Metformin Relieves Bortezomib-Induced Neuropathic Pain by Regulating AMPKa2-Mediated Autophagy in the Spinal Dorsal Horn.

Chemotherapy-induced neuropathic pain is a major clinical problem with limited treatment options. Here, we show that metformin relieves bortezomib (BTZ)-evoked induction and maintenance of neuropathic pain by preventing the reduction in the expression of Beclin-1, an autophagy marker, in the spinal dorsal horn. Application of rapamycin or 3-methyladenine, autophagy inducer and inhibitor, respectively, affected the mechanical allodynia differently. Co-application of 3-methyladenine and metformin partially inhibited the effect of metformin in recovering Beclin-1 expression and in reducing the pain behavior in rats subjected to BTZ treatment. BTZ treatment also reduced the expression of AMPKa2 in the dorsal horn, which was recovered by metformin treatment. Overexpression of AMPKa2 attenuated the BTZ-evoked reduction in Beclin-1 expression and mechanical allodynia, whereas intrathecal injection of AMPKa2 siRNA decreased the Beclin-1 expression and induced mechanical allodynia in naive rats. Moreover, BTZ treatment increased the GATA3 expression in the dorsal horn, and GATA3 siRNA attenuated the AMPKa2 downregulation and mechanical allodynia induced by BTZ. Chromatin immunoprecipitation further showed that BTZ induced an increased recruitment of GATA3 to multiple sites in the AMPKa2 promoter region. Furthermore, decreased acetylation and increased methylation of histone H3 in the AMPKa2 promoter in the spinal dorsal horn was detected after BTZ treatment. Our findings suggest that metformin may regulate AMPKa2-mediated autophagy in the dorsal horn and alleviate the behavioral hypersensitivity induced by BTZ.

MiR-30d Participates in Vincristine-Induced Neuropathic Pain by Down-Regulating GAD67.

Vincristine is a common chemotherapeutic agent in cancer treatment, while it often causes chemotherapy-induced peripheral neuropathy(CIPN), which brings patients a great disease burden and associated economic pressure. The mechanism under CIPN remains mostly unknown. The previous study has shown that cell-type-specific spinal synaptic plasticity in the dorsal horn plays a pivotal role in neuropathic pain. Downregulation of GABA transmission, which mainly acts as an inhibitory pathway, has been reported in the growing number of research. Our present study found that GAD67, responsible for > 90% of basal GABA synthesis, is down-regulated, while its relative mRNA remains unchanged in vincristine-induced neuropathy. Considering microRNAs (miRNAs) as a post-transcription modifier by degrading targeted mRNA or repressing mRNA translation, we performed genome-wide miRNA screening and revealed that miR-30d might contribute to GAD67 down-regulation. Further investigation confirmed that miR-30d could affect the fluorescence activity of GAD67 by binding to the 3 'UTR of the GAD67 gene, and intrathecal injection of miR-30d antagomir increased the expression of GAD67, partially rescued vincristine-induced thermal hyperalgesia and mechanical allodynia. In summary, our study revealed the molecule interactions of GAD67 and miR-30d in CIPN, which has not previously been discussed in the literature. The results give more profound insight into understanding the CIPN mechanism and hopefully helps pain control.

Exercise for Neuropathic Pain: A Systematic Review and Expert Consensus.

Background: Neuropathic pain (NP), a severe and disruptive symptom following many diseases, normally restricts patients' physical functions and leads to anxiety and depression. As an economical and effective therapy, exercise may be helpful in NP management. However, few guidelines and reviews focused on exercise therapy for NP associated with specific diseases. The study aimed to summarize the effectiveness and efficacy of exercise for various diseases with NP supported by evidence, describe expert recommendations for NP from different causes, and inform policymakers of the guidelines. Design: A systematic review and expert consensus. Methods: A systematic search was conducted in PubMed. We included systematic review and meta-analysis, randomized controlled trials (RCTs), which assessed patients with NP. Studies involved exercise intervention and outcome included pain intensity at least. Physiotherapy Evidence Database and the Assessment of Multiple Systematic reviews tool were used to grade the quality assessment of the included RCTs and systematic reviews, respectively. The final grades of recommendation were based on strength of evidence and a consensus discussion of results of Delphi rounds by the Delphi consensus panel including 21 experts from the Chinese Association of Rehabilitation Medicine. Results: Eight systematic reviews and 21 RCTs fulfilled all of the inclusion criteria and were included, which were used to create the 10 evidence-based consensus statements. The 10 expert recommendations regarding exercise for NP symptoms were relevant to the following 10 different diseases: spinal cord injury, stroke, multiple sclerosis, Parkinson's disease, cervical radiculopathy, sciatica, diabetic neuropathy, chemotherapy-induced peripheral neuropathy, HIV/AIDS, and surgery, respectively. The exercise recommended in the expert consensus involved but was not limited to muscle stretching, strengthening/resistance exercise, aerobic exercise, motor control/stabilization training and mind-body exercise (Tai Chi and yoga). Conclusions: Based on the available evidence, exercise is helpful to alleviate NP intensity. Therefore, these expert consensuses recommend that proper exercise programs can be considered as an effective alternative treatment or complementary therapy for most patients with NP. The expert consensus provided medical staff and policymakers with applicable recommendations for the formulation of exercise prescription for NP. This consensus statement will require regular updates after five-ten years.

ZEB1 Induces Ddr1 Promoter Hypermethylation and Contributes to the Chronic Pain in Spinal Cord in Rats Following Oxaliplatin Treatment.

Application of chemotherapeutic oxaliplatin represses gene transcription through induction of DNA methylation, which may contribute to oxaliplatin-induced chronic pain. Here, Ddr1, which showed an increased methylation in the promoter, was screened from the SRA methylation database (PRJNA587622) after oxaliplatin treatment. qPCR and MeDIP assays verified that oxaliplatin treatment increased the methylation in Ddr1 promoter region and decreased the expression of DDR1 in the neurons of spinal dorsal horn. In addition, overexpression of DDR1 by intraspinal injection of AAV-hSyn-Ddr1 significantly alleviated the mechanical allodynia induced by oxaliplatin. Furthermore, we found that oxaliplatin treatment increased the expression of DNMT3b and ZEB1 in dorsal horn neurons, and promoted the interaction between DNMT3b and ZEB1. Intrathecal injection of ZEB1 siRNA inhibited the enhanced recruitment of DNMT3b and the hypermethylation in Ddr1 promoter induced by oxaliplatin. Finally, ZEB1 siRNA rescued the DDR1 downregulation and mechanical allodynia induced by oxaliplatin. In conclusion, these results suggested that the ZEB1 recruited DNMT3b to the Ddr1 promoter, which induced the DDR1 downregulation and contributed to the oxaliplatin-induced chronic pain.

Chinese Association for the Study of Pain: Expert consensus on chronic postsurgical pain.

Chronic postsurgical pain is a common surgical complication that severely reduces a patient's quality of life. Many perioperative interventions and management strategies have been developed for reducing and managing chronic postsurgical pain. Under the leadership of the Chinese Association for the Study of Pain, an editorial committee was formed for chronic postsurgical pain diagnosis and treatment by experts in relevant fields. The editorial committee composed the main content and framework of this consensus and established a working group. The working group conducted literature review (1989-2020) using key words such as "surgery", "post-surgical", "post-operative", "pain", "chronic", and "persistent" in different databases including MEDLINE, EMBASE, PubMed, Cochrane Central Register of Controlled Trials and Cochrane Database of Systematic Reviews. Only publications in the English language were included. The types of literature included systematic reviews, randomized controlled studies, cohort studies and case reports. This consensus was written based on clinical practice combined with literature evidence. The first draft of the consensus was rigorously reviewed and edited by all the editorial committee experts before being finalized. The level of evidence was assessed by methodological experts based on the Oxford Centre for Evidence-Based Medicine Levels of Evidence. The strength of recommendation was evaluated by all editorial committee experts, and the opinions of most experts were adopted as the final decision. The recommendation level "strong" generally refers to recommendations based on high-level evidence and consistency between clinical behavior and expected results. The recommendation level "weak" generally refers to the uncertainty between clinical behavior and expected results based on low-level evidence.

DNMT3b SUMOylation Mediated MMP-2 Upregulation Contribute to Paclitaxel Induced Neuropathic Pain.

Paclitaxel is a common chemotherapeutic agent in cancer treatment, while it often causes chemotherapy-induced peripheral neuropathy (CIPN), which manifested as hyperalgesia and allodynia, and its mechanism remains largely unknown. The previous study has shown that matrix metalloproteinase-2 (MMP-2) plays a pivotal role in spinal nerve ligation (SNL) induced neuropathic pain, but its function in CIPN and exact molecular mechanisms underlying upregulation is not explored. Our present study revealed that MMP-2 is also upregulated in paclitaxel induced neuropathic pain (NP), and knockdown it by siRNA can ameliorate mechanical allodynia. Since DNA methylation is closely related to gene transcription, we explored the methylation status of the MMP-2 gene and demonstrated that MMP-2 upregulation is related to the reduced methylation level of its promoter. DNA methylation is mediated by DNA methyltransferases (DNMTs), and previous studies suggested that three main types of DNMTs can undergo SUMOylation. Our next study revealed that SUMO1 modification of DNMT3b is significantly enhanced. Intrathecal administration of SUMOylation inhibitor, ginkgolic acid (GA), could reverse enhanced SUMO1 modification of DNMT3b and upregulation of MMP-2 in the model rats. Further investigation suggested that DNMT3b binding activity to the promoter region of the MMP-2 gene is significantly decreased in paclitaxel treated rats, and the administration of GA can reverse these effects, which is also accompanied by changes in the promoter methylation status of the MMP-2 gene. Our study demonstrates that MMP-2 up-regulation mediated by DNMT3b SUMOylation is essential for paclitaxel induced NP development, which brings us new therapeutic options for CIPN.

NFATc2-dependent epigenetic upregulation of CXCL14 is involved in the development of neuropathic pain induced by paclitaxel.

BACKGROUND: The major dose-limiting toxicity of paclitaxel, one of the most commonly used drugs to treat solid tumor, is painful neuropathy. However, the molecular mechanisms underlying paclitaxel-induced painful neuropathy are largely unclarified. METHODS: Paw withdrawal threshold was measured in the rats following intraperitoneal injection of paclitaxel. The qPCR, western blotting, protein or chromatin immunoprecipitation, ChIP-seq identification of NFATc2 binding sites, and microarray analysis were performed to explore the molecular mechanism. RESULTS: We found that paclitaxel treatment increased the nuclear expression of NFATc2 in the spinal dorsal horn, and knockdown of NFATc2 with NFATc2 siRNA significantly attenuated the mechanical allodynia induced by paclitaxel. Further binding site analysis utilizing ChIP-seq assay combining with gene expression profile revealed a shift of NFATc2 binding site closer to TTS of target genes in dorsal horn after paclitaxel treatment. We further found that NFATc2 occupancy may directly upregulate the chemokine CXCL14 expression in dorsal horn, which was mediated by enhanced interaction between NFATc2 and p300 and consequently increased acetylation of histone H4 in CXCL14 promoter region. Also, knockdown of CXCL14 in dorsal horn significantly attenuated mechanical allodynia induced by paclitaxel. CONCLUSION: These results suggested that enhanced interaction between p300 and NFATc2 mediated the epigenetic upregulation of CXCL14 in the spinal dorsal horn, which contributed to the chemotherapeutic paclitaxel-induced chronic pain.

The Diagnosis and Therapy of Degenerative Knee Joint Disease: Expert Consensus from the Chinese Pain Medicine Panel.

At present, there are many constantly updated guidelines and consensuses on the diagnosis and treatment of osteoarthritis both at home and abroad. The recommendations established using methods of evidence-based medicine has experienced strict research on controlling bias and promoting reproduction rate. As a result, the previous evidence was reevaluated, and a lot of changes were provoked in the diagnosis and treatment concept of osteoarthritis. However, several methods not recommended by foreign guidelines are still in use in the current clinical practice in China. On the one hand, Chinese experts have not reached extensive consensus on whether it is necessary to make changes according to foreign guidelines. On the other hand, almost all the current relevant guidelines are on osteoarthritis, but the lesions around knee joints which, as a whole, bear the largest weight in human body, cannot be ignored. For this purpose, Chinese Association for the Study of Pain (CASP) organized some leading experts to formulate this Chinese Pain Specialist Consensus on the diagnosis and treatment of degenerative knee osteoarthritis (DKOA) in combination with the guidelines in foreign countries and the expert experience of clinical practice in China. The consensus, which includes the definition, pathophysiology, epidemiology, clinical manifestation, diagnostic criteria, and treatments of DKOA, is intended to be used by first-line doctors, including pain physicians to manage patients with DKOA.

CX3CR1-Mediated Akt1 Activation Contributes to the Paclitaxel-Induced Painful Peripheral Neuropathy in Rats.

Painful peripheral neuropathy is a serious dose-limiting side effect of paclitaxel therapy, which unfortunately often happens during the optimal clinical management of chemotherapy in cancer patients. Currently the underlying mechanisms of the painful peripheral neuropathy remain largely unknown. Here, we found that paclitaxel treatment (3 × 8 mg/kg, cumulative dose 24 mg/kg) upregulated the expression of CX3CR1 and phosphorylated Akt1 in DRG and spinal dorsal horn. Blocking of Akt1 pathway activation with different inhibitor (MK-2206 or LY294002) significantly attenuated mechanical allodynia and thermal hyperalgesia induced by paclitaxel. Furthermore, inhibition of CX3CR1 by using neutralizing antibody not only prevented Akt1 activation in DRG and spinal dorsal horn but also alleviated pain-related behavior induced by paclitaxel treatment. This study suggested that CX3CR1/Akt1 signaling pathway may be a potential target for prevention and reversion of the painful peripheral neuropathy induced by paclitaxel.

p38 and interleukin-1 beta pathway via toll-like receptor 4 contributed to the skin and muscle incision and retraction-induced allodynia.

BACKGROUND: Persistent postsurgical pain, as an important clinical problem, seriously affects the quality of life in patients. However, the mechanism underlying persistent postsurgical pain remains largely unclear. The present study aims to elucidate the involvement of toll-like receptor 4 (TLR4) and its interaction with p38 and interleukin [IL]-1ß signaling in dorsal root ganglion (DRG) in the persistent postsurgical pain. METHODS: Skin and muscle incision and retraction (SMIR) surgery-induced paw withdrawal threshold (PWT) change was determined by applying mechanical stimuli to the plantar surface of the hind paw using von Frey hairs. The PE-10 catheter intrathecal placement was used to deliver LPS-RS, interleukin-1 receptor antagonist, or SB203580. Western blot analysis was performed to measure the expression of the TLR4, mitogen-activated protein kinases family, and IL-1ß in ipsilateral L3 and L4 DRG. Immunofluorescence staining was performed to further investigate the cell type of TLR4 expression. All data were expressed as means ± standard error of the mean and analyzed using SPSS 13.0. RESULTS: The results showed that the SMIR surgery, a rat model of persistent postoperative pain, decreased the ipsilateral 50% PWT, and the decrease lasted for at least 20 d. The expression of TLR4 and phosphorylation of p38 were upregulated in ipsilateral L3 and L4 DRG neurons after SMIR surgery. Pretreatment with LPS-RS, an established TLR4 antagonist, prevented p38 activation and attenuated mechanical allodynia induced by SMIR surgery. In addition, the expression of IL-1ß was significantly increased after SMIR surgery. Blocking IL-1ß by interleukin-1 receptor antagonist significantly improved the decreased PWT evoked by SMIR. Moreover, inhibition of TLR4 or p38 pathway prevented the IL-1ß upregulation and mechanical allodynia induced by SMIR. CONCLUSIONS: These findings suggest that the activation of p38 and IL-1ß signaling pathway via TLR4 mediate mechanical allodynia after SMIR surgery.

Involvement of spinal microglia and interleukin-18 in the anti-nociceptive effect of dexmedetomidine in rats subjected to CCI.

Dexmedetomidine, a selective alpha 2-adrenoceptor (α2AR) agonist, has provided significant analgesia in neuropathic pain. However, its underlying molecular mechanism has not been fully elucidated. In the present study, we found that intrathecal administration of dexmedetomidine alleviated mechanical allodynia induced by chronic constriction injury (CCI), and pretreatment with BRL44408 significantly reversed the dexmedetomidine-induced anti-nociceptive effect. Western blotting revealed that dexmedetomidine reduced the activation of microglia and the upregulation of interleukin-18 (IL-18) protein expression in the ipsilateral lumbar spinal dorsal horn, while BRL44408 pretreatment significantly blocked these effects of dexmedetomidine. Immunocytochemistry/immunohistochemistry indicated that the α2A-adrenoceptor was localised to microglia in primary culture, and IL-18 predominantly colocalised with the microglial marker Iba-1 in the dorsal horn of the spinal cord. These results suggest that the IL-18 signalling pathway in microglia may be involved in the anti-nociceptive effect of dexmedetomidine in rats subjected to CCI.

Dexmedetomidine inhibits the secretion of high mobility group box 1 from lipopolysaccharide-activated macrophages in vitro.

BACKGROUND: High mobility group box 1 (HMGB1) is a critical proinflammatory factor that is closely related to mortality in sepsis patients. Dexmedetomidine has been proven to reduce the mortality rate from endotoxin shock and attenuate endotoxin-induced acute lung injury. These effects result from reduced secretion of many proinflammatory mediators, although it is not clear whether dexmedetomidine affects the secretion of HMGB1. In this study, we explored the effect of dexmedetomidine on the expression and secretion of HMGB1 from lipopolysaccharide (LPS)-activated macrophages. METHODS: We incubated RAW264.7 cells with LPS in the presence or absence of various concentrations of dexmedetomidine. We used an enzyme-linked immunosorbent assay to detect the secretion levels of HMGB1 in the culture supernatant. We employed real-time polymerase chain reaction to assess the expression of HMGB1 mRNA, and used a nuclear/cytoplasm extraction kit to extract the nuclear and cytoplasmic proteins. We employed Western blotting to observe changes in the translocation of HMGB1 from the nucleus to the cytoplasm. In addition, we used a nuclear factor (NF)-κB p50/p65 transcription factor assay kit to analyze NF-κB activity in the nuclear extract. RESULTS: Dexmedetomidine inhibited the translocation of HMGB1 from the nucleus to the cytoplasm and its extracellular secretion in LPS-activated macrophages while suppressing the expression of HMGB1 mRNA. Dexmedetomidine inhibited the translocation of NF-κB from the cytoplasm to the nucleus in LPS-activated macrophages in a dose-dependent manner. Moreover, these effects were significantly reversed by the α2-adrenergic receptor antagonist yohimbine. CONCLUSIONS: Our study demonstrates that dexmedetomidine inhibits the translocation of HMGB1 from the nucleus to the cytoplasm and the expression of HMGB1 mRNA at clinically relevant dosages. The mechanism responsible for these effects may be through the NF-κB signaling pathway and the α2-adrenergic receptors.

[Effect of L-838,417 on pain behavior in a rat model of trigeminal neuralgia].

OBJECTIVE: To investigate the effect of L-838,417 on the results of behavioral test in rats with experimentally induced trigeminal neuralgia. METHODS: Male SD rats were randomized into model group (n=34), sham-operated group (n=30) and control group (n=6). Thirty rats with trigeminal neuralgia induced by chronic constriction injury of the infraorbital nerve below the zygomatic bone were randomly divided into 5 equal groups for treatment with 1.0 mg/kg L-838,417 (L1 group), 10.0 mg/kg L-838,417 (L10 group), 5 mg/kg morphine (M group), 3 mg/kg diazepam (D group), or normal saline (NS group). The pain threshold of the tentacles pad to von-Frey filament stimulation was measured in the rats before and at 1, 2, 3, 4, 5 h after the treatments. The sedative effect of L-838,417 was evaluated by recording the position scores and righting reflex scores, and the drug tolerance was also evaluated. RESULTS: Nine days after the operation, the pain threshold of the rats in the model group was significantly decreased compared with that before operation and that of the sham group (P<0.01). The threshold of L1 and L10 groups were both significantly increased 1 h after L-838,417 administration (P<0.01). The rats in the NS, L1, and L10 groups did not show unusual posture or righting reflex. In L1 and L10 groups, L838,417 did not show attenuated efficacy after prolonged use (10 days). CONCLUSION: L-838,417 can effectively improve hyperalgesia in rats with trigeminal neuralgia without causing sedation, motor impairment, or drug tolerance.

Analgesic effects of gabapentin on mechanical hypersensitivity in a rat model of chronic pancreatitis.

Gabapentin, an anticonvulsant, is widely accepted as an alternative therapeutic agent for neuropathic pain and has proved to produce analgesic effects in a mouse model of visceral pain. However, it is unknown whether gabapentin is also analgesically effective in chronic pancreatitis. The aim of the present study was to investigate the role and underlying mechanisms of gabapentin in a rat model of chronic pancreatitis. Chronic pancreatitis induced by dibutyltin dichloride (DBTC) produced a marked increase in mechanical sensitivity of the abdomen after the establishment of the model. During the first day to the sixth day in the fourth week, Gabapentin was administered intraperitoneally daily at a dose of 100mg/kg. The behavioral test began 1h after drug administration. The analgesic effect of gabapentin was not evident with a single injection, but gabapentin significantly reduced the responsive frequencies to mechanical stimulation in rats with chronic pancreatitis from the third day to the end of the experiment. To explore the underlying mechanisms, the expression of alpha(2)delta-1 calcium channel subunit was examined in the thoracic spinal cord (T8-11). There was no significant change in alpha(2)delta-1 level of T8-11 following the first injection. But after the sixth injection, the alpha(2)delta-1 level of T8-11 in rats with chronic pancreatitis was declined. Taken together, the present study suggested that repeated administration of gabapentin daily could reduce mechanical hypersensitivity in the upper abdomen and produce an analgesic effect in a rat model of chronic pancreatitis. The down-regulation of alpha(2)delta-1 calcium channel subunit might be one of the mechanisms underlying the analgesic effect of gabapentin.

Administration of midazolam in infancy does not affect learning and memory of adult mice.

1. Midazolam is a common fast-acting GABA(A) receptor agonist. Recent data suggest that exposure to midazolam in early life may cause long-term effects on brain function through stable epigenetic reprogramming. The aim of the present study was to determine whether the administration of midazolam to infant mice would affect their learning and memory in adulthood. 2. An open-field test was conducted before and then 3, 24, 48 and 72 h after administration of midazolam (50 mg/kg, i.p.) to infant mice. Saline control mice received an equal volume of saline i.p. 3 h before the open-field test. Total movements, total movement time, total movement distance and velocity were analysed. Novel object recognition (NOR), Morris water-maze and passive avoidance tests were performed when the treated mice grew to adulthood (105 days of age). 3. The results of open-field test showed that midazolam significantly reduced locomotor activity (total movements, total movement time, total movement distance and velocity) in infant mice 3 and 24 h after drug administration and that these effects had disappeared by 72 h after drug administration. The results of the water-maze, NOR and passive avoidance tests in adulthood (at 105 days of age) indicated that administration of midazolam in infancy had no long-term effects on the learning and memory behaviours of adult mice compared with the saline control. 4. Acute midazolam administration to infant mice affected spontaneous locomotor activity for approximately 2 days, but did not seem to have any significant impact on cognitive functioning that lasted into adulthood.

Blood serum profiling of the rat spinal nerve ligation model using ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry.

Peripheral nerve injury, which gives rise to persistent chronic pain, has become an area of intense research activity, largely because it represents a disorder with a high unmet medical need. In this study, serum biomarkers of the spinal nerve ligation model were successfully investigated with the metabolomic method. The regulatory effect of gabapentin, a novel clinical antineuralgia drug, on biomarker levels in serum was also investigated. Rat serum extract samples were analyzed by ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS). A method of supervised multivariate analysis, the partial least squares-discrimination analysis (PLS-DA), was used to validate metabolic changes. In addition, another multivariate method, the orthogonal partial least-squares analysis (OPLS), was used to monitor the real biological variability and to detect potential biomarkers in the spinal nerve ligation model. The results demonstrated that the spinal nerve ligation model had several discriminating ions compared with the control model. Among the detectable metabolites, levels of norepinephrine were increased in the spinal nerve ligation model and were decreased to control levels by gabapentin.

Edaravone, a free radical scavenger, is effective on neuropathic pain in rats.

Recent studies indicate that reactive oxygen species (ROS) are involved in persistent pain, including neuropathic and inflammatory pain. Edaravone, a free radical scavenger, which is widely used clinically in Japan for acute cerebral infarction to prevent ischemia reperfusion injury, has been shown to inhibit inflammatory-induced pain in rats. However, it is unknown whether edaravone is effective on neuropathic pain. In the present study, we used the spinal nerve ligation (SNL)-induced neuropathic pain model of rats to investigate the role of edaravone in the generation or development of neuropathic pain. Edaravone was administrated intraperitoneally per day at a dose of 4 mg/kg. We found that preemptive treatment of edaravone had analgesic effects on SNL-induced chronic pain without inducing any behavioral side-effects or motor disturbances at the dose given. By contrast, when administered on the third day after SNL surgery, edaravone cannot reverse the established pain but only produced tenuous analgesic effects on the rats of neuropathic pain. To explore the underlying mechanisms, effects of edaravone on the excitability of dorsal root ganglion (DRG) neurons and activation of JNK in DRG were observed. We found that preemptive edaravone treatment can decrease the H(2)O(2)-induced depolarization in the acutely dissociated DRG neurons. Furthermore, we found that preemptive edaravone treatment can reduce the SNL-induced pJNK expression in the ipsilateral DRG. Taken together, the present study indicated that edaravone could prevent the development of SNL-induced neuropathic pain but had little effects on the established neuropathic pain. The inhibition of the signaling pathway of JNK cascade or suppression of the possible ROS-induced hyper-excitability of DRG neurons might be, at least in part, mechanisms underlying the effects of edaravone on SNL-induced neuropathic pain.