脊髓p38丝裂原活化蛋白激酶激活参与坐骨神经压迫性损伤所致神经病理性痛

本研究旨在观察脊髓p38丝裂原活化蛋白激酶（p38 mitogen-activated protein kinase,p38 MAPK）在坐骨神经压迫性损伤所致神经病理性痛中的作用。雄性Sprague-Dawley大鼠鞘内置管后,4-0丝线松结扎左侧坐骨神经制作慢性压迫性损伤（chronic constriction injury,CCI）模型。CCI后第5天,鞘内注射不同剂量的p38 MAPK特异性抑制剂SB203580,并在给药前及给药后不同时间点,分别用von Frey机械痛敏监测仪和热辐射刺激仪监测大鼠损伤侧后爪机械和热刺激反应闽值,用免疫印迹技术（Western blot）观察给药前后脊髓磷酸化p38 MAPK（p-p38 MAPK）和磷酸化环磷酸腺苷反应元件结合蛋白（phosphorylated cAMP response element binding protein,pCREB）表达变化。结果发现：坐骨神经压迫性损伤引起脊髓p-p38 MAPK蛋白表达明显增加;鞘内注射SB203580能剂量依赖性逆转CCI引起的机械性痛觉异常和热痛觉过敏及脊髓水平p-p38 MAPK表达的增加,也明显抑制CCI引起的脊髓pCREB表达的增加。结果提示,脊髓水平p38 MAPK激活参与坐骨神经压迫性损伤所致神经病理性痛的发展,其作用可能通过pCREB介导。     

脊髓IL-6在脊神经结扎模型所引起的热痛敏中的作用

目的：研究脊髓中IL-6在大鼠脊神经结扎（spinal nerve ligation,SNL）所引起的神经病理性痛中的作用。方法：建立大鼠SNL模型,以ELISA法检测脊髓IL-6含量。鞘内分别给予外源性IL-6,以及IL-6的中和抗体以拮抗内源性的IL-6,观察大鼠对热刺激的缩足反应潜伏期（paw withdrawal latencies,PWL）。结果：①SNL手术后3天和7天,脊髓IL-6水平明显上调（P〈0.05）。②手术7天后给予外源性IL-6不能明显引起假手术组的PWL变化,但是与给予生理盐水的假手术组和SNL组相比,给予IL-6的SNL组PWL明显下降（P〈0.05）。③手术7天后给予IL-6的中和抗体不能引起假手术组的PWL改变,但是与给予生理盐水的SNL组相比,给予中和抗体的SNL组PWL明显上升（P〈0.05）。结论：IL-6在脊神经结扎模型所引起的神经病理性痛中发挥促伤害性作用     

Ketamine depresses toll-like receptor 3 signaling in spinal microglia in a rat model of neuropathic pain

Reports suggest that microglia play a key role in spinal nerve ligation (SNL)-induced neuropathic pain, and toll-like receptor 3 (TLR3) has a substantial role in the activation of spinal microglia and the development of tactile allodynia after nerve injury. In addition, ketamine application could suppress microglial activation in vitro, and ketamine could inhibit proinflammatory gene expression possibly by suppressing TLR-mediated signal transduction. Therefore, the present study was designed to disclose whether intrathecal ketamine could suppress SNL-induced spinal microglial activation and exert some antiallodynic effects on neuropathic pain by suppressing TLR3 activation. Behavioral results showed that intrathecal ketamine attenuated SNL-induced mechanical allodynia, as well as spinal microglial activation, in a dose-dependent manner. Furthermore, Western blot analysis displayed that ketamine application downregulated SNL-induced phosphorylated-p38 (p-p38) expression, which was specifically expressed in spinal microglia but not in astrocytes or neurons. Besides, ketamine could reverse TLR3 agonist (polyinosine-polycytidylic acid)-induced mechanical allodynia and spinal microglia activation. It was concluded that intrathecal ketamine depresses TLR3-induced spinal microglial p-p38 mitogen-activated protein kinase pathway activation after SNL, probably contributing to the antiallodynic effect of ketamine on SNL-induced neuropathic pain.     

大鼠脑实质内远位触液神经元中5-HT1A受体的分布及其在神经病理性痛中的表达

本文旨在探讨大鼠脑实质内远位触液神经元中5-HT1A受体的分布及其在神经病理性痛中的作用.慢性结扎损伤坐骨神经建立大鼠神经病理性痛模型,分别以缩足潜伏期(paw withdrawal latency,PWL)和缩足阈值(paw withdrawal threshold,PWT)对大鼠热痛敏和机械触诱发痛反应进行评分,以可靠CB-HRP(cholera toxin subunit B with horseradish peroxidase)法追踪标记脑实质内远位触液神经元,用CB-HRP/5-HT1A受体免疫组织化学双重标记技术定位、鉴别5-HT1A受体在远位触液神经元中的表达,并计数分析5-HT1A受体分布和表达变化与痛行为表现之间的关系.结果表明,在神经病理性痛第1、3、A7、14天,大鼠的PWL分别为19.37±2.74、12.04±1.77、8.74±1.15、12.31±1.94,PWT分别为18.58±3.62、13.05±1.81、6.66±1.43、1 1.55±2.01.CB-HRP标记细胞出现的位置和数量恒定.每只动物CB-HRP/5-HT1A受体双重标记的细胞数量分别为276.14±36.00、161.72±28.41、108.64±6.8l、139.76±44.64,分别占该动物CB-HRP标记细胞总数的95%、60%、40%和55%.与对照组相比,神经病理性痛大鼠PWL、PWT及CB.HRP/5-HT1A受体双标细胞数均有显著性差异(P<0.01).结果提示,大鼠脑实质的特定部位恒定存在远位触液神经元,该类神经元大多含有5-HT1A受体,该受体的表达与神经病理性痛行为表现之间呈负相关关系.     

Suberoylanilide Hydroxamic Acid Triggers Autophagy by Influencing the mTOR Pathway in the Spinal Dorsal Horn in a Rat Neuropathic Pain Model

Histone acetylation levels can be upregulated by treating cells with histone deacetylase inhibitors (HDACIs), which can induce autophagy. Autophagy flux in the spinal cord of rats following the left fifth lumber spinal nerve ligation (SNL) is involved in the progression of neuropathic pain. Suberoylanilide hydroxamic acid (SAHA), one of the HDACIs can interfere with the epigenetic process of histone acetylation, which has been shown to ease neuropathic pain. Recent research suggest that SAHA can stimulate autophagy via the mammalian target of rapamycin (mTOR) pathway in some types of cancer cells. However, little is known about the role of SAHA and autophagy in neuropathic pain after nerve injury. In the present study, we aim to investigate autophagy flux and the role of the mTOR pathway on spinal cells autophagy activation in neuropathic pain induced by SNL in rats that received SAHA treatment. Autophagy-related proteins and mTOR or its active form were assessed by using western blot, immunohistochemistry, double immunofluorescence staining and transmission electron microscopy (TEM). We found that SAHA decreased the paw mechanical withdrawal threshold (PMWT) of the lower compared with SNL. Autophagy flux was mainly disrupted in the astrocytes and neuronal cells of the spinal cord dorsal horn on postsurgical day 28 and was reversed by daily intrathecal injection of SAHA (n?=?100 nmol/day or n?=?200 nmol/day). SAHA also decreased mTOR and phosphorylated mTOR (p-mTOR) expression, especially p-mTOR expression in astrocytes and neuronal cells of the spinal dorsal horn. These results suggest that SAHA attenuates neuropathic pain and contributes to autophagy flux in astrocytes and neuronal cells of the spinal dorsal horn via the mTOR signaling pathway.

     

姜黄素下调脊髓Toll样受体4及下游细胞因子减弱大鼠神经病理性痛

观察鞘内注射姜黄素对坐骨神经慢性压迫性损伤(CCI)大鼠痛阈和脊髓组织Toll样受体4(TLR4)及TNF-α、IL-1β和IL-10表达的影响．鞘内置管的120只大鼠随机均分为4组：假手术组(Sham),CCI组,溶剂对照组(SC),姜黄素治疗组(Cur,100 μg/天),建立CCI大鼠疼痛模型,术后第1、3、7、10和14天鞘内给药并测定痛阈,第3、7天取腰段脊髓第4～6节段(L4～L6)以Real-time PCR与Western blotting方法检测TLR4、HMGB1 mRNA和蛋白质的表达,ELISA法观察脊髓组织中TNF-α、IL-1β及IL-10表达变化．与Sham组相比,CCI组大鼠机械性痛阈与热痛阈显著降低(均P<0.05),同时脊髓组织TLR4、HMGB1 mRNA和蛋白质的表达明显增加(均P<0.05),TNF-α、IL-1β与IL-10的含量也明显升高(均P<0.05);鞘内注射姜黄素明显降低脊髓TLR4、高迁移率族蛋白1(HMGB1),TNF-α和IL-1β的表达,显著升高脊髓IL-10的表达,同时明显改善CCI大鼠疼痛行为(P<0.05)．姜黄素减轻神经病理性疼痛可能与下调TLR4途径促炎症因子表达有关,抑制TLR4途径有望成为治疗神经病理性疼痛的新策略．     

鞘内联合给予米诺环素和IL-6的中和抗体对脊神经结扎模型所引起的热痛敏的镇痛作用

目的:研究鞘内联合给予米诺环素和IL-6的中和抗体在大鼠脊神经结扎(spinal nerve ligation,SNL)模型所引起的神经病理性痛中的镇痛作用。方法:建立大鼠SNL模型,分别在手术前和手术后鞘内给予米诺环素100μg、在手术后鞘内给予IL-6的中和抗体0.03μg、手术后鞘内联合给予两种药物,观察给药3天各组大鼠热刺激的缩足反应潜伏期(paw withdrawal latencies,PWL)。结果:①SNL手术前后给予米诺环素都可以提高大鼠的PWL(P<0.05),但SNL手术前给药对大鼠PWL的提升明显高于手术后给药(P<0.05)。②手术后给予IL-6的中和抗体可以有效提升SNL组的PWL(P<0.05),但是还是比给予生理盐水的假手术组大鼠的PWL明显减少(P<0.05)。③手术后联合给予两种药物可以明显逆转SNL组的PWL(P<0.05)。④联合给药对大鼠PWL的提高明显高于SNL手术后给予米诺环素组和给予IL-6的中和抗体组(P<0.05),但与手术前给予米诺环素组的PWL相比无明显差异(P>0.05)。结论:鞘内联合给予米诺环素和IL-6的中和抗体对SNL引起的神经病理性痛有明显的镇痛作用。     

Intra-amygdala microinfusion of neuropeptide S attenuates neuropathic pain and suppresses the response of spinal microglia and astrocytes after spinal nerve ligation in rats

The amygdala circuitry and neuropeptide S (NPS) have been shown to play an important role in the pain modulation. However, the alleviative effect of NPS in amygdala on neuropathic pain (NP) is not fully understood. Here, we demonstrate a possibility that the intra-amygdala microinfusion of NPS attenuates NP symptoms and suppresses the response of spinal microglia and astrocytes after spinal nerve injury. Spinal nerve ligation (SNL) in rats resulted in a striking decline in level of NPS and density of NPS-immunopositive cells in amygdala. SNL rats randomly received chronic bilateral microinjections of NPS (1, 10 and 100 pmol/side) or saline into the amygdala via cannulas on days 3, 6, 9, 12, 15 and 18 post-surgery. Chronic treatment with NPS increased thermal withdrawal latency (TWL) and mechanical withdrawal threshold (MWT) on day 11–21 post-SNL. The simultaneous treatment with SHA68 as non-peptide NPS receptor antagonist decreased the TWL and MWT, and reversed the inhibitory effects of NPS in SNL rats. NPS also significantly attenuated immunoreactivities of ionized calcium-binding adapter molecule 1 and glial fibrillary acidic protein for microglia and astrocytes. Furthermore, the elevated levels of inflammatory mediators and expressions of nuclear factor κB p65 and CX3C chemokine receptor 1 due to SNL were significantly attenuated by NPS in amygdala. These effects of NPS were also counteracted by SHA 68. SHA 68 per se deteriorated the symptom of NP and the response of spinal microglia and astrocytes in SNL rats. Our study identified a protective role for NPS in amygdala against the development of NP, possibly attributing to its anti-inflammatory activity and inhibition of spinal microglia and astrocytes.     

Tyrosine phosphorylation of the N-Methyl-D-Aspartate receptor 2B subunit in spinal cord contributes to remifentanil-induced postoperative hyperalgesia: the preventive effect of ketamine

Neuropathic pain is a debilitating pain condition that occurs after nerve damage. Such pain is considered to be a reflection of the aberrant excitability of dorsal horn neurons. Emerging lines of evidence indicate that spinal microglia play a crucial role in neuronal excitability and the pathogenesis of neuropathic pain, but the mechanisms underlying neuron-microglia communications in the dorsal horn remain to be fully elucidated. A recent study has demonstrated that platelet-derived growth factor (PDGF) expressed in dorsal horn neurons contributes to neuropathic pain after nerve injury, yet how PDGF produces pain hypersensitivity remains unknown. Here we report an involvement of spinal microglia in PDGF-induced tactile allodynia. A single intrathecal delivery of PDGF B-chain homodimer (PDGF-BB) to naive rats produced a robust and long-lasting decrease in paw withdrawal threshold in a dose-dependent manner. Following PDGF administration, the immunofluorescence for phosphorylated PDGF β-receptor (p-PDGFRβ), an activated form, was markedly increased in the spinal dorsal horn. Interestingly, almost all p-PDGFRβ-positive cells were double-labeled with an antibody for the microglia marker OX-42, but not with antibodies for other markers of neurons, astrocytes and oligodendrocytes. PDGF-stimulated microglia in vivo transformed into a modest activated state in terms of their cell number and morphology. Furthermore, PDGF-BB-induced tactile allodynia was prevented by a daily intrathecal administration of minocycline, which is known to inhibit microglia activation. Moreover, in rats with an injury to the fifth lumbar spinal nerve (an animal model of neuropathic pain), the immunofluorescence for p-PDGFRβ was markedly enhanced exclusively in microglia in the ipsilateral dorsal horn. Together, our findings suggest that spinal microglia critically contribute to PDGF-induced tactile allodynia, and it is also assumed that microglial PDGF signaling may have a role in the pathogenesis of neuropathic pain.     

Galectin-3 Inhibition Is Associated with Neuropathic Pain Attenuation after Peripheral Nerve Injury

Neuropathic pain remains a prevalent and persistent clinical problem because it is often poorly responsive to the currently used analgesics. It is very urgent to develop novel drugs to alleviate neuropathic pain. Galectin-3 (gal3) is a multifunctional protein belonging to the carbohydrate-ligand lectin family, which is expressed by different cells. Emerging studies showed that gal3 elicits a pro-inflammatory response by recruiting and activating lymphocytes, macrophages and microglia. In the study we investigated whether gal3 inhibition could suppress neuroinflammation and alleviate neuropathic pain following peripheral nerve injury. We found that L5 spinal nerve ligation (SNL) increases the expression of gal3 in dorsal root ganglions at the mRNA and protein level. Intrathecal administration of modified citrus pectin (MCP), a gal3 inhibitor, reduces gal3 expression in dorsal root ganglions. MCP treatment also inhibits SNL-induced gal3 expression in primary rat microglia. SNL results in an increased activation of autophagy that contributes to microglial activation and subsequent inflammatory response. Intrathecal administration of MCP significantly suppresses SNL-induced autophagy activation. MCP also inhibits lipopolysaccharide (LPS)-induced autophagy in cultured microglia in vitro. MCP further decreases LPS-induced expression of proinflammatory mediators including IL-1β, TNF-α and IL-6 by regulating autophagy. Intrathecal administration of MCP results in adecreased mechanical and cold hypersensitivity following SNL. These results demonstrated that gal3 inhibition is associated with the suppression of SNL-induced inflammatory process andneurophathic pain attenuation.     

Electroacupuncture alleviates diabetic neuropathic pain in rats by suppressing P2X3 receptor expression in dorsal root ganglia

Diabetic neuropathic pain (DNP) is a troublesome diabetes complication all over the world. P2X3 receptor (P2X3R), a purinergic receptor from dorsal root ganglion (DRG), has important roles in neuropathic pain pathology and nociceptive sensations. Here, we investigated the involvement of DRG P2X3R and the effect of 2 Hz electroacupuncture (EA) on DNP. We monitored the rats’ body weight, fasting blood glucose level, paw withdrawal thresholds, and paw withdrawal latency, and evaluated P2X3R expression in DRG. We found that P2X3R expression is upregulated on DNP, while 2 Hz EA is analgesic against DNP and suppresses P2X3R expression in DRG. To evaluate P2X3R involvement in pain modulation, we then treated the animals with A317491, a P2X3R specific antagonist, or α β-me ATP, a P2X3R agonist. We found that A317491 alleviates hyperalgesia, while α β-me ATP blocks EA’s analgesic effects. Our findings indicated that 2 Hz EA alleviates DNP, possibly by suppressing P2X3R upregulation in DRG.

     

Suppressing PKC-dependent membrane P2X3 receptor upregulation in dorsal root ganglia mediated electroacupuncture analgesia in rat painful diabetic neuropathy

Painful diabetic neuropathy (PDN) is a common and troublesome diabetes complication. Protein kinase C (PKC)-mediated dorsal root ganglia (DRG) P2X3 receptor upregulation is one important mechanism underlying PDN. Accumulating evidence demonstrated that electroacupuncture (EA) at low frequency could effectively attenuate neuropathic pain. Our previous study showed that 2-Hz EA could relieve pain well in PDN. The study aimed to investigate whether 2-Hz EA relieves pain in PDN through suppressing PKC-mediated DRG P2X3 receptor upregulation. A 7-week feeding of high-fat and high-sugar diet plus a single injection of streptozotocin (STZ) in a dose of 35 mg/kg after a 5-week feeding of the diet successfully induced type 2 PDN in rats as revealed by the elevated body weight, fasting blood glucose, fasting insulin and insulin resistance, and the reduced paw withdrawal threshold (PWT), as well as the destructive ultrastructural change of sciatic nerve. DRG plasma membrane P2X3 receptor level and DRG PKC expression were elevated. Two-hertz EA failed to improve peripheral neuropathy; however, it reduced PWT, DRG plasma membrane P2X3 receptor level, and DRG PKC expression in PDN rats. Intraperitoneal administration of P2X3 receptor agonist αβ-meATP or PKC activator phorbol 12-myristate 13-acetate (PMA) blocked 2-Hz EA analgesia. Furthermore, PMA administration increased DRG plasma membrane P2X3 receptor level in PDN rats subject to 2-Hz EA treatment. These findings together indicated that the analgesic effect of EA in PDN is mediated by suppressing PKC-dependent membrane P2X3 upregulation in DRG. EA at low frequency is a valuable approach for PDN control.     

miR-32-5p-mediated Dusp5 downregulation contributes to neuropathic pain

Previous studies have demonstrated that microRNAs (miRNAs) play important roles in the pathogenesis of neuropathic pain. In the present study, we found that miR-32-5p was significantly upregulated in rats after spinal nerve ligation (SNL), specifically in the spinal microglia of rats with SNL. Functional assays showed that knockdown of miR-32-5p greatly suppressed mechanical allodynia and heat hyperalgesia, and decreased inflammatory cytokine (IL-1β, TNF-α and IL-6) protein expression in rats after SNL. Similarly, miR-32-5p knockdown alleviated cytokine production in lipopolysaccharide (LPS)-treated spinal microglial cells, whereas its overexpression had the opposite effect. Mechanistic investigations revealed Dual-specificity phosphatase 5 (Dusp5) as a direct target of miR-32-5p, which is involved in the miR-32-5p-mediated effects on neuropathic pain and neuroinflammation. We demonstrated for the first time that miR-32-5p promotes neuroinflammation and neuropathic pain development through regulation of Dusp5. Our findings highlight a novel contribution of miR-32-5p to the process of neuropathic pain, and suggest possibilities for the development of novel therapeutic options for neuropathic pain.     

Aloperine attenuated neuropathic pain induced by chronic constriction injury via anti-oxidation activity and suppression of the nuclear factor kappa B pathway

Objective

To investigate whether aloperine (ALO) has antinociceptive effects on neuropathic pain induced by chronic constriction injury, whether ALO reduces ROS against neuropathic pain, and what are the mechanisms involved in ALO attenuated neuropathic pain.

Methods

Mechanical and cold allodynia, thermal and mechanical hyperalgesia and spinal thermal hyperalgesia were estimated by behavior methods such as Von Frey filaments, cold-plate, radiant heat, paw pressure and tail immersion on one day before surgery and days 7, 8, 10, 12 and 14 after surgery, respectively. In addition, T-AOC, GSH-PX, T-AOC and MDA in the spinal cord (L4/5) were measured to evaluate anti-oxidation activity of ALO on neuropathic pain. Expressions of NF-κB and pro-inflammatory cytokines (TNF-α, IL-6, IL-1β) in the spinal cord (L4/5) were analyzed by using Western blot.

Results

Administration of ALO (80 mg/kg and 40 mg/kg, i.p.) significantly increased paw withdrawal threshold, paw pressure, paw withdrawal latencies, tail-curling latencies, T-AOC, GSH-PX and T-SOD concentration, reduced the numbers of paw lifts and MDA concentration compared to CCI group. ALO attenuated CCI induced up-regulation of expressions of NF-κB, TNF-α, IL-6, IL-1β at the dose of 80 mg/kg (i.p.). Pregabalin produced similar effects serving as positive control at the dose of 10 mg/kg (i.p.).

Conclusion

ALO has antinociceptive effects on neuropathic pain induced by CCI. The antinociceptive effects of ALO against neuropathic pain is related to reduction of ROS, via suppression of NF-κB pathway.     

The Red Nucleus Interleukin-6 Participates in the Maintenance of Neuropathic Pain Induced by Spared Nerve Injury

Previous studies have demonstrated that the red nucleus (RN) is involved in the regulation of neuropathic pain and plays both facilitated and inhibitory roles through different cytokines. Here, we aim to investigate the expression changes and roles of interleukin-6 (IL-6), a pleiotropic cytokine, as well as its receptor (IL-6R) in the RN of rats with neuropathic pain induced by spared nerve injury (SNI). Immunohistochemistry indicated that IL-6 and IL-6R were weakly expressed in the RN of normal rats, and were mainly co-localized with neurons and oligodendrocytes. Following SNI, the expression levels of IL-6 and IL-6R in the RN did not show obvious changes at 1 week and 2 weeks postinjury. However, both of them were significantly increased in the RN contralateral (but not ipsilateral) to the nerve ligation side at 3 weeks postinjury, and co-localized not only with neurons and oligodendrocytes, but also with numerous astrocytes. Injection of different doses of anti-IL-6 antibody (100, 250, 500 ng) into the RN contralateral to the nerve ligation side at 3 weeks postinjury dose-dependently increased the paw withdrawal threshold (PWT) of rats and alleviated SNI-induced mechanical allodynia. Conversely, injection of different doses of recombinant rat IL-6 (5.0, 10, 20 ng) into the unilateral RN of normal rats dose-dependently decreased the PWT of contralateral (but not ipsilateral) hind paw and evoked significant mechanical allodynia, which was similar to SNI-induced neuropathic allodynia. These results further support the conclusion that the RN is involved in the modulation of neuropathic pain, and suggest that IL-6 and IL-6R in the RN play a facilitated role in the later maintenance of SNI-induced neuropathic pain.     

Imaging P2X4 receptor lateral mobility in microglia: regulation by calcium and p38 MAPK

ATP-gated ionotropic P2X4 receptors are up-regulated in activated microglia and are critical for the development of neuropathic pain, a microglia-associated disorder. However, the nature of how plasma membrane P2X4 receptors are regulated in microglia is not fully understood. We used single-molecule imaging to track quantum dot-labeled P2X4 receptors to explore P2X4 receptor mobility in the processes of resting and activated microglia. We find that plasma membrane P2X4 receptor lateral mobility in resting microglial processes is largely random, consisting of mobile and slowly mobile receptors. Moreover, lateral mobility is P2X subunit- and cell-specific, increased in an ATP activation and calcium-dependent manner, and enhanced in activated microglia by the p38 MAPK pathway that selectively regulates slowly mobile receptors. Thus, our data indicate that P2X4 receptors are dynamically regulated mobile ATP sensors, sampling more of the plasma membrane in response to ATP and during the activated state of microglia that is associated with nervous system dysfunction.     

Loganin prevents CXCL12/CXCR4-regulated neuropathic pain via the NLRP3 inflammasome axis in nerve-injured rats

BackgroundNeuropathic pain has been shown to be modulated by the activation of the chemokine C-X-C motif ligand 12 (CXCL12)/chemokine CXC receptor 4 (CXCR4) dependent nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome. Loganin, an iridoid glycoside, was proven to prevent neuropathic pain, but its underlying mechanisms related to NLRP3 activation are still unknown.PurposeThis study investigated the underlying mechanisms of loganin's effect on chronic constriction injury (CCI)-induced NLRP3 inflammasome activation in the spinal cord.MethodsSprague-Dawley rats were randomly divided into four groups: sham, CCI, sham + loganin, and CCI + loganin. Loganin (5 mg/kg/day) was administered intraperitoneally starting the day after surgery. Paw withdrawal threshold (PWT) and latency (PWL) were assessed before CCI and on days 1, 3, 7 and 14 after CCI. Spinal cords were collected for western blots and immunofluorescence studies.ResultsLoganin prevented CCI-attenuated PWT and PWL, suggesting improved mechanical allodynia and thermal hyperalgesia. The expression of CXCL12, CXCR4, thioredoxin-interacting protein (TXNIP), NLRP3 inflammasome (NLRP3, ASC, and caspase-1), IL-1β, and IL-18 were enhanced on day 7 after CCI, and all were reduced after loganin treatment. Dual immunofluorescence also showed that increased CXCL12, CXCR4, and NLRP3 were colocalized with NeuN (neuronal marker), GFAP (astrocyte marker), and Iba1 (microglial marker) on day 7 in the ipsilateral spinal dorsal horn (SDH). These immunoreactivities were attenuated in loganin-treated rats. Moreover, loganin decreased the assembly of NLRP3/ASC inflammasome after CCI in the ipsilateral SDH. Loganin appears to attenuate CCI-induced neuropathic pain by suppressing CXCL12/CXCR4-mediated NLRP3 inflammasome.ConclusionOur findings suggest that loganin might be a suitable candidate for managing CCI-provoked neuropathic pain.     

Intrathecal Infusion of Hydrogen-Rich Normal Saline Attenuates Neuropathic Pain via Inhibition of Activation of Spinal Astrocytes and Microglia in Rats

Background

Reactive oxygen and nitrogen species are key molecules that mediate neuropathic pain. Although hydrogen is an established antioxidant, its effect on chronic pain has not been characterized. This study was to investigate the efficacy and mechanisms of hydrogen-rich normal saline induced analgesia.

Methodology/Principal findings

In a rat model of neuropathic pain induced by L5 spinal nerve ligation (L5 SNL), intrathecal injection of hydrogen-rich normal saline relieved L5 SNL-induced mechanical allodynia and thermal hyperalgesia. Importantly, repeated administration of hydrogen-rich normal saline did not lead to tolerance. Preemptive treatment with hydrogen-rich normal saline prevented development of neuropathic pain behavior. Immunofluorochrome analysis revealed that hydrogen-rich normal saline treatment significantly attenuated L5 SNL-induced increase of 8-hydroxyguanosine immunoreactive cells in the ipsilateral spinal dorsal horn. Western blot analysis of SDS/PAGE-fractionated tyrosine-nitrated proteins showed that L5 SNL led to increased expression of tyrosine-nitrated Mn-containing superoxide dismutase (MnSOD) in the spinal cord, and hydrogen-rich normal saline administration reversed the tyrosine-nitrated MnSOD overexpression. We also showed that the analgesic effect of hydrogen-rich normal saline was associated with decreased activation of astrocytes and microglia, attenuated expression of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) in the spinal cord.

Conclusion/Significance

Intrathecal injection of hydrogen-rich normal saline produced analgesic effect in neuropathic rat. Hydrogen-rich normal saline-induced analgesia in neuropathic rats is mediated by reducing the activation of spinal astrocytes and microglia, which is induced by overproduction of hydroxyl and peroxynitrite.     

The rate and magnitude of atmospheric pressure change that aggravate pain-related behavior of nerve injured rats

Complaints of patients with chronic pain may increase when the weather changes. The exact mechanism for weather change-induced pain has not been clarified. We have previously demonstrated that artificially lowering barometric pressure (LP) intensifies pain-related behaviors in rats with neuropathic pain [chronic constriction injury (CCI) and spinal nerve ligation (SNL)]. In the present study, we examined the rate and magnitude of LP that aggravates neuropathic pain. We measured pain-related behaviors [number of paw lifts to von Frey hair (VFH) stimulation] in awake rats after SNL or CCI surgery, and found that rates of decompression ≥5 hPa/h and ≥10 hPa/h and magnitudes of decompression ≥5 hPa and ≥10 hPa augmented pain-related behaviors in SNL and CCI rats, respectively. These results indicate that LP within the range of natural weather patterns augments neuropathic pain in rats, and that SNL rats are more sensitive to LP than CCI rats.