Neuropathic Pain In Rats Research Articles

Microinjection of histamine and its H3 receptor agonist and antagonist into the agranular insular cortex influence sensory and affective components of neuropathic pain in rats

Many areas of the brain along with neurotransmitters involve in processing of nociceptive, emotional and cognitive dimensions of neuropathic pain. Brian neuronal histamine through H1, H2, H3 and H4 receptors mediates many physiological functions such as cognition, emotion and pain. In the present study we investigated the effects of intra-agranular insular cortex microinjection of histamine and its H3 receptor agonist and antagonist on sensory and affective aspects of neuropathic pain. Spared nerve injury model of neuropathic pain was used. Two guide cannulas were surgically implanted in the right and left sides of agranular insular cortex. Sensory component (mechanical hyperalgesia) was recorded by application of von Frey filaments onto the plantar surface of the hind paw. Area under curve of mechanical hyperalgesia was calculated. Affective aspect (place escape avoidance paradigm) was recorded using an inverse white/black chamber. Histamine (0.5, 1 and 2 μg/site) and thioperamide (a histamine H3 receptor antagonist, 4 μg/site) decreased, whereas immepip (a histamine H3 receptor agonist, 2 μg/site) increased the percentages of paw withdrawal frequency and time spent in white side of white/black box. Prior administration of thioperamide (4 μg/site) increased the suppressive effects induced by histamine and inhibited immepip (2 μg/site)-induced hyperalgesia and aversion. Based on the present results, it is concluded that histamine and its H3 receptor at the agranular insular cortex level may involve in modulation of sensory and affective components of neuropathic pain.

In search of a rodent model of placebo analgesia in chronic orofacial neuropathic pain

All treatments are given in a context, suggesting that conditioning cues may significantly influence therapeutic outcomes. We tested the hypothesis that context affects placebo analgesia in rodents. To produce neuropathic pain in rats, we performed chronic constriction injury of the infraorbital nerve. We then treated the rats daily, over a seven day period, with injections of either fentanyl or saline, with or without associated conditioning cues; a fourth group received no treatment. On the eighth day, we replaced fentanyl with saline to test for conditioned placebo analgesia.We tested the effects of treatment by measuring sensitivity to mechanical stimuli and grimace scale scores. We found no significant differences in either of these outcomes among the four experimental groups. These findings suggest that chronic, neuropathic pain in rats may not be susceptible to placebo analgesia.

MiR-30b-5p attenuates oxaliplatin-induced peripheral neuropathic pain through the voltage-gated sodium channel Nav1.6 in rats

Oxaliplatin is a third-generation derivative of platinum that is effective in the treatment of multiple solid tumors. However, it can cause peripheral neuropathic pain, and the molecular mechanisms of this effect remain unknown. We induced a model of peripheral neuropathic pain in rats by intraperitoneally injecting them with oxaliplatin twice a week for 4.5 weeks. We found that both the mRNA and protein expression levels of Nav1.6 (encoded by the gene Scn8a) increased while the miR-30b-5p (shorthand for miR-30b) expression decreased in the dorsal root ganglion (DRG) of treated rats. Using TargetScan and miRanda predictive software, we discovered that Scn8a was a major target of miR-30b. Moreover, we found that miR-30b negatively regulated Scn8a by binding to the Scn8a 3′UTR in PC12 cells. In addition, Nav1.6 and miR-30b were colocalized in the DRG neurons of naive rats. Overexpression of miR-30b using an miR-30b agomir attenuated neuropathic pain induced by oxaliplatin and inhibited both the mRNA and protein expression levels of Nav1.6 both in vitro and in vivo. Conversely, the inhibition of miR-30b with an miR-30b antagomir resulted in neuropathic pain and an increase in the expression of Nav1.6. More importantly, overexpression of miR-30b inhibited the proliferation of LS-174t cells (Colorectal cancer cells). These data suggest that miR-30b contributes to oxaliplatin-induced chronic neuropathic pain through Nav1.6 downregulation and could be a novel therapeutic target for the treatment of oxaliplatin-induced neuropathic pain as a side effect of chemotherapy in cancer patients.

PINK1 mediates spinal cord mitophagy in neuropathic pain.

Background: Mitophagy is the selective engulfment of mitochondria by autophagosomes and the subsequent mitochondrial catabolism by lysosomes. Evidence has suggested an important role for mitochondrial dynamics and mitophagic flux in the development of many different neurodegenerative diseases.Objectives: The potential role of the mechanism underlying mitochondrial dynamics and mitophagic flux as it may relate to neuropathic pain is not well understood. This is a disease that largely remains an area of mechanistic uncertainty. PINK1 is a PTEN-induced mitochondrial kinase that can be selectively activated under mitochondrial stress conditions and lead to the induction of mitophagy.Materials and methods: A neuropathic pain rat model was established via spinal nerve ligation (SNL) and nociception was assayed via the von Frey filament method. Increased expression of PINK1 and the mechanism of mitophagy was detected in GABAergic interneurons of dorsal horn neurons of mice that underwent L5 SNL in comparison to control mice counterparts (n=8, P<0.001) by Western blotting, immunohistochemistry and double immunofluorescence staining.Results: Elevated expression of PINK1 appeared to localize selectively to GABAergic interneurons, particularly within autophagic mitochondria as evidenced by co-localization studies of PINK1 with BECN1, LC3II and COX IV on immunofluorescent microscopy. Furthermore, we also detected a significant increase in autophagosomes in dorsal horn neurons of SNL mice and this was consistent with increased autophagic activity as measured by the p62 autophagic substrate.Conclusion: These results demonstrate that neuropathic pain causes aberrant mitophagic flux selectively in GABAergic interneurons and provide evidence implicating mitophagy as an important area of future molecular studies to enhance our understanding of neuropathic pain.

Microglial BDNF, PI3K, and p-ERK in the Spinal Cord Are Suppressed by Pulsed Radiofrequency on Dorsal Root Ganglion to Ease SNI-Induced Neuropathic Pain in Rats.

Background Pulsed radiofrequency (PRF) on the dorsal root ganglion (DRG) has been applied to alleviate neuropathic pain effectively, yet the mechanisms underlying pain reduction owing to this treatment are not clarified completely. The activated microglia, brain-derived neurotrophic factor (BDNF), phosphatidylinositol 3-kinase (PI3K), and phosphorylated extracellular signal-regulated kinase (p-ERK) in the spinal cord were demonstrated to be involved in developing neuropathic pain. Also, it has been just known that PRF on DRG inhibits the microglial activation in nerve injury rats. Here, we aim to investigate whether PRF treatment could regulate the levels of BDNF, PI3K, and p-ERK in the spinal cord of rats with spared nerve injury (SNI) via suppressing the spinal microglia activation to ease neuropathic pain. Methods The rats with SNI were intrathecally treated with minocycline (specific microglia inhibitor) or same volume of dimethyl sulfoxide once daily, beginning from 1 h before nerve transection to 7 days. PRF was applied adjacent to the L4-L5 DRG of rats with SNI at 45 V for 6 min on the seventh postoperative day, whereas the free-PRF rats were treated without PRF. The withdrawal thresholds were studied, and the spinal levels of ionized calcium-binding adapter molecule 1 (Iba1), BDNF, PI3K, and p-ERK were calculated by western blot analysis, reverse transcription-polymerase chain reaction, and immunofluorescence. Results The paw withdrawal mechanical threshold and paw withdrawal thermal latency decreased in the ipsilateral hind paws after SNI, and the spinal levels of Iba1, BDNF, PI3K, and p-ERK increased on day 21 after SNI compared with baseline (P < 0.01). An intrathecal injection of minocycline led to the reversal of SNI-induced allodynia and increase in levels of Iba1, BDNF, PI3K, and p-ERK. Withdrawal thresholds recovered partially after a single PRF treatment for 14 days, and SNI-induced microglia hyperactivity, BDNF upregulation, and PI3K and ERK phosphorylation in the spinal cord reduced on D14 due to the PRF procedure. Conclusion Microglial BDNF, PI3K, and p-ERK in the spinal cord are suppressed by the therapy of PRF on DRG to ease SNI-induced neuropathic pain in rats.

Dose-Dependent Effect of Hyperbaric Oxygen Treatment on Burn-Induced Neuropathic Pain in Rats.

Hyperbaric oxygen treatment (HBOT) has been used to reduce neuropathic pain. Melatonin and opioid receptors are involved in neuropathic pain, but it is not known if HBOT works through these pathways to achieve its antinociceptive effect. We divided anesthetized rats into two treatment and three sham groups. The two treatment groups received third-degree burns on their right hind paws, one treated in a hyperbaric chamber for a week and the other for two weeks. We evaluated the mechanical paw-withdrawal threshold (MWT) and expression of melatonin receptor 1 (MT1), melatonin receptor 2 (MT2), μ (MOR) and κ (KOR) opioid receptor, brain-derived neurotrophic factor (BDNF), Substance P, and calcitonin gene-related peptide (CGRP) in cuneate nucleus, dorsal horn, and hind paw skin by immunohistochemical, immunofluorescence assays and real-time quantitative polymerase chain reaction (RT-PCR). The group receiving one-week HBOT had increased expressions of MT1, MT2, MOR and KOR and decreased expressions of BDNF, Substance P, and CGRP. Their mechanically measured pain levels returned to normal within a week and lasted three weeks. This anti-allodynia effect lasted twice as long in those treated for two weeks. Our findings suggest that increasing the duration of HBOT can reduce burn-induced mechanical allodynia for an extended period of time in rats. The upregulation of melatonin and opioid receptors observed after one week of HBOT suggests they may be partly involved in attenuation of the mechanical allodynia. Downregulation of BDNF, substance P and CGRP may have also contributed to the overall beneficial effect of HBOT.

Dehydrocrenatidine Inhibits Voltage-Gated Sodium Channels and Ameliorates Mechanic Allodia in a Rat Model of Neuropathic Pain.

Picrasma quassioides (D. Don) Benn, a medical plant, is used in clinic to treat inflammation, pain, sore throat, and eczema. The alkaloids are the main active components in P. quassioides. In this study, we examined the analgesic effect of dehydrocrenatidine (DHCT), a β-carboline alkaloid abundantly found in P. quassioides in a neuropathic pain rat model of a sciatic nerve chronic constriction injury. DHCT dose-dependently attenuated the mechanic allodynia. In acutely isolated dorsal root ganglion, DHCT completely suppressed the action potential firing. Further electrophysiological characterization demonstrated that DHCT suppressed both tetrodotoxin-resistant (TTX-R) and sensitive (TTX-S) voltage-gated sodium channel (VGSC) currents with IC50 values of 12.36 μM and 4.87 µM, respectively. DHCT shifted half-maximal voltage (V1/2) of inactivation to hyperpolarizing direction by ~16.7 mV in TTX-S VGSCs. In TTX-R VGSCs, DHCT shifted V1/2 of inactivation voltage to hyperpolarizing direction and V1/2 of activation voltage to more depolarizing potential by ~23.9 mV and ~12.2 mV, respectively. DHCT preferred to interact with an inactivated state of VGSCs and prolonged the repriming time in both TTX-S and TTX-R VGSCs, transiting the channels into a slow inactivated state from a fast inactivated state. Considered together, these data demonstrated that the analgesic effect of DHCT was likely though the inhibition of neuronal excitability.

Effects of resveratrol in the signaling of neuropathic pain involving P2X3 in the dorsal root ganglion of rats.

Neuropathic pain is a major public health problem because it has a considerable impact on life quality of patients. Neuropathic pain caused by a lesion or disease of the somatosensory nervous system, which causes unpleasant and abnormal sensation (dysesthesia), an increased response to painful stimuli (hyperalgesia), and pain in response to a stimulus that does not normally provoke pain (allodynia). P2X receptors from dorsal root ganglion (DRG) play a crucial role in facilitating pain transmission at peripheral and spinal sites. Resveratrol (Res) has neuroprotective effects and improves the pathological and behavioral outcomes of various types of nerve injury. The present study examined the effects of Res on neuropathic pain. Neuropathic pain animal model was created by partial sciatic nerve ligation (pSNL) surgery. We found that consecutive intraperitoneal administration of Res for 21 days reduced the mechanical and thermal nociceptive responses induced by pSNL in a dose-dependent manner. Moreover, Res administration reversed P2X3 expression and phosphorylation of ERK in DRG neurons after peripheral nerve injury. Our results suggested that Res may ameliorate neuropathic pain by suppressing P2X3 up-regulation and ERK phosphorylation in DRG of neuropathic pain rats. Therefore, we concluded that Res has a significant analgesic effect on alleviating neuropathic pain, and thus may serve as a therapeutic approach for neuropathic pain.

Alleviation of trigeminal neuropathic pain by electroacupuncture: the role of hyperpolarization-activated cyclic nucleotide-gated channel protein expression in the Gasserian ganglion.

The aim of this study was to examine the effect of electroacupuncture (EA) on trigeminal neuropathic pain in rats and explore the potential mechanism underlying the putative therapeutic effect of EA. Trigeminal neuropathic pain behavior was induced in rats by unilateral chronic constriction injury of the distal infraorbital nerve (dIoN-CCI). EA was administered at ST2 (Sibai) and Jiachengjiang. A total of 60 Sprague Dawley rats were divided into the following four groups (n = 15 per group) to examine the behavioral outcomes after surgery and/or EA treatment: sham (no ligation); dIoN-CCI (received isoflurane only, without EA treatment); dIoN-CCI+EA-7d (received EA treatment for 7 days); and dIoN-CCI+EA-14d (received EA treatment for 14 days). Both evoked and spontaneous nociceptive behaviors were measured. Of these, 12 rats (n = 4 from sham, dIoN-CCI, and dIoN-CCI+EA-14d groups, respectively) were used to analyze protein expression of hyperpolarization-activated cyclic nucleotide-gated (HCN) channel in the Gasserian ganglion (GG) by immunohistochemistry. dIoN-CCI rats exhibited mechanical allodynia and increased face-grooming activity that lasted at least 35 days. EA treatment reduced mechanical allodynia and face-grooming in dIoN-CCI rats. Overall, 14 days of EA treatment produced a prolonged anti-nociceptive effect as compared to 7-day EA treatment. The counts of HCN1 and HCN2 immunopositive puncta were increased in the ipsilateral GG in dIoN-CCI rats and were reduced by 14 days of EA treatment. EA treatment relieved trigeminal neuropathic pain in dIoN-CCI rats, and this effect was dependent on the duration of EA treatment. The downregulation of HCN expression may contribute to the anti-nociceptive effect of EA in this rat model of trigeminal neuropathic pain.

Inhibition of apoptosis signal-regulating kinase by paeoniflorin attenuates neuroinflammation and ameliorates neuropathic pain

BackgroundNeuropathic pain is a serious clinical problem that needs to be solved urgently. ASK1 is an upstream protein of p38 and JNK which plays important roles in neuroinflammation during the induction and maintenance of chronic pain. Therefore, inhibition of ASK1 may be a novel therapeutic approach for neuropathic pain. Here, we aim to investigate the effects of paeoniflorin on ASK1 and neuropathic pain.MethodsThe mechanical and thermal thresholds of rats were measured using the Von Frey test. Cell signaling was assayed using western blotting and immunohistochemistry.ResultsChronic constrictive injury (CCI) surgery successfully decreased the mechanical and thermal thresholds of rats and decreased the phosphorylation of ASK1 in the rat spinal cord. ASK1 inhibitor NQDI1 attenuated neuropathic pain and decreased the expression of p-p38 and p-JNK. Paeoniflorin mimicked ASK1 inhibitor NQDI1 and inhibited ASK1 phosphorylation. Paeoniflorin decreased the expression of p-p38 and p-JNK, delayed the progress of neuropathic pain, and attenuated neuropathic pain. Paeoniflorin reduced the response of astrocytes and microglia to injury, decreased the expression of IL-1β and TNF-α, and downregulated the expression of CGRP induced by CCI.ConclusionsPaeoniflorin is an effective drug for the treatment of neuropathic pain in rats via inhibiting the phosphorylation of ASK1, suggesting it may be effective in patients with neuropathic pain.

Resveratrol alleviated paclitaxel-induced neuropathic pain by silent information regulator 2-related enzymes 1/peroxisome proliferator-activated receptor-gamma coactivator 1α signaling pathway

Objective To investigate the effect of resveratrol (Res) on paclitaxel-induced neuropathic pain in rats by silent information regulator 2-related enzymes 1/peroxisome proliferator-activated receptor-gamma coactivator 1α (SIRT1/PGC1α) signaling pathway. Methods Fifty male Sprague-Dawley rats (weighing 180-200 g), after intrathecal intubation, were randomly assigned into five groups (n=10): control group (C group), paclitaxel group (P group), Res group (R group), Res pretreated group (R+ P group) and EX-527 (the specific inhibitor of SIRT1) + Res pretreated group (E+ R+ P group). Paclitaxel (2 mg/kg) was intraperitoneally injected on the 1st, 3rd, 5th and 7 day. Res (intraperitoneal injection, 40 mg/kg) and EX-527 (intrathecal injection, 10 μg/10 μl) were administered daily from the 1st day to the 14th day. We measured 50% paw withdrawal mechanical threshold (PWT) at three time points: 1 day before chemotherapy (T0), 8 days after chemotherapy (T1) and 14 days after chemotherapy (T2). The corpus striatum was harvested at the 15th day after paclitaxel intraperitoneal injection. Transmission electron microscope was applied to observe the mitochondrial histomorphology in five groups. The cell apoptosis in the corpus striatum was measured by terminal-deoxynucleotidyl transferase mediated nick end labeling (TUNEL). The expression of SIRT1 and PGC1α was detected using Western blotting. The levels of IL-1β and IL-10 in the corpus striatum were determined by enzyme linked immunosorbent assay (ELISA). Results At T2, as compared with C group (13.1±1.0), the PWT in P group and E+ R+ P group was decreased to (6.2±1.0) and (5.6±3.4) respectively (P<0.05); as compared with P group, the PWT in R+ P group was increased to (14.3±2.7) (P<0.05). In P group and E+ R+ P group, we observed swellings and vacuolations in the mitochondria, and these changes in R+ P group was alleviated. As compared with C group, the apoptosis cells in the corpus striatum were increased in P group (P<0.05), and they were significantly reduced in R+ P group as compared with P group (P<0.05). As compared with levels of SIRT1 (0.650±0.074) and PGC1α (0.590±0.057) in C group, the expression levels of SIRT1 and PGC1α in P group were decreased to (0.320±0.032) and (0.200±0.067) respectively (P<0.05); as compare with P group, the expression levels of SIRT1 and PGC1α in R+ P group were increased to (0.530±0.010) and (0.530±0.041) respectively (P<0.05). As compared with IL-1β (7.57±0.09) pg/ml and IL-10 (32.65±0.16) pg/ml in C group, the levels of IL-1β in P group were increased to (15.11±0.20) pg/ml (P<0.05), and those of IL-10 in P group were decreased to (12.92±0.17) pg/ml (P<0.05); as compared with P group, the level of IL-1β in R+ P group was significantly decreased to (9.42±0.13) pg/ml (P<0.05), and that of IL-10 in P group was significantly increased to (24.77±0.12) pg/ml (P<0.05). Conclusion Res alleviates paclitaxel-induced neuralgia, which is related with activation of SIRT1/PGC1α signaling pathway, reduction of cell apoptosis, inhibition of inflammation, and improvement of mitochondrial damage. Key words: Paclitaxel; Neuropathic pain; Resveratrol; Mitochondrial; Silent information regulator 2-related enzymes 1; Peroxisome proliferator-activated receptor-gamma coactivator 1α

Decreased expression of lncRNA Malat1 in rat spinal cord contributes to neuropathic pain by increasing neuron excitability after brachial plexus avulsion.

Purpose: Neuropathic pain (NP) is a challenging clinical problem due to its complex pathogenesis. In our previous study using microarray, we found that the levels of lncRNA Malat1 were decreased in the spinal cord of NP rat after brachial plexus avulsion, but its contribution to NP remain unclear. The purpose of this study was to investigate its role in the pathogenesis of NP.Methods: In the NP model of complete brachial plexus avulsion rat, spinal cords were harvested, and fluorescence in situ hybridization (FISH) was used to test the spatial expression of Malat1 and qRT-PCR was used to confirm the quantitative expression of Malat1. In primary cultured neurons, Malat1 expression interfered with adenovirus. Spontaneous electric activities of neurons were tested using multi-electrode arrays and apoptosis of neurons was tested using TUNEL method. The change of intracellular calcium concentration was analyzed using calcium imaging method.Results: Decreased Malat1 expression was confirmed using qRT-PCR, and Malat1 was identified in the cytoplasm of neurons in spinal cord, but not in glia. In vitro, the decrease of Malat1 resulted in an increase in the frequency of spontaneous electric activity in neurons but had no effect on neuronal apoptosis. Further analysis indicated during glutamate stimulation, the change of intracellular calcium concentration in neurons with downregulated Malat1 expression was significantly greater than that in normal neurons.Conclusion: Reduced Malat1 expression may induce NP by increasing neuronal excitability in the spinal cord via regulation of calcium flux.

Effects of Zingiberis Rhizoma Pharmacopuncture Injected at GB30and ST36on Neuropathic Pain in Rats

Effects of Zingiberis Rhizoma Pharmacopuncture Injected at GB₃₀and ST₃₆on Neuropathic Pain in Rats

Antinociceptive and anti-inflammatory effects of cryptotanshinone through PI3K/Akt signaling pathway in a rat model of neuropathic pain

Peripheral nerve injuries often induce neuropathic pain through inflammation. Cryptotanshinone isolated from Salvia miltiorrhiza Bunge has been found to exert anti-inflammatory and analgesic activities. Thus, this study aimed to determine whether cryptotanshinone inhibits chronic constriction injury (CCI)-induced neuropathic pain in rats and its mechanism of action. CCI was performed by applying four loose ligatures to rat sciatic nerve. Cryptotanshinone was orally administered using pre-surgery, acute or repeated post-surgery treatment. The pain behaviors were determined by recording paw withdrawal mechanical threshold (PWMT) and thermal withdrawal latency (TWL). ELISA kits were used to measure interleukin (IL)-6, IL-1β and tumor necrosis factor (TNF)-α levels. qRT-PCR were performed to detect IL-6, IL-1β, TNF-α, PI3K and Akt expression. The phosphorylation of PI3K/Akt signaling was assessed using western blotting. PWMT and TWL in CCI group were higher than those in the control and sham groups. The acute post-CCI cryptotanshinone treatment but not pre-surgery treatment reduced PWMT and TWL. The effect of cryptotanshinone is more prominent when it was repeatedly administered after CCI. The CCI-induced increase in IL-6, IL-1β, TNF-α, PI3K/Akt signaling and their phosphorylation was also suppressed by repeated post-CCI cryptotanshinone treatment. This study suggested that post-CCI cryptotanshinone treatment reduced the surgery-induced neuropathic pain by suppressing PI3K/Akt signaling therefore inhibited inflammation.

(407) Preclinical Evaluation of Human Somatostatin Receptor 4 (hSSTR4) Agonist CNTX-0290 for Mixed Pain Conditions

CNTX-0290 is an oral, nonopioid hSSTR4 agonist under investigation for analgesia. Activity was assessed in acute, nociceptive, and neuropathic rat pain models. In the Complete Freund's Adjuvant (CFA) model, maximum efficacy of CNTX-0290 0.03–3 mg/kg vs vehicle was compared with indomethacin 30 mg/kg and celecoxib 10 mg/kg; minimal effective dose (MED) was determined. In the monosodium iodoacetate (MIA) osteoarthritis model, weight-bearing deficit (WBD) was assessed following CNTX-0290 0.01–30 mg/kg administration. Paw withdrawal threshold (PWT) was determined for CNTX-0290 0.03–0.3 mg/kg vs vehicle in the partial nerve ligation (PNL) model (control: lamotrigine 30 mg/kg) and at 3–30 mg/kg in the streptozocin diabetes model (control: duloxetine 30 mg/kg). In vitro potency and selectivity were evaluated. General/safety pharmacology studies were conducted in rats and cynomologus monkeys. Effects on growth hormone (GH) release and glucose tolerance were compared with octreotide. CNTX-0290 demonstrated potent, selective hSSTR4 agonism (EC50=2.6 nM; Ki=41 nM; hSSTR 1, 2, 3, and 5 Ki >10,000 nM). CNTX-0290 showed dose-dependent antinociceptive effects in the CFA model. Maximum efficacy was achieved at 3 mg/kg; MED was 0.1 mg/kg (minimal effective concentration [MEC]: 32 nM). In the MIA model, CNTX-0290 1–30 mg/kg significantly reversed WBD vs vehicle, and was comparable to morphine at 3 and 30 mg/kg. Efficacy up to 24 hours was observed in both models. In the PNL model, CNTX-0290 achieved maximum efficacy (comparable to lamotrigine) at 0.3 mg/kg; MED: 0.1 mg/kg (MEC: 25 nM). CNTX-0290 10 and 30 mg/kg significantly increased PWT vs vehicle in the streptozocin model, comparable to duloxetine. GH release and glucose tolerance were not significantly altered, and no dose-limiting CNS AEs were observed. CNTX-0290, a potent, selective, full hSSTR4 agonist, showed analgesic efficacy in models of nociceptive and neuropathic pain, demonstrating potential for treating mixed pain conditions. (Funding: Centrexion Therapeutics Corp.)

Progressive Increase of Inflammatory CXCR4 and TNF-Alpha in the Dorsal Root Ganglia and Spinal Cord Maintains Peripheral and Central Sensitization to Diabetic Neuropathic Pain in Rats.

Diabetic neuropathic pain (DNP) is a common and serious complication of diabetic patients. The pathogenesis of DNP is largely unclear. The proinflammation proteins, CXCR4, and TNF-α play critical roles in the development of pain, while their relative roles in the development of DNP and especially its progression is unknown. We proposed that establishment of diabetic pain models in rodents and evaluating the stability of behavioral tests are necessary approaches to better understand the mechanism of DNP. In this study, Von Frey and Hargreaves Apparatus was used to analyze the behavioral changes of mechanical allodynia and heat hyperalgesia in streptozotocin-induced diabetic rats at different phases of diabetes. Moreover, CXCR4 and TNF-α of spinal cord dorsal and dorsal root ganglia (DRG) were detected by western blotting and immunostaining over time. The values of paw withdrawal threshold (PWT) and paw withdrawal latencies (PWL) were reduced as early as 1 week in diabetic rats and persistently maintained at lower levels during the progression of diabetes as compared to control rats that were concomitant with significant increases of both CXCR4 and TNF-α protein expressions in the DRG at 2 weeks and 5 weeks (the end of the experiments) of diabetes. By contrast, CXCR4 and TNF-α in the spinal cord dorsal horn did not significantly increase at 2 weeks of diabetes while both were significantly upregulated at 5 weeks of diabetes. The results indicate that central sensitization of spinal cord dorsal may result from persistent peripheral sensitization and suggest a potential reference for further treatment of DNP.

Upregulation of interleukin-6 on Cav3.2 T-type calcium channels in dorsal root ganglion neurons contributes to neuropathic pain in rats with spinal nerve ligation

The T-type calcium channels Cav3.2, one of the low voltage-activated (LVA) calcium channels, have been found to play important roles in the neuronal excitability. Recently, we and others have demonstrated that accumulation of Cav3.2 channels in the dorsal root ganglion (DRG) neurons and sensory nerves contributes to neuropathic pain after peripheral nerve injury. In the present study, we aimed to further investigate the regulation of Cav3.2 channels by interleukin-6 (IL-6) in DRG neurons in neuropathic pain rats after spinal nerve ligation (SNL). The results showed that Cav3.2 channel protein expression in L5 DRG neurons was upregulated and blockade of this channel decreased the hyperexcitability of DRG neurons and mechanical allodynia in SNL neuropathic pain rats. Furthermore, inhibition of IL-6 trans-signaling reduced the upregulation of Cav3.2 T-type channel induced by FIL-6 (a fusion protein of IL-6 and sIL-6R) in primary cultured DRG neurons in vitro. In vivo, inhibition of IL-6 trans-signaling reversed the upregulation of Cav3.2, reduced the hyperexcitability of L5 DRG neurons and alleviated mechanical allodynia in SNL rats. Our results suggest that IL-6 upregulates Cav3.2 T-type channels expression and function through the IL-6/sIL-6R trans-signaling pathway in DRG neurons, thus contributes to the development of neuropathic pain in SNL rats.

Puerarin suppresses TRPV1, calcitonin gene-related peptide and substance P to prevent paclitaxel-induced peripheral neuropathic pain in rats.

Chemotherapy-induced peripheral neuropathic pain is a major dose-limiting and therapy-limiting adverse effect that is particularly difficult to treat. Puerarin, a major active ingredient of traditional Chinese plant medicine Gegen, is commonly used in the treatment of myocardial and cerebral ischemia. However, the effects of puerarin on neuropathic pain are still unknown. Therefore, the aim of this study is to examine the effects of puerarin on neuropathic pain. In this study, the effects of puerarin were tested in-vivo on a rat model of paclitaxel-induced peripheral neuropathic pain (PIPNP). The results show that a single injection of puerarin produced short-term analgesic effect on pre-established PIPNP, as indicated by decreased mechanical allodynia and thermal hyperalgesia in comparison with paclitaxel-treated rats. Repeated doses of puerarin, given during PIPNP induction, prevented the development of PIPNP. This prophylactic effect of puerarin was associated with suppressed paclitaxel-induced transient receptor potential vanilloid 1, calcitonin gene-related peptide and substance P up-regulation in the dorsal root ganglia. These findings revealed the therapeutic potential of puerarin in treating and preventing chemotherapy-induced peripheral neuropathic pain.

Resveratrol inhibits paclitaxel-induced neuropathic pain by the activation of PI3K/Akt and SIRT1/PGC1α pathway.

BackgroundPhosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) is one of the essential signaling pathways for the development and maintenance of neuropathic pain.ObjectiveTo investigate the effect of resveratrol (RES) on paclitaxel-induced neuropathic pain in rats and elucidate the underlying molecular mechanisms.MethodMale Sprague Dawley rats were randomly divided into seven groups (n=10/group): Group C, Group P, Group R, Group R+P, Group LY + R+P, Group LY (the specific inhibitor of PI3K), Group E (the specific inhibitor of sirtuin 1 [SIRT1]). Paw withdrawal mechanical threshold (PWT) and thermal withdrawal latency (TWL) were recorded. Mitochondrial histomorphology was performed by transmission electron microscope. PI3K, p-Akt, and t-Akt expressions were tested using immunohistochemistry. Western blot was used to detect p-Akt, t-Akt, SIRT1, and PGC1α expressions. The apoptosis in the striatum, spinal dorsal horns (SDH), and dorsal root ganglions (DRG) tissues was assayed by TUNEL. ELISA was used to detect the contents of IL-β, IL-10, malondialdehyde (MDA), and superoxide dismutase (SOD) in striatum, SDH, and DRG tissues.ResultsCompared to the control group, PWT and TWL in the P and LY +R+P groups were significantly decreased on 8th and 14th day after paclitaxel administration (P<0.05). The expressions of p-Akt, SIRT1, and PGC1α were decreased in paclitaxel-induced neuropathic rats; however, the expressions of p-Akt, SIRT1, and PGC1α were significantly increased after RES treatment (P<0.05). Furthermore, the expression of p-Akt was decreased by LY294002 (P<0.05), and amount of SIRT1 and PGC1α expression was inhibited by EX-527 (P<0.05). The t-Akt level was not significantly changed in all groups. RES prevented paclitaxel-induced mitochondrial damage by PI3K/Akt. RES improves the pain symptoms of paclitaxel neuralgia rats by increasing the IL-10 and decreasing the expression of IL-1β. RES increases the SOD and reduces the MDA. RES reduces apoptosis by SIRT1/PGC1α signal pathway.ConclusionOur results suggest that RES may inhibit paclitaxel-induced neuropathic pain via PI3K/Akt and SIRT1/PGC1α pathways.

Silencing of spinal Trpv1 attenuates neuropathic pain in rats by inhibiting CAMKII expression and ERK2 phosphorylation

Accumulating evidence suggests a potential role of transient receptor potential vanilloid 1 (TRPV1) channels in inflammatory and cancer-related pain. However, the role of TRPV1 in the maintenance of neuropathic pain remains elusive. The current study investigated the effects of transient Trpv1 gene silencing using a small interference RNA (siRNA) on neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve in rats. Seven days after CCI, the TRPV1 siRNA was intrathecally administered (5 µg/15 µl, once daily for 2 days). TRPV1 and Ca2+/calmodulin-dependent protein kinase II (CAMKII) expression and extracellular signal-regulated kinase (ERK) phosphorylation in the spinal cord were detected using western blotting. The thresholds to mechanical and thermal stimuli were determined before and after intrathecal TRPV1 siRNA administration. TRPV1 and CAMKII expression and ERK2 phosphorylation in the spinal cord were upregulated after CCI. Intrathecal administration of the TRPV1 siRNA not only attenuated behavioural hyperalgesia but also reduced the expression of TRPV1 and CAMKII, as well as ERK2 phosphorylation. Based on these results, silencing of the TRPV1 gene in the spinal cord attenuates the maintenance of neuropathic pain by inhibiting CAMKII/ERK2 activation and suggests that TRPV1 represents a potential target in pain therapy.