吗啡镇痛耐受大鼠背根神经节κ阿片受体mRNA表达下调

DECREASED mRNA EXPRESSION OF KAPPA-OPIOID RECEPTOR IN DORSAL ROOT GANGLIA OF MORPHINE ANTINOCICEPTIVE TOLERANT RATS

目的:测定吗啡镇痛耐受大鼠背根神经节(DRG)中μ、δ、κ阿片受体的mRNA表达,进一步探索吗啡镇痛耐受中DRG阿片受体的作用。方法:健康成年♂Wistar大鼠20只,随机平均分为生理盐水对照组(NS组,n=10)和吗啡组(MS组,n=10)。采用盲法进行给药和疼痛行为测定。每天早、晚两次皮下注射(sc)药物,并于上午注射药物前、后30 min测定大鼠的热甩尾潜伏期(TFL)作为痛阈指标。NS组sc生理盐水1 ml.kg-1,MS组sc吗啡10mg.kg-1,连续注射7 d,d8早晨各组分别取5只处死,剩余大鼠(分别记为NSN亚组和MSN亚组)d8早晚两次sc纳洛酮0.4 mg.kg-1,并在d9处死。以TFL恢复至基础水平作为出现吗啡耐受的标准。大鼠处死后采用实时聚合酶链反应(real time PCR)方法检测L4-S4节段DRG中3种阿片受体的mRNA表达。结果:观察期两组大鼠的体重增加量差异无显著性,两组大鼠每天注射前测定的TFL差异无显著性。MS组大鼠在d1 sc吗啡后,TFL明显升高(P<0.05);d2注射吗啡后TFL达到最高,且明显高于d1用药后水平(P<0.01),随着吗啡用药次数增加,MS组用药后的TFL逐渐下降,d7应用吗啡后TFL降至基础水平(P>0.05),d8应用纳洛酮后,MSN亚组和NSN亚组的TFL并未发生显著性变化。采用real time PCR的2-ΔΔCt方法计算DRG中阿片受体的表达,MS组大鼠L4-S4节段DRG中μ受体和δ受体的mRNA表达与NS组差异无显著性,而κ受体的mRNA表达显著低于NS组;应用纳洛酮前、后,3种阿片受体的mRNA表达水平无明显改变。结论:DRG中κ受体的mRNA表达下调可能参与了吗啡镇痛耐受的形成。

To evaluate the changes of κ -opioid receptor mRNA in dorsal root ganglia （DRG） of morphine antinociceptive tolerant rats, and to further explore the mechanisms of opioid receptors in DRG level of morphine antinociceptive tolerant rats. Methods： Twenty adult male Wistar rats were randomly allocated equally to Group NS （n = 10） ,which received subcutaneous （sc）injections of 1 ml · kg^-1 normal saline in the nape, and Group MS （n = 10） , which received sc injections of morphine 10 mg · kg^-1. All rats were housed in the same environment and received sc injections twice a day for 7 days. In the morning of the 8th day,5 control rats and 5 morphine rats were killed. The remaining rats, which named as NSN subgroup and MSN subgroup, respectively, received no further morphine injections,but received 2 injections of naloxone （0.4 mg · kg^-1 ） on the 8th day,and were killed on the 9th day morning. The hot water tail -flick latency（TFL） was measured 30 min before and after every morning injection as an index of pain threshold, and the first average TFL before injection was considered baseline level. Morphine tolerance was developed as TFL returned to the baseline level. The expression of μ - , δ - , κ - opioid receptor mRNAs in L4 - S4 DRG of all rats was analyzed by using the method of real time PCR,respectively. Results ：The rats＇ weight gain in the observation period was not significantly different between the two groups. The pain behaviors indicated that TFLs before injection every morning were not signifieandy different between groups. The pain threshold of Group MS increased significantly after first morphine injection （P 〈 0. 05） and reached the highest value on the second day, even higher than the first day value （P 〈 0.01 ）. But as injections increasing, the average pain threshold after injection in Group MS shortened gradually and returned to baseline level after 7 day injections. There was no significant difference in TFL after naloxone injection between groups and the baseline value. After 7 day injection, the mRNA expression of DRG μ and 8 opioid receptor in Group MS was not different significantly from the expression level of Group NS, but a significant lower expression with respect to DRG κ -opioid receptor mRNA in Group MS. Naloxone injection also made no significant difference in mRNA expression of three opioid receptors between groups. Conclusion：The down - regulation of DRG κ - opioid receptor mRNA may play a role in the development of morphine antinoeiceptive tolerance.