Mechanical Allodynia In Rats Research Articles

Electroacupuncture ameliorates mechanical hypersensitivity by down-regulating spinal Janus kinase 2/signal transducer and activation of transcription 3 and interleukin 6 in rats with spared nerve injury.

Evidence shows that the Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway participates in the pathogenesis of neuropathic pain. Our previous study revealed that electroacupuncture (EA) attenuated neuropathic pain via activation of alpha-7 nicotinic acetylcholine receptor (α7nAChR) in the spinal cord. However, whether 2 Hz EA alleviates neuropathic pain by regulating the downstream molecules JAK2/STAT3 has not been fully clarified. Paw withdrawal threshold (PWT) was used as a marker of mechanical allodynia in rats with spared nerve injury (SNI). After applying 2 Hz EA on day 3, 7, 14 and 21 post-surgery, spinal expression of JAK2, STAT3 and pro-inflammatory cytokine interleukin (IL)-6 was examined using quantitative reverse transcription and real-time polymerase chain reaction (qRT-PCR) and Western blot analysis. Intrathecal injection of the α7nAChR antagonist alpha-bungarotoxin (α-Bgtx) was used to further explore the mechanism underlying the effects of 2 Hz EA on expression of JAK2/STAT3 in SNI rats. It was found that levels of spinal STAT3 and IL-6 mRNA, as well as levels of phosphorylated (p)-JAK2, p-STAT3 and IL-6 protein, were markedly increased in SNI rats. 2 Hz EA attenuated the SNI-induced up-regulation of p-JAK2, p-STAT3 and IL-6 expression in the spinal cord. Furthermore, intrathecal injection of α-Bgtx (1.0 μg/kg) not only inhibited the effect of 2 Hz EA on mechanical hypersensitivity but also ameliorated the down-regulation of p-JAK2, p-STAT3 and IL-6 expression induced by 2 Hz EA. This study revealed that 2 Hz EA attenuated SNI-induced mechanical hypersensitivity and the concomitant up-regulation of spinal JAK2, STAT3 and IL-6 in SNI rats, suggesting that suppression of the JAK2/STAT3 signaling pathway might be the mechanism underlying the therapeutic effect of 2 Hz EA on neuropathic pain.

Resveratrol alleviates diabetic mechanical allodynia in rats by downregulating P2X3R.

Mechanical allodynia, which develops in patients of diabetes mellitus as a neuropathic manifestation, remains without an effective treatment. The aim of the present study was to investigate the effects and potential mechanisms underlying resveratrol (RES) in a rat model of streptozocin (STZ)-induced diabetic mechanical allodynia (DMA). The rat model of DMA was established by the administration of an intraperitoneal injection of STZ. From day 8 post-STZ injection, rats were administered with an intragastric injection of various doses of RES for 14 consecutive days. The von Frey filaments were applied to detect the paw withdrawal threshold and evaluate the analgesic effects of RES. Based on the dose-effect curve, the ED50 of RES was calculated. Immunofluorescence staining and western blotting were performed to detect the expression of purinergic receptor P2X3 (P2X3R) in the dorsal root ganglion (DRG) and spinal dorsal horn (SDH) following RESED50 treatment. The results indicated that RES significantly alleviated mechanical allodynia in DMA model rats in a dose-dependent manner. Compared with the control group, the expression of P2X3R in DRG neurons and SDH terminals was markedly decreased following the administration of RESED50 (P<0.05). Collectively, the results indicated that RES displayed a dose-dependent analgesic effect on DMA model rats. Furthermore, P2X3R expression downregulation in the DRG and SDH may be a mechanism underlying the analgesic effects of RES on DMA-related behaviors.

&lt;p&gt;Wnt3a Inhibitor Attenuates Remifentanil-Induced Hyperalgesia via Downregulating Spinal NMDA Receptor in Rats&lt;/p&gt;

PurposeThe upregulation of spinal NMDA receptor is a crucial mechanism in remifentanil-induced hyperalgesia (RIH). Wnt3a/β-catenin pathway plays an important role in neuropathic pain. We hypothesized that wnt3a inhibitor (iwp-2) could downregulate the expression of NR2B subunit in NMDA receptor, in order to relieve RIH.Materials and MethodsThe study has 2 phases. The phase 1 study is designed by different doses of iwp-2 groups to create an appropriate iwp-2 dose used in RIH alleviation. The phase 2 study is designed to prove that the wnt3a inhibitor could downregulate the activation of the NR2B to inhibit RIH in rats. Thermal hyperalgesia (PWTL) and mechanical allodynia (PWMT) were evaluated after RIH. The area under the PWTL and PWMT curves (AUC) were calculated. The amount of activated NR2B subunit, c-fos, NF-κB, β-catenin, wnt3a and p-GSK-3β (Ser9) were detected in the lumbar spinal cord.ResultsRemifentanil infusion could induce overexpression of β-catenin and wnt3a in rats. Iwp-2 (60μM, 120μM, 180μM) could dose-dependently inhibit thermal hyperalgesia and mechanical allodynia in rats. In phase 2 study, both NR2B subunit antagonist Ro25-6981 and iwp-2 decreased the amount of activated NR2B, enhanced p-GSK-3β (Ser9), reduced β-catenin, c-fos and NF-κB in the lumbar spinal cord (p < 0.001). In comparison with the group iwp-2, the group of Ro25-6981 had more benefit in reversing hyperalgesia, including higher AUC value of PWTL (p = 0.022) and PWMT (p = 0.035).ConclusionRemifentanil exposure could induce overexpression of wnt3a and enhance the production of β-catenin in the spinal dorsal horn. Inhibition of wnt3a response was capable of attenuating RIH in alleviating hyperalgesia-related behavioral parameters, as well as reducing overexpression of c-fos, NF-κB, NR2B in spinal dorsal horn.

Photobiomodulation and B vitamins administration produces antinociception in an orofacial pain model through the modulation of glial cells and cytokines expression

Chronic constriction injury (CCI) of infraorbital nerve (IoN) results in whisker pad mechanical allodynia in rats and activation glial cells contributing to the development of orofacial pain. Whisker pad mechanical allodynia (von Frey stimuli) was tested pre and postoperatively and conducted during the treatment time. Photobiomodulation (PBM) and vitamins B complex (VBC) has been demonstrated therapeutic efficacy in ameliorate neuropathic pain. The aim of this study was to evaluate the antinociceptive effect of PBM, VBC or the combined treatment VBC ​+ ​PBM on orofacial pain due to CCI-IoN. Behavioral and molecular approaches were used to analyses nociception, cellular and neurochemical alterations. CCI-IoN caused mechanical allodynia and cellular alterations including increased expression of glial fibrillary acid protein (GFAP) and ionized calcium binding adaptor molecule 1 (Iba-1), administration of VBC (B1/B6/B12 at 180/180/1.8 ​mg/kg, s.c., 5 times all long 10 sessions) and PBM therapy (904 ​nm, power of 75Wpico, average power of 0.0434 ​W, pulse frequency of 9500 ​Hz, area of the beam 0.13 ​cm2, 18 ​s duration, energy density 6 ​J/cm2, with an energy per point of 0.78 ​J for 10 sessions) or their combination presented improvement of the nociceptive behavior and decreased expression of GFAP and Iba-1. Additionally, CCI-IoN rats exhibited an upregulation of IL1β, IL6 and TNF-α expression and all treatments prevented this upregulation and also increased IL10 expression. Overall, the present results highlight the pain reliever effect of VBC or PBM alone or in combination, through the modulation of glial cells and cytokines expression in the spinal trigeminal nucleus of rats.

Pyridin-2(1H)one derivatives: A possible new class of therapeutics for mechanical allodynia

Mechanical Allodynia (MA), a frequent chronic pain symptom caused by innocuous stimuli, constitutes an unmet medical need, as treatments using analgesics available today are not always effective and can be associated with important side-effects. A series of 3,5-disubstituted pyridin-2(1H)-ones was designed, synthesized and evaluated in vivo toward a rat model of inflammatory MA. We found that the series rapidly and strongly prevented the development of MA. 3-(2-Bromophenyl)-5-(phenylamino)pyridin-2(1H)-one 69, the most active compound of the series, was also able to quickly reverse neuropathic MA in rats. Next, when 69 was evaluated toward a panel of 50 protein kinases (PK) in order to identify its potential biological target(s), we found that 69 is a p38α MAPK inhibitor, a PK known to contribute to pain hypersensitivity in animal models. 3,5-Disubstituted pyridin-2(1H)-ones thus could represent a novel class of analgesic for the treatment of MA.

Inhibition of COX-2 alleviates lumbar spinal stenosis-induced chronic mechanical allodynia in rats

Chronic low back pain due to lumbar spinal stenosis (LSS) is common, costly, mechanistically complex, and clinically challenging. However, the factors and mechanisms causing and mediating chronic pain induced by cauda equina compression remain unclear. Here, we examined the role of cyclooxygenase (COX)-2 in infiltrated macrophages, a key mediator of inflammation, in chronic neuropathic pain by LSS using an animal model. LSS was induced in adult male rats by cauda equina compression procedure using a silicone block within the epidural spaces of L5-L6 vertebrae. Locomotor deficit was observed after compression and mechanical allodynia was developed progressively for 4 weeks after injury. A number of macrophage were also infiltrated into the spinal parenchyma and cauda equina and COX-2 was expressed in infiltrated macrophages at 28 days after cauda equina compression. The administration of COX-2 inhibitors, celecoxib and MPO-0029, significantly alleviated LSS-induced chronic mechanical allodynia and inhibited the mRNA expression of inflammatory mediators such as tnf-α, Il-1β, il-6, and inos. Furthermore, COX-2 inhibitors significantly reduced prostaglandin E2 production. These results demonstrated the role of COX-2 in LSS-induced chronic neuropathic pain and suggest that the regulation of COX-2 can be considered as a therapeutic target to relive neuropathic pain.

Comparing the Neuroprotective Efficacy of P7C3‐A20 to Novel P7C3 Derivatives in a Rodent Model of Paclitaxel‐Induced Peripheral Neuropathy

Chemotherapy‐induced peripheral neuropathy (CIPN) is a prevalent adverse effect of anti‐cancer chemotherapeutics like paclitaxel (PTX), a microtubule targeting agent known to induce severe and persistent neuropathic pain. The development of CIPN not only diminishes the quality of life of cancer patients, but also downgrades their cancer prognosis as dose reduction or cessation of their anti‐cancer regimen are the only clinical interventions currently available for CIPN. Thus, the development of a pharmacological intervention that limits the neuropathic side‐effects of anti‐cancer chemotherapy is urgently needed. Here we tested the neuroprotective effects of the aminopropyl carbazole, P7C3‐A20 (A20), and several A20 derivatives in a rat model of paclitaxel‐induced peripheral neuropathy. All experiments were done by investigators blinded to the drug treatments. Racemic A20 (2.2, 6.6, 20 mg/kg, i.p., q.d.), or vehicle, was administered daily to male Sprague‐Dawley rats over a 14‐day period beginning 2 days before PTX treatment (11.7 mg/kg/day, i.p.; every other day for 3 injections). A20 dose‐dependently attenuated PTX‐induced mechanical allodynia in rats. Evaluation of intraepidermal nerve fiber (IENF) density in rat paw biopsies using immunohistochemical staining revealed that treatment with PTX produced a profound loss in IENF density that was prevented by treatment with A20. Further, statistical analysis indicated strong correlations between IENF density, a diagnostic marker of CIPN in humans, and nociceptive threshold to mechanical stimuli. Enantiomer specific mixtures of A20 (20 mg/kg, i.p., q.d.), racemic A20 (20 mg/kg, i.p., q.d.), or vehicle were then administered utilizing the same behavioral paradigm and PTX dosing schedule as above. Consistent with our previous data, racemic A20 attenuated PTX‐induced mechanical allodynia and the S‐enantiomer was identified as the active component of the racemic mixture. We have also tested the neuroprotective efficacy of four novel A20 derivatives coded as compounds A through D. The A20 derivatives were administered daily at 20 mg/kg by i.p. injection and mechanical allodynia was assayed as described above. One compound, Drug C, provided robust protection against PTX‐induced mechanical allodynia, whereas the compounds A, B, and D demonstrated limited neuroprotective efficacy. Taken together, A20 and perhaps its derivatives are an exciting new class of pharmacological agents that may have clinical utility for alleviating peripheral neuropathies caused by various anti‐cancer chemotherapeutics.Support or Funding InformationSupported in part by Calico Life Sciences and Proneurotech.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

New pharmacological effect of fulvestrant to prevent oxaliplatin-induced neurodegeneration and mechanical allodynia in rats.

Oxaliplatin, which is widely used as chemotherapy for certain solid cancers, frequently causes peripheral neuropathy. Commonly described neuropathic symptoms include aberrant sensations such as mechanical allodynia (hypersensitivity to normally innocuous stimuli). Although oxaliplatin neuropathy is a dose-limiting toxicity, there are no established preventive strategies available at present. By screening several sets of small-molecule chemical libraries (more than 3,000 compounds in total) using a newly established in vitro high-throughput phenotypic assay, we identified fulvestrant, a clinically approved drug for the treatment of breast cancer in postmenopausal women, as having a protective effect on oxaliplatin-induced neuronal damage. Furthermore, histological and behavioural analyses using a rat model of oxaliplatin neuropathy demonstrated the in vivo efficacy of fulvestrant to prevent oxaliplatin-induced axonal degeneration of the sciatic nerve and mechanical allodynia. Furthermore, fulvestrant did not interfere with oxaliplatin-induced cytotoxicity against cancer cells. Thus, our findings reveal a previously unrecognised pharmacological effect of fulvestrant to prevent oxaliplatin-induced painful peripheral neuropathy without impairing its cytotoxicity against cancer cells and may represent a novel prophylactic option for patients receiving oxaliplatin chemotherapy.

Cannabinoid Type 2 Receptor System Modulates Paclitaxel-Induced Microglial Dysregulation and Central Sensitization in Rats

Paclitaxel induces microglial activation and production of proinflammatory mediators in the dorsal horn, which contribute to the development and maintenance of central sensitization and pain behavior. MDA7, 1-([3-benzyl-3-methyl-2,3-dihydro-1-benzofuran-6-yl]carbonyl) piperidine, is a novel highly selective cannabinoid type 2 (CB2) agonist. We tested the hypothesis that activation of CB2 receptor by MDA7 modulates microglial dysregulation, suppresses the overexpression of brain-derived neurotrophic factor (BDNF) in microglia in the dorsal horn, and attenuates the central sensitization and pain behavior induced by paclitaxel. For 4 consecutice days, groups of rats randomly received saline or 1.0 mg/kg of paclitaxel daily intraperitoneally for a total cumulative dose of 4 mg/kg. MDA7 15 mg/kg intraperitoneally or vehicle were administered 15 min before administering paclitaxel for 4 days and then continued for another 10 days. Behavioral and molecular studies were performed. Paclitaxel induced the expression of CB2 receptors and production of interleukin (IL)-6 in microglia in the dorsal horn. MDA7 attenuated the expression of IL-6 and promoted the expression of IL-10. Paclitaxel induced epigenetic upregulation of IRF8 and P2X purinoceptor 4 (P2X4) in microglia and subsequently increased the expression of alpha isoform of calcium/calmodulin-dependent protein kinase II (CaMKIIα), transcriptional factors p-CREB and ΔFosB, leading to the overproduction of BDNF in microglia. Paclitaxel also upregulated the expression of glutamate receptor subunits GluR1 and NR2B, decreased the expression of K+-Cl− cotransporter, and induced mechanical allodynia in rats. All of the aforementioned molecular changes were attenuated by MDA7. Our data show that MDA7 attenuated paclitaxel-induced molecular and behavioral changes in rats.Perspective: This study provides evidence that paclitaxel induced microglia dysregulation and epigenetically upregulated the microglial expression of BDNF, which led to sensitization of dorsal horn neurons and mechanical allodynia in rats. The CB2 agonist MDA7 alleviated these pathological processes. MDA7 represents an innovative therapeutic approach for treatment of chemotherapy-induced neuropathy.

A new central post-stroke pain rat model: autologous blood injected thalamic hemorrhage involved increased expression of P2X4 receptor

Stroke is the leading cause of disability and death in the world. Central post-stroke pain (CPSP), a central neuropathic pain syndrome occurring after cerebral stroke, is a serious problem. But on account of the lack of reliable animal models, the mechanisms underlying CPSP remains poorly understood. To better understand of the pathophysiological basis of CPSP, we developed and characterized a new rat model of CPSP. This model is based on a hemorrhagic stroke lesion with intra-thalamic autologous blood (ITAB) injection in the ventral posterolateral nucleus of the thalamus. Behavioral analysis demonstrated that the animals displayed a significant decrease in mechanical allodynia threshold. We found a significant increase in P2 × 4 receptor expression in microglia in thalamic peri-lesion tissues post-hemorrhage. The mechanical allodynia in rats with CPSP were reversed by blocking P2 × 4 receptors. A significant alleviation of mechanical allodynia was achieved following the administration of adrenergic antidepressants and antiepileptics. Meanwhile, we found a significant decrease in P2 × 4 receptor expression after treatment with these drugs. Taken together, our results suggest that targeting P2 × 4 receptor may be effective in the treatment of CPSP.

Effects of systemic inhibitors of acid-sensing ion channels 1 (ASIC1) against acute and chronic mechanical allodynia in a rodent model of migraine.

Acid-sensing ion channels (ASICs) are neuronal proton sensors emerging as potential therapeutic targets in pain of the orofacial region. Amiloride, a non-specific ASIC blocker, has been shown to exert beneficial effects in animal models of migraine and in patients. We explored the involvement of the ASIC1-subtype in cutaneous allodynia, a hallmark of migraine affecting cephalic and extra-cephalic regions in about 70% of migrainers. We investigated the effects of systemic injections of amiloride and mambalgin-1, a specific inhibitor of ASIC1a- and ASIC1b-containing channels, on cephalic and extra-cephalic mechanical sensitivity in a rodent model of acute and chronic migraine induced by i.p. injections of isosorbide dinitrate. I.v. injections of these inhibitors reversed cephalic and extra-cephalic acute cutaneous mechanical allodynia in rats, a single injection inducing a delay in the subsequent establishment of chronic allodynia. Both mambalgin-1 and amiloride also reversed established chronic allodynia. The anti-allodynic effects of mambalgin-1 were not altered in ASIC1a-knockout mice, showing the ASIC1a subtype is not involved in these effects which were comparable to those of the anti-migraine drug sumatriptan and of the preventive drug topiramate on acute and chronic allodynia respectively. A single daily injection of mambalgin-1 also had a significant preventive effect on allodynia chronification. These pharmacological data support the involvement of peripheral ASIC1-containing channels in migraine cutaneous allodynia as well as in its chronification. They highlight the therapeutic potential of ASIC1 inhibitors as both an acute and prophylactic treatment for migraine.

Jingshu Keli attenuates cervical spinal nerve ligation-induced allodynia in rats through inhibition of spinal microglia and Stat3 activation.

Cervical radicular pain resulting from mechanical compression of a spinal nerve secondary to spinal degenerative alternations negatively impacts patients' quality of life. Jingshu Keli (JSKL), a traditional Chinese medicine formula with multiple active compounds, has been prescribed for pain management in patients with cervical radiculopathy for decades. Two major components of JSKL, ferulic acid and cinnamaldehyde, were identified to have anti-inflammation effect via inhibiting activation of Stat3. To investigate the efficacy of JSKL by investigating its mechanism in attenuating cervical radiculopathy-induced mechanical allodynia via modulation activation of spinal microglia and phosphorylation of signal transducer and activator of transcription 3 (Stat3). An in vivo animal experiment. Cervical radiculopathy of rats was established by C7 spinal nerve ligation (SNL) with 6-0 silk suture. The effect of postoperational daily gavage of JSKL on mechanical allodynia of rats was tested on day 3, 7, and 14 after surgery. Furthermore, spinal glial cells activation and phosphorylation of Stat3 (p-Stat3) were tested with immunofluorescence imaging and Western blot. The JSKL significantly inhibited SNL-induced allodynia as well as microglia activation in the spinal cord on day 7 and 14 after surgery. Moreover, expression of p-Stat3 was decreased in rats with SNL and JSKL treatment in comparison with rats with SNL and vehicle treatment. The JSKL attenuated SNL-induced mechanical allodynia in rats. This analgesic effect might be explained by the suppression of activations of spinal microglia as well as p-Stat3. Our study provides experimental evidence for JSKL as an alternative approach to manage refractory pain in patients with cervical radiculopathy.

Orientin and neuropathic pain in rats with spinal nerve ligation

Neuropathic pain affects patients worldwide. The therapeutic effects of current methods are still poor. This study was performed to investigate the neuro-protective effect of orientin in rats with spinal nerve ligation (SNL). In this study, the paw mechanical withdrawal threshold (PWT) and the paw thermal withdrawal latency (PWL) behavioral assays indicated that orientin alleviated the warm and mechanical allodynia in rats with SNL. The enzyme-linked immunosorbent assay (ELISA) showed that orientin suppressed the levels of pro-inflammatory cytokines interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor alpha (TNF-α) and increased the levels of anti-inflammatory cytokine interleukin-10 (IL-10). Malondialdehyde (MDA) levels were down-regulated while superoxide dismutase (SOD) and glutathione (GSH) levels were up-regulated by orientin. OX42 and GFAP immune fluorescent staining results demonstrated that orientin inhibited the activation of microglia and astrocytes in rats with SNL. Western blot analysis indicated that the neuroprotective effect of orientin was mediated by inhibition of Toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-kappa B) signaling pathway. This study suggested that orientin is a promising neuroprotective agent suitable for therapy for neuropathic pain.

Nuclear factor kappa B regulated monocyte chemoattractant protein-1/chemokine CC motif receptor-2 expressing in spinal cord contributes to the maintenance of cancer-induced bone pain in rats.

Background: Chemokine, monocyte chemoattractant protein-1 (MCP-1), is a potential factor to cause cancer-induced bone pain (CIBP). NF-κB signaling is very important in mediating the expression of chemokines and may have a role in CIBP. However, the mechanism is still unclear. This study investigates the role of NF-κB in CIBP by regulating MCP-1/chemokine CC motif receptor-2 (CCR2) signaling pathway.Methods: A rat CIBP model was established by injecting Walker-256 cells into the tibia medullary cavity. Nine days later, animals were intrathecally administrated with MCP-1 neutralizing antibody, CCR2 antagonist (RS504393), or NF-кB inhibitor (BAY11–7081). Mechanical paw withdrawal threshold was used to assess pain behavior and sciatic functional index, and radiographic images were adopted to evaluate the damage of nerve and bone. The spinal cords were harvested for Western blot and quantitative reverse transcription polymerase chain reaction. The distribution of MCP-1, CCR2, and NF-кB was detected by double immunofluorescent staining.Results: CIBP caused remarkable bone destruction, injury of sciatic and femoral nerve, and persistent (>15 days) mechanical allodynia in rats. Tumor cell inoculation upregulate MCP-1 and NF-кB in activated neurons as well as CCR2 in neurons and microglia of the spinal cord. MCP-1 antibody, RS504393, and BAY11–7081 partially reversed CIBP-induced mechanical allodynia, and CIBP regulated the expression levels of pro-inflammatory cytokines, tumor necrosis factor-α and interferon-γ, and anti-inflammatory cytokine, interleukin 4, and BAY11–7081 lowered CIBP-induced MCP-1 and CCR2 expressions in a dose-dependent manner.Conclusion: In conclusion, NF-кB signaling pathway regulates the expressions of MCP-1/CCR2-induced inflammatory factors in the spinal cord of CIBP rats.

Sinomenine attenuates cancer-induced bone pain via suppressing microglial JAK2/STAT3 and neuronal CAMKII/CREB cascades in rat models.

Cancer-induced bone pain is one of the most severe types of pathological pain, which often occurs in patients with advanced prostate, breast, and lung cancer. It is of great significance to improve the therapies of cancer-induced bone pain due to the opioids’ side effects including addiction, sedation, pruritus, and vomiting. Sinomenine, a traditional Chinese medicine, showed obvious analgesic effects on a rat model of chronic inflammatory pain, but has never been proven to treat cancer-induced bone pain. In the present study, we investigated the analgesic effect of sinomenine after tumor cell implantation and specific cellular mechanisms in cancer-induced bone pain. Our results indicated that single administration of sinomenine significantly and dose-dependently alleviated mechanical allodynia in rats with cancer-induced bone pain and the effect lasted for 4 h. After tumor cell implantation, the protein levels of phosphorylated-Janus family tyrosine kinase 2 (p-JAK2), phosphorylated-signal transducers and activators of transcription 3 (p-STAT3), phosphorylated-Ca2+/calmodulin-dependent protein kinase II (p-CAMKII), and phosphorylated-cyclic adenosine monophosphate response element-binding protein (p-CREB) were persistently up-regulated in the spinal cord horn. Chronic intraperitoneal treatment with sinomenine markedly suppressed the activation of microglia and effectively inhibited the expression of JAK2/STAT3 and CAMKII/CREB signaling pathways. We are the first to reveal that up-regulation of microglial JAK2/STAT3 pathway are involved in the development and maintenance of cancer-induced bone pain. Moreover, our investigation provides the first evidence that sinomenine alleviates cancer-induced bone pain by inhibiting microglial JAK2/STAT3 and neuronal CAMKII/CREB cascades.

Preemptive application of QX-314 attenuates trigeminal neuropathic mechanical allodynia in rats.

The aim of the present study was to examine the effects of preemptive analgesia on the development of trigeminal neuropathic pain. For this purpose, mechanical allodynia was evaluated in male Sprague-Dawley rats using chronic constriction injury of the infraorbital nerve (CCI-ION) and perineural application of 2% QX-314 to the infraorbital nerve. CCI-ION produced severe mechanical allodynia, which was maintained until postoperative day (POD) 30. An immediate single application of 2% QX-314 to the infraorbital nerve following CCI-ION significantly reduced neuropathic mechanical allodynia. Immediate double application of QX-314 produced a greater attenuation of mechanical allodynia than a single application of QX-314. Immediate double application of 2% QX-314 reduced the CCI-ION-induced upregulation of GFAP and p-p38 expression in the trigeminal ganglion. The upregulated p-p38 expression was co-localized with NeuN, a neuronal cell marker. We also investigated the role of voltage-gated sodium channels (Navs) in the antinociception produced by preemptive application of QX-314 through analysis of the changes in Nav expression in the trigeminal ganglion following CCI-ION. Preemptive application of QX-314 significantly reduced the upregulation of Nav1.3, 1.7, and 1.9 produced by CCI-ION. These results suggest that long-lasting blockade of the transmission of pain signaling inhibits the development of neuropathic pain through the regulation of Nav isoform expression in the trigeminal ganglion. Importantly, these results provide a potential preemptive therapeutic strategy for the treatment of neuropathic pain after nerve injury.

Excessive spinal glutamate transmission is involved in oxaliplatin-induced mechanical allodynia in rats

Excessive spinal glutamate transmission is involved in oxaliplatin-induced mechanical allodynia in rats

Neural Mobilization Attenuates Mechanical Allodynia and Decreases Proinflammatory Cytokine Concentrations in Rats With Painful Diabetic Neuropathy.

Painful diabetic neuropathy (PDN) is a common complication in patients with diabetes. It is related to ischemic nerve damage and the increase in the levels of proinflammatory mediators, such as tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β). Neural mobilization may have the potential to alleviate PDN, but it has not yet been tested. Also, the physiological mechanism of neural mobilization is unclear. The objective of this study was to investigate treatment effect and physiological mechanism of neural mobilization. This was an experimental study using rats with streptozocin (or streptozotocin)-induced type 1 diabetes. Three groups were used in the study, the control group (vehicle), the diabetes group (PDN group), and the neural mobilization treatment group (PDN-NM group) (n = 6). Rats in the vehicle group were healthy rats. Rats in the PDN and PDN-NM groups were rats with diabetes. Rats in the PDN-NM group received treatment in the right sciatic nerve, whereas rats in the PDN group did not. Mechanical pain sensitivity and the levels of IL-1β and TNF-α in the sciatic nerve branches and trunk, the L4 to L6 dorsal horn ganglion, and the spinal cord dorsal horn were measured. Techanical allodynia was alleviated after treatment, but the effect was limited to the treatment side. The concentrations of proinflammatory cytokines were decreased in the nerves that received treatment compared with those on the other side, indicating that neural mobilization may reduce mechanical sensitivity by decreasing the concentrations of local sensitizing agents. A limitation of this study was that no direct measurement of nerve blood flow was done. The results of this study showed that neural mobilization effectively alleviated mechanical allodynia in rats with PDN. The side that received treatment had lower concentrations of TNF-α and IL-1β in the sciatic nerve branches and sciatic nerve trunk; this result may have been related to the alleviation of mechanical allodynia.

Oligodendrocyte precursor cell transplantation promotes functional recovery following contusive spinal cord injury in rats and is associated with altered microRNA expression.

It has been reported that oligodendrocyte precursor cells (OPCs) may be used to treat contusive spinal cord injury (SCC), and may alter microRNA (miRNA/miR) expression following SCC in rats. However, the association between miRNA expression and the treatment of rats with SCC with OPC transplantation remain unclear. The present study transplanted OPCs into the spinal cord of rats with SCC and subsequently used the Basso, Beattie and Bresnahan (BBB) score to assess the functional recovery and pain scores. An miRNA assay was performed to detect differentially expressed miRNAs in the spinal cord of SCC rats transplanted with OPCs, compared with SCC rats transplanted with medium. Quantitative polymerase chain reaction was used to verify significantly altered miRNA expression levels. The results demonstrated that OPC transplantation was able to improve motor recovery and relieve mechanical allodynia in rats with SCC. In addition, through a miRNA assay, 45 differentially expressed miRNAs (40 upregulated miRNAs and 5 downregulated miRNAs) were detected in the spinal cord of rats in the OPC group compared with in the Medium group. Differentially expressed miRNAs were identified according to the following criteria: Fold change >2 and P<0.05. Furthermore, quantitative polymerase chain reaction was used to verify the most highly upregulated (miR-375-3p and miR-1-3p) and downregulated (miR-363-3p, miR-449a-5p and miR-3074) spinal cord miRNAs that were identified in the miRNA assay. In addition, a bioinformatics analysis of these miRNAs indicated that miR-375 and miR-1 may act primarily to inhibit cell proliferation and apoptosis via transcriptional and translational regulation, whereas miR-363, miR-449a and miR-3074 may act primarily to inhibit cell proliferation and neuronal differentiation through transcriptional regulation. These results suggested that OPC transplantation may promote functional recovery of rats with SCC, which may be associated with the expression of various miRNAs in the spinal cord, including miR-375-3p, miR-1-3p, miR-363-3p, miR-449a-5p and miR-3074.

Reactive oxygen species scavengers ameliorate mechanical allodynia in a rat model of cancer-induced bone pain

Cancer-induced bone pain (CIBP) is a frequent complication in patients suffering from bone metastases. Previous studies have demonstrated a pivotal role of reactive oxygen species (ROS) in inflammatory and neuropathic pain, and ROS scavengers exhibited potent antinociceptive effect. However, the role of spinal ROS remains unclear. In this study, we investigated the analgesic effect of two ROS scavengers in a well-established CIBP model. Our results found that intraperitoneal injection of N-tert-Butyl-α-phenylnitrone (PBN, 50 and 100mg/kg) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol, 100 and 200mg/kg) significantly suppressed the established mechanical allodynia in CIBP rats. Moreover, repeated injection of PBN and Tempol showed cumulative analgesic effect without tolerance. However, early treatment with PBN and Tempol failed to prevent the development of CIBP. Naive rats received repetitive injection of PBN and Tempol showed no significant change regarding the nociceptive responses. Finally, PBN and Tempol treatment notably suppressed the activation of spinal microglia in CIBP rats. In conclusion, ROS scavengers attenuated established CIBP by suppressing the activation of microglia in the spinal cord.