Chronic Constriction Injury Surgery Research Articles

MiR-31-5p regulates the neuroinflammatory response via TRAF6 in neuropathic pain

BackgroundNeuropathic pain is chronic pain and has few effective control strategies. Studies have demonstrated that microRNAs have functions in neuropathic pain. However, no study has been conducted to demonstrate the role and mechanism of microRNA (miR)-31-5p in neuropathic pain. Accordingly, this study sought to determine the pathological role of miR-31-5p in chronic constriction injury (CCI) -induced neuropathic pain mouse models.MethodsWe used CCI surgery to establish mouse neuropathic pain model. Behavioral tests were performed to evaluate pain sensitivity of mice. Expressions of miR-31-5p and inflammatory cytokines in dorsal root ganglion (DRG) were examined by polymerase chain reaction. Animals or cells were received with/without miR-31-5p mimic or inhibitor to investigate its role in neuropathic pain. The mechanism of miR-31-5p was assayed using western blotting, immunofluorescence staining and dual-luciferase reporter assay.ResultsWe found that CCI led to a significant decrease in miR-31-5p levels. Knockout of miR-31-5p and administration of miPEP31 exacerbated pain in C57BL/6 mice. Meanwhile, miR-31-5p overexpression increased the paw withdrawal threshold and latency. TRAF6 is one of the target gene of miR-31-5p, which can trigger a complex inflammatory response. TRAF6 was associated with pain and that reducing the DRG expression of TRAF6 could alleviate pain. In addition, miR-31-5p overexpression inhibited the TRAF6 expression and reduced the neuroinflammatory response.ConclusionsAll the results reveal that miR-31-5p could potentially alleviate pain in CCI mouse models by inhibiting the TRAF6 mediated neuroinflammatory response. MiR-31-5p upregulation is highlighted here as new target for CCI treatment.

Phase-specific differential regulation of mechanical allodynia in a murine model of neuropathic pain by progesterone.

Progesterone has been shown to have neuroprotective capabilities against a wide range of nervous system injuries, however there are negative clinical studies that have failed to demonstrate positive effects of progesterone therapy. Specifically, we looked into whether progesterone receptors or its metabolizing enzymes, cytochrome P450c17 and 5α-reductase, are involved in the effects of progesterone on neuropathic pain after chronic constriction injury (CCI) of the sciatic nerve in mice. Intrathecal progesterone administration during the induction phase of chronic pain enhanced mechanical allodynia development and spinal glial fibrillary acidic protein (GFAP) expression, and this enhancement was inhibited by administration of ketoconazole, a P450c17 inhibitor, but not finasteride, a 5α-reductase inhibitor. Furthermore, phospho-serine levels of P450c17 in the spinal cord were elevated on day 1 after CCI operation, but not on day 17. In contrast, intrathecal progesterone administration during the maintenance phase of chronic pain decreased the acquired pain and elevated GFAP expression; this inhibition was restored by finasteride administration, but not by ketoconazole. The modification of mechanical allodynia brought on by progesterone in CCI mice was unaffected by the administration of mifepristone, a progesterone receptor antagonist. Collectively, these findings imply that progesterone suppresses spinal astrocyte activation via 5α-reductase activity during the maintenance phase of chronic pain and has an analgesic impact on the mechanical allodynia associated with the growing neuropathy. Progesterone, however, stimulates spinal astrocytes during the induction stage of peripheral neuropathy and boosts the allodynic impact caused by CCI through early spinal P450c17 activation.

Systemic administration of NIS-lncRNA antisense oligonucleotide alleviates neuropathic pain

ObjectiveThe antisense oligonucleotide (ASO) is an FDA-approved strategy in the treatment of neurological diseases. We have shown the viability of using intrathecal ASO to suppress nerve injury-specific long noncoding RNA (NIS-lncRNA) in dorsal root ganglion (DRG), resulting in a stable and long-lasting antinociceptive effect on NP. This study examined whether systemic administration of NIS-lncRNA ASO relieved the chronic constriction injury (CCI)-induced nociceptive hypersensitivity. MethodsA single subcutaneous injection of NIS-lncRNA ASO at a dose of 1,000 µg was carried out 7 days after CCI or sham surgery in male mice. Behavioral tests were performed one day before surgery and at different days after surgery. DRG and spinal cord were finally collected for quantitative real-time RT-PCR and Western blot assays. ResultsNIS-lncRNA ASO significantly alleviated CCI-induced mechanical allodynia, heat hyperalgesia, and cold hyperalgesia starting on day 14 or 21 post-ASO injection and lasting for at least 7 days on the ipsilateral side. Additionally, CCI-induced spontaneous pain and ipsilateral dorsal horn neuronal and astrocyte hyperactivation were blocked on day 28 after NIS-lncRNA ASO injection. As predicted, the CCI-induced increases in the levels of NIS-lncRNA and its downstream target C-C motif chemokine ligand 2 in the ipsilateral lumbar 3 and 4 DRGs were attenuated on day 28 following NIS-lncRNA ASO injection. ConclusionOur findings indicate that systemic administration of NIS-lncRNA ASO also produces a stable and long-lasting antinociceptive effect on neuropathic pain. NIS-lncRNA ASO may have potential clinical application in the treatment of this disorder.

Evaluation of novel epibatidine analogs in the rat nicotine drug discrimination assay and in the rat chronic constriction injury neuropathic pain model.

Nicotine is the primary psychoactive component responsible for maintaining tobacco dependence in humans. Chronic pain is often a consequence of tobacco-related pathologies, and the development of a dual therapeutic that could treat chronic pain and tobacco dependence would be advantageous. Epibatidine reliably substitutes for nicotine in the drug discrimination assay, and is a potent analgesic, but has a side-effect profile that limits its therapeutic potential. Thus, considerable efforts to produce epibatidine derivatives are underway. Here we tested three epibatidine derivatives, 2'-fluoro-3'-(4-nitrophenyl)deschloroepibatidine (RTI-7527-102; i.e., RTI-102), 2'-fluorodeschloroepibatidine (RTI-7527-36; i.e., RTI-36), and 3'-(3″-dimethylaminophenyl)-epibatidine (RTI-7527-76; i.e., RTI-76) in both the rat nicotine drug discrimination assay as well as in the rat chronic constriction injury (CCI) of the sciatic nerve neuropathic pain model. Male and female Sprague-Dawley rats were trained on a fixed-ratio 10 schedule to discriminate nicotine (0.32mg/kg base) from vehicle. All compounds dose-dependently substituted for nicotine, without significant decreases in response rates. In the discrimination assay the rank order potency was RTI-36 > nicotine > RTI-102 > RTI-76. Evidence suggests the α4β2* subtype is particularly important to nicotine-related abuse potential. Thus, here we utilized the antagonist dihydro-β-erythroidine (DHβE) to examine relative β2 subunit contribution. DHβE (3.2mg/kg, s.c.) antagonized the discriminative stimulus effects of nicotine. However, relative to antagonism of nicotine, DHβE produced less antagonism of RTI-102 and RTI-76 and greater antagonism of RTI-36. It is likely that at nicotinic receptor subunits RTI-102, RTI-76 and RTI-36 possess differing activity. To confirm that the full discriminative stimulus of these compounds was due to nAChR activity beyond the β2 subunit, we examined these compounds in the presence of the non-selective nicotinic receptor antagonist mecamylamine. Mecamylamine (0.56mg/kg, s.c.) pretreatment abolished nicotine-paired lever responding for all compounds. In a separate cohort, male and female Sprague-Dawley rats underwent CCI surgery and tested for CCI-induced mechanical allodynia via the von Frey assay. Each compound produced CCI-induced mechanical allodynia reversal. RTI-36 displayed higher potency than either RTI-102 or RTI-76. These novel epibatidine analogs may prove to be useful tools in the fight against nicotine dependence as well as novel neuropathic pain analgesics.

Chinese Tuina remodels the synaptic structure in neuropathic pain rats by downregulating the expression of N-methyl D-aspartate receptor subtype 2B and postsynaptic density protein-95 in the spinal cord dorsal horn.

To investigate whether the Chinese massage system, Tuina, exerts analgesic effects in a rat model of chronic constriction injury (CCI) by remodeling the synaptic structure in the spinal cord dorsal horn (SCDH). Sixty-nine male Sprague-Dawley rats were randomly and evenly divided into the normal group, sham group, CCI group, CCI + Tuina group, CCI + MK-801 [an -methyl D-aspartate receptor subtype 2B (NR2B) antagonist] group, and CCI + MK-801 + Tuina group. The neuropathic pain model was established using CCI with right sciatic nerve ligation. Tuina was administered 4 d after CCI surgery, using pressing manipulation for 10 min, once daily. Motor function was observed with the inclined plate test, and pain behaviors were observed by the Von Frey test and acetone spray test. At 19 d after surgery, the L3-L5 spinal cord segments were removed. Glutamate, interleukin 1β (IL-1β), and tumor necrosis factor-α (TNF-α) levels were detected by enzyme-linked immunosorbent assay. The protein expression levels of NR2B and postsynaptic density protein-95 (PSD-95) were detected by Western blot, and the synaptic structure was observed by transmission electron microscopy (TEM). CCI reduced motor function and caused mechanical and cold allodynia in rats, increased glutamate concentration and TNF-α and IL-1β levels, and increased expression of synapse-related proteins NR2B and PSD-95 in the SCDH. TEM revealed that the synaptic structure of SCDH neurons was altered. Most of these disease-induced changes were reversed by Tuina and intrathecal injection of MK-801 ( < 0.05 or < 0.01). For the majority of experiments, no significant differences were found between the CCI + MK-801 and CCI + MK-801 + Tuina groups. Chinese Tuina can alleviate pain by remodeling the synaptic structure, and NR2B and PSD-95 receptors in the SCDH may be among its targets.

Taselisib moderates neuropathic pain through PI3K/AKT signaling pathway in a rat model of chronic constriction injury

BackgroundNeuropathic pain is a chronic condition commonly caused by inflammation-induced disturbances or lesions of somatosensory functions in the nervous system. The aim of this study was to investigate the effects and mechanisms of Taselisib on chronic constriction injury (CCI)-induced neuropathic pain in rats. MethodsThe rats were divided into four groups: sham group, sham + Taselisib (10 mg/kg orally once a day) group, CCI group, and CCI + Taselisib (10 mg/kg orally once a day) group. Pain behavioral tests, recorded by measuring paw withdrawal threshold (PWT) and thermal withdrawal latency (TWL), were conducted on days 0, 3, 7, 14, and 21 after surgery. After testing, the animals were euthanized and spinal dorsal horns were collected. Pro-inflammatory cytokines were quantified using ELISA and qRT-PCR. PI3K/pAKT signaling was assessed using Western blot and immunofluorescence. ResultsPWT and TWL were significantly reduced after CCI surgery, but were successfully increased by Taselisib treatment. Taselisib treatment notably suppressed the upregulation of pro-inflammatory cytokines, including IL-6, IL-1β, and TNF-⍺. Taselisib treatment significantly reduced the elevated phosphorylation of AKT and PI3K induced by CCI. ConclusionTaselisib can alleviate neuropathic pain by inhibiting the pro-inflammatory response, potentially through the PI3K/AKT signaling pathway.

Transforming Growth Factor-β-Activated Kinase 1 (TAK1) Mediates Chronic Pain and Cytokine Production in Mouse Models of Inflammatory, Neuropathic, and Primary Pain

The origin of chronic pain is linked to inflammation, characterized by increased levels of proinflammatory cytokines in local tissues and systemic circulation. Transforming growth factor beta-activated kinase 1 (TAK1) is a key regulator of proinflammatory cytokine signaling that has been well characterized in the context of cancer and autoimmune disorders, yet its role in chronic pain is less clear. Here, we evaluated the ability of our TAK1 small-molecule inhibitor, takinib, to attenuate pain and inflammation in preclinical models of inflammatory, neuropathic, and primary pain. Inflammatory, neuropathic, and primary pain was modeled using intraplantar complete Freund’s adjuvant (CFA), chronic constriction injury (CCI), and systemic delivery of the catechol-O-methyltransferase (COMT) inhibitor OR486, respectively. Behavioral responses evoked by mechanical and thermal stimuli were evaluated in separate groups of mice receiving takinib or vehicle prior to pain induction (baseline) and over 12 days following CFA injection, 4 weeks following CCI surgery, and 6 hours following OR486 delivery. Hindpaw edema was also measured prior to and 3 days following CFA injection. Upon termination of behavioral experiments, dorsal root ganglia (DRG) were collected to measure cytokines. We also evaluated the ability of takinib to modulate nociceptor activity via in vitro calcium imaging of neurons isolated from the DRG of Gcamp3 mice. In all 3 models, TAK1 inhibition significantly reduced hypersensitivity to mechanical and thermal stimuli and expression of proinflammatory cytokines in DRG. Furthermore, TAK1 inhibition significantly reduced the activity of tumor necrosis factor (TNF)-primed/capsaicin-evoked DRG nociceptive neurons. Overall, our results support the therapeutic potential of TAK1 as a novel drug target for the treatment of chronic pain syndromes with different etiologies. PerspectiveThis article reports the therapeutic potential of TAK1 inhibitors for the treatment of chronic pain. This new treatment has the potential to provide a greater therapeutic offering to physicians and patients suffering from chronic pain as well as reduce the dependency on opioid-based pain treatments.

Alterations of endogenous pain-modulatory system of the cerebral cortex in the neuropathic pain

Neuropathic pain (NeP) remains a significant clinical challenge owing to insufficient awareness of its pathological mechanisms. We elucidated the aberrant metabolism of the cerebral cortex in NeP induced by the chronic constriction injury (CCI) using metabolomics and proteomics analyses. After CCI surgery, the values of MWT and TWL markedly reduced and maintained at a low level. CCI induced the significant dysregulation of 57 metabolites and 31 proteins in the cerebral cortex. Integrative analyses showed that the differentially expressed metabolites and proteins were primarily involved in alanine, aspartate and glutamate metabolism, GABAergic synapse, and retrograde endocannabinoid signaling. Targeted metabolomics and western blot analysis confirmed the alterations of some key metabolites and proteins in endogenous pain-modulatory system. In conclusion, our study revealed the alterations of endocannabinoids system and purinergic system in the CCI group, and provided a novel perspective on the roles of endogenous pain-modulatory system in the pathological mechanisms of NeP.

Paeonol alleviates neuropathic pain by modulating microglial M1 and M2 polarization via the RhoA/p38MAPK signaling pathway.

This study aimed to investigate the potential mechanism of paeonol in the treatment of neuropathic pain. Relevant mechanisms were explored through microglial pseudotime analysis and the use of specific inhibitors in cell experiments. In animal experiments, 32 SD rats were randomly divided into the sham operation group, the chronic constrictive injury (CCI) group, the ibuprofen group, and the paeonol group. We performed behavioral testing, ELISA, PCR, Western blotting, immunohistochemistry, and immunofluorescence analysis. The pseudotime analysis of microglia found that RhoA, Rock1, and p38MAPK were highly expressed in activated microglia, and the expression patterns of these genes were consistent with the expression trends of the M1 markers CD32 and CD86. Paeonol decreased the levels of M1 markers (IL1β, iNOS, CD32, IL6) and increased the levels of M2 markers (IL10, CD206, ARG-1) in LPS-induced microglia. The expression of iNOS, IL1β, RhoA, and Rock1 was significantly increased in LPS-treated microglia, while paeonol decreased the expression of these proteins. Thermal hyperalgesia occurred after CCI surgery, and paeonol provided relief. In addition, paeonol decreased the levels of IL1β and IL8 and increased the levels of IL4 and TGF-β in the serum of CCI rats. Paeonol decreased expression levels of M1 markers and increased expression levels of M2 markers in the spinal cord. Paeonol decreased IBA-1, IL1β, RhoA, RhoA-GTP, COX2, Rock1, and p-p38MAPK levels in the spinal dorsal horn. Paeonol relieves neuropathic pain by modulating microglial M1 and M2 phenotypes through the RhoA/p38 MAPK pathway.

Transcriptome Analysis of the Mouse Medial Prefrontal Cortex in a Chronic Constriction Injury Model.

The medial prefrontal cortex (mPFC) is critical for both the sensory and emotional/cognitive components of pain. However, the underlying mechanism remains largely unknown. Here, we examined changes in the transcriptomic profiles in the mPFC of mice with chronic pain using RNA sequencing (RNA-seq) technology. A mouse model of peripheral neuropathic pain was established via chronic constriction injury (CCI) of the sciatic nerve. CCI mice developed sustained mechanical allodynia and thermal hyperalgesia, as well as cognitive impairment four weeks after surgery. RNA-seq was conducted 4weeks after CCI surgery. Compared with contral group, RNA-seq identified a total 309 and 222 differentially expressed genes (DEGs) in the ipsilateral and contralateral mPFC of CCI model mice, respectively. GO analysis indicated that the functions of these genes were mainly enriched in immune- and inflammation-related processes such as interferon-gamma production and cytokine secretion. KEGG analysis further showed the enrichment of genes involved in the neuroactive ligand-receptor interaction signaling pathway and Parkinson disease pathway that have been reported to be importantly involved in chronic neuralgia and cognitive dysfunction. Our study may provide insights into the possible mechanisms underlying neuropathic pain and pain-related comorbidities.

Inhibition of microRNA-19a-3p alleviates the neuropathic pain (NP) in rats after chronic constriction injury (CCI) via targeting KLF7

Background/purposeNeuropathic pain(NP) is derived from the dysfunctions of nerve system. The current research is to explore the impact and mechanism of miR-19a-3p in neuropathic pain in rats. MethodsThe NP was induced through the chronic constriction injury (CCI) surgery in rats. The pro-inflammatory factors (IL-1β, IL-6, TNF-α) in spinal cord tissues from rats were measured using Elisa kits. Moreover, the different levels of thermal hyperalgesia and mechanical allodynia in rats were examined through paw withdrawal latency (PWL) and paw withdrawal threshold (PWT). To investigate into the role of miR-19a-3p and KLF7 in NP of rats, the knockdown of miR-19a-3p alone or along with KLF7 downregulation in rats were achieved through lentivirus injection. The miR-19a-3p and KLF7 expression in spinal cord of rats on Day 3,7,14 after CCI were detected using RT-qPCR. The protein expression of KLF7 were measured by Western blot. Bioinformatics and luciferase assays were used for the prediction and verification of bindings between KLF7 and miR-19a-3p. ResultsCCI surgery caused neuropathic pain in rats with the levels of inflammatory cytokines increased and PWL and PWT decreased. Moreover, miR-19a-3p expression was increased while the protein and mRNA levels were decreased in spinal cord tissues in rats after CCI surgery. In rat microglial cells, miR-19a-3p downregulation could promote the KLF7 in both mRNA and protein expression. In spinal cord tissues of rats, the inhibition of miR-19a-3p enhanced the KLF7 expression. Furthermore, miR-19a-3p downregulation suppressed the IL-1β, IL-6 and TNF-α concentrations, and could decrease the NP but inhibition of KLF7 could partially reverse this in CCI rats. ConclusionmiR-19a-3p inhibition may alleviate NP via KLF7 in CCI rats.

Interaction effects of intracerebroventricular injection of crocin with the α2-adrenoceptors on memory deficit and hippocampal synaptic plasticity following chronic pain in rat

Patients with chronic pain exhibit anxiety and deficits in memory. Additionally, α2-adrenoceptors that are wildly expressed in the brain have an important role in modulating both pain and memory formation. In the present study, we investigated the interaction effects of crocin with central α2-adrenoceptors on pain comorbidity and hippocampal synaptic plasticity changes following chronic constriction injury (CCI) of the sciatic nerve in rats. All the drugs (crocin, an antagonist (yohimbine) and agonist (clonidine) of α2-adrenergic receptors) were injected (via intracerebroventricular injection) from the day of CCI operation (day 0) and continued daily (once per day) until the 14th day post-CCI. The effects of drugs on the cold allodynia (using acetone test) and anxiety-like behaviors (using elevated plus maze, EPM and open field tests) were assessed. Spatial memory (using Barnes maze) was assessed on day 14 post-CCI operation. Hippocampal synaptic plasticity (using in-vivo extracellular field potential recording) was performed on day 14 post-CCI operation. We observed that crocin induced analgesic, anxiolytic and memory enhancer action following CCI surgery. Furthermore, crocin significantly increased long-term potentiation (LTP) (increased fEPSP slope and population spike amplitude). Furthermore, the co-injection of yohimbine effectively decreased analgesic, anxiolytic and enhancer action of crocin on the LTP parameters (fEPSP slope and population spike amplitude). Our study provided information that protective effects of crocin on pain/anxiety responses and synaptic plasticity were possibly mediated by central α2-adrenoceptor in the rats with chronic pain.

Analgesic effects of Terminalia chebula extract are mediated by the suppression of the protein expression of nerve growth factor and nuclear factor-κB in the brain and oxidative markers following neuropathic pain in rats.

Due to the complications related to the use of the current pharmacological approach for the alleviation of neuropathic pain, searching for effective compound with fewer complications is a requirement of the present era. It is well known that the pathophysiological mechanism of neuropathic pain is related to excessive inflammation in the nervous system. Hence, the present study focuses on whether the potential analgesic effects of Terminalia chebula (TC) extract are mediated by the changes in the protein expression of nerve growth factor (NGF) and nuclear factor-kappa B (NF-κB) in the brain in a rat model of sciatic nerve chronic constriction injury (CCI). Neuropathic pain was induced by the left sciatic nerve CCI. Male Wistar rats were assigned to three groups: sham, CCI, and CCI + TC (40mg/kg). Animals received either normal saline (1 mL) or the aqueous-alcoholic extract of TC (40mg/kg) for 30 days via gavage needles once a day. Cold allodynia and anxiety-like behaviors were examined one day before CCI surgery (day - 1), as well as days 2, 7, 14, and 30 following CCI. We also assessed the effects of the TC extract oxidative stress markers on day 30 following CCI. Moreover, a western blot analysis was performed on day 30 following CCI to evaluate the effects of the TC extract on the protein expression of NGF and NF-κB in the brain. Oral gavage of the TC extract significantly decreased cold allodynia on days 2 and 14 following CCI. Additionally, the CCI model of chronic pain significantly increased the protein expression of NGF and NF-κB in the brain on day 30 following CCI. Furthermore, the TC extract significantly decreased the protein expression of NGF and NF-κB in the brain. The TC extract also significantly increased the brain glutathione (GSH) content and decreased the malondialdehyde (MDA) content. It is suggested that the analgesic effects of the TC extract are mediated by the suppression of brain NGF, NF-κB, and by its antioxidant activity in the brain following neuropathic pain in rats.

α-Asarone attenuates chronic sciatica by inhibiting peripheral sensitization and promoting neural repair.

This study explored the therapeutic effect of α-asarone on chronic sciatica. Thirty-two Sprague-Dawley (SD) rats were divided into four groups: the sham group, chronic constriction injury (CCI) group, pregabalin group, and α-asarone group. Hot hyperalgesia was induced after the CCI operation, and α-asarone was found to relieve chronic neuralgia. Furthermore, α-asarone reduced IL1β, IL6, TNF-α, CRP, and LPS levels and increased IL10 levels in serum. α-Asarone decreased the protein levels of TRPA1, TRPM8, and TRPV1-4 and the mRNA levels of TRPA1, TRPM8, TRPV1-4, IL1β, and TNF-α in dorsal root ganglion neurons. In the sciatic nerve, α-asarone treatment reduced the number of inflammatory cells and promoted the proliferation of Schwann cells, favouring recovery of the nerve structure. In cellular experiments, LPS induced Schwann cell apoptosis via TLR4/p38MAPK signalling; α-asarone attenuated LPS-induced Schwann cell apoptosis by decreasing TLR4, p-p38MAPK, cleaved-caspase3, and cleaved-caspase7 levels and increasing Bcl-2 and Bcl-xl expression. Overall, these findings suggest that α-asarone relieves chronic sciatica by decreasing the levels of inflammatory factors, inhibiting peripheral sensitization, and favouring the repair of damaged nerves.

Ferulic acid alleviates sciatica by inhibiting peripheral sensitization through the RhoA/p38MAPK signalling pathway

BackgroundNonsteroidal anti-inflammatory drugs are used to relieve sciatica, but their effects are not satisfactory. PurposeThis study aimed to explore the therapeutic effects of ferulic acid on sciatica. MethodsThirty-two SD rats were randomly divided into 4 groups, i.e., sham operation group, chronic constriction injury (CCI) group, mecobalamin group, and ferulic acid group. We conducted behavioural tests, ELISA, PCR, Western blots, and immunofluorescence analysis. Specific inhibitors were used in cell experiments to explore the related mechanisms. ResultsThermal hyperalgesia was induced after CCI operation, and ferulic acid relieved thermal hyperalgesia. In addition, ferulic acid decreased the IL1β, IL6, TNF-α, and CRP mRNA levels; the IBA-1, iNOS, IL1β, RhoA, RhoA-GTP, COX2, Rock1, TRPV1, TRPA1, and p-p38MAPK levels in dorsal root ganglion (DRG) neurons; and the LPS, CRP, substance P (SP), and prostaglandin E2 (PGE2) levels in serum, and these levels were higher in the CCI group. In the cell experiments, LPS induced M1 polarization of GMI-R1 cells via the RhoA/Rock pathway. Ferulic acid attenuated LPS-induced M1 polarization by decreasing the levels of M1 polarization markers, including IL1β, IL6, TNF-α, iNOS, and CD32, and increased M2 polarization by increasing the levels of M2 polarization markers, including CD206 and Arg-1. LPS treatment clearly increased the iNOS, IL1β, RhoA, Rock1, Rock2 and p-p38 MAPK levels and reduced Arg-1 expression, and ferulic acid reversed these changes. ConclusionFerulic acid can inhibit peripheral sensitization by reducing the levels of inflammatory factors, TRPA1 and TRPV1 through the RhoA/p38 MAPK pathway to alleviate sciatica.

Low-Intensity Focused Ultrasound Alleviates Chronic Neuropathic Pain-Induced Allodynia by Inhibiting Neuroplasticity in the Anterior Cingulate Cortex.

Low-intensity focused ultrasound (LIFU) is a potential noninvasive method to alleviate allodynia by modulating the central nervous system. However, the underlying analgesic mechanisms remain unexplored. Here, we assessed how LIFU at the anterior cingulate cortex (ACC) affects behavior response and central plasticity resulting from chronic constrictive injury (CCI). The safety of LIFU stimulation was assessed by hematoxylin and eosin (H&E) and Fluoro-Jade C (FJC) staining. A 21-day ultrasound exposure therapy was conducted from day 91 after CCI surgery in mice. We assessed the 50% mechanical withdrawal threshold (MWT50) using Von Frey filaments (VFFs). The expression levels of microtubule-associated protein 2 (MAP2), growth-associated protein 43 (GAP43), and tau were determined via western blotting (WB) and immunofluorescence (IF) staining to evaluate the central plasticity in ACC. The regions of ACC were activated effectively and safely by LIFU stimulation, which significantly increased the number of c-fos-positive cells (P < 0.05) with no bleeding, coagulative necrosis, and neuronal loss. Under chronic neuropathic pain- (CNP-) induced allodynia, MWT50 decreased significantly (P < 0.05), and overexpression of MAP2, GAP43, and tau was also observed. After 3 weeks of treatment, significant increases in MWT50 were found in the CCI+LIFU group compared with the CCI group (P < 0.05). WB and IF staining both demonstrated a significant reduction in the expression levels of MAP2, GAP43, and tau (P < 0.05). LIFU treatment on ACC can effectively attenuate CNP-evoked mechanical sensitivity to pain and reverse aberrant central plasticity.

Frozen vein wrapping for chronic nerve constriction injury reduces sciatic nerve allodynia in a rat model

BackgroundAutologous vein wrapping (VW) is used in the treatment of recurrent chronic constriction neuropathy and traumatic peripheral nerve injury. However, use of autologous veins is limited by the inability to obtain longer veins of sufficient length for larger sites. Frozen allograft tissue has several advantages, including its availability for large grafts, avoidance of donor-site morbidity, and shorter operation time. Here, we investigated the effect of frozen vein wrapping (FVW) in Wistar rats as a model of sciatic nerve injury.ResultsThe rats were grouped by treatment as (i) untreated after chronic constriction injury surgery (CCI; control group), (ii) treated with vein wrapping using freshly isolated vein (VW), and (iii) treated with vein wrapping using frozen vein (FVW). Mechanical allodynia was assessed with von Frey filaments on postoperative days (PODs) 1, 3, 5, 7, and 14. Gene expression of HO-1 was evaluated by quantitative polymerase chain reaction (qPCR). The response of heme oxygenase-1 gene, Hmox-1, expression to VW and FVW was assessed by RT-PCR. Both VW and FVW significantly increased withdrawal threshold levels compared to the untreated control group on POD 1, 3, and 5. Both VW and FVW also showed increased HO-1 expression compared to the CCI group.ConclusionsFVW increased the withdrawal threshold similar to VW in a rat CCI model for short periods. Frozen vein wrapping using vein allograft without donor site morbidity may be an alternative therapeutic option.

Therapeutic effect of paeoniflorin on chronic constriction injury of the sciatic nerve via the inhibition of Schwann cell apoptosis.

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

Microglia Activation Tracking across Brain Regions over the Development of Neuropathic Pain

Neuropathic pain is a chronic, debilitating condition associated with impaired cognitive, affective and sensory dimensions. One of the mechanisms underlying neuropathic pain is neuroinflammation. Microglia are resident macrophages in the central nervous system and plays an important role in setting neuroinflammation during chronic pain conditions. Microglial mechanisms of pain have been broadly studied in the spinal cord. However, brain mapping of microglial activation over the development of neuropathic pain has not been performed. Adult male and female Sprague-Dawley rats (n=4-6/group) were submitted to a chronic constriction injury (CCI) model of neuropathic pain. After mechanical allodynia assessment by von Frey tests, the whole brain tissue was collected prior the surgery (day 0), or after 7 and 28 days. Microglia activation was assessed by CD11b densitometry using immunohistochemistry in brain regions associated with pain (sensory, affective, motor, and reward system areas). Male rats show a strongly activated microglia in somatosensory cortical regions (Insular and dorsolateral-prefrontal cortex) at 7 but not 28 days. However, it shows a sustained CD11b activation in mediodorsal thalamic nuclei and parabrachial nucleus at 7 and 28 days after CCI surgery. Central medial and paraventricular thalamic nucleus show microglia activation only at 28 days. Affective associated regions (anterior cingulate cortex, medial prefrontal cortex and central amygdala) also shown a sustained microglia activation. Brain reward system regions like the ventral tegmental area, nucleus accumbens and substantia nigra displays microglia activation at 7 and 28 days. Neuropathic pain induces widespread microglia activation across the brain. Microglia activation in somatosensory cortex occurs at 7 but not 28 days whilst affective-motivational regions display a sustained or stronger activation. Sensory regions microglia activation could develop rather than maintain neuropathic pain. Long-lasting effective disorders may be associated with microglial activation in affective-motivational encoding regions. NARSAD - YOUNG INVESTIGATOR GRANT from BRAIN & BEHAVIOR RESEARCH FOUNDATION.

Mechanism of emodin in relieving neuropathic pain by regulating serum metabolism

The present study investigated the effect of emodin on the serum metabolite profiles in the chronic constriction injury(CCI) model by non-target metabolomics and explored its analgesic mechanism. Twenty-four Sprague Dawley(SD) rats were randomly divided into a sham group(S), a CCI group(C), and an emodin group(E). The rats in the emodin group were taken emodin via gavage once a day for fifteen days(50 mg·kg~(-1)) on the first day after the CCI surgery. Mechanical withdrawal threshold(MWT) and thermal withdrawal threshold(TWL) in each group were performed before the CCI surgery and 3,7, 11, and 15 days after surgery. After 15 days, blood samples were collected from the abdominal aorta. The differential metabolites were screened out by non-target metabolomics and analyzed with Kyoto Encyclopedia of Genes and Genomes(KEGG) and ingenuity pathway analysis(IPA). From the third day after CCI surgery, the MWT and TWL values were reduced significantly in both CCI group and emodin group, compared with the sham group(P&lt;0.01). At 15 days post-surgery, the MWT and TWL values in emodin group increased significantly compared with the CCI group(P&lt;0.05). As revealed by non-target metabolomics, 72 differential serum metabolites were screened out from the C-S comparison, including 41 up-regulated and 31 down-regulated ones, while 26 differential serum metabolites from E-C comparison, including 10 up-regulated and 16 down-regulated ones. KEGG analysis showed that the differential metabolites in E-C comparison were enriched in the signaling pathways, such as sphingolipid metabolism, arginine biosynthesis, glycerophospholipid metabolism, and tryptophan metabolism. IPA showed that the differential metabolites were mainly involved in the lipid metabolism-molecular transport-small molecule biochemistry network. In conclusion, emodin can exert an analgesic role via regulating sphingolipid metabolism and arginine biosynthesis.