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Increasing evidence supported that oxidative stress induced by herniated lumbar disc played important role in the formation of lumbar disc herniation sciatica (LDHS), however, the neural mechanisms underlying LDHS need further clarification. Endomorphin-2 (EM2) is the endogenous ligand for mu-opioid receptor (MOR), and there is increasing evidence implicating the involvement of spinal EM2 in neuropathic pain. In this study, using an nucleus pulposus implantation induced LDHS rat model that displayed obvious mechanical allodynia, it was found that the expression of EM2 in dorsal root ganglion (DRG) and spinal cord was significantly decreased. It was further found that oxidative stress in DRG and spinal cord was significantly increased in LDHS rats, and the reduction of EM2 in DRG and spinal cord was determined by oxidative stress dominated increment of dipeptidylpeptidase IV activity. A systemic treatment with antioxidant could prevent the forming of mechanical allodynia in LDHS rats. In addition, MOR expression in DRG and spinal cord remained unchanged in LDHS rats. Intrathecal injection of MOR antagonist promoted pain behavior in LDHS rats, and the analgesic effect of intrathecal injection of EM2 was stronger than that of endomorphin-1 and morphine. Taken together, our findings suggest that oxidative stress mediated decrement of EM2 in DRG and spinal cord causes the loss of endogenous analgesic effects and enhances the pain sensation of LDHS., Competing Interests: Declaration of competing interest Each author listed in the manuscript had no conflicts of interest to declare in relation to this article., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Introduction: Sciatica causes intense pain. No satisfactory therapeutic drugs exist to treat sciatica. This study aimed to probe the potential mechanism of ferulic acid in sciatica treatment., Methods: Thirty-two SD rats were randomly divided into 4 groups: sham operation, chronic constriction injury (CCI), mecobalamin, and ferulic acid. We conducted RNA sequencing, behavioral tests, ELISA, PCR, western blotting, and immunofluorescence analysis. TAK-242 and JSH23 were administered to RSC96 and GMI-R1 cells to explore whether ferulic acid can inhibit apoptosis and alleviate inflammation., Results: RNA sequencing showed that TLR4/NF-κB pathway is involved in the mechanism of sciatica. CCI induced cold and mechanical hyperalgesia; destroyed the sciatic nerve structure; increased IL-1β, IL-6, TNF-α, IL-8, and TGF-β protein levels and IL-1β, IL-6, TNF-α, TGF-β, TLR4, and IBA-1 mRNA levels; and decreased IL-10 and INF-γ protein levels and IL-4 mRNA levels. Immunohistochemistry showed that IBA-1, CD32, IL-1β, iNOS, nNOS, COX2, and TLR4 expression was increased while S100β and Arg-1 decreased. CCI increased TLR4, IBA-1, IL-1β, iNOS, Myd88, p-NF-κB, and p-p38MAPK protein levels. Treatment with mecobalamin and ferulic acid reversed these trends. Lipopolysaccharide (LPS) induced RSC96 cell apoptosis by reducing Bcl-2 and Bcl-xl protein and mRNA levels and increasing Bax and Bad mRNA and IL-1β, TLR4, Myd88, p-NF-κB, and p-p38MAPK protein levels, while ferulic acid inhibited cell apoptosis by decreasing IL-1β, TLR4, Myd88, p-NF-κB, and p-p38MAPK levels and increasing Bcl-2 and Bcl-xl levels. In GMI-R1 cells, Ferulic acid attenuated LPS-induced M1 polarization by decreasing the M1 polarization markers IL-1β, IL-6, iNOS, and CD32 and increasing the M2 polarization markers CD206, IL-4, IL-10 and Arg-1. After LPS treatment, IL-1β, iNOS, TLR4, Myd88, p-p38MAPK, and p-NF-κB levels were obviously increased, and Arg-1 expression was reduced, while ferulic acid reversed these changes., Conclusion: Ferulic acid can promote injured sciatic nerve repair by reducing neuronal cell apoptosis and inflammatory infiltration though the TLR4/NF-κB pathway., (© 2023 The Authors. CNS Neuroscience & Therapeutics published by John Wiley & Sons Ltd.)

Therapeutic drugs of chronic neuralgia have a high risk of addiction, making it crucial to identify novel drugs for chronic neuralgia. This study aimed to explore the therapeutic effect of paeoniflorin on chronic sciatica via inhibiting Schwann cell apoptosis. 28 SD rats were randomly divided into four groups, including the sham operation group, chronic constriction injury (CCI) group, mecobalamin group, and paeoniflorin group. The therapeutic effect and mechanism of paeoniflorin were evaluated via rat and cell experiments. Mechanical, hot, or cold hyperalgesia was induced in the rats after CCI operation, while paeoniflorin relieved chronic neuralgia. Besides, paeoniflorin decreased the levels of IL1, IL6, TNF-α, CRP, and LPS and increased the level of IL10 in serum. As for the sciatic nerve, the number of inflammatory cells was decreased, and Schwann cells were present after paeoniflorin treatment, and paeoniflorin promoted the recovery of nerve structure. In cell experiments, LPS induced Schwann cell apoptosis via the TLR4/NF-kB pathway. And paeoniflorin attenuated LPS-induced Schwann cell apoptosis by decreasing the levels of TLR4, p-NF-kB, caspase3, cleaved-caspase3, and cleaved-caspase7. Overall, these results suggest that paeoniflorin alleviates chronic sciatica by decreasing inflammatory factor levels and promotes the repair of damaged nerves by reducing Schwann cell apoptosis., (© 2022 The Authors. Phytotherapy Research published by John Wiley & Sons Ltd.)

Background: RUNX Family Transcription Factor 2 (Runx2) promotes neurite outgrowth after sciatic nerve injury, and Curcumin can promote the expression of Runx2. It is worthwhile to explore whether curcumin's repair effect on sciatic nerve injury is related to Runx2., Objective: To investigate the repair effect of curcumin on sciatic nerve injury and its possible mechanism., Results: Curcumin improved the sciatic functional index (SFI) and toe spread index (TSI) of rats with sciatic nerve injury and increased the number and diameter of myelinated axons in the sciatic nerve. Curcumin promoted the myelination of SCs (Schwann cells) by increasing the expression of peripheral myelin protein 22 (PMP22), fibrin, S100, and proliferating cell nuclear antige (PCNA). Curcumin treatment increased the proliferation of SCs and the expression of Runx2. Cell experiments further confirmed that curcumin promoted Schwann cell proliferation and myelination through Runx2., Conclusion: Curcumin promotes SCs proliferation and myelination through Runx2 and improves sciatic nerve repair., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Neuropathic pain is a debilitating chronic pain condition, and its treatment remains a clinical challenge. Curcumin, a naturally occurring phenolic compound, possesses diverse biological and pharmacological effects but has not yet been approved as a drug due to its low bioavailability. In order to overcome this limitation, we synthesized a potential ester prodrug of curcumin, curcumin diethyl diglutarate (CurDDG). In this study, we evaluated the pharmacological advantages of CurDDG over curcumin in a mouse model of chronic constriction injury (CCI), and the anti-inflammatory effect of CurDDG in LPS-induced RAW 264.7 macrophage cells was accessed to clarify the underline mechanism. Mice were treated with various oral doses of curcumin (25, 50, 100 and 200 mg/kg/day, daily for 14 days) or equimolar doses of CurDDG. CurDDG at all doses tested significantly attenuated CCI-induced thermal hyperalgesia and mechanical allodynia compared with the CCI-control group. CurDDG at 25, 50 and 100 mg/kg demonstrated significantly greater efficacy on both mechanical and thermal hypersensitivities compared to that of curcumin. The effect of CurDDG correlated well with the inhibition of TNF-α and IL-6 levels in both the sciatic nerve and the spinal cord, as compared to its respective control groups. Similarly, in the in vitro study, CurDDG significantly reduced the LPS-induced expression of TNF-α and IL-6. Moreover, CurDDG significantly decreased COX-2 and iNOS levels and attenuated p38, JNK, and ERK1/2 phosphorylation as compared to the curcumin-treated cells. Altogether, this study demonstrated the improved pharmacological effects of curcumin by its diglutarate conjugate, CurDDG., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The use of morphine is controversial due to the incidence of rewarding behavior, respiratory depression, and tolerance, leading to increased drug dose requirements, advancing to morphine addiction. To overcome these barriers, strategies have been taken to combine morphine with other analgesics. Neuropeptide B23 and neuropeptide W23 (NPB23 and NPW23) are commonly used to relieve inflammatory pain and neuropathic pain. As NPB23 and NPW23 system shares similar anatomical basis with opioid system at least in the spinal cord we hypothesized that NPB23 or NPW23 and morphine may synergistically relieve inflammatory pain and neuropathic pain. To test this hypothesis, we demonstrated that μ opioid receptor and NPBW1 receptor (receptor of NPB23 and NPW23) are colocalized in the superficial dorsal horn of the spinal cord. Secondly, co-administration of morphine witheitherNPB23 or NPW23 synergistically attenuated inflammatory and neuropathic pain. Furthermore, either NPB23 or NPW23 significantly reduced morphine-induced conditioned place preference (CPP) and constipation. We also found that phosphorylation of extracellular-regulated protein kinase (ERK1/2) following morphine was profoundly potentiated by the application of NPB23 or NPW23. Hence, combination of morphine with either NPB23 or NPW23 reduced dose of morphine required for pain relief in inflammatory and neuropathic pain, while effectively prevented some side-effects of morphine., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Objective: There is still no effective treatment of neuropathic pain. Sanguinarine is a natural plant medicine with anti-inflammatory effects, but its effect on neuropathic pain remains unclear. This study was aimed at investigating the potential of sanguinarine to attenuate neuropathic pain., Methods: Neuropathic pain was induced by chronic constriction injury (CCI) of the sciatic nerve. Rats were randomly divided into several groups: sham, CCI, CCI+SG (1.00 mg/kg), CCI+SG (2.50 mg/kg), and CCI+SG (6.25 mg/kg). SG was injected intraperitoneally from the day of surgery every three days. The mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were recorded before surgery and on days 1, 3, 7, and 14 after surgery. The microglia in the spinal dorsal horn were examined by immunofluorescence. p38 MAPK expression in the spinal dorsal horn was detected by PCR and Western blot analysis. Cytokine levels in the spinal dorsal horn were measured by ELISA., Results: MWT and TWL were significantly reduced in the CCI group, but sanguinarine recovered MWT and TWL in the CCI group. In addition, sanguinarine inhibited the activation of microglia and decreased the expression of p-p38 and TNF- α , IL-1 β , and IL-6 in the spinal dorsal horn of the CCI group in a dose-dependent manner., Conclusions: Our results suggest that sanguinarine can attenuate neuropathic pain via inhibiting the activation of microglia and the activation of the p38 MAPK signaling pathway., Competing Interests: The authors declare that they have no conflict of interest., (Copyright © 2021 Ping Li et al.)

Background: Gut microbiota, a consortium of diverse microorganisms residing in the gastrointestinal tract, has emerged as a key player in neuroinflammatory responses, supporting the functional relevance of the "gut-brain axis." Chronic-constriction injury of the sciatic nerve (CCI) is a commonly used animal model of neuropathic pain with a major input from T cell-mediated immune responses. In this article, we sought to examine whether gut microbiota influences CCI neuropathic pain, and, if so, whether T-cell immune responses are implicated., Methods: We used a mixture of wide-spectrum oral antibiotics to perturbate gut microbiota in mice and then performed CCI in these animals. Nociceptive behaviors, including mechanical allodynia and thermal hyperalgesia, were examined before and after CCI. Additionally, we characterized the spinal cord infiltrating T cells by examining interferon (IFN)-γ, interleukin (IL)-17, and Foxp3. Using a Foxp3-GFP-DTR "knock-in" mouse model that allows punctual depletion of regulatory T cells, we interrogated the role of these cells in mediating the effects of gut microbiota in the context of CCI neuropathic pain., Results: We found that oral antibiotics induced gut microbiota changes and attenuated the development of CCI neuropathic pain, as demonstrated by dampened mechanical allodynia and thermal hyperalgesia. Percentages of IFN-γ-producing Th1 cells and Foxp3+ regulatory T cells were significantly different between animals that received oral antibiotics (Th1 mean = 1.0, 95% confidence interval [CI], 0.9-1.2; Foxp3 mean = 8.1, 95% CI, 6.8-9.3) and those that received regular water (Th1 mean = 8.4, 95% CI, 7.8-9.0, P < .01 oral antibiotics versus water, Cohen's d = 18.8; Foxp 3 mean = 2.8, 95% CI, 2.2-3.3, P < .01 oral antibiotics versus water, Cohen's d = 6.2). These T cells characterized a skewing from a proinflammatory to an anti-inflammatory immune profile induced by gut microbiota changes. Moreover, we depleted Foxp3+ regulatory T cells and found that their depletion reversed the protection of neuropathic pain mediated by gut microbiota changes, along with a dramatic increase of IFN-γ-producing Th1 cell infiltration in the spinal cord (before depletion mean = 2.8%, 95% CI, 2.2-3.5; after depletion mean = 9.1%, 95% CI, 7.2-11.0, p < .01 before versus after, Cohen's d = 5.0)., Conclusions: Gut microbiota plays a critical role in CCI neuropathic pain. This role is mediated, in part, through modulating proinflammatory and anti-inflammatory T cells., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2020 International Anesthesia Research Society.)

Ethnopharmacology Relevance: Escin is a natural mixture of triterpene saponins extracted from the seeds of Aesculus wilsonii Rehd. And has been reported to possess the therapeutic effects against neuropathic pain (NP). However, the underlying mechanisms remain unclear., Aim of the Study: The present study aimed to investigate the therapeutic effects and explore the underlying mechanisms of escin on rats of NP induced by chronic constriction injury (CCI) of sciatic nerve., Materials and Methods: Rats were treated with escin (7, 14, and 28 mg/kg, i. g.) daily from the third day after the surgery (day 0) for consecutive 14 days. Regular behavior and thermal threshold were measured on days 0, 3, 5, 7, 10 and 14. Investigations into mechanisms involved measurement of inflammatory factors and biochemical factors in dorsal root ganglion (DRG). Inflammatory pain responses and nerve injuries were induced by the CCI model. Tonic pain model and acute inflammatory model induced by formalin or carrageenan were established to evaluated the pharmacological effects of escin on acute inflammatory pain. Corresponding behaviors were monitored and relevant gene expression such as c-fos, mu opioid receptor (MOR) and KCNK1 were detected by qRT-PCR. Investigate the neuroprotective effects of escin on PC12 cell injury induced by lipopolysaccharide (LPS). Cell morphology was observed under inverted microscope and neuroprotective effect of escin on cell activity was assessed by MTT assay., Results: Escin could widen thermal threshold, downregulate the concentration of inflammatory factors like tumor necrosis factor (TNF)-α and interleukin (IL)-1β, suppress the gene expression of toll-like receptor 4 (TLR4), nuclear factor κB (NF-κB), decrease the level of glial fibrillary acidic protein (GFAP) and nerve growth factor (NGF) remarkably. In addition, escin significantly lowered the duration of licking, numbers of flinches and increase in paw edema, showing great therapeutic effects on inflammatory pain responses. Moreover, the activity of injured PC12 cells was significantly improved after escin administrated., Conclusion: Escin exerted the ameliorative effects on NP induced by CCI which may be related to downregulating the release of pro-inflammatory cytokines, suppressing TLR-4/NF-κB signal pathway, thereafter decreasing the level of GFAP and NGF., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Researches have shown that calcitonin gene-related peptide (CGRP) plays a pivotal role in pain modulation. Nociceptive information from the periphery is relayed from parabrachial nucleus (PBN) to brain regions implicated involved in pain. This study investigated the effects and mechanisms of CGRP and CGRP receptors in pain regulation in the PBN of naive and neuropathic pain rats. Chronic sciatic nerve ligation was used to model neuropathic pain, CGRP and CGRP 8-37 were injected into the PBN of the rats, and calcitonin receptor-like receptor (CLR), a main structure of CGRP receptor, was knocked down by lentivirus-coated CLR siRNA. The hot plate test (HPT) and the Randall Selitto Test (RST) was used to determine the latency of the rat hindpaw response. The expression of CLR was detected with RT-PCR and western blotting. We found that intra-PBN injecting of CGRP induced an obvious anti-nociceptive effect in naive and neuropathic pain rats in a dose-dependent manner, the CGRP-induced antinociception was significantly reduced after injection of CGRP 8-37, Moreover, the mRNA and protein levels of CLR, in PBN decreased significantly and the antinociception CGRP-induced was also significantly lower in neuropathic pain rats than that in naive rats. Knockdown CLR in PBN decreased the expression of CLR and the antinociception induced by CGRP was observably decreased. Our results demonstrate that CGRP induced antinociception in PBN of naive or neuropathic pain rats, CGRP receptor mediates this effect. Neuropathic pain induced decreases in the expression of CGRP receptor, as well as in CGRP-induced antinociception in PBN., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Preclinical studies have reported that sigma-1 receptor antagonists may have efficacy in neuropathic pain states. The sigma-1 receptor is a unique ligand-operated chaperone present in crucial areas for pain control, in both the peripheral and central nervous system. This study assesses the synergistic antihyperalgesic and antiallodynic effect of haloperidol, a sigma-1 antagonist, combined with gabapentin in rats with peripheral neuropathy. Wistar rats male were subjected to chronic constriction injury (CCI) of the sciatic nerve. The effects of systemic administration of gabapentin and the sigma-1 receptor antagonist, haloperidol, were examined at 11 days post-CCI surgery. An analysis of Surface of Synergistic Interaction was used to determine whether the combination's effects were synergistic. Twelve combinations showed various degrees of interaction in the antihyperalgesic and antiallodynic effects. In hyperalgesia, three combinations showed additive effects, four combinations showed supra-additive effects, and three combinations produced an effect limited by the maximum effect. In allodynia, five combinations showed additive effects, two combinations showed supra-additive effects, and five combinations produced antihyperalgesic effects limited by the maximum effect. These findings indicate that the administration of some specific combination of gabapentin and haloperidol can synergistically reduce nerve injury-induced allodynia and hyperalgesia. This suggests that the haloperidol-gabapentin combination can improve the antiallodynic and antihyperalgesic effects in a neuropathic pain model., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Multiple sclerosis (MS) is a well-known neurodegenerative disorder, causing toxicity in different organs, such as spinal cord tissue. The goal of this study was to investigate the protective effect of ellagic acid (EA) against spinal cord and sciatica function in cuprizone (Cup)-induced demyelination model. Animals were divided into six equal groups. The first group received tap water as the control. Cup group was treated with Cup (0.2% w/w in fed). EA 100 group was orally treated with EA (100 mg/kg). EA + Cup groups were orally treated with three doses of 5, 50, and 100 mg/kg of EA plus Cup (0.2% w/w). All groups received treatment for 42 days. Open field, rotarod, and gait tests were done to evaluate the behavioral changes following Cup and/or EA treatment. Also, lipid peroxidation, reactive oxygen species (ROS) content, antioxidant capacity, superoxide dismutase (SOD), and catalase enzymes activity in spinal cord was evaluated. Luxol fast blue (LFB) staining also the behavioral tests were performed to evaluate the model. Cup increased ROS levels and oxidative stress in their spinal cord tissues. Also, Cup reduced antioxidant capacity, SOD, and catalase activity. EA (especially at 100 mg/kg) prevented these abnormal changes. EA co-treatment dose-dependently was able to ameliorate behavioral impairments in mice that received Cup. EA might act as a protective agent in MS by modulating spinal cord function., (© 2020 Wiley Periodicals LLC.)

Piwi-Interacting RNA (piRNA) is the largest class of small noncoding RNA and is involved in various physiological and pathological processes. However, whether it has a role in pain modulation remains unknown. In the present study, we found that spinal piRNA-DQ541777 (piR-DQ541777) was significantly increased in the male mouse model of sciatic nerve chronic constriction injury (CCI)-induced neuropathic pain. Knockdown of spinal piR-DQ541777 alleviated CCI-induced thermal hyperalgesia and mechanical allodynia and spinal neuronal sensitization. However, the overexpression of spinal piR-DQ541777 in naive mice produced pain behaviors and increased spinal neuron sensitization. Furthermore, we found that piR-DQ541777 regulates pain behaviors by targeting CDK5 regulatory subunit-associated protein 1 (Cdk5rap1). CCI increased the methylation level of CpG islands in the cdk5rap1 promoter and consequently reduced the expression of Cdk5rap1, which was reversed by the knockdown of piR-DQ541777 and mimicked by the overexpression of piR-DQ541777 in naive mice. Finally, piR-DQ541777 increased the methylation level of CpG islands by recruiting DNA methyltransferase 3A (DNMT3a) to cdk5rap1 promoter. In conclusion, this study represents a novel role of piR-DQ541777 in the regulation of neuropathic pain through the methylation of cdk5rap1 SIGNIFICANCE STATEMENT Chronic pain affects ∼20% of the population of the world and is a major global public health problem. Although we have studied the neurobiological mechanism of neuropathic pain for decades, there is still no ideal drug available to treat it. This work indicates that a novel role of Piwi-interacting RNA (piRNA) DQ541777 in the regulation of neuropathic pain through the methylation of cdk5rap1 Our findings provide the first evidence of the regulatory effect of piRNAs on neuropathic pain, which may improve our understanding of pain mechanisms and lead to the discovery of novel drug targets for the prevention and treatment of neuropathic pain., (Copyright © 2019 the authors.)

Residual lower-limb pain after low back surgery (postsurgical sciatica) and complex regional pain syndrome (CRPS) involving a lower limb are separate conditions but may share some mechanisms (eg, tissue inflammation, neuroimmune disturbances, and central neuroplasticity). As adrenergically evoked pain contributes, in part, to CRPS, whether an adrenergic mechanism also contributes to postsurgical sciatica was investigated in this study. Immunohistochemistry was used to identify α1-adrenoceptors (α1-AR) on nerve fibres and other targets in the affected and contralateral skin of 25 patients with postsurgical sciatica, and α1-AR expression was investigated in relation to pain and pinprick hyperalgesia after intradermal injection of the α1-AR agonist phenylephrine. In addition, quantitative sensory testing was performed on all 4 limbs and on each side of the forehead. α1-AR expression was greater in keratinocytes (but not blood vessels or nerve fibres) in the symptomatic than contralateral leg, and dermal nerve fibre density was reduced in both legs. However, distal adrenergic involvement in pain in postsurgical sciatica seems unlikely, as neither heightened α1-AR expression in keratinocytes nor reduced dermal nerve fibre density were associated with pain or hyperalgesia to intradermal phenylephrine injection. Sensitivity to pressure-pain, pinprick, and cold-pain was greater in the ipsilateral than contralateral forehead of the entire cohort, but sensory disturbances were most pronounced in patients with additional CRPS-like features. Together, these findings suggest that bilateral distal neuropathy and central neuroplastic changes are involved not only in the pathophysiology of CRPS but also in postsurgical sciatica. This may have treatment implications for patients with postsurgical sciatica.

Neuropathic pain caused by somatosensory nervous system dysfunction is a serious public health problem. Some long noncoding RNAs (lncRNAs) can participate in physiological processes involved in neuropathic pain. However, the effects of lncRNA DGCR5 in neuropathic pain have not been explored. Therefore, in our current study, we concentrated on the biological roles of DGCR5 in neuropathic pain. Here, it was observed that DGCR5 was significantly decreased in chronic sciatic nerve injury (CCI) rat models. DGCR5 overexpression was able to alleviate neuropathic pain development including mechanical and thermal hyperalgesia. In addition, the current understanding of miR-330-3p function in neuropathic pain remains largely incomplete. Here, we found that miR-330-3p was greatly increased in CCI rats and DGCR5 can modulate miR-330-3p expression negatively. Upregulation of DGCR5 repressed inflammation-correlated biomarkers including interleukin 6 (IL-6), tumor necrosis factor α, and IL-1β in CCI rats by sponging miR-330-3p. The negative correlation between DGCR5 and miR-330-3p was confirmed in our current study. Inhibition of miR-330-3p suppressed neuropathic pain progression by restraining neuroinflammation in vivo. In addition, PDCD4 was predicted as a downstream target of miR-330-3p. Furthermore, PDCD4 was significantly increased in CCI rats and DGCR5 regulated PDCD4 expression through sponging miR-330-3p in CCI rat models. Taken these together, it was implied that DGCR5/miR-330-3p/PDCD4 axis participated in neuropathic pain treatment., (© 2018 Wiley Periodicals, Inc.)

Context: Accumulating evidence has demonstrated that Toll-like receptors (TLRs), especially TLR4 localized on microglia/macrophages, may play a significant role in nociception., Objective: We examine the role of TLR4 in a neuropathic pain model. Using behavioural/biochemical methods, we examined the influence of TLR4 antagonist on levels of hypersensitivity and nociceptive factors whose contribution to neuropathy development has been confirmed., Materials and Methods: Behavioural (von Frey's/cold plate) tests were performed with Wistar male rats after intrathecal administration of a TLR4 antagonist (LPS-RS ULTRAPURE (LPS-RSU), 20 μG: lipopolysaccharide from Rhodobacter sphaeroides, InvivoGen, San Diego, CA) 16 H and 1 h before chronic constriction injury (cci) to the sciatic nerve and then daily for 7 d. three groups were used: an intact group and two cci-exposed groups that received vehicle or LPS-RSU. tissue [spinal cord/dorsal root ganglia (DRG)] for western blot analysis was collected on day 7., Results: The pharmacological blockade of TLR4 diminished mechanical (from ca. 40% to 16% that in the INTACT group) and thermal (from ca. 51% to 32% that in the INTACT group) hypersensitivity despite the enhanced activation of IBA-1-positive cells in DRG. Moreover, LPS-RSU changed the ratio between IL-18/IL-18BP and MMP-9/TIMP-1 in favour of the increase of antinociceptive factors IL-18BP (25%-spinal; 96%-DRG) and TIMP-1 (15%-spinal; 50%-DRG) and additionally led to an increased IL-6 (40%-spinal; 161%-DRG), which is known to have analgesic properties in neuropathy., Conclusions: Our results provide evidence that LPS-RSU influences pain through the expression of TLR4. TLR4 blockade has analgesic properties and restores the balance between nociceptive factors, which indicates its engagement in neuropathy development.

Background: microRNA-146a-5p (miRNA-146a-5p) is a key molecule in the negative regulation pathway of TLRs and IL-1 receptor (TIR) signaling. Our recent study demonstrated that MyD88-dependent signaling pathway of TIR in the dorsal root ganglion (DRG) and spinal dorsal horn (SDH) plays a role in peripheral nerve injury-induced neuropathic pain. However, it was not clear whether and how miRNA-146a-5p regulates the TIR pathway of DRG and SDH in the development of neuropathic pain., Methods: The sciatic nerve chronic constriction injury (CCI) model of rat was used to induce chronic neuropathic pain. The levels and cellular distribution of miRNA-146a-5p were detected with quantitative real-time PCR (qPCR) and fluorescent in situ hybridization (FISH). The RNA level, protein level, and cellular distribution of IRAK1 and TRAF6 that is targeted by miRNA-146a-5p were detected with qPCR, western blot, and immunofluorescent. The pain-related behavioral effect of miRNA-146a-5p was accessed after intrathecal administration. Mechanical stimuli and radiant heat were used to evaluate mechanical allodynia and thermal hyperalgesia., Results: We found that the level of miRNA-146a-5p significantly increased in L4-L6 DRGs and SDH after CCI surgery; meanwhile, the protein level of IRAK1 and TRAF6 in DRGs was significantly increased after CCI. Intrathecal injection of miR146a-5p agomir or miRNA-146a-5p antagomir regulates miRNA-146a-5p level of L4-L6 DRGs and SDH. We found that intrathecal injection of miR146a-5p agomir can alleviate mechanical and thermal hyperalgesia in CCI rats and reverse the upregulation of IRAK1 and TRAF6 of L4-L6 DRGs and SDH induced by CCI. We furthermore found that intrathecal injection of miRNA-146a-5p antagomir can exacerbate the mechanical and thermal pain-related behavior of CCI rats and meanwhile increase IRAK1 and TRAF6 of L4-L6 DRGs and SDH expression even further., Conclusions: miRNA-146a-5p of DRG and SDH can modulate the development of CCI-induced neuropathic pain through inhibition of IRAK1 and TRAF6 in the TIR signaling pathway. Hence, miRNA-146a-5p may serve as a potential therapeutic target for neuropathic pain.

Many studies have reported that microRNAs participate in neuropathic pain development. Previously, miR-200b and miR-429 are reported to be involved in various diseases. In our current study, we focused on their roles in neuropathic pain and we found that miR-200b and miR-429 were significantly decreased in chronic constriction injury (CCI) rat spinal cords and isolated microglials. miR-200b and miR-429 overexpression were able to relieve neuropathic pain through modulating PWT and PWL in CCI rats. Meanwhile, we observed that both miR-200b and miR-429 upregulation could repress neuroinflammation via inhibiting inflammatory cytokines such as IL-6, IL-1β, and TNF-α in CCI rats. By carry out bioinformatics technology, Zinc finger E box binding protein-1 (ZEB1) was predicted as target of miR-200b, and miR-429 and dual-luciferase reporter assays confirmed the correlation between them. ZEB1 has been reported to regulate a lot of diseases. Here, we found that ZEB1 was greatly increased in CCI rats and miR-200b and miR-429 overexpression markedly suppressed ZEB1 mRNA expression in rat microglial cells. In addition, knockdown of ZEB1 can reduce neuropathic pain development and co-transfection of LV-anti-miR-200b/miR-429 reversed this phenomenon in vivo. Taken these together, our results suggested that miR-200b/miR-429 can serve as an important regulator of neuropathic pain development by targeting ZEB1., (© 2017 Wiley Periodicals, Inc.)

Neuropathic pain is characterized by central sensitization. The interaction between N-methyl-D-aspartate receptors (NMDARs) and postsynaptic density protein-95 (PSD-95) plays a major role in central sensitization. Here, we aimed to investigate the analgesic effect of disruption of the interaction between NMDAR and PSD-95. Chronic dorsal root ganglia compression model rats were used to mimic sciatica. Thermal hyperalgesia and mechanical allodynia were evaluated. The expression of spinal phospho-NR2B, PSD-95, calcium/calmodulin-dependent protein kinase II (CaMKII), and cAMP response element binding protein (CREB) was measured using western blotting. A mimetic peptide Myr-NR2B9c was injected intrathecally to disrupt the interaction between PSD-95 and NR2B and detected by coimmunoprecipitation. Chronic dorsal root ganglia compression surgery induced thermal hyperalgesia and mechanical allodynia, and upregulated pain-related proteins such as phospho-NR2B, PSD-95, CaMKII, and CREB expressions in the spinal cord. Myr-NR2B9c disrupted the interaction between NR2B-containing NMDARs and PSD-95 in the spinal cord. Intrathecal administration of Myr-NR2B9c attenuated neuropathic pain behaviors and downregulated the expressions of phospho-NR2B, PSD-95, CaMKII, and CREB in the spinal cord. The present study indicates that dissociation of NR2B-containing NMDARs from PSD-95 inactivates CaMKII and CREB signaling and relieves pain.

Background: Although there are several evidences that suggest efficacies of therapeutic ultrasound (TU) or treadmill exercise (TE) to alleviate nerve injury-associated pain, molecular mechanisms are less clear. We aimed to investigate the impact of TU and/or TE on neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve and their roles of proinflammatory and anti-inflammatory cytokines., Methods: Rats were randomly divided into (n = 10 per group) sham operation (sham), CCI procedure followed by false application of TU (CCI + TU0), CCI procedure followed by false application of TU and TE (CCI + TU0 + TE), CCI, and CCI procedure followed by TU alone (CCI + TU), TE alone (CCI + TE), or both TU and TE (CCI + TU + TE) groups. TU and TE were administered daily, starting on postoperative day 8 (POD 8) for 3 weeks. Mechanical and thermal hypersensitivity, tumor necrosis factor-α (TNF-α), interleukin-10 (IL-10), and IL-6 in the sciatic nerve were assessed on PODs 14 and 28. Data were analyzed by 1-way, 2-way, or 3-way analysis of variance of repeated measures or 1-way analysis of variance., Results: After the interventions, there was statistical significance (all P ≤ .0001) between the groups for all outcome parameters, all in favor of the experimental group: 4.2 for mean mechanical withdrawal thresholds (95% confidence interval, 1.8-7.6) and 4.8 for mean thermal withdrawal latencies (95% confidence interval, 2.2-8.1). TU and/or TE provoked an increase in mechanical withdrawal thresholds and thermal withdrawal latencies in CCI rats. TU + TE was more effective to reverse pain hypersensitivity than having each treatment alone. On PODs 14 and 28, the CCI rats exhibited an upregulation of sciatic TNF-α and IL-6 expression, whereas TU or TE alone or TU + TE combination prevented the upregulation. TU and/or TE also showed the upregulation of less IL-10 expression in the sciatic nerve., Conclusions: We found that TU + TE is better than TU or TE alone for treating neuropathic pain. TU and/or TE for pain management may be straightly associated with less TNF-α and IL-6 expression and more IL-10 expression.

Objective: To investigate the effect and underlying mechanisms of combined medicated thread moxibustion therapy plus needle picking therapy of Zhuang nationality medicine on antioxidant levels in a rat model of sciatica., Methods: One hundred Wistar rats, of specific pathogen free level, were randomly divided into five groups: normal control group, model group, medicated thread moxibustion group, needle picking group, and combination group. Each group contained 20 rats. In the model, medicated thread moxibustion, needle picking, and combination groups, sciatica models were established through chronic constriction injury of the sciatic nerve. After the model was established, the rats in the medicated thread moxibustion, needle picking, and combination groups were given the corresponding therapies for 21 days. The control and model groups received no treatment. Reactive oxygen species, superoxide dismutase, malondialdehyde, and total antioxidant capacity changes were determined. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit NADPH oxidases 4 (NOX4) mRNA expression and the morphology of cells were observed to detect apoptosis of gamma- aminobutyric acid ergic (GABAergic) neurons., Results: Compared with control group, reactive oxygen species and malondialdehyde levels rose significantly in the model group (P < 0.01), while superoxide dismutase and total antioxidant capacity levels were lowered (P < 0.05). Compared with the model group, reactive oxygen species and malondialdehyde decreased in the needle picking group (P < 0.05), while superoxide dismutase levels were increased (P < 0.05); reactive oxygen species and malondialdehyde significantly decreased in the combination group (P < 0.01). In addition, the model group had higher NOX4 mRNA expression than that of the control group (P < 0.05), and the combination group had lower expression levels than that of the model group (P < 0.05). Apoptosis of GABAergic neurons was observed in the model group, and was attenuated after combined therapy., Conclusion: The medicated thread moxibustion therapy plus needle picking therapy of Zhuang nationality medicine can prevent oxidative damage in the rat model of sciatica via down-regulating NOX4 expression, improving antioxidant capacity, and inhibiting the oxidative damage pathway of GABAergic neurons.

Neuroimaging studies of patients with chronic pain have shown that neurotransmitter abnormalities, including increases in glutamate and decreases in GABA, could be responsible for the cortical hyperactivity and hyperalgesia/allodynia observed in some pain conditions. These finding are particularly evident in the insula, a brain region known to play a role in both the sensory-discriminative and the affective-motivational aspects of pain processing. However, clinical studies are not entirely able to determine the directionality of these findings, nor whether they are causal or epiphenomenon. Thus, a set of animal studies was performed to determine whether alterations in glutamate and GABA are the result of injury, the cause of augmented pain processing, or both. Compared with controls, the excitatory neurotransmitters glutamate and aspartate are significantly higher in the rat insula after chronic constriction injury of the sciatic nerve (CCI). The CCI also produced significant increases in allodynia (mechanical and cold), thermal hyperalgesia, and nociceptive aversiveness. Unilateral microinjection of ionotropic glutamate receptor antagonists restored these nociceptive behaviors to preinjury values. Increasing endogenous levels of GABA or enhancing signaling at inhibitory glycinergic receptors had similar effects as the glutamate receptor antagonists. In naive rats, increasing endogenous levels of glutamate, decreasing endogenous levels of GABA, or blocking strychnine-sensitive glycine receptors in the insula significantly increased thermal hyperalgesia and mechanical allodynia. These data support the hypothesis that an altered balance of excitatory and inhibitory neurotransmitters in brain regions such as the insula occurs in chronic pain states and leads to augmented central pain processing and increased pain sensitivity.

Background Context: Sciatica is a condition characterized by radicular pain that can be secondary to a lumbar disc herniation (LDH). More than 10% of patients report persistent pain after surgery. The underlying mechanisms of postoperative sciatica remain unclear. There is evidence demonstrating that inflammation plays a role in the pathophysiology of sciatica., Purpose: The study aimed to assess if the expression of tumor necrosis factor (TNF)-α and its receptors (TNFR) was correlated with the severity of pre- and postoperative leg pain in LDH patients who underwent single or multiple decompressive discectomies., Setting: This is an experimental prospective human study of intraoperative intervertebral disc (IVD) samples, as well as a clinical scores evaluation., Methods: We analyzed the mRNA and protein levels of TNF-α, TNFR1, and TNFR2 in IVD biopsies, and correlated them with visual analogue scale (VAS) scores 1 day before surgery to 6 weeks and 6 months postoperatively., Results: We evaluated the correlation between the inflammation in IVD with pre- and postoperative pain scores after discectomy in LDH patients operated for the first time (fLDH, N=12) and for recurrent cases (rLDH, N=8). This analysis showed that TNF-α and TNFR1 mRNA levels were significantly greater in rLDH patients; there was a twofold increase for TNF-α and a 50% increase for TNFR1. Similarly, protein levels in IVD samples positively correlated with postoperative VAS scores, whereas TNFR2 protein levels negatively correlated with postoperative VAS scores., Conclusions: These findings indicate that rLDH patients present higher postoperative VAS scores compared with fLDH patients, and also that these scores are correlated with increased inflammation and may contribute to pain chronicity., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Background: Mitochondria play an important role in many cellular and physiologic functions. Mitochondria are dynamic organelles, and their fusion and fission regulate cellular signaling, development, and mitochondrial homeostasis. The most common complaint of human immunodeficiency virus (HIV)-sensory neuropathy is pain on the soles in patients with HIV, but the exact molecular mechanisms of HIV neuropathic pain are not clear. In the present study, we investigated the role of mitochondrial dynamin-related protein 1 (Drp1, a GTPase that mediates mitochondrial fission) in the perineural HIV coat glycoprotein gp120-induced neuropathic pain state., Methods: Neuropathic pain was induced by the application of recombinant HIV-1 envelope protein gp120 into the sciatic nerve. Mechanical threshold was tested using von Frey filaments. The mechanical threshold response was assessed over time using the area under curves. Intrathecal administration of antisense oligodeoxynucleotide (ODN) against Drp1, mitochondrial division inhibitor-1 (mdivi-1), or phenyl-N-tert-butylnitrone (a reactive oxygen species scavenger) was given. The expression of spinal Drp1 was examined using western blots. The expression of mitochondrial superoxide in the spinal dorsal horn was examined using MitoSox imaging., Results: Intrathecal administration of either antisense ODN against Drp1 or mdivi-1 decreased mechanical allodynia (a sensation of pain evoked by nonpainful stimuli) in the gp120 model. Intrathecal ODN or mdivi-1 did not change basic mechanical threshold in sham surgery rats. Intrathecal Drp1 antisense ODN decreased the spinal expression of increased Drp1 protein induced by peripheral gp120 application. Intrathecal phenyl-N-tert-butylnitrone reduced mechanical allodynia. Furthermore, both intrathecal Drp1 antisense ODN and mdivi-1 reversed the upregulation of mitochondrial superoxide in the spinal dorsal horn in the gp120 neuropathic pain state., Conclusions: These data suggest that mitochondrial division plays a substantial role in the HIV gp120-related neuropathic pain state through mitochondrial reactive oxygen species and provides evidence for a novel approach to treating chronic pain in patients with HIV.

Cone snails, also known as marine gastropods, from Conus genus produce in their venom a diverse range of small pharmacologically active structured peptides called conotoxins. The cone snail venoms are widely unexplored arsenal of toxins with therapeutic and pharmacological potential, making them a treasure trove of ligands and peptidic drug leads. Conotoxins are small disulfide bonded peptides, which act as remarkable selective inhibitors and modulators of ion channels (calcium, sodium, potassium), nicotinic acetylcholine receptors, noradrenaline transporters, N-methyl-D-aspartate receptors, and neurotensin receptors. They are highly potent and specific against several neuronal targets making them valuable as research tools, drug leads and even therapeutics. In this review, we discuss their gene superfamily classification, nomenclature, post-translational modification, structural framework, pharmacology and medical applications of the active conopeptides. We aim to give an overview of their structure and therapeutic potential. Understanding these aspects of conopeptides will help in designing more specific peptidic analogues.

Purpose: The aim of this study was to evaluate prognostic importance of interleukin-6 (IL-6), matrix metalloproteinase (MMP)-1, insulin-like growth factor (IGF)-1, and Bcl-2-associated X protein (BAX) levels in biopsy specimens taken from the intervertebral disk specimens and the posterior longitudinal ligaments of patients with sciatic pain., Methods: The specimens of the intervertebral disk and the posterior longitudinal ligament were obtained from 52 patients undergoing herniectomy and diskectomy at the Neurosurgery Department of the Abant Izzet Baysal University Izzet Baysal Training and Research Hospital between April 2012 and February 2014. The immunohistochemical expressions of IL-6, MMP-1, IGF-1, and BAX were evaluated in three categories: mild, moderate, and intense., Results: The IL-6 expression in the intervertebral disk specimens was intense in the sequestration group when compared with that of the "protrusion" and "extrusion" groups. The intervertebral disk specimens in "extrusion" and "sequestration" groups were stained intensely for MMP-1. The IGF-1 expression was stained intensely in the intervertebral disk tissue of the extrude group patients. For the "extrusion" and "sequestration" groups, the intervertebral disk specimens were stained intensely for BAX compared with the protrude group. The IL-6 expression in the posterior longitudinal ligament specimens was more intense in the "sequestration" and "extrusion" groups when compared with that of the protrude group. The MMP-1 expressions were milder in the sequestration group when compared with that of the "extrusion" and "protrusion" groups., Conclusions: Our findings suggest that the cytokines, enzymes, growth factors, and proapoptotic proteins, such as IL-6, MMP-1, IGF-1, and BAX, may be critical factors in the pathophysiology of the degeneration of the intervertebral disks in patients with symptomatic degenerative disk disease., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Background: Insulin therapy plays a critical role in managing type 1 diabetes mellitus, and exercise produces alterations in pain sensation. This experiment explored the effects of insulin therapy combined with treadmill training on diabetic neuropathic pain and on the expression of malondialdehyde (MDA) and cytokines., Methods: Rats were given 4 weeks of insulin (100 IU/kg) therapy and treadmill training (30-60 min/d of training at 20-25 m/min) each day beginning on day 3 after streptozotocin (65 mg/kg, IV) injection and continuing until day 27. Sensitivity to heat and mechanical stimuli and the expression of interleukin (IL)-10, IL-6, tumor necrosis factor-α, and MDA in the sciatic nerve were estimated., Results: We showed that 2 to 4 weeks of treadmill training, insulin treatment, or their combination increased both paw withdrawal thresholds and latencies compared with the same regimen in sedentary diabetic rats (all P < 0.0022). Treatment with insulin, but without treadmill training, had significant effects on glycemic control (P < 0.0001) and restored body weight (P < 0.0001) in the diabetic rats. The diabetic rats demonstrated the upregulation (all P < 0.009) of IL-6, MDA, and tumor necrosis factor-α in the sciatic nerve on days 14 and 28 after streptozotocin treatment, whereas in diabetic rats receiving insulin, treadmill training, or a combination (all P < 0.01), this upregulation was decreased. Insulin, treadmill training, or the combination increased IL-10 expression (all P < 0.0051) in all diabetic rats., Conclusions: Treadmill training combined with insulin therapy showed the best improvements in tactile allodynia and thermal hyperalgesia among our 3 treatment groups. The benefits of insulin intervention and treadmill training could be related to chronic inflammation (proinflammatory cytokines) and oxidative stress (MDA).

G-protein receptor 84 (GPR84) is an orphan receptor that is induced markedly in monocytes/macrophages and microglia during inflammation, but its pathophysiological function is unknown. Here, we investigate the role of GPR84 in a murine model of traumatic nerve injury. Naive GPR84 knock-out (KO) mice exhibited normal behavioral responses to acute noxious stimuli, but subsequent to partial sciatic nerve ligation (PNL), KOs did not develop mechanical or thermal hypersensitivity, in contrast to wild-type (WT) littermates. Nerve injury increased ionized calcium binding adapter molecule 1 (Iba1) and phosphorylated p38 MAPK immunoreactivity in the dorsal horn and Iba1 and cluster of differentiation 45 expression in the sciatic nerve, with no difference between genotypes. PCR array analysis revealed that Gpr84 expression was upregulated in the spinal cord and sciatic nerve of WT mice. In addition, the expression of arginase-1, a marker for anti-inflammatory macrophages, was upregulated in KO sciatic nerve. Based on this evidence, we investigated whether peripheral macrophages behave differently in the absence of GPR84. We found that lipopolysaccharide-stimulated KO macrophages exhibited attenuated expression of several proinflammatory mediators, including IL-1β, IL-6, and TNF-α. Forskolin-stimulated KO macrophages also showed greater cAMP induction, a second messenger associated with immunosuppression. In summary, our results demonstrate that GPR84 is a proinflammatory receptor that contributes to nociceptive signaling via the modulation of macrophages, whereas in its absence the response of these cells to an inflammatory insult is impaired., (Copyright © 2015 Nicol et al.)

Inflammation plays a key role in the development of sensitization after peripheral nerve damage. We recently demonstrated that tumor necrosis factor-α receptor (TNFR) levels in the spinal cord correlate with pain sensation in herniated disc patients in a rat chronic constriction injury (CCI) model. By using the sciatic nerve CCI model, we studied the effect of anti-TNF-α treatment on recovery from hypersensitivity and TNFR expression in the dorsal root ganglion (DRG) and dorsal horn (DH). Experimental groups consisted of sham-operated and CCI-operated rats that received two s.c. injections (one immediately after surgery, the other 5 days later), both containing saline, etanercept (3 mg/kg body weight), or infliximab (10 mg/kg body weight). Mechanical allodynia (with von Frey filaments) and thermal hyperalgesia (Hargreaves test) were assessed preoperatively and weekly during the first 4 postoperative weeks. DRG and DH samples were collected 2 and 4 weeks after surgery and analyzed for TNFR1 and TNFR2 protein levels by Western blotting and analyzed for mRNA levels by quantitative real-time polymerase chain reaction. Anti-TNF-α treatment resulted in a significant alleviation of pain. TNFR levels were increased five- to sixfold in CCI rats compared with sham controls. Both treatments significantly diminished these increased levels. Treated animals that showed a ≥50% alleviation of pain exhibited a significantly reduced TNF R1/R2 mRNA ratio compared with treated animals that recovered less well. These results demonstrate that attenuation of TNFR expression is associated with recovery from nerve injury and suggest that this may be one of the working mechanisms of anti-TNF therapies., (Copyright © 2014 Wiley Periodicals, Inc.)

Sensory nerve fibers differ not only with respect to their sensory modalities and conduction velocities, but also in their relative roles for pain hypersensitivity. It is presently largely unknown which types of sensory afferents contribute to various forms of neuropathic and inflammatory pain hypersensitivity. Vesicular glutamate transporter 3-positive (VGluT3(+)) primary afferents, for example, have been implicated in mechanical hypersensitivity after inflammation, but their role in neuropathic pain remains under debate. Here, we investigated a possible etiology-dependent contribution of VGluT3(+) fibers to mechanical and cold hypersensitivity in different models of inflammatory and neuropathic pain. In addition to VGluT3(-/-) mice, we used VGluT3-channelrhodopsin 2 mice to selectively stimulate VGluT3(+) sensory afferents by blue light, and to assess light-evoked behavior in freely moving mice. We show that VGluT3(-/-) mice develop reduced mechanical hypersensitivity upon carrageenan injection. Both mechanical and cold hypersensitivity were reduced in VGluT3(-/-) mice in neuropathic pain evoked by the chemotherapeutic oxaliplatin, but not in the chronic constriction injury (CCI) model of the sciatic nerve. Further, we provide direct evidence that, despite not mediating painful stimuli in naive mice, activation of VGluT3(+) sensory fibers by light elicits pain behavior in the oxaliplatin but not the CCI model. Immunohistochemical and electrophysiological data support a role of transient receptor potential melastatin 8-mediated facilitation of synaptic strength at the level of the dorsal horn as an underlying mechanism. Together, we demonstrate that VGluT3(+) fibers contribute in an etiology-dependent manner to the development of mechano-cold hypersensitivity., (Copyright © 2014 the authors 0270-6474/14/3412015-14$15.00/0.)

Background and Objective: Currently, no satisfactory treatment is available for sciatica caused by herniated discs and/or spinal stenosis. The objective of this study is to assess the value of tumor necrosis factor (TNF)-α inhibitors in the treatment of sciatica., Methods: Without language restrictions, we searched PubMed, OVID, EMBASE, the Web of Science, the Clinical Trials Registers, the Cochrane Central Register of Controlled Trials and the China Academic Library and Information System. We then performed a systematic review and meta-analysis on the enrolled trials that met the inclusion criteria., Results: Nine prospective randomized controlled trials (RCTs) and two before-after controlled trials involving 531 patients met our inclusion criteria and were included in this study. Our systematic assessment and meta-analysis demonstrated that in terms of the natural course of the disease, compared with the control condition, TNF-α inhibitors neither significantly relieved lower back and leg pain (both p > 0.05) nor enhanced the proportion of patients who felt overall satisfaction (global perceived effect (satisfaction)) or were able to return to work (return to work) (combined endpoint; p > 0.05) at the short-term, medium-term and long-term follow-ups. In addition, compared with the control condition, TNF-α inhibitors could reduce the risk ratio (RR) of discectomy or radicular block (combined endpoint; RR = 0.51, 95% CI 0.26 to 1.00, p = 0.049) at medium-term follow-up, but did not decrease RR at the short-term (RR = 0.64, 95% CI 0.17 to 2.40, p = 0.508) and long-term follow-ups (RR = 0.64, 95% CI 0.40 to 1.03, p = 0.065)., Conclusion: The currently available evidence demonstrated that other than reducing the RR of discectomy or radicular block (combined endpoint) at medium-term follow-up, TNF-α inhibitors showed limited clinical value in the treatment of sciatica caused by herniated discs and/or spinal stenosis.

Background: The molecular mechanisms underlying neuropathic pain are constantly being studied to create new opportunities to prevent or alleviate neuropathic pain. The aim of our study was to determine the gene expression changes induced by sciatic nerve chronic constriction injury (CCI) that are modulated by minocycline, which can effectively diminish neuropathic pain in animal studies. The genes associated with minocycline efficacy in neuropathic pain should provide insight into the etiology of neuropathic pain and identify novel therapeutic targets., Results: We screened the ipsilateral dorsal part of the lumbar spinal cord of the rat CCI model for differentially expressed genes. Out of 22,500 studied transcripts, the abundance levels of 93 transcripts were altered following sciatic nerve ligation. Percentage analysis revealed that 54 transcripts were not affected by the repeated administration of minocycline (30 mg/kg, i.p.), but the levels of 39 transcripts were modulated following minocycline treatment. We then selected two gene expression patterns, B1 and B2. The first transcription pattern, B1, consisted of 10 mRNA transcripts that increased in abundance after injury, and minocycline treatment reversed or inhibited the effect of the injury; the B2 transcription pattern consisted of 7 mRNA transcripts whose abundance decreased following sciatic nerve ligation, and minocycline treatment reversed the effect of the injury. Based on the literature, we selected seven genes for further analysis: Cd40, Clec7a, Apobec3b, Slc7a7, and Fam22f from pattern B1 and Rwdd3 and Gimap5 from pattern B2. Additionally, these genes were analyzed using quantitative PCR to determine the transcriptional changes strongly related to the development of neuropathic pain; the ipsilateral DRGs (L4-L6) were also collected and analyzed in these rats using qPCR., Conclusion: In this work, we confirmed gene expression alterations previously identified by microarray analysis in the spinal cord and analyzed the expression of selected genes in the DRG. Moreover, we reviewed the literature to illustrate the relevance of these findings for neuropathic pain development and therapy. Further studies are needed to elucidate the roles of the individual genes in neuropathic pain and to determine the therapeutic role of minocycline in the rat neuropathic pain model.

Opiate analgesia in the spinal cord is impaired during neuropathic pain. We hypothesized that this is caused by a decrease in μ-opioid receptor inhibition of neurotransmitter release from primary afferents. To investigate this possibility, we measured substance P release in the spinal dorsal horn as neurokinin 1 receptor (NK1R) internalization in rats with chronic constriction injury (CCI) of the sciatic nerve. Noxious stimulation of the paw with CCI produced inconsistent NK1R internalization, suggesting that transmission of nociceptive signals by the injured nerve was variably impaired after CCI. This idea was supported by the fact that CCI produced only small changes in the ability of exogenous substance P to induce NK1R internalization or in the release of substance P evoked centrally from site of nerve injury. In subsequent experiments, NK1R internalization was induced in spinal cord slices by stimulating the dorsal root ipsilateral to CCI. We observed a complete loss of the inhibition of substance P release by the μ-opioid receptor agonist [D-Ala(2), NMe-Phe(4), Gly-ol(5)]-enkephalin (DAMGO) in CCI rats but not in sham-operated rats. In contrast, DAMGO still inhibited substance P release after inflammation of the hind paw with complete Freund's adjuvant and in naïve rats. This loss of inhibition was not due to μ-opioid receptor downregulation in primary afferents, because their colocalization with substance P was unchanged, both in dorsal root ganglion neurons and primary afferent fibers in the dorsal horn. In conclusion, nerve injury eliminates the inhibition of substance P release by μ-opioid receptors, probably by hindering their signaling mechanisms., (Published by Elsevier Ltd.)

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.

Background: Somatostatin (SST) and some of its receptor subtypes have been implicated in pain signaling at the spinal level. In this study we have investigated the role of SST and its sst2A receptor (sst2A) in dorsal root ganglia (DRGs) and spinal cord., Results: SST and sst2A protein and sst2 transcript were found in both mouse and human DRGs, sst2A-immunoreactive (IR) cell bodies and processes in lamina II in mouse and human spinal dorsal horn, and sst2A-IR nerve terminals in mouse skin. The receptor protein was associated with the cell membrane. Following peripheral nerve injury sst2A-like immunoreactivity (LI) was decreased, and SST-LI increased in DRGs. sst2A-LI accumulated on the proximal and, more strongly, on the distal side of a sciatic nerve ligation. Fluorescence-labeled SST administered to a hind paw was internalized and retrogradely transported, indicating that a SST-sst2A complex may represent a retrograde signal. Internalization of sst2A was seen in DRG neurons after systemic treatment with the sst2 agonist octreotide (Oct), and in dorsal horn and DRG neurons after intrathecal administration. Some DRG neurons co-expressed sst2A and the neuropeptide Y Y1 receptor on the cell membrane, and systemic Oct caused co-internalization, hypothetically a sign of receptor heterodimerization. Oct treatment attenuated the reduction of pain threshold in a neuropathic pain model, in parallel suppressing the activation of p38 MAPK in the DRGs, Conclusions: The findings highlight a significant and complex role of the SST system in pain signaling. The fact that the sst2A system is found also in human DRGs and spinal cord, suggests that sst2A may represent a potential pharmacologic target for treatment of neuropathic pain.

Background: Glutamate homeostasis and microglia activation play an important role in the development and maintenance of neuropathic pain. We designed this investigation to examine whether ultra-low dose naloxone administered alone or in combination with morphine could alter the concentration of the excitatory amino acids (EAAs) glutamate and aspartate, as well as the expression of tumor necrosis factor-α (TNF-α) and its receptors (TNFR1 and TNFR2) in the spinal cord dorsal horn of rats with partial sciatic nerve transection (PST)., Methods: Male Wistar rats underwent intrathecal catheter implantation for drug delivery and were divided in 7 groups: sham-operated + saline (sham), PST + saline (S), PST + 15 ng naloxone (n), PST + 15 µg naloxone (N), PST + 10 µg morphine (M), PST + 15 ng naloxone + 10 µg morphine (Mn), PST + 15 µg naloxone + 10 µg morphine (MN). Thermal withdrawal latency and mechanical withdrawal threshold, TNF-α and TNFR expression in the spinal cord and dorsal root ganglia, and EAAs glutamate and aspartate concentration in cerebrospinal fluid dialysates were measured., Results: Ten days after PST, rats developed hyperalgesia (P < 0.0001) and allodynia (P < 0.0001), and increased TNF-α (P < 0.0001) and TNFR1 expression (P = 0.0009) were measured in the ipsilateral spinal cord dorsal horn. The antihyperalgesic and antiallodynic effects of morphine (10 μg) were abolished by high-dose naloxone (15 μg; P = 0.0031) but enhanced by ultra-low dose naloxone (15 ng; P = 0.0015), and this was associated with a reduction of TNF-α (P < 0.0001) and TNFR1 (P = 0.0009) expression in the spinal cord dorsal horn and EAAs concentration (glutamate: P = 0.0001; aspartate: P = 0.004) in cerebrospinal fluid dialysate. Analysis of variance (ANOVA) or Student t test with Bonferroni correction were used for statistical analysis., Conclusions: Ultra-low dose naloxone enhances the antihyperalgesia and antiallodynia effects of morphine in PST rats, possibly by reducing TNF-α and TNFR1 expression, and EAAs concentrations in the spinal dorsal horn. Ultra-low dose naloxone may be a useful adjuvant for increasing the analgesic effect of morphine in neuropathic pain conditions.

Objective: To observe the temporal changes of basic fibroblast growth factor (FGF-2) expression in the spinal cord of a rat model of spared nerve injury (SNI) of the sciatic nerve., Methods: A total of 100 male SD rats were randomly divided into sham-operated group and SNI group. The paw withdrawal threshold to mechanical stimulation was recorded at 1 day before and at 1, 4, 7, 14 and 28 days after the operation. The expressions of FGF-2, tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the L4-6 spinal cord segments of the rats were measured at the specified time points., Results: The paw withdrawal threshold began to decline at 1 day after SNI, reached the lowest level at 7 days, and maintained a low level till 28 days (P<0.05). The expression of FGF-2 began to increase significantly on postoperative day 4, reached the peak level on day 14 and maintained the high level till day 28 (P<0.05). The rats with SNI showed significantly higher expressions of TNF-α and IL-6A in the spinal cord than those in the sham-operated group at each time point of measurement (P<0.05)., Conclusions: SNI of the sciatic nerve can induce neuropathic tactile allodynia and causes up-regulation of FGF-2 and inflammatory cytokines in the spinal cord.

Purpose: Previous experimental models have shown that proinflammatory cytokines modulate peripheral and central nociception. However, the direct correlation between inflammation and pain in patients remains unclear. Our aim is to correlate the levels of inflammation in the spine with pre- and postoperative pain scores after discectomy., Methods: Paravertebral muscle, annulus fibrosus (AF) and nucleus pulposus (NP) biopsies were intraoperatively collected from ten lumbar disc hernia (LDH) patients suffering from chronic sciatic pain and, as painless controls, five scoliosis patients. IL-1β and IL-6 expressions in these biopsies were assessed by qPCR and western blot. The amount of pain, indicated on a 0-10 point visual analogue scale (VAS), was assessed 1 day before surgery and 6 weeks and 1 year after surgery. For analysis purposes, LDH patients were grouped into painful (VAS ≥ 3.5) and non-painful (VAS < 3.5). LDH painful patient group showed a onefold increased mRNA expression of IL-1β in the NP, and IL-6 in the AF and NP (p < 0.05 vs. controls)., Results: By western blot analysis, both cytokines were clearly visible in all LDH biopsies, but not in controls. However, cytokine expression of the painful patient group did not differ from those of the non-painful patient group. In addition, there was no correlation between VAS scores and either marker., Conclusions: These findings support the idea that LDH is accompanied by a local inflammatory process. Yet, the lack of correlation between IL-1β or IL-6 expression and the severity pain suggests that these cytokines may not play a leading role in maintaining a pain generating network.

Pyrroloquinoline quinone PQQ is a naturally occurring redox cofactor that acts as an essential nutrient, antioxidant, and redox modulator. PQQ has been demonstrated to oxidize the redox modulatory site of N-methyl-d-aspartic acid (NMDA) receptors. Such agents are known to be neuroprotective in experimental stroke models. However, there is not report about the therapeutic effect of PQQ on neuropathic pain. We tested the effects of oral administration of PQQ on neuropathic pain of rats with chronic constriction injury (CCI) of the sciatic nerve. The repeated oral administration of PQQ (20 and 40mg/kg, once a day for 4 weeks, from day 1 after the injury) attenuated both thermal and mechanical hyperalgesia, and also attenuated the muscle atrophy. The anti-hyperalgesic activity of PQQ was associated with a significant reduction of pro-inflammatory mediators such as tumor necrosis factor alpha (TNF-α) and lipid peroxide malondialdehyde (MDA) levels. In the present investigation, PQQ is shown to have analgesic effect which was found in the first time, probably through reducing the release of pro-inflammatory mediator and inhibiting oxidative stress., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Melatonin (MT) is a neurohormone synthesized and secreted by the pineal gland. MT plays an important role in the regulation of physiological and neuroendocrine functions. The purpose of this study was to assess the overall effect of melatonin on neuropathic pain, the type of melatonin receptor involved, and potential role of the opioid system and GABA(A) receptors. The experiments were conducted by using the animal neuropathic pain model (CCI). The rats with CCI showed the characteristic for the mechanical allodynia and thermal hyperalgesia signs that were calculated by using the von Frey's and Hargreaves' tests. The conducted studies measured the effects of intraperitoneal administration of naloxone (opioid antagonist), prazosin (MT3 antagonist), luzindole (MT1/MT2 receptor antagonist), picrotoxin (GABA(A) antagonist) and flumazenil (benzodiazepine antagonist) on the antinociceptive effects caused by melatonin. Melatonin caused the increase in the pain threshold of the mechanical allodynia and the slight increase in the threshold of the thermal hyperalgesia. The pre-treatment with naloxone completely abolished the antinociceptive effects of melatonin in von Frey's test, but not thermal sensation in the Hargreaves's test. Prazosin did not have any effects, while administration of luzindole significantly suppressed the antinociceptive effect of melatonin. The antiallodynic effect of MT was also abolished by flumazenil and picrotoxin. Melatonin influences the mechanical allodynia but not thermal hyperalgesia via activation of opioid system and benzodiazepine-GABAergic pathway. Antinociceptive effects of melatonin are mostly related to the MT1/MT2 receptors interaction.

Unlabelled: We previously demonstrated that a single injection of diluted bee venom (DBV) temporarily alleviates thermal hyperalgesia, but not mechanical allodynia, in neuropathic rats. The present study was designed to determine whether repetitive injection of DBV produces more potent analgesic effects on neuropathy-induced nociception and whether those effects are associated with increased neuronal activity in the locus coeruleus (LC) and with the suppression of spinal NMDA receptor NR1 subunit phosphorylation (pNR1). DBV (.25 mg/kg) was administered subcutaneously twice a day for 2 weeks beginning on day 15 post-chronic constrictive injury surgery. Pain responses were examined and potential changes in LC Fos expression and spinal pNR1 expression were determined. Repetitive DBV administration significantly reduced mechanical allodynia, as well as thermal hyperalgesia. The activity of LC noradrenergic neurons was increased and spinal pNR1 expression was significantly suppressed by repetitive DBV as compared with those of vehicle or single DBV injection. These suppressive effects of repetitive DBV on neuropathic pain and spinal pNR1 were prevented by intrathecal pretreatment of idazoxan, an alpha-2 adrenoceptor antagonist. These results indicate that repetitive DBV produces potent analgesic effects on neuropathic pain and this is associated with the activation of the LC noradrenergic system and with a reduction in spinal pNR1., Perspective: The results of current study demonstrate that repetitive administration of DBV significantly suppresses neuropathic pain. Furthermore, this study provides mechanistic information that repetitive treatment of DBV can produce more potent analgesic effect than single DBV treatment, indicating a potential novel strategy for the management of chronic pain., (Copyright © 2012 American Pain Society. Published by Elsevier Inc. All rights reserved.)

Dysfunction at glutamatergic synapses has been proposed as a mechanism in the development of neuropathic pain. Here we sought to determine whether peripheral nerve injury-induced neuropathic pain results in functional changes to primary afferent synapses. Signs of neuropathic pain as well as an induction of glial fibrillary acidic protein in immunostained spinal cord sections 4 days after partial ligation of the sciatic nerve indicated the induction of neuropathic pain. We found that following nerve injury, no discernable change to kinetics of dl-α-amino-3-hydroxy-5-methylisoxazole-propionic acid (AMPA) or N-methyl-d-aspartate receptor (NMDAR)-mediated evoked excitatory postsynaptic currents (eEPSCs) could be observed in dorsal horn (lamina I/II) neurons compared with those of naïve mice. However, we did find that nerve injury was accompanied by slowed decay of the early phase of eEPSCs in the presence of glutamate transporter inhibition by the competitive nontransportable inhibitor dl-threo-β-benzyloxyaspartic acid (TBOA). Concomitantly, expression patterns for the two major glutamate transporters in the spinal cord, excitatory amino acid transporters (EAAT) 1 and EAAT2, were found to be reduced at this time (4 days postinjury). We then sought to directly determine whether nerve injury results in glutamate spillover to NMDARs at dorsal horn synapses. By employing the use-dependent NMDAR blocker (±)MK-801 to block subsynaptic receptors, we found that although TBOA-induced spillover to extrasynaptic receptors trended to increased activation of these receptors after nerve injury, this was not significant compared with naïve mice. Together, these results suggest the development of neuropathic pain involves subtle changes to glutamate transporter expression and function that could contribute to neuropathic pain during excessive synaptic activity.

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.

Aim: Deep Oscillation® is an apparatus that produces low frequency electromagnetic radiations able to modulate immune reactions and, therefore, applicable to pain, tumour and inflammation treatments. The aim of this study is to evaluate how the Deep Oscillation® therapy works on conventional therapy resistant patients as the apparatus can be applied either to trauma derived fom surgical wounds or on sports post-traumatic oedema, low back pain and/or sciatalgic pain and cervicobrachial pain., Methods: In the first part of the study, 34 cases of recent surgical wounds have been treated with Deep Oscillation® with 3 times a week visits for 20 minutes. In the same way 30 cases of sports post-traumatic oedema, 20 cases of low back pain and/or sciatalgic pain and 10 cases of cervicobrachial pain were treated. Among these patients, 15 cases had also undergone contemporaneous nonsteroidal anti-inflammatory drugs intravenous drip, electrolytes and vitamins to verify the probable synergetic efficacy of both treatments., Results: The results confirm that in some cases the Deep Oscillation® treatment is effective since the first/third therapy up to the restitutio ad integrum. It has also been demonstrated that the maximum efficiency of the Deep Oscillation® and nonsteroidal anti-inflammatory drugs synergetic treatment is probably due to the electromagnetic radiations able to facilitate the pharmacological uptake., Conclusion: This study confirms the capacity of the electrostatic energy, released by Deep Oscillation®, to stimulate the patient's neurosensory system, raising his pain threshold and facilitating his pharmacological uptake and restoring his functional recovery more quickly.

Objective: To study the effects of osthole on sciatica induced by lumber disc herniation and its mechanisms., Methods: 54 male SD rats were randomly divided into 6 groups. Model (M) group (n = 12): Autologous nucleus pulposus was harvested from the tail and applied to the L5 dorsal root ganglion (DRG) and epidural space. Epidural catheterization was performed. Control(C) group (n = 12): On the basis of nucleus pulposus group, 50 microL tween-80 was administered epidurally on the day 6th after surgery. T2 (n = 6), T6 (n = 12), T13 (n = 6) and T20 (n = 6) group: 50 microL 2% osthole was administered epidurally on the 2th, 6th, 13th day and 20th after surgery respectively. General behaviors were observed and 50% paw withdrawal threshold (50% PWT) was measured 1 day before surgery, on the 1st, 3th, 7th,14th, 21th, 28th day after surgery, immediately before and 1 hour after osthole or tween-80 administration in each group. On the 7th day after surgery, the left L5 DRGs were obtained for detecting the expression of NOS and COX-2 in M, C and T6 group with 6 rats., Results: No lameness or autophagy was oberserved. 50% PWT decreased after surgery (P < 0.05). In T2 and T6 group, 50% PWT after osthole administration were significantly higher than those of M group and C group (P < 0.05), which recovered to the same level as 1 day before surgery (P > 0.05). In T13 and T20 group, 50% PWT 1 hour after osthole administration were significantly higher than those of M group and C group (P < 0.05), which recovered to the same level as 1 day before surgery (P > 0.05), but on days after 1 hour after administration, there was no significant difference when 50% PWT compared with M group or nucleus C group (P > 0.05). NOS positive cells and COX-2 positive cells were no significant difference when M group compared with C group (P > 0.05). But these positive cells in T6 group were significantly lower than those of M group and C group (P < 0.05)., Conclusion: 50 microL 2% osthole could completely inhibit the mechanical allodynia in the rat model of sciatica induced by lumbar disc herniation when it was administered epidurally on 2 or 6 day after surgery. But when administered on 13 or 20 day after surgery, its analgesic effect was transient. The effect of 50 microL 2% osthole epidural administration on day 6 after surgery on the rat model of sciatica induced by lumbar disc herniation may relate to inhibition of the expression of COX-2 and NOS in DRG.

Unlabelled: Cytokines, essential mediators of inflammatory and immune responses, play an important role in the pathophysiological processes associated with neuropathic pain following peripheral nerve injury. Recently, a novel proinflammatory cytokine, the interleukin (IL)-17, was found to orchestrate inflammatory responses in a wide range of inflammatory and autoimmune diseases of the nervous system. Here, we investigated the role of IL-17 in mediating neuroinflammation and pain hypersensitivity using the neuropathic pain model of partial ligation of the sciatic nerve in mice. Compared to wild-type, IL-17 knockout (KO) mice displayed significantly decreased mechanical pain hypersensitivity as well as decreased infiltration of T cells and macrophages to the injured sciatic nerves and the L3-L5 dorsal root ganglia and decreased activation of microglia and astrocytes in the L3-5 dorsal and ventral horns of the spinal cord. Further, intraplantar and intraneural injection of recombinant IL-17 into the hind paw and the sciatic nerve, respectively, induced both mechanical allodynia and thermal hyperalgesia, whereas intrathecal injection produced thermal hyperalgesia. IL-17 administration was associated with a significant increase in the numbers of infiltrating neutrophils and activated dendritic cells in the injected hind paws and infiltrating neutrophils in the injected sciatic nerves. Taken together, our results demonstrate that IL-17 contributes to the regulation of immune cell infiltration and glial activation after peripheral nerve injury and the ensuing neuropathic pain., Perspective: IL-17 is an important regulator of immune responses and is involved in inducing and mediating proinflammatory reactions. Using IL-17 KO mice, we have demonstrated that IL-17 contributes to neuroinflammatory responses and pain hypersensitivity following neuropathic injury. This work identifies IL-17 as a potential therapeutic target in neuropathic pain., (Copyright © 2011 American Pain Society. Published by Elsevier Inc. All rights reserved.)

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.

Acupuncture is an invasive procedure commonly used to relieve pain. Acupuncture is practiced worldwide, despite difficulties in reconciling its principles with evidence-based medicine. We found that adenosine, a neuromodulator with anti-nociceptive properties, was released during acupuncture in mice and that its anti-nociceptive actions required adenosine A1 receptor expression. Direct injection of an adenosine A1 receptor agonist replicated the analgesic effect of acupuncture. Inhibition of enzymes involved in adenosine degradation potentiated the acupuncture-elicited increase in adenosine, as well as its anti-nociceptive effect. These observations indicate that adenosine mediates the effects of acupuncture and that interfering with adenosine metabolism may prolong the clinical benefit of acupuncture.

The maintenance of chronic pain states requires the regulation of gene expression, which relies on an influx of calcium. Calcium influx through neuronal L-type voltage-gated calcium channels (LTCs) plays a pivotal role in excitation-transcription coupling, but the involvement of LTCs in chronic pain remains unclear. We used a peptide nucleic acid (transportan 10-PNA conjugates)-based antisense strategy to investigate the role of the LTC subtypes Ca(V)1.2 and Ca(V)1.3 in long-term pain sensitization in a rat model of neuropathy (spinal nerve ligation). Our results demonstrate that specific knockdown of Ca(V)1.2 in the spinal dorsal horn reversed the neuropathy-associated mechanical hypersensitivity and the hyperexcitability and increased responsiveness of dorsal horn neurons. Intrathecal application of anti-Ca(V)1.2 siRNAs confirmed the preceding results. We also demonstrated an upregulation of Ca(V)1.2 mRNA and protein in neuropathic animals concomitant to specific Ca(V)1.2-dependent phosphorylation of the cAMP response element (CRE)-binding protein (CREB) transcription factor. Moreover, spinal nerve ligation animals showed enhanced transcription of the CREB/CRE-dependent gene COX-2 (cyclooxygenase 2), which also depends strictly on Ca(V)1.2 activation. We propose that L-type calcium channels in the spinal dorsal horn play an important role in pain processing, and that the maintenance of chronic neuropathic pain depends specifically on channels comprising Ca(V)1.2.

Metabotropic glutamate (mGlu) receptors, which are present on neurons and glial cells, have been shown to play a role in neuropathic pain. The present study sought to investigate how the glial inhibitors minocycline and pentoxifylline alter the effect that chronic constriction injury (CCI) has on the expression of mGlu receptors and on their associated ligands. RT-PCR analysis revealed that seven days after CCI, the mRNA levels of glial markers C1q and GFAP, as well as those of mGlu5 and mGlu3, but not mGlu7, were elevated in the lumbar spinal cord - ipsilateral to the injury. The protein levels of the microglial marker OX42, the astroglial marker GFAP, and mGlu5 receptor protein were increased, whereas the levels of mGlu2/3 and mGlu7 receptor proteins were reduced. Preemptive and repeated intraperitoneal (i.p.) administration (16 and 1h before nerve injury and then twice daily for seven days) of minocycline (30mg/kg) and pentoxifylline (20mg/kg) prevented the injury-induced changes in the levels of mGlu3 and mGlu5 receptor mRNAs and the injury-induced changes in the protein levels of all the receptors. Repeated administration of minocycline and pentoxifylline significantly attenuated CCI-induced allodynia (von Frey test) and hyperalgesia (cold plate test) measured on day seven after injury and potentiated the antiallodynic and antihyperalgesic effects of single i.p. and intrathecal (i.t.) injections of mGlu receptor ligands: MPEP, LY379268 or AMN082. We conclude that attenuation of injury-induced glial activation can reduce glutamatergic activity, thereby contributing to regulation of pain sensation.