骨癌痛大鼠脊髓背角Nogo-A 及其受体NgR1表达的变化

目的 观察骨癌痛大鼠脊髓背角Nogo-A 及其受体NgR1 表达的变化。方法 雌性未交 配SD 大鼠60 只,体重160～200 g,采用随机数字表法将其分为两组（n=30）：假手术组（S 组）和骨癌痛组 （BCP组）。BCP组于左侧胫骨骨髓腔内注射5 μl Walker256 乳腺癌细胞制备骨癌痛模型,S 组左侧胫骨 骨髓腔内注射生理盐水5 μl。选用von Frey 纤维丝检测各组大鼠造模前1 d 及造模后3、7、14、21 d 机 械缩足阈值（MWT）,评价疼痛行为学变化。于造模后7、14、21 d痛阈测定后取大鼠L 4～5脊髓背角,采 用Western Blot法测定 Nogo-A及其受体NgR1的表达。结果 与S组比较,BCP组肿瘤细胞接种后第7 天 MWT［（3.63±1.61）g］、第14天MWT［ （2.53±1.39）g］、第21天MWT［（2.40±1.16）g］降低（P＜0.05）;与 S 组比较,BCP 组大鼠术后7、14、21 d 脊髓背角Nogo-A 及其受体NgR1 表达上调（P＜ 0.05）。结论 脊髓 背角Nogo-A 及其受体NgR1 可能参与了骨癌痛机械痛敏的形成。     

鞘内注射甘珀酸对大鼠热痛刺激反应的影响

目的：研究甘珀酸对大鼠热痛刺激反应的影响。方法：向实验组大鼠鞘内注射一种缝隙连接的阻断剂甘珀酸。对照组大鼠鞘内注射生理盐水，在注射前和注射后测定热痛刺激大鼠缩足潜伏期（PWTL）的变化，并观察对脊髓背角胶质原纤维酸性蛋白（GFAP）和Fos蛋白表达的影响。结果：实验组阻断后PWTL测定值明显延长，与对照组差异具有统计学意义（P＜0．05）；且阻断后Fos阳性神经元与对照组相比数量明显减少，GFAP阳性细胞则未见明显增加或减少。结论：本研究表明大鼠鞘内注射甘珀酸后（1）痛阈升高；（2）神经元对伤害性刺激信息的反应程度减弱，而AS析GFAP表达反应并未受影响。这提示，缝隙连接在疼痛的发生和维持中起着重要作用，AS有可能是通过缝隙连接参与对疼痛反应的过程。     

谷氨酸对丘脑束旁核痛兴奋神经元放电的影响

目的：观察脑室注射谷氨酸（Glu)对大鼠丘脑束旁核（PF）痛兴奋神经元（PEN）电变化的影响。方法：以电脉冲刺激右侧坐骨神经作为伤害性痛刺激，用玻璃微电极细胞外记录神经元放电的变化。结果：（1）伤害性刺激使大鼠丘脑PF的PEN诱发放电频率增加；（2）脑室注射Glu(1.5μg/10μl）加强PEN的电活动，使PEN放电频率的净增值增加，潜伏期缩短；（3）这种作用可被Glu的NMDA受体拮抗剂MK－801（0．17μg/0.5μl)所阻断。结论：Glu在中枢痛沉调制中可能起兴奋作用，而NMDA受体参与介导中枢伤害性信息的传递过程。     

MEK阻滞剂U0126对背根神经节压迫神经痛模型大鼠nNOS表达的影响

摘要 背景：胞外信号调节激酶（ERK）信号通路以及NO激活,是伤害性刺激引起中枢敏化和长时程神经元可塑性中的重要因素,但二者在慢性压迫性损伤引起的神经痛的形成和维持中的作用尚未见报道。 目的：研究ERK信号传导通路阻滞剂U0126对背根神经节压迫神经痛大鼠脊髓背角内神经型一氧化氮合酶表达。 设计,时间及地点：随机对照的实验研究,于2008年7月至2009年3月在吉林大学第一医院耳鼻咽喉头颈外科研究所完成。 材料：雄性Wistar大鼠由吉林大学实验动物中心提供;U0216（美国Bio-Mol公司产品） 方法：CCD模型建立后第五天,采用单次鞘内注射方法行U0126注射,同时在对照组给予鞘内注射无菌的5%二甲基亚砜。 主要观察指标：采用von Frey纤维丝和热痛刺激仪观察CCD大鼠鞘内应用U0126后机械性痛敏和热痛敏阈值的变化,同时应用免疫荧光染色和免疫印记方法观察其对大鼠脊髓背角内nNOS活性的影响。 结果：CCD引起大鼠脊髓背角内nNOS活性的增强,鞘内注射U0126抑制nNOS活性的同时能明显减轻由CCD导致的大鼠机械性痛敏和热痛敏。 结论：脊髓背角神经元胞内ERK信号通路活性的变化能够影响脊髓背角内nNOS表达,ERK参与介导了NO在神经病理性疼痛中的作用。。 主题词：细胞外信号调节激酶;一氧化氮合成酶;神经痛;中枢敏化;痛觉过敏     

在尾核痛反应神经元和整体甩尾反射水平上研究CCK-8对抗电针的镇痛作用

目的 研究八肽胆囊收缩素（CCK-8）对抗电针（EA）对大鼠尾核（Cd）中痛反应神经元放电和甩尾潜伏期（TFL）痛阈的同时影响。方法 采用同步记录大鼠Cd中痛兴奋神经元（PEN）或痛抑制神经元（PIN）电变化与辐射热照大鼠尾所引起TFL的方法。结果 （1）辐射热照大鼠尾可使PEN诱发放电增加或PIN诱发放电减少的同时发生甩尾反射，表现出辐射热致疼痛效应。（2）EA双侧“足三里”15min，可抑制PEN的电活动或加强PIN的电活动，同时使TFL延长，即呈现出EA的镇痛效应。（3）脑室（icv）注射CCK-8（10ng／10μl）能同时对抗EA所引起的PEN或PIN和TFL的镇痛作用。结论 CCK-8的抗EA镇痛作用，在中枢痛反应神经元电活动和整体行为反射水平上是协调一致的。揭示，PEN和PIN的电活动作为疼痛和镇痛指标是确实可行的。     

NMDA受体激活诱导甲醛炎性痛大鼠脊髓HO-1蛋白表达增加

目的本实验通过在甲醛炎性痛大鼠鞘内注射N-甲基-D-d门冬氨酸(NMDA)受体抑制剂地卓西平马来酸盐(MK-801)以及在正常大鼠鞘内注射NMDA受体激动剂NMDA,观察二者对甲醛炎性痛大鼠以及正常大鼠脊髓血红素氧合酶-1(HO-1)表达的影响,探讨甲醛炎性痛诱导的大鼠脊髓HO-1蛋白表达改变是否受NMDA受体激活的影响。方法采用右后掌足底注射甲醛复制炎性痛模型,采用免疫组织化学方法观察脊髓HO-1蛋白表达。结果甲醛炎性痛大鼠L5脊髓后角Ⅰ-Ⅱ板层HO-1蛋白免疫反应阳性细胞数目、平均光密度值均明显大于正常对照组,预先鞘内注射MK-801可明显抑制甲醛炎性痛诱导的大鼠双侧脊髓后角Ⅰ-Ⅱ板层HO-1蛋白的表达,正常大鼠鞘内注射NMDA可诱导脊髓后角HO-1蛋白表达增加。结论 NMDA受体激活可促进脊髓神经元HO-1蛋白的表达。     

鞘内注射曲马多对手术致痛大鼠脊髓c-fos蛋白表达的影响

目的在大鼠手术致痛模型中研究鞘内注射曲马多对脊髓c-fos蛋白的影响,探讨曲马多的超前镇痛效应。方法选取鞘内置管成功的32只雄性大鼠随机分为4组,每组8只,分别为假手术组(S组),实验对照组(EC组),术前曲马多组(TP20组,20μg/10μl)以及术后曲马多组(PT20组,20μg/10μl)。按照Brennan法制成大鼠切口痛模型,致痛2 h后,深麻醉大鼠,灌注固定,取脊髓L4～L6节段做c-fos免疫组化染色,观察大鼠脊髓c-fos蛋白表达的变化情况。结果 3个实验组的IOD值与假手术组相比较,均有不同程度的升高,差异有统计学意义(P0.05);TP20组、PT20组的IOD值与EC组相比较,均弱于实验对照组,差异有统计学意义(P0.05);TP20组的IOD值与PT20组相比较,差异有统计学意义(P0.05)。结论手术致痛前或后,鞘内注射曲马多均能抑制大鼠脊髓背角c-fos蛋白的表达;曲马多预先给药,抗伤害作用更好,具有超前镇痛效应。     

侧脑室微量注射左旋多巴治疗大鼠帕金森病

目的观察经侧脑室注射左旋多巴对帕金森病（PD）大鼠的影响。方法应用“羟基多巴胺立体定向脑内注射制备偏侧损毁的PD大鼠模型，并用阿扑吗啡（APO）皮下注射诱发大鼠向健侧旋转。将24只PD大鼠随机分为4组（n=6），经侧脑室注入生理盐水组为对照组，余3组分别经侧脑室注射浓度为0．1μg／μl、1μg／μl和5μg／μl的左旋多巴1μl，4μl／d，连续1周；观察在注射后不同时间大鼠旋转行为以及中脑黑质多巴胺能神经元数量的变化。结果经侧脑室注射1μg/μl和5μg/μl的左旋多巴后。与对照组相比，PD大鼠向健侧的旋转圈数明显减少（P〈0．01），左旋多巴效果在2h左右达到高峰，且中脑黑质多巴胺能神经元的数量也明显增多（P〈0．01）。结论经侧脑室注射适当剂量的左旋多巴可有效地改善PD大鼠的旋转行为，并增加中脑黑质多巴胺能神经元数量。     

蓝斑核注射乙酰胆碱对大鼠蓝斑核痛反应神经元电活动的影响

[摘要] 目的 观察蓝斑核（LC）注射乙酰胆碱(ACh)后,蓝斑核（LC）中痛反应神经元的放电变化,研究ACh与LC在痛觉信息通路中的作用。 方法 以电脉冲刺激坐骨神经作为伤害性刺激,用玻璃微电极引导LC中痛反应神经元的电变化。结果 ① LC内注入ACh能够使大鼠LC中痛兴奋神经元（PEN）痛诱发放电频率增加、潜伏期缩短;痛抑制神经元（PIN）痛诱发放电频率减少、完全抑制时程延长;② LC内注入ACh 的M受体拮抗剂阿托品能够阻断ACh的上述效应。结论 ACh可使正常大鼠LC中痛反应神经元对伤害性刺激的反应增强,表现为致痛效应;揭示了ACh和LC在痛觉调制中具有非常重要的作用。     

福尔马林致炎大鼠鞘内注射布托啡诺后脊髓背角NMDA受体的表达

研究背景与目的: 酒石酸布托啡诺是一种阿片类镇痛剂,对阿片受体具有激动/拮抗双重作用。其在临床和动物实验中的应用已有报道,但还未见鞘内应用于福尔吗林炎性痛大鼠模型的报道.另外在疼痛机制形成过程中,NMDA受体激活起着非常重要的作用。故我们假设鞘内注射酒石酸布托啡诺应用于福尔马林炎性痛大鼠时能产生明显的镇痛效果,其产生镇痛的机制可能是通过抑制NMDA受体表达来实现. 方法: 在大鼠的左后足掌面皮下注射5%福尔马林50μl致痛前30min,健康雄性SD大鼠接受生理盐水,低剂量布托啡诺（12.5μg）,高剂量布托啡诺（25μg）鞘内注射;对照组在福尔马林注射前不注射任何试剂,为了更进一步的研究,我们在设计中加入鞘内注射非选择性NMDA受体拮抗剂氯胺酮,也分别在福尔马林致痛前30min,鞘内注射低剂量（50μg）,高剂量（100μg）或低剂量（50μg）混合低剂量布托啡诺进行注射。与疼痛相关的行为学测定通过计算大鼠后爪理毛行为（后爪的离地、舔足/咬足）总计反应时间来确定,记录福尔马林诱导出注射后爪的双相理毛行为时间(在福尔马林注射后第1时相, 0-5 min; 第 2时相, 10-60 min ).所有大鼠均在注射后2h处死,用免疫组化法测定大鼠L5节段脊髓背角NMDA受体的表达。 结果：鞘内单独用布托啡诺当剂量增加到25μg时,以及鞘内低剂量布托啡诺和氯胺酮联合使用时都引起第1和2时相的后爪理毛行为的总计反应时间明显减少;其余的组别对福尔马林1和2时相都没有明显影响。鞘内单独用高剂量布托啡诺以及低剂量布托啡诺和氯胺酮联合处理都可以显著降低福尔马林致痛大鼠L5脊髓背角NMDA受体表达。 结论：本研究结果揭示鞘内用布托啡诺能够对福尔马林诱导的疼痛产生明显的镇痛作用,并具有剂量依赖性,其镇痛机制可能是通过抑制NMDA受体激活产生;不过具体NMDA受体抑制机制是否与鞘内布托啡诺激活к受体或μ受体有关还需要更进一步的研究来确定。     

Thermal hyperalgesia and mechanical allodynia produced by intrathecal administration of the human immunodeficiency virus-1 (HIV-1) envelope glycoprotein, gp120

Astrocytes and microglia in the spinal cord have recently been reported to contribute to the development of peripheral inflammation-induced exaggerated pain states. Both lowering of thermal pain threshold (thermal hyperalgesia) and lowering of response threshold to light tactile stimuli (mechanical allodynia) have been reported. The notion that spinal cord glia are potential mediators of such effects is based on the disruption of these exaggerated pain states by drugs thought to preferentially affect glial function. Activation of astrocytes and microglia can release many of the same substances that are known to mediate thermal hyperalgesia and mechanical allodynia. The aim of the present series of studies was to determine whether exaggerated pain states could also be created in rats by direct, intraspinal immune activation of astrocytes and microglia. The immune stimulus used was peri-spinal (intrathecal, i.t.) application of the Human Immunodeficiency Virus type 1 (HIV-1) envelope glycoprotein, gp120. This portion of HIV-1 is known to bind to and activate microglia and astrocytes. Robust thermal hyperalgesia (tail-flick, TF, and Hargreaves tests) and mechanical allodynia (von Frey and touch-evoked agitation tests) were observed in response to i.t. gp120. Heat denaturing of the complex protein structure of gp120 blocked gp120-induced thermal hyperalgesia. Lastly, both thermal hyperalgesia and mechanical allodynia to i.t. gp120 were blocked by spinal pretreatment with drugs (fluorocitrate and CNI-1493) thought to preferentially disrupt glial function.     

Effects of morphine on mechanical allodynia in a rat model of central neuropathic pain

We examined whether morphine reduced the behavioral signs of neuropathic pain below level induced by T13 spinal hemisection in rats. In order to examine the effect of morphine on the mechanical allodynia, morphine alone, morphine with naloxone and saline were administered intraperitoneally and intrathecally and behavioral tests were conducted. In systemic injection, mechanical allodynia was reduced only when a higher concentration of morphine (5 mg/kg) was used. Intrathecally injected morphine (0.5, 1, 2, 5 microg) reduced mechanical allodynia dose-dependently. It is suggested that systemic morphine has limited effect on mechanical allodynia but direct spinal administration of morphine is more effective in controlling central pain following spinal cord injury.     

Intrathecal injection of carbenoxolone, a gap junction decoupler, attenuates the induction of below-level neuropathic pain after spinal cord injury in rats

The most common type of chronic pain following spinal cord injury (SCI) is central neuropathic pain and SCI patients typically experience mechanical allodynia and thermal hyperalgesia. The present study was designed to examine the potential role of astrocyte gap junction connectivity in the induction and maintenance of “below-level” neuropathic pain in SCI rats. We examined the effect of intrathecal treatment with carbenoxolone (CARB), a gap junction decoupler, on SCI-induced bilateral thermal hyperalgesia and mechanical allodynia during the induction phase (postoperative days 0 to 5) and the maintenance phase (days 15 to 20) following T13 spinal cord hemisection. Immunohistochemistry was performed to determine potential SCI-induced changes in spinal astrocyte activation and phosphorylation of the NMDA receptor NR1 subunit (pNR1). CARB administered during the induction period dose-dependently attenuated the development of bilateral thermal hyperalgesia and mechanical allodynia. Intrathecal CARB also significantly reduced the bilateral SCI-induced increase in GFAP-immunoreactive (ir) staining and the number of pNR1-ir cell profiles in the spinal cord dorsal horn compared to vehicle-treated rats. In contrast, CARB treatment during the maintenance phase had no effect on the established thermal hyperalgesia and mechanical allodynia nor on spinal GFAP expression or the number of pNR1-ir cell profiles. These results indicate that gap junctions play a critical role in the activation of astrocytes distant from the site of SCI and in the subsequent phosphorylation of NMDA receptors in the lumbar spinal cord. Both of these processes appear to contribute to the induction of bilateral below-level pain in SCI rats.     

Enhanced thermal antinociceptive potency and anti-allodynic effects of morphine following spinal administration of endotoxin

Recently, an animal model of central inflammation characterized by widespread cutaneous hyperalgesia and allodynia following intracerebroventricular (i.c.v.) administration of lipopolysaccharide (LPS) was described. In the present study, we demonstrate that central administration of LPS via intrathecal (i.t.) injection produces bilateral tactile allodynia and thermal hyperalgesia in the rat. Also, the effects of morphine-induced antinociception were determined in this model. Here we demonstrate enhanced thermal antinociceptive potency of i.t. morphine in LPS-treated rats compared to controls. Intrathecal morphine was also effective in alleviating the tactile allodynia induced by LPS. Both the antinociceptive and anti-allodynic effects produced by i.t. morphine were completely antagonized by pretreatment with subcutaneous naloxone (1 mg kg⁻¹). This study demonstrates the presence of both heat hyperalgesia and mechanical allodynia following central administration of LPS, and an increased antinociceptive potency of i.t. morphine in this model.     

High Dose Therapy With Alpha-Lipoic Acid Improves Cutaneous Vasomotor Response In Patients With Diabetic Neuropathy

The saposin C-derived peptide TX14(A) prevents onset of functional and structural disorders in the peripheral nerve of diabetic rats. We have now investigated the ability of TX14(A) to alleviate behavioral indices of abnormal pain perception in adult female rats 4-6 weeks after onset of STZ-induced diabetes. Untreated diabetic rats exhibited tactile allodynia (response threshold = 3 ± 1 g) compared to age-matched controls (10 ± 1g). A single ip injection of TX14(A) transiently alleviated tactile allodynia, with an effect that was maximal 6 hours (11 ± 1g) after injection and diminished within 48 hours. Maximal efficacy was seen with a 1 mg/kg dose while no effects were noted in control rats. Control rats exhibited a transient thermal hyperalgesia (77 ± 5% of baseline paw withdrawal latency) 15 minutes after intrathecal delivery of substance P (30 nmol) that resolved within 30 minutes. Untreated diabetic rats exhibited substance P evoked thermal hyperalgesia of similar magnitude (82 ± 5% at 15 minutes) but of greater duration (83 ± 4% at 1 hour). Intrathecal delivery of TX14(A) 30 minutes before intrathecal substance P was without effect on the transient thermal hyperalgesia in control rats (74 ± 9% at 15 minutes). In diabetic rats, the prolonged thermal hyperalgesia was abolished by prior intrathecal delivery of TX14(A), although the transient thermal hyperalgesia (72 ± 8% at 15 minutes) remained. These studies show that TX14(A) can rapidly allevate diabetes-induced allodynia and hyperalgesia for up to 48 hours.     

Lumbar transplant of neurons genetically modified to secrete galanin reverse pain-like behaviors after partial sciatic nerve injury

The use of cell lines as biologic "minipumps" to chronically deliver antinociceptive molecules such as the peptide galanin near the pain processing centers of the spinal cord after nerve injury is a newly developing technology for the treatment of neuropathic pain. The neuronal rat cell line, RN33B, derived from E13 brainstem raphe and immortalized with the SV40 temperature-sensitive allele of large T antigen (tsTag), was transfected with rat preprogalanin (GAL) cDNA and the galanin-synthesizing and -secreting cell line, 33GAL.19, was isolated [1]. The 33GAL.19 cells transfected with the GAL gene expressed immunoreactivity (ir) for the GAL protein and synthesized low levels of GAL-ir at permissive temperature (33 degrees C), when the cells were proliferating, and increased GAL-ir during terminal differentiation at non-permissive temperature (39 degrees C) in vitro. A control cell line, 33V.1, RN33B cells transfected with the pCEP4 vector alone and similarly isolated by subcloning, contained no detectible GAL-ir at either temperature in vitro. These cell lines were used as grafts in a model of chronic neuropathic pain induced by unilateral chronic constriction injury (CCI) of the sciatic nerve. Pain-related behaviors, including cold and tactile allodynia and thermal and mechanical hyperalgesia, were evaluated in the affected hindpaw after CCI and transplants. The 33GAL.19 and 33V.1 cells transplanted in the lumbar subarachnoid space near the spinal cord one week after CCI, survived at least seven weeks on the pial surface around the spinal cord and only the 33GAL.19 cells expressed GAL-ir in vivo after transplant. Furthermore, the tactile and cold allodynia and tactile and thermal hyperalgesia induced by CCI was significantly reduced or eliminated during the two to seven week period after grafts of 33GAL.19 cells. The maximal effect on chronic pain behaviors with the GAL grafts occurred one to three weeks after transplantation. Transplants of 33V.1 control cells had no effect on the allodynia and hyperalgesia induced by CCI. These data suggest that a chronically applied, low local dose of galanin supplied by transplanted cells near the lumbar spinal dorsal horn was able to reverse the development of chronic neuropathic pain following CCI. The use of transplants of genetically modified neural cell lines that are able to deliver antinociceptive molecules, such as galanin, offers a safe and novel approach to pain management.     

鞘内注射催产素对大鼠神经痛反应的影响

目的 :观察不同剂量催产素对神经痛大鼠热痛敏的影响。方法 :在脊神经结扎致坐骨神经损伤大鼠模型上采用辐射热缩腿反射的方法 ,以抬脚潜伏期作为观察指标。结果 :蛛网膜下腔注射催产素 (1ng ,2 5ng ,5ng)对神经痛大鼠有镇痛作用 ,呈剂量相关关系。结论 :鞘内注射催产素对神经痛大鼠有镇痛作用。     

Chronic pain after clip-compression injury of the rat spinal cord

Chronic tactile allodynia and hyperalgesia are frequent complications of spinal cord injury (SCI) with poorly understood mechanisms. Possible causes are plastic changes in the central arbors of nociceptive and nonnociceptive primary sensory neurons and changes in descending modulatory serotonergic pathways. A clinically relevant clip-compression model of SCI in the rat was used to investigate putative mechanisms of chronic pain. Behavioral testing (n = 18 rats) demonstrated that moderate (35 g) or severe (50 g) SCI at the 12th thoracic spinal segment (T-12) reliably produces chronic tactile allodynia and hyperalgesia that can be evoked from the hindpaws and back. Quantitative morphometry (n = 37) revealed no changes after SCI in the density or distribution of Abeta-, Adelta-, and C-fiber central arbors of primary sensory neurons within the thoracolumbar segments T-6 to L-4. This observation rules out a mandatory relationship between pain-related behaviors and changes in the distribution or density of central afferent arbors. The area of serotonin immunoreactivity in the dorsal horn (n = 12) decreased caudal to the injury site (L1-4) and increased threefold rostral to it (T9-11). The decreased serotonin and presence of tactile allodynia and hyperalgesia caudal to the injury are consistent with disruption of descending antinociceptive serotonergic tracts that modulate pain transmission. The functional significance of the increased serotonin in rostral segments may relate to the development of tactile allodynia as serotonin also has known pronociceptive actions. Changes in the descending serotonergic pathway require further investigation, as a disruption of the balance of serotonergic input rostral and caudal to the injury site may contribute to the etiology of chronic pain after SCI.     

Antibody directed against GD(2) produces mechanical allodynia, but not thermal hyperalgesia when administered systemically or intrathecally despite its dependence on capsaicin sensitive afferents

Anti-GD₂ antibodies have been shown to be effective for immunotherapy of neuroblastoma and other GD₂ enriched malignancies. Infusion of anti-GD₂ antibodies frequently causes spontaneous pain and allodynia for the duration of the immunotherapy and occasionally longer lasting neuropathic pain. Bolus intravenous injection of anti-GD₂ in rats initiates mechanical allodynia as measured by withdrawal threshold of the hindpaws. In this study, thermal thresholds were measured prior to and for up to 6 h following systemic anti-GD₂ administration in adult rats. In addition, both thermal and mechanical thresholds were tested following intrathecal administration of anti-GD₂ and IgG_2a. Murine anti-GD₂ elicited mechanical allodynia when administered into either the vasculature or the intrathecal space. Effective systemic doses were 1–3 mg/kg as previously shown. Intrathecally, optimal doses ranged from 0.01 to 0.1 ng; a higher dose was ineffective. Thermal hyperalgesia was not observed via either route of administration. Intrathecal pretreatment 48–72 h prior to the experiment with capsaicin at doses sufficient to cause a 50% depletion of dorsal horn CGRP, caused a total blockade of the mechanical allodynia indicating an involvement of peptidergic fine afferent fibers. It is likely that the antibody reacts with an antigen on peripheral nerve and/or myelin to initiate its effect. The lack of observed thermal hyperalgesia is surprising especially in light of the capsaicin-associated blockade, however, it is consistent with several other immune system related models of pain.     

Microglial IL-10 and β-endorphin expression mediates gabapentinoids antineuropathic pain

Gabapentinoids are recommended first-line treatments for neuropathic pain. They are neuronal voltage-dependent calcium channel α2δ-1 subunit ligands and have been suggested to attenuate neuropathic pain via interaction with neuronal α2δ-1 subunit. However, the current study revealed their microglial mechanisms underlying antineuropathic pain. Intrathecal injection of gabapentin, pregabalin and mirogabalin rapidly inhibited mechanical allodynia and thermal hyperalgesia, with projected ED₅₀ values of 30.3, 6.2 and 1.5 µg (or 176.9, 38.9 and 7.2 nmol) and E_max values of 66%, 61% and 65% MPE respectively for mechanical allodynia. Intrathecal gabapentinoids stimulated spinal mRNA and protein expression of IL-10 and β-endorphin (but not dynorphin A) in neuropathic rats with the time point parallel to their inhibition of allodynia, which was observed in microglia but not astrocytes or neurons in spinal dorsal horns by using double immunofluorescence staining. Intrathecal gabapentin alleviated pain hypersensitivity in male/female neuropathic but not male sham rats, whereas it increased expression of spinal IL-10 and β-endorphin in male/female neuropathic and male sham rats. Treatment with gabapentin, pregabalin and mirogabalin specifically upregulated IL-10 and β-endorphin mRNA and protein expression in primary spinal microglial but not astrocytic or neuronal cells, with EC₅₀ values of 41.3, 11.5 and 2.5 µM and 34.7, 13.3 and 2.8 µM respectively. Pretreatment with intrathecal microglial metabolic inhibitor minocycline, IL-10 antibody, β-endorphin antiserum or μ-opioid receptor antagonist CTAP (but not κ- or δ-opioid receptor antagonists) suppressed spinal gabapentinoids-inhibited mechanical allodynia. Immunofluorescence staining exhibited specific α2δ-1 expression in neurons but not microglia or astrocytes in the spinal dorsal horns or cultured primary spinal cells. Thus the results illustrate that gabapentinoids alleviate neuropathic pain through stimulating expression of spinal microglial IL-10 and consequent β-endorphin.