection of p38 mitogen-activated protein kinase inhibitor does not affect calcitonin gene-related peptide expression in dorsal root ganglion neurons innervating punctured discs in rats

STUDY DESIGN.: Immunohistological analysis of punctured disc after application of a p38 MAP kinase inhibitor. OBJECTIVE.: To examine effect of direct application on dorsal root ganglion (DRG) neurons innervating damaged rat discs. SUMMARY OF BACKGROUND DATA.: Degeneration of lumbar discs is one cause of low back pain. Pathogenesis may involve sensory nerve ingrowth into disc inner layers; tumor necrosis factor-alpha (TNF-alpha) is thought to be a major inducer of ingrowth. Because p38 mitogen-activated protein kinase (p38) upregulates TNF-alpha expression and may play a crucial role in pain sensation, we investigated the effect of one injection of inhibitor on expression of the pain-related neuropeptide calcitonin gene-related peptide (CGRP). METHODS.: The neuro-tracer fluoro-gold was applied to the surfaces of L4/5 discs to label the innervating DRG neurons (n = 30). Of 30 rats, 10 were controls, whereas the other 20 were the experimental model (i.e., discs were punctured with 23-gauge needle). P38 specific inhibitor or saline was applied simultaneously (n = 10 each, Puncture + inhibitor and puncture + saline groups). Fourteen days postsurgery, DRGs from L1 to L6 were harvested, sectioned, and immunostained for CGRP. Proportion of CGRP-immunoreactive DRG neurons was evaluated in all groups. RESULTS.: Fluoro-gold-labeled neurons innervating the L4/5 disc were distributed throughout L1 to L6 DRGs in all groups. Proportions of labeled neurons positive for CGRP were 15.2% +/- 8% (controls), 27.2% +/- 10% (puncture + saline), and 25.2% +/- 8% (puncture + inhibitor). Proportion of immunoreactive neurons was significantly increased in the puncture groups compared with controls. However, there was no significant difference between the 2 puncture groups (P > 0.1). CONCLUSION.: In this model, CGRP was upregulated in DRG neurons innervating the damaged disc. However, a direct single application of p38 inhibitor did not suppress CGRP expression in innervating DRG neurons. Future research with p38 inhibitor in this model should evaluate multiple or systemic administration of inhibitor.

Targeting protein kinases in central nervous system disorders

Protein kinases are a growing drug target class in disorders in peripheral tissues, but the development of kinase-targeted therapies for central nervous system (CNS) diseases remains a challenge, largely owing to issues associated specifically with CNS drug discovery. However, several candidate therapeutics that target CNS protein kinases are now in various stages of preclinical and clinical development. We review candidate compounds and discuss selected CNS protein kinases that are emerging as important therapeutic targets. In addition, we analyse trends in small-molecule properties that correlate with key challenges in CNS drug discovery, such as blood-brain barrier penetrance and cytochrome P450-mediated metabolism, and discuss the potential of future approaches that will integrate molecular-fragment expansion with pharmacoinformatics to address these challenges.

Comparison of neuropathic pain and neuronal apoptosis following nerve root or spinal nerve compression

Altered dorsal root ganglion (DRG) function is associated with neuropathic pain following spinal nerve injury. However, compression of the cauda equina and dorsal rhizotomy proximal to the DRG do not induce significant pain, whereas in the spinal nerve and peripheral nerve, injury distal to the DRG does induce neuropathic pain. Caspase signaling induces apoptosis, and caspase inhibitors prevent pain-related behavior. The degree of DRG neuronal apoptosis is thought to play a role in pain behavior. We suggest that differences in pain behavior according to the injury sites within the DRG may be related to imbalances in apoptotic injuries. The aim of this study was to determine which compression injury was more painful and to compare behavior with expression of tumor necrosis factor (TNF)-alpha in DRG and apoptosis in the DRG following crush injury to the L5 nerve root or L5 spinal nerve. Sprague–Dawley rats received a crush injury to the L5 spinal nerve (distal to the DRG), crush injury to the L5 nerve root (proximal to the DRG), or no crush injury (sham). Mechanical allodynia was determined by the von Frey test. Expression of TNF-alpha was compared among three groups using immunoblot findings. Furthermore, we compared the percentage of neurons injured in the DRG using immunostaining for apoptotic cells and localization of activated caspase 3. Mechanical allodynia was observed in both crush injury groups. The duration of mechanical allodynia in the distal crush group was significantly longer than in the proximal crush group (P < 0.05). TNF-alpha expression was increased in DRG neurons following injury. DRG apoptosis in the distal crush group was significantly higher than in the proximal group at each time point (P < 0.05). This study suggests that spinal nerve crush injuries produce a greater degree of DRG apoptosis than do corresponding nerve root crush injuries, and that the former injuries are associated with longer lasting mechanical allodynia. Thus, differences in the time course of mechanical allodynia might be associated with an imbalance in DRG apoptosis.

MKK3, an upstream activator of p38, contributes to formalin phase 2 and late allodynia in mice

Spinal p38 mitogen activated (MAP) kinase plays a key role in chronic pain behavior. However, clinical development of p38 inhibitors has been hindered by significant toxicity. To evaluate alternative strategies of p38 regulation, we determined if known upstream activators of p38 (mitogen activated kinase kinase [MKK] 3 and MKK6), are involved in development and maintenance of pain and spinal p38 phosphorylation. Acute pain behaviors were not altered in MKK3 or MKK6 deficient mice. The phase 2 formalin response was delayed in MKK3-/- mice, but unchanged in magnitude, while the response remained normal in MKK6-/- mice. More striking, late formalin allodynia (3-18 days post-injection) was prominent in wild type and MKK6-/- mice, but was delayed for several days in MKK3-/- mice. In wild type, but not MKK3-/- mice, intraplantar formalin elicited increases in ipsilateral spinal MKK3/6 phosphorylation acutely and again at 9 days postinjection. Phosphorylation of MKK3/6 correlated with phase 2 formalin behavior. Wild type (WT) and MKK3-/- mice both expressed increases in spinal phosphorylated p38, however in WT mice this response began several days earlier, and was of higher magnitude and duration than in MKK3-/- mice. This phosphorylation correlated with the late allodynia. Phosphorylated MKK3/6 was detected only in astrocytes, given that phosphorylated p38 (P-p38) is usually not seen in astrocytes this argues for astrocytic release of soluble mediators that affect p38 phosphorylation in microglia. Taking these data together, MKK3, but not MKK6, is necessary for normal development of chronic pain behavior and phosphorylation of spinal p38.

Direct application of the TNF-alpha inhibitor, etanercept, does not affect CGRP expression and phenotypic change of DRG neurons following application of nucleus pulposus onto injured sciatic nerves in rats

STUDY DESIGN

Immunohistological and behavioral analysis of the effect of a tumor necrosis factor alpha (TNF-alpha) inhibitor in an injured-nerve model.

OBJECTIVE

To examine the effect of direct application of a TNF-alpha inhibitor (etanercept) on injured-nerve pain caused by nucleus pulposus.

SUMMARY AND BACKGROUND DATA

TNF-alpha is thought to play a crucial role in radicular pain. Calcitonin gene-related peptide (CGRP) is an inflammatory neuropeptide found in small sensory neurons. We have reported that CGRP appears in medium and large dorsal root ganglion (DRG) neurons that transmit proprioception in physiologic conditions. The purpose of the current study was to examine the change in behavior and phenotypic change of CGRP-immunoreactive DRG neurons by the TNF-alpha inhibitor, etanercept, in a disc herniation model.

METHODS

For the injured-nerve model, nucleus pulposus was applied to the sciatic nerve and the sciatic nerve pinched. Saline (10 microL; n = 10), as a control, or etanercept (150 microg: n = 10) were applied to sciatic nerves simultaneously. Mechanical allodynia was examined. Immunohistochemistry was used to examine CGRP expression in L5 DRGs.

RESULTS

Significant mechanical allodynia for 10 days was seen in the injured-nerve group compared with sham-operated animals. Etanercept ameliorated the mechanical allodynia slightly on day 2; however, there was no effect on other days. CGRP immunoreactivity was upregulated in the L5 DRG neurons of injured-nerve groups compared with the sham-operated group (P < 0.01). However, etanercept did not affect CGRP expression after nerve injury (P > 0.05). Proportions of CGRP- immunoreactive medium and large neurons were not significantly different in the nerve injury + saline group compared with the injury + etanercept group (P > 0.05).

CONCLUSION

Our results indicate that direct application of a TNF-alpha inhibitor had a small effect on acute pain behavior and may not be effective for suppression of inflammatory peptides in the current disc-herniation model.

Sympathectomy reduces mechanical allodynia, tumor necrosis factor-alpha expression, and dorsal root ganglion apoptosis following nerve root crush injury

STUDY DESIGN

An analysis of pain behavior and neuronal apoptosis in the dorsal root ganglion (DRG) following crush injury to the L5 nerve root, with or without surgical sympathectomy.

OBJECTIVES

To determine whether sympathectomy prevents pain behavior and to compare pain behavior with expression of tumor necrosis factor (TNF)-alpha and apoptosis in the DRG.

SUMMARY OF BACKGROUND DATA

Sympathetic block is used to relieve symptoms in radiculopathy patients. One effect of the block is improvement of blood flow to the nerve. However, this beneficial effect continues longer than the expected duration of local anesthesia, suggesting an unknown neuroprotective effect involving interference with sympathetic activity.

METHODS

Sprague-Dawley rats (n = 102) were used and divided into 4 experimental groups. In the crush group, animals received a crush injury to the L5 nerve root. In the sympathectomy group, animals received sympathectomy (Syx) on the left side. In the Syx + crush group, both sympathectomy and crush injury were performed. In the sham group, the surgical procedure was the same, but neither sympathectomy nor crush injury took place. Mechanical allodynia was determined in 4 groups. Expression of TNF-alpha was compared in rats with crush injury, with and without sympathectomy. Using immunostaining for caspase 3, NeuN, and GFAP, localization of apoptotic cells was observed. In addition, we compared the percentage of neurons undergoing apoptosis in the DRG.

RESULTS

Sympathectomy prevented mechanical allodynia throughout the 14-day experimental period. TNF-alpha expression was increased in the DRG following crush-only injury, whereas it was decreased in animals undergoing sympathectomy after the crush injury. DRG apoptosis in the crush group was significantly higher than in the sympathectomy group at day 7 (P < 0.05).

CONCLUSION

Surgical sympathectomy reduced mechanical allodynia for 14 days after nerve root crush injury, and that DRG apoptosis was decreased in injured animals that underwent sympathectomy. Sympathetic block may not only cause an increase in nerve blood flow, but may also prevent the development of significant TNF-alpha elevation, DRG apoptosis, and neuropathic pain.