小剂量氯胺酮对慢性神经痛大鼠的镇痛效应和背根神经节P2X3受体表达的影响

【 目的 观测腹腔注射小剂量氯胺酮对慢性神经痛大鼠镇痛效应和背根神经节P2X3受体表达的影响，以探讨其在神经性疼痛中的作用。方法 大鼠随机分为4组：空白对照组(C组)、假手术组(S组)、腹腔注射生理盐水组(NS组)与氯胺酮组(K组)，每组8只。在大鼠右后足检测冷刺激反应、热痛敏阈基础值后，腹腔注射10%水合氯醛400 mg∕kg进行麻醉。NS组和K组构建大鼠右侧坐骨神经慢性结扎损伤模型，S组暴露坐骨神经但不结扎，C组不进行手术。手术后K组每天上午10时腹腔注射10mg·kg-1氯胺酮(用生理盐水稀释至0.5ml)，NS组则腹腔注射等量生理盐水，连续2周。14d后测定各组大鼠右后足冷刺激反应、热痛敏阈值。尔后各组取手术侧L4背根神经节，并采用免疫组化法观测P2X3受体的表达。结果 手术后14 d，NS组和K组大鼠右足热痛敏阈值均明显低于C组和S组（P<0.05），冷刺激反应则显著高于C组和S组（P<0.05）；但K组大鼠右足热痛敏阈值明显高于NS组，而冷刺激反应明显低于NS组(P<0.05)；NS组和 K组大鼠背根神经节P2X3受体免疫反应阳性细胞数量多于C组和S组，但K组显著少于NS组比较则明显降低(P<0.05)；NS组与S组大鼠背根神经节神经元P2X3受体免疫组化评分高于C组和S组，而K组却低于NS组，(P<0.05)。结论 腹腔注射小剂量氯胺酮可提高慢性神经性疼痛大鼠痛敏阈值及减弱冷刺激反应，其作用机制可能与减少背根神经节神经元P2X3受体表达有关。【关键词】背根神经节 神经痛 氯胺酮 三磷酸腺苷 P2X3

Effect of low-dose katemine on P2X3 receptors expression in dorsal root ganglion of the rats with chronic neuropathic pain

【ABSTRACT 】 Objective this study has been addressed to observe the expression of dorsal root ganglion P2X3 receptor in chronic neuropathic pain rat models and the impact and analgesic effects after abdominal cavity injection of small doses of ketamine to the models by applying immunohistochemistry methods. Methods 32 SD adult male rats, weighting 180-220g, were randomly divided into four groups? negative control group (Group C, n=8), sham-operated group (group S, n=8), abdominal cavity injection physiological saline group (group NS, n=8) and the abdominal cavity injection of ketamine group (group K, n=8). After examining the thermal nociceptive threshold and the basal values of thermal hyperalgesia mesured with ice-cold water on rats’ right hind paw and narcotizing them with 10% chlorine hydrate aldehyde 400mg•kg-1 by abdominal cavity injection, the chronic constriction injury (CCI) model was set up in surgical group by right sciatic nerve exposure and ligation, then the same operation was applied in sham-operated group except ligation, and no surgery was operated in negative control group. After operation, a daily abdominal cavity injection of ketamine 10mg•kg-1 (diluted in physiological saline solution to 0.5ml) was being applied in ketamine group at 10?, and the same volume physiological saline solution was being injected to NS group for two weeks. After 14 days, rats’ right hind paw thermal nociceptive threshold and the response to thermal hyperalgesia mesured with ice-cold water was measured to each group. After test, rats were fixed and the surgical side L4 dorsal root ganglions were taken out under deep narcosis. The P2X3 receptor expression in the surgical side L4 dorsal root ganglion in each group was investigated by immunohistochemistry methods. Results (1) 14 days later, chronic neuropathic pain was being observed in NS group and K group rats, which expressed as the thermal nociceptive threshold was significantly less than C group and sham-operated group, and the response of thermal hyperalgesia mesured with ice-cold water was measured in an opposite direction with a significant p value ( P<0.05 ). (2) There were more dorsal root ganglion P2X3 receptors immune response-positive cells in NS group and K group than in C group and sham-operated group, but those cells saw a much lower number in K group comparing with NS group, and the difference is significant ( P<0.05 ). (3) The immunohistochemistic dyeing grade of dorsal root ganglion P2X3 receptors for NS group is significantly higher than C group and sham-operated group with a p value less than 0.05, and the grade for K group is significantly lower than NS group. Conclusion (1) Abdominal cavity injection of small doses of ketamine has a significant analgesic effect on chronic neuropathic pain rat models. (2) Dorsal root ganglion P2X3 receptors expression increased in chronic neuropathic pain rat models, which suggests that P2X3 receptors might play an important role in chronic neuropathic pain. (3) Abdominal cavity injection of small doses of ketamine can significantly inhibit the increase of dorsal root ganglion P2X3 receptors, which indicates that small doses ketamine reducing chronic neuropathic pain at least partly functions through decreasing the expression of dorsal root ganglion P2X3 receptors.