Participation of 5-hydroxytryptamine in pain-related behavior induced by nucleus pulposus applied on the nerve root in rats

Exploring the Mechanism of Immediate Analgesia Induced by Tuina Intervention on Minor Chronic Constriction Injury in Rats Using LC-MS

Purpose

This study aimed to investigate changes in metabolomic expression in the spinal dorsal horn (SDH) and thalamus during a Tuina session, aiming to elucidate the mechanism of immediate analgesia.

Methods

The rats were randomly divided into three groups: the Sham group, the Model group, and the Tuina group. A minor chronic constriction injury (minor CCI) model was established in both the Model group and the Tuina group. The therapeutic effect of Tuina was determined using the mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) tests. Differential metabolites of the SDH and thalamus were detected using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Bioinformatic analysis was performed using CV, PCA, Venn, and KEGG.

Results

The therapeutic effect of MWT and TWL after instant Tuina intervention was significant. The therapeutic effect of Tuina instant was significantly better compared to the Model group. In the Veen analysis, it was found that Tuina instantly regulates 10 differential metabolites in the SDH and 5 differential metabolites in the thalamus. In the KEGG enrichment analysis, we found that differential metabolites were enriched in 43 pathways in the thalamus and 70 pathways in the SDH.

Conclusion

Tuina therapy may have analgesic effects by metabolizing neurotransmitters such as 2-Picolinic Acid, 5-Hydroxy-Tryptophan Glutathione Betaine-aldehyde-chloride Leucine Lysine Methionine Sarcosine Succinic Acid Histidine Acetylcholine and 5-Hydroxyindoleacetic Acid through the cAMP pathway. It also affects pathways of neurodegeneration-multiple diseases, butanoate metabolism, tyrosine metabolism.

Intervertebral disc degeneration and how it leads to low back pain

The purpose of this review was to evaluate data generated by animal models of intervertebral disc (IVD) degeneration published in the last decade and show how this has made invaluable contributions to the identification of molecular events occurring in and contributing to pain generation. IVD degeneration and associated spinal pain is a complex multifactorial process, its complexity poses difficulties in the selection of the most appropriate therapeutic target to focus on of many potential candidates in the formulation of strategies to alleviate pain perception and to effect disc repair and regeneration and the prevention of associated neuropathic and nociceptive pain. Nerve ingrowth and increased numbers of nociceptors and mechanoreceptors in the degenerate IVD are mechanically stimulated in the biomechanically incompetent abnormally loaded degenerate IVD leading to increased generation of low back pain. Maintenance of a healthy IVD is, thus, an important preventative measure that warrants further investigation to preclude the generation of low back pain. Recent studies with growth and differentiation factor 6 in IVD puncture and multi-level IVD degeneration models and a rat xenograft radiculopathy pain model have shown it has considerable potential in the prevention of further deterioration in degenerate IVDs, has regenerative properties that promote recovery of normal IVD architectural functional organization and inhibits the generation of inflammatory mediators that lead to disc degeneration and the generation of low back pain. Human clinical trials are warranted and eagerly anticipated with this compound to assess its efficacy in the treatment of IVD degeneration and the prevention of the generation of low back pain.

Clinical Evaluation of Efficacy on Ultrasound Combined with Neuromuscular Electrical Stimulation in Treating Lumbar Disc Herniation

Purpose. To investigate the clinical efficacy of ultrasound (US) combined with neuromuscular electrical stimulation (NMES) in treating lumbar disc herniation (LDH) and its effect on the level of inflammatory factors. Methods. The data of 240 patients with LDH treated at our hospital from January 2020 to February 2021 were reviewed and classified into an US combined with NMES treatment group (US+NMES, $n=80$ ), NMES only treatment group (NMES, $n=80$ ), and US only treatment group (US, $n=80$ ). Their Visual Analogue Scale (VAS) and Oswestry Disability Index (ODI) scores, levels of inflammatory factors and pain mediators, recovery rate, and total recovery time before and after treatment were compared. Additionally, the incidence of complications/adverse reactions was also investigated. Results. Compared with data before treatment, the three groups had lower VAS and ODI scores, inflammatory factor levels (interleukin- [IL-] 1, IL-6, and tumor necrosis factor- [TNF-] α), and pain mediators (transforming growth factor- [TGF-] β1, prostaglandin E2 [PEG2], and 5-hydroxytryptamine [5-HT]) after treatment, with the most significant decrease observed in the US+NMES group. Compared with patients who received US or NMES treatment alone, patients from the US+NMES had faster recovery time and lower incidence of complications/adverse reactions. Conclusion. Collectively, US combined with NMES was associated with significant relief in pain and lumbar dysfunction and reduced local inflammatory response and pain mediator levels in LDH patients, suggesting that this combined approach could achieve better efficacy than US or NMES alone.

AAAPT Diagnostic Criteria for Acute Low Back Pain with and Without Lower Extremity Pain

OBJECTIVE

Low back pain is one of the most common reasons for which people visit their doctor. Between 12% and 15% of the US population seek care for spine pain each year, with associated costs exceeding $200 billion. Up to 80% of adults will experience acute low back pain at some point in their lives. This staggering prevalence supports the need for increased research to support tailored clinical care of low back pain. This work proposes a multidimensional conceptual taxonomy.

METHODS

A multidisciplinary task force of the ACTTION-APS-AAPM Pain Taxonomy (AAAPT) with clinical and research expertise performed a focused review and analysis, applying the AAAPT five-dimensional framework to acute low back pain.

RESULTS

Application of the AAAPT framework yielded the following: 1) Core Criteria: location, timing, and severity of acute low back pain were defined; 2) Common Features: character and expected trajectories were established in relevant subgroups, and common pain assessment tools were identified; 3) Modulating Factors: biological, psychological, and social factors that modulate interindividual variability were delineated; 4) Impact/Functional Consequences: domains of impact were outlined and defined; 5) Neurobiological Mechanisms: putative mechanisms were specified including nerve injury, inflammation, peripheral and central sensitization, and affective and social processing of acute low back pain.

CONCLUSIONS

The goal of applying the AAAPT taxonomy to acute low back pain is to improve its assessment through a defined evidence and consensus-driven structure. The criteria proposed will enable more rigorous meta-analyses and promote more generalizable studies of interindividual variation in acute low back pain and its potential underlying mechanisms.

Can Implementation of Genetics and Pharmacogenomics Improve Treatment of Chronic Low Back Pain?

Etiology of back pain is multifactorial and not completely understood, and for the majority of people who suffer from chronic low back pain (cLBP), the precise cause cannot be determined. We know that back pain is somewhat heritable, chronic pain more so than acute. The aim of this review is to compile the genes identified by numerous genetic association studies of chronic pain conditions, focusing on cLBP specifically. Higher-order neurologic processes involved in pain maintenance and generation may explain genetic contributions and functional predisposition to formation of cLBP that does not involve spine pathology. Several genes have been identified in genetic association studies of cLBP and roughly, these genes could be grouped into several categories, coding for: receptors, enzymes, cytokines and related molecules, and transcription factors. Treatment of cLBP should be multimodal. In this review, we discuss how an individual's genotype could affect their response to therapy, as well as how genetic polymorphisms in CYP450 and other enzymes are crucial for affecting the metabolic profile of drugs used for the treatment of cLBP. Implementation of gene-focused pharmacotherapy has the potential to deliver select, more efficacious drugs and avoid unnecessary, polypharmacy-related adverse events in many painful conditions, including cLBP.

Involvement between social defeat stress and pain-related behavior in a rat lumbar disk herniation model

INTRODUCTION

Psychological and social factors are involved in the disability and chronicity of pain. Our study aim was to investigate whether social defeat stress (SDS) as a psychophysical stress affected mechanical withdrawal thresholds in the lumbar disk herniation (LDH) rat model. Changes in microglia and astrocytes, which play important roles in neuropathic pain states, were also investigated.

MATERIALS AND METHODS

For the LDH model, nucleus pulposus (NP) was applied to the L5 dorsal root ganglion (DRG) in adult female Sprague-Dawley rats. SDS was performed 15 min daily for 8 days. Mechanical withdrawal thresholds were measured, and immunoreactive cells of glial fibrillary acidic protein (GFAP) and ionized calcium-binding adaptor molecule-1 (Iba-1), which were used as markers of microglia, satellite glial cells, and astrocytes, were assessed in the DRG, spinal cord (SC), and ventrolateral periaqueductal gray matter (VLPAG).

RESULTS

Mechanical withdrawal thresholds decreased in the NP group for 21 days and for 35 days in the NP + SDS group. Expression of GFAP and Iba-1 in the DRG and SC increased up to day 21 in the NP and NP + SDS groups. In the sham + SDS and NP + SDS groups, expression of GFAP in the VLPAG decreased until day 35.

CONCLUSION

SDS prolongs mechanical allodynia induced by NP. Changes of GFAP expression in the VLPAG were associated with mechanical allodynia of the NP + SDS group during the late phase. These results suggest that psychological chronic stress might delay recovery from mechanical allodynia induced by the LDH model.

Acetaminophen combined with tramadol is more effective than acetaminophen or tramadol to reduce neuropathic root pain: an experimental study with application of nucleus pulposus in a rat model

INTRODUCTION

Various drugs are used to treat patients with neuropathic pain; however, optimal treatment using acetaminophen (A) and/or tramadol (T) remains unclear. The evidence supporting the drug choice and the timing of administration is insufficient. Therefore, the objective of the present study was to investigate the effect of T and/or A on pain-related behavior in a nucleus pulposus (NP) rat model.

MATERIALS AND METHODS

Sprague-Dawley rats (n = 180) were divided into NP-A (52 mg/kg), NP-T (6 mg/kg), NP-AT (combined A and T), NP-S (saline), and sham groups (n = 36 per group). The rats received 0.2 mL of treatment solution orally once daily for 7 days after application of NP on the left L5 dorsal root ganglion (DRG). Behavioral testing and immunohistochemistry analysis for some markers' expressions in DRGs and the spinal cord were performed.

RESULTS

Pain thresholds in the NP-AT group did not significantly differ from the sham at all time points, while those were significantly lower in the NP-A and in the NP-T groups at D7 and/or D14 (p < 0.05). Tumor necrosis factor-α in the NP-S group was significantly higher at D2 and D7 (p < 0.05). Among the three treatment groups, activating transcriptional factor 3 and growth-associated protein 43 showed a tendency toward an increase at D7-D21.

CONCLUSION

Combined administration of acetaminophen and tramadol maintained in the pain threshold in the rat NP model. These findings suggest that the combination of acetaminophen and tramadol might be a potential therapeutic modality for patients with lumbar disc herniation. These slides can be retrieved under Electronic Supplementary Material.

Temporal and Spatial Changes of μ-Opioid Receptors in the Brain, Spinal Cord and Dorsal Root Ganglion in a Rat Lumbar Disc Herniation Model

STUDY DESIGN

Controlled, interventional, animal study.

OBJECTIVE

To investigate the spatial and temporal changes of μ-opioid receptor (MOR) expression in a rat lumbar disc herniation (LDH) model.

SUMMARY OF BACKGROUND DATA

MORs widely express in the peripheral and central nervous systems, and opioid drugs produce an analgesic effect through their activation. However, the efficacy of opioid drugs is sometimes inadequate in several pathological conditions of pain. MORs in the brain as well as the spinal cord (SC) and dorsal root ganglion (DRG) are thought to be associated with pain-related behavior, but the underlying mechanisms are not completely understood.

METHODS

In all, 91 adult female Sprague-Dawley rats were used. Autologous nucleus pulposus (NP) was applied onto the left L5 DRG in the NP group rats. Rats were divided into two surgical groups, the NP and the sham group. The von Frey test of left hind paw was performed before surgery, and 2, 7, 14, 21 and 28 days after surgery. Immunohistochemistry and immunoblotting in the DRG, SC, Caudate putamen, nucleus accumbens (NAc) and periaqueductal grey matter were performed before surgery, and 2, 7, 14, 21 and 28 days after surgery.

RESULTS

The thresholds in the NP group were significantly lower than those in the sham group from day 2 onwards. At days 7 and 14, MOR expression in the injured-side SC and DRG were significantly lower than those in the sham group. At day 21, MOR in the NAc was significantly decreased compared to that in the sham group.

CONCLUSION

Changes of MOR expression in the NAc, SC and DRG were associated with pain-related behavior. This result might show the underling pathogenesis of the resistance to MOR agonists in the patient with LDH.

LEVEL OF EVIDENCE

N/A.

Regenerative Treatments for Spinal Conditions

A literature review of clinical and translational studies was performed to provide an overview of current concepts on regenerative treatments for spinal conditions, including platelet rich plasma and stem cell treatments to treat low back pain.

Lumbar Disc Herniation

PURPOSE OF REVIEW

Substantial advancements have been made in the cause, diagnosis, imaging, and treatment options available for patients with lumbar disc herniation (LDH). We examined the current evidence and highlight the concepts on the frontline of discovery in LDH.

RECENT FINDINGS

There are a myriad of novel etiologies of LDH detailed in recent literature including inflammatory factors and infectious microbes. In the clinical setting, recent data focuses on improvements in computer tomography as a diagnostic tool and non-traditional injection options including tumor necrosis alpha inhibitors and platelet-rich plasma. Operative treatment outcomes have focused on minimally invasive endoscopic approaches and demonstrated robust 5-year post-operative outcomes. Advances in the molecular etiology of LDH will continue to drive novel treatment options. The role of endoscopic treatment for LDH will continue to evolve. Further research into10-year outcomes will be necessary as this surgical approach continues to gain widespread popularity.

Measurement of mechanical withdrawal thresholds and gait analysis using the CatWalk method in a nucleus pulposus-applied rodent model

Background

There are some previous reports of gait analysis using a rodent pain model. Applying the CatWalk method, objective measurements of pain-related behavior could be evaluated, but this method has not been investigated using the nucleus pulposus (NP) applied model, which was developed as a model of lumber disc herniation. We aimed to measure mechanical withdrawal thresholds and analyze gait patterns using the CatWalk method for the evaluation of the pain-related behavior caused by NP application.

Methods

Twenty-four nine-week-old female Sprague-Dawley rats were randomly divided into two experimental groups, the NP group (n = 12), in which autologous NP from the tail was applied to the left L5 dorsal root ganglion, and the sham-operated group (n = 12). Measurements of mechanical withdrawal thresholds were performed using von Frey filaments touching the left footpads, and gait analysis was performed using the CatWalk method. These experiments were conducted 1 day before surgery and 7, 14, 21, and 28 days after surgery. Data were statistically analyzed using the Wilcoxon rank-sum test.

Results

The NP group showed significantly lower withdrawal thresholds than the sham group at days 14 and 21. Stand (duration of contact of a paw with the glass plate) was significantly higher in the NP group at days 7 and 14, whereas step cycle (duration between two consecutive initial contacts of the same paw) and duty cycle (stand as a percentage of step cycle) were the same at day 7. Long initial dual stance (duration of ground contact for both hind paws simultaneously, but the first one in a step cycle of a target hind paw) of the right hind paw was measured at days 7 and 14. The left hind paw per right hind paw ratio of the stand index (speed at which the paw loses contact with the glass plate) and mean intensity (mean intensity of the complete paw) changed at day 7 or 14. Phase dispersion (parameter describing the temporal relationship between placement of two paws) of the hind paws decreased at day 7.

Conclusions

Rats with applied NP showed a decreased withdrawal threshold and abnormal gait. The differences in gait parameters between the NP and sham groups were observed at an earlier time point than the withdrawal thresholds. Gait analysis could be an effective method for understanding pain caused by applied NP.

Effect of an Acid-sensing Ion Channels Inhibitor on Pain-related Behavior by Nucleus Pulposus Applied on the Nerve Root in Rats

STUDY DESIGN

Controlled, interventional animal study.

OBJECTIVE

To examine the effect of an inhibitor of acid-sensing ion channel 3 (ASIC3) on pain-related behavior induced by application of the nucleus pulposus (NP) onto the dorsal root ganglion (DRG) in rats.

SUMMARY OF BACKGROUND DATA

ASIC3 is associated with acidosis pain in inflamed or ischemic tissues and is expressed in sensory neurons and NP cells. The ASIC3 inhibitor, APETx2, increases the mechanical threshold of pain in models of knee osteoarthritis or postoperative pain. However, the efficacy of APETx2 for pain relief in the NP application model remains unknown.

METHODS

Autologous NP was applied to the left L5 nerve root of 183 adult female Sprague-Dawley rats. The DRGs were treated with NP plus one of the following four treatments: saline solution (SM), low (0.01 μg: LD), medium (0.1 μg: MD), or high dose (1.0 μg: HD) of APETx2. Behavioral testing was performed to investigate the mechanical withdrawal threshold using von Frey hairs. Expression of nerve growth factor, hypoxia-inducible factor-1α (HIF1α), activating transcription factor-3, and ionized calcium-binding adaptor molecule-1 was evaluated using immunohistochemistry. Statistical differences among multiple groups were assessed using the Steel test, the Tukey-Kramer test, and the Dunnett test. P < 0.05 were considered significant.

RESULTS

The thresholds in the HD group were higher than those in the SM group at Days 14 and 21 (P < 0.05). In the MD group, the threshold was higher than in the SM group at Day 14 (P < 0.05). High doses of APETx2 reduced the expression of HIF1α after Day 14 compared with the SM group (P < 0.05).

CONCLUSION

APETx2 significantly improved pain-related behavior in a dose-dependent manner. APETx2 may inhibit ASIC3 and partly inhibit Nav1.8 channels. This ASIC3 channel inhibitor may be a potential therapeutic agent in early-stage lumbar disc herniation.

LEVEL OF EVIDENCE

N/A.

Assessment of Pain Sensitivity in Patients With Chronic Low Back Pain and Association With HTR2A Gene Polymorphism

Objectives

This study aims to investigate the association of two common HTR2A gene polymorphisms, rs6313 (102 T/C) and rs6311 (1438 A/G), with chronic low back pain (CLBP) and the pain threshold, disability, and sex differences.

Patients and methods

A total of 121 patients (40 males, 81 females; mean age 36.8±9.9 years; range 18 to 50 years) having CLBP and 91 healthy controls (26 males, 65 females; mean age 34.1±10.2 years; range 18 to 55 years) were included. Pressure pain thresholds (PPTs) of all participants were examined with manual algometer in certain sites of their body.

Results

The PPTs were all decreased in CLBP patients (p<0.05). Although PPTs were lower in healthy female subjects, there was no sex difference regarding PPTs in CLBP patients (p>0.05). rs6311 polymorphism of HTR2A gene was associated with CLBP (p<0.05). In rs6313 polymorphism, at least one copy of T carriers and in rs6311 polymorphism, at least one copy of G carriers showed higher disability.

Conclusion

The PPT decreases in CLBP patients similar to other chronic pain conditions without any sex difference. Although rs6311 single nucleotide polymorphism of HTR2A gene was associated with CLBP and rs6313 polymorphism was not, rs6311 might have a protective effect on disability of these patients.

Expression of inflammation/pain-related genes in the dorsal root ganglion following disc puncture in rats

PURPOSE

To determine the expression of inflammation- and pain-related genes at days 1 and 3 in the dorsal root ganglion (DRG) of rats with or without disc puncture, using real-time quantitative polymerase chain reaction (RT-qPCR) with the TaqMan low-density array (TLDA).

METHODS

53 female Sprague-Dawley rats were used. The left facet joint between L4 and L5 was removed, and the DRG and intervertebral disc between the vertebrae were exposed. The L4-5 intervertebral disc was punctured using a 0.4-mm diameter injection needle (disc puncture group) or left unpunctured (sham group). After one or 3 days, the 53 DRGs were harvested, frozen, and assessed for expression of inflammation-related genes. Total RNA was isolated from the DRGs. Expression of 119 genes related to inflammation and pain in the DRG after disc puncture were analysed using RT-qPCR with the TLDA.

RESULTS

Of the 95 inflammation-related genes, 78 genes were reliably detected. Two genes were significantly up-regulated: cysteinyl leukotriene receptor 1 (CYSLTR1) at day 3 and interleukin 2 receptor gamma (IL2RG) at day 1, and one gene was significantly down-regulated: phospholipase C beta 3 (PLCB3) at day 1. Of the 24 pain-related genes, 18 genes were reliably detected. Two genes were significantly up-regulated: nitric oxide synthase 1 (NOS1) at days 1 and 3 and 5-HT2A receptor (HTR2A) at day 1.

CONCLUSION

Disc puncture may elicit changes in the expression of a variety of genes. Gene expression profiling is a useful tool for detecting new potential pharmaceutical targets for spinal pain syndromes.

Thalidomide represses inflammatory response and reduces radiculopathic pain by inhibiting IRAK-1 and NF-κB/p38/JNK signaling

Intervertebral disc (IVD) disease, the most common cause of disc failure and low back pain, is characterized by age-related changes in the adult disc. In this study we aimed to analyze the potential of thalidomide for the treatment of IVD disease, through identifying and explaining its anti-inflammatory and anti-catabolic activity in both in vitro IVD cell culture and in vivo animal model. Inflammatory response was induced by IL-1β, then the activity and expression of inflammatory mediators and pathways were assessed in the presence or absence of thalidomide. The p38 inhibitor SB203580 was also used to investigate the involvement of the MAPK pathway in the observed effects. Moreover the analgesic properties of thalidomide were analyzed by the von Frey filament test in Sprague-Dawley rats. Our results indicated that thalidomide significantly inhibited the expression of pro-inflammatory mediators and matrix metalloproteinases in vitro, as well as radiculopathic pain in vivo, most probably by modulation of the activity of IRAK-1 and its downstream effectors p38, JNK and NF-κB. Our current study strongly supports the potential of thalidomide for the treatment of pain and inflammation in degenerative disc disease.

Tanshinone IIA represses inflammatory response and reduces radiculopathic pain by inhibiting IRAK-1 and NF-κB/p38/JNK signaling

Intervertebral disc (IVD) disease, a most common cause of disc failure and low back pain, is characterized by age-related changes in the adult disc. In this study we aimed to investigate the potential of Tanshinone IIA (TSA) for the treatment of IVD disease, through exploring its anti-inflammatory and anti-catabolic activities in both in vitro IVD cell culture and in vivo animal models. After the inflammatory response was induced in IVD cells by IL-1β, the activity and expression of inflammatory mediators, and potentially involved pathways were investigated in the presence or absence of TSA. The p38-MAPK inhibitor, SB239063, was also used to investigate the involvement of the MAPK signaling pathway in the observed effects. Meanwhile, the analgesic properties of TSA were analyzed by the von Frey filament test in Sprague-Dawley rats. Our results indicated that TSA significantly inhibited the expression of pro-inflammatory mediators and matrix metalloproteinases in vitro, as well as radiculopathic pain in vivo, probably by modulation of the activity of interleukin-1 receptor-associated kinase 1 (IRAK-1) and its downstream effectors p38, JNK and NF-κB. Our current study strongly demonstrates the potential of TSA for the treatment of inflammation and followed pain in degenerative disc disease.

Experimental Disc Herniation in the Rat Causes Downregulation of Serotonin Receptor 2c in a TNF-dependent Manner

BACKGROUND

During recent decades, the knowledge of the pathophysiology of disc herniation and sciatica has drastically improved. What previously was considered a strict biomechanical process is now considered a more complex interaction between leaked nucleus pulposus and the tissue in the spinal canal. An inflammatory reaction, with tumor necrosis factor (TNF) playing an essential role, has been demonstrated. However, the exact mechanisms of the pathophysiology of disc herniation remain unknown.

QUESTIONS/PURPOSES

In this study we use an animal model to investigate (1) if and/or how experimental disc herniation affects gene expression in the early phase (24 hours postsurgery) in the dorsal root ganglion; and (2) if TNF inhibition can reduce any observed changes.

METHODS

A rat model of disc herniation was used. Twenty rats were evenly divided into four groups: naïve, sham, disc herniation, and disc herniation with TNF inhibition. The dorsal root ganglion of the affected nerve root was harvested 24 hours after surgery and analyzed with a TaqMan Low Density Array(®) quantitative polymerase chain reaction assay. Gene expression levels in sham were compared with disc herniation to assess question 1 and disc herniation to disc herniation with TNF inhibition to assess question 2.

RESULTS

Experimental disc herniation caused a decrease in the expression of the serotonin receptor 2c gene (p = 0.022). TNF inhibition was found to reduce the observed decrease in expression of serotonin receptor 2c (p = 0.037).

CONCLUSIONS

Our results suggest that a decrease in the expression of the serotonin receptor 2c gene may contribute to the pathophysiology of disc herniation. Further research on its involvement is warranted.

CLINICAL RELEVANCE

This pilot study gives a brief insight into cellular changes that may contribute to the pathophysiology of disc herniation. This knowledge may contribute to the development of more and better treatment options for patients with disc herniation and sciatica.

The effect of a 5-HT2A receptor antagonist on pain-related behavior, endogenous 5-hydroxytryptamine production, and the expression 5-HT2A receptors in dorsal root ganglia in a rat lumbar disc herniation model

STUDY DESIGN

Controlled, interventional, animal study.

OBJECTIVE

To evaluate the effect of a 5-HT2A receptor antagonist on pain-related behavior, endogenous 5-hydroxytryptamine (5-HT) plasma levels, and expression of 5-HT2A receptors in dorsal root ganglia (DRGs) in a rat lumbar disc herniation model.

SUMMARY OF BACKGROUND DATA

Application of nucleus pulposus on the nerve root induces immediate peripheral 5-HT production and the expression of 5-HT2A receptors in the adjacent DRG. However, the efficacy of a 5-HT2A receptor antagonist for pain relief in this situation and the mechanism remain unknown.

METHODS

Autologous nucleus pulposus was applied to the left L5 nerve root of 91 adult female Sprague-Dawley rats. The selective 5-HT2A receptor antagonist sarpogrelate hydrochloride (SPG; 1 mg/kg or 10 mg/kg) or vehicle was administered orally once a day from 1 to 21 days postoperatively. Von Frey tests were used to test pain behavior before and after surgery. To assess the effect of SPG on endogenous 5-HT release surrounding the inflamed nerve root, we measured levels of 5-hydroxyindole acetic acid, a 5-HT metabolite, in plasma. Expression of 5-HT2A receptors in the left L5 DRG was examined with immunoblotting.

RESULTS

The higher dose (10 mg/kg) of SPG significantly improved the mechanical withdrawal thresholds from 5 to 21 days after surgery compared with vehicle treatment. 5-hydroxyindole acetic acid in plasma was not significantly different among any groups at any time points. Both doses of SPG inhibited the expression of 5-HT2A receptors after surgery compared with vehicle treatment.

CONCLUSION

A selective 5-HT2A receptor antagonist attenuated pain-related behavior and suppressed 5-HT2A receptor expression in the DRG, but did not affect peripheral 5-HT production. Selective 5-HT2A receptor antagonists may attenuate sciatica by blocking and downregulating 5-HT2A receptors in DRGs in lumbar disc herniation.

LEVEL OF EVIDENCE

NA.

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.

Changes in midbrain pain receptor expression, gait and behavioral sensitivity in a rat model of radiculopathy

Intervertebral disc herniation may contribute to inflammatory processes that associate with radicular pain and motor deficits. Molecular changes at the affected dorsal root ganglion (DRG), spinal cord, and even midbrain, have been documented in rat models of radiculopathy or nerve injury. The objective of this study was to evaluate gait and the expression of key pain receptors in the midbrain in a rodent model of radiculopathy. Radiculopathy was induced by harvesting tail nucleus pulposus (NP) and placing upon the right L5 DRG in rats (NP-treated, n=12). Tail NP was discarded in sham-operated animals (n=12). Mechanical allodynia, weight-bearing, and gait were evaluated in all animals over time. At 1 and 4 weeks after surgery, astrocyte and microglial activation was tested in DRG sections. Midbrain sections were similarly evaluated for immunoreactivity to serotonin (5HT_2B), mu-opioid (µ-OR), and metabotropic glutamate (mGluR4 and 5) receptor antibodies. NP-treated animals placed less weight on the affected limb 1 week after surgery and experienced mechanical hypersensitivity over the duration of the study. Astroctye activation was observed at DRGs only at 4 weeks after surgery. Findings for pain receptors in the midbrain of NP-treated rats included an increased expression of 5HT_2B at 1, but not 4 weeks; increased expression of µ-OR and mGluR5 at 1 and 4 weeks (periaqueductal gray region only); and no changes in expression of mGluR4 at any point in this study. These observations provide support for the hypothesis that the midbrain responds to DRG injury with a transient change in receptors regulating pain responses.

A comparison of pain-related behavior following local application of nucleus pulposus and/or mechanical compression on the dorsal root ganglion

Symptomatic induction of disc herniation involves both mechanical compression and chemical factors. Inhibitors of tumor necrosis factor-alpha (TNF-α) are known to reduce pain-related behavior in experimental models. Animals were divided into mechanical compression (MC) group; a stainless steel rod was inserted on the dorsal root ganglion, nucleus pulposus (NP) group: NP was harvested from the coccygeal vertebral disc, MC and NP group; rats were received stainless rod and NP, and sham group; rats were received neither rod nor NP. Rats in the MC group received a TNF-α antibody (10 mg/kg) (antibody group) or were not treatment (untreated group). The withdrawal thresholds of the MC, NP and MC+NP groups decreased significantly compared with the sham group. In the antibody group, the threshold was significantly higher than that of the untreated group. An anti-TNF-α antibody reduced allodynia caused by DRG compression.

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.

The effect of repeated restraint stress in pain-related behavior induced by nucleus pulposus applied on the nerve root in rats

INTRODUCTION

Chronic pain has an impact on psychological and social factors. It is known that stress influences physiological and behavioral changes and affects several neurotransmitter and hormonal systems. It is also known that corticosterone is increased by stress. The role of chronic stress in sciatica in lumbar disc herniation (LDH) in rats has not been investigated. The aim of this study was to investigate the effect of the restraint stress (RS) on pain-related behavior induced by application of nucleus pulposus (NP) in rats.

MATERIALS AND METHODS

Adult female Sprague-Dawley rats were divided into six experimental groups (naive group; naive + RS; sham group; sham + RS; autologous nucleus pulposus [NP] applied on the left L5 nerve root [NP group]; and NP + RS group). Von Frey tests were used to test pain-related behavior. Concentrations of plasma corticosterone were measured to assess changes in levels of endogenous corticosterone caused by RS. Expression of ATF-3 in the left L5 DRG was examined by immunohistochemical analyses in each group.

RESULTS

Mechanical withdrawal thresholds of the NP and NP + RS groups were significantly decreased after surgery compared with the naive group. Although the thresholds in the NP group recovered after 28 days, the thresholds in the NP + RS group were significantly decreased during the 42 days after surgery. RS increased the concentration of plasma corticosterone at 21 and 42 days after surgery. In the NP and the NP + RS groups, the expression of ATF-3 was significantly increased at 7 days after surgery. The expression of ATF-3 was sustained for 21 days by RS.

CONCLUSION

Concentrations of plasma corticosterone were increased in three groups that underwent RS. The pain-related behavior persisted for the long term in the LDH model. The expression of ATF-3 in DRG neurons increased for 21 days by RS. These results suggest that RS plays a role in the chronicity of pain-related behavior in the LDH rats.

Anti-HMGB1 neutralization antibody improves pain-related behavior induced by application of autologous nucleus pulposus onto nerve roots in rats

STUDY DESIGN

Controlled, interventional, animal study.

OBJECTIVE

To examine the involvement of high-mobility group box 1 (HMGB1) in the neuropathic pain state induced by the application of nucleus pulposus onto the dorsal root ganglion (DRG) and to investigate the effect of HMGB1 neutralization antibody in the pathogenesis.

SUMMARY OF BACKGROUND DATA

HMGB1 is a potent proinflammatory mediator when present extracellularly, and anti-HMGB1 neutralization antibody inhibits inflammation, cytokine expression, and macrophage activation.

METHODS

Thirty-nine adult female Sprague-Dawley rats (200-300 g) were used. The left L5/6 facet joint was removed, and the L5 DRG was exposed. Nucleus pulposus harvested from the tail was applied to the left L5 DRG. Then, 400 μg of anti-HMGB1 neutralization antibody was administered intraperitoneally after surgery. Behavioral testing using von Frey hairs was performed to investigate the mechanical withdrawal threshold. Neuronal damage was investigated by counting the number of activating transcription factor 3 (ATF3) neurons. The expressions of tumor necrosis factor-α (TNF-α) and HMGB1 were measured by double-labeled immunohistochemistry and immunoblotting.

RESULTS

Immunoblotting of harvested nucleus pulposus revealed HMGB1 in the nucleus pulposus. Double-labeled immunohistochemistry revealed that macrophages in the applied nucleus pulposus expressed HMGB1 and TNF-α. Administration of anti-HMGB1 neutralization antibody significantly reduced the TNF-α expression in the DRG and improved the pain-related behavior from day 2 to day 14.

CONCLUSION

HMGB1 appears to play an important role in the development of pain-related behavior induced by the application of nucleus pulposus onto the DRG. HMGB1 from applied nucleus pulposus and actively secreted from macrophages would act as a proinflammatory mediator together with proinflammatory cytokines. HMGB1 blocking therapy might become a new treatment method for neuropathic pain.

Interaction of 5-hydroxytryptamine and tumor necrosis factor-α to pain-related behavior by nucleus pulposus applied on the nerve root in rats

STUDY DESIGN

The effects of exogenous 5-hydroxytryptamine (5-HT), tumor necrosis factor(TNF)-α, 5-HT + TNF in combination, and autologous nucleus pulposus (NP) at dorsal root ganglion (DRG) were examined using rat models.

OBJECTIVE

To examine the interaction of 5-HT with TNF for pain-related behavior in a rat lumbar disc herniation (LDH) model.

SUMMARY OF BACKGROUND DATA

5-HT and TNF have been shown to play roles in sciatica in lumbar disc herniation as chemical factors.

METHODS

Adult female Sprague-Dawley rats were divided into six groups: 5-HT group, TNF group, 5-HT + TNF (combination) group, NP group, control group, and naive group. Von Frey tests were used for pain-related behavior testing. Expressions of activating transcription factor 3 and calcitonin gene-related peptide (CGRP) were evaluated immunohistochemically. Expressions of TNF, TNF receptor 1 (TNFR1), and 5-HT2A receptors in the left L5 DRG were examined using western blotting. Plasma levels of 5-hydroxyindole acetic acid, a metabolite of 5-HT, were measured.

RESULTS

Mechanical withdrawal thresholds were significantly decreased in the 5-HT, TNF, combination, and NP groups compared with controls. Thresholds recovered after 14 days in the 5-HT and TNF groups, and after 28 days in the combination group. Exogenous 5-HT and TNF to the nerve root induced pain-related behavior and lasted for a shorter period compared with combination and NP groups. Activating transcription factor 3- and calcitonin gene-related peptide-immunoreactive DRG neurons were significantly increased only in the early phase in 5-HT, TNF, combination, and NP groups. TNF induced 5-HT2A receptor expressions in the DRG, while 5-HT induced TNF and TNF receptor 1 expressions.

CONCLUSION

The present findings suggest that both 5-HT and TNF induce pain-related behavior and interact with each other to prolong pain-related behavior in a rat LDH model.

Distribution and tumor necrosis factor-alpha isoform binding specificity of locally administered etanercept into injured and uninjured rat sciatic nerve

Tumor necrosis factor-alpha (TNF) is a pro-inflammatory cytokine that is implicated in the initiation of neuropathic pain. Locally administered TNF antagonist etanercept offers a promising new treatment approach to target neuropathic pain. Here we evaluate the distribution and binding specificity for TNF isoforms of locally administered etanercept into injured and uninjured rat sciatic nerve. Distribution and co-localization of etanercept and TNF in the injured and uninjured nerve was evaluated at 1, 24, 48 and 96 h after etanercept local application using immunohistochemistry. In addition, binding specificity of etanercept for TNF isoforms was analyzed using immunoblot assay system in nerve lysates. A new observation was that locally administered etanercept reached the endoneurium of the injured but not the uninjured nerve 1 h after its application and mainly co-localized with TNF-positive structures, morphologically similar to Schwann cells and macrophages. We further noticed that immunoblot analyses for etanercept demonstrated its preferential binding to transmembrane and trimer TNF isoforms. Finally, locally administered etanercept inhibited pain-related behaviors in a rat sciatic nerve crush model. We conclude that locally administered etanercept reaches the endoneurial space in the injured nerve and preferentially binds to transmembrane and bioactive trimer TNF isoforms to modulate neuropathic pain. Locally administered etanercept has potential as a targeted immunomodulating agent to treat local pathogenesis in neuropathic pain after peripheral nerve injury.