丘脑中央下核在不同强度电针引起镇痛效应中的作用

Different-intensity electroacupuncture at thalamic nucleus submedius for analgesic effects

目的:观察双侧丘脑中央下核内微量注射局麻药20g/L利多卡因0.5mL对不同强度电针引起的镇痛效应的影响。方法:实验于2005-07/10在首都医科大学生理学系实验室进行。健康SD大鼠51只,随机分为4组:强电针+丘脑中央下核利多卡因注射组(n=22),强电针+丘脑中央下核生理盐水注射组(n=8),弱电针+丘脑中央下核利多卡因注射组(n=13),弱电针+丘脑中央下核生理盐水注射组(n=8)。以强电刺激(5.0～6.0mA,5Hz)和弱刺激(1mA,50Hz)外周感受野诱发的脊髓背角WDR和NS神经元的晚串放电(C-反应)作为伤害感受性反应,观察双侧丘脑中央下核内微量注射局麻药利多卡因对不同强度电针引起的镇痛效应的影响。结果:43只大鼠进入结果分析。①强电针组注药前电针期间1,5,10,15min时C-反应的抑制率依次为(20.94±3.34)%,(36.83±3.45)%,(49.34±3.08)%,(47.32±3.48)%,停电针后5和10min的C-反应的抑制率分别是(20.68±4.33)%,(5.26±5.45)%,停电针后15min恢复至电针前水平,各时间点C-反应的变化与电针前相比差异均具有显著意义(P<0.05或P<0.001);双侧丘脑中央下核注药后,电针期间1,5,10,15minC-反应的抑制率相应减小为(4.06±3.42)%,(12.10±4.66)%,(22.24±3.17)%,(17.14±6.47)%,停电针后5min抑制率减小为(5.18±4.32)%。只有电针10和15min时的C-反应与电针前相比差异有显著性意义(P<0.01或P<0.001)。注药后电针期间各点及电针后5min时C-反应的抑制率显著高于注药前,差异有显著性意义(P<0.01或P<0.001)。在8个神经元观察到,双侧丘脑中央下核内注射等量生理盐水对电针的抑制效应无明显影响。②弱电针注药前电针期间1,5,10,15min时C-反应的抑制率分别为(9.02±2.59)%,(19.91±3.35)%,(28.20±1.91)%,(34.00±2.11)%;注药后相应的数值为(11.03±2.71)%,(17.13±2.54)%,(26.75±2.28)%,(29.68±2.06)%,注药前后差异无显著性意义(P>0.05)。双侧丘脑中央下核内注射生理盐水对弱电针的抑制效应亦无明显影响。结论:不同强度的电针刺激可能由粗细不同的纤维传入,通过不同的中枢机制产生镇痛作用;强电针兴奋细纤维产生的镇痛作用至少部分是通过丘脑中央下核激活下行抑制系统实现的。

AIM： To observe the effect on different-intensity of electroacupuncture （EA） induced-analgesic effects by microinjection of lidocaine （2%, 0.5 μL） in inferior central nucleus of bilateral thalamus. METHODS： The experiment was conducted in the Laboratory of Physiology, Capital University of Medical Sciences from July to October 2005. Fiftyone healthy SD rats were randomly divided into 4 groups： high-intensity EA ＋ injection of lidocaine into inferior central nucleus of thalamus group （n=22）, high-intensity EA ＋ injection of normal saline into inferior central nucleus of thalamus group （n=8）, low-intensity EA ＋ injection of lidocaine into inferior central nucleus of thalamus group （n=13） and low-intensity EA ＋ injection of lidoeaine into inferior central nucleus of thalamus group （n=8）. High-intensity （5.0-6.0 mA,5 Hz） and low-intensity （1 mA,50 Hz）EA were used to simulate the WDR and NS neurons in the dorsal horn of lumbar spinal cord induced by peripheral receptive field. The late train discharges （C-response） of the neurons evoked by intense electrical stimulation of the skin were taken as a noeieepive response. The effect on different-intensity of EA induced-analgesic effects by mieroinjeetion of lidoeaine in inferior central nucleus of bilateral thalamus was observed. RESULTS： A total of 43 rats were involved in the analysis of results.①In the high-intensity EA group, the inhibition ratios of C-response on the 1^st, 5^th,10^th and 15^th mioute of EA before administration were （20.94±3.34）%, （36.83±3.45）%, （49.34±3.08）% and （47.32±3.48）% respectively, and that at 5 and 10 minutes after EA were （20.68±4.33）% and （5.26±5.45）% respectively, which returned to the level before EA at 15 minutes after EA, The differences in changes of C-response between each time-point and that before EA were significant （P 〈 0.05 or P 〈 0.001）. After administration in inferior centrtd nucleus of bilateral thalamus, the inhibition ratio of C-re sponse on the 1^st, 5^th, 10^th and 15^th minute of EA were correspondingly reduced to （4.06 ±3.42）% , （12.10 ±4.66）% , （22.24±3.17）% and （17.14±6.47）%, and the ratio at 5 minutes after EA was （5.18±4.32）%. Only differences in C-response between 10^th and 15^th minute of EA and that before EA was significant （P 〈 0.01 or P 〈 0.001）, The inhibition ratio of C-response after administration at each time-point of EA as well as 5 minutes after EA were obviously higher that that before administration, and the differences were remarkable （P 〈 0.01 or P 〈 0.001）, It could be seen on 8 neurons that there were no significant effects on the inhibition of EA by injection of same-volume normal saline into the inferior central nucleus of bilateral tbalamus,②The inhibition ratios of C-response at 1^st, 5^th, 10^th, 15^th minutes of low-intensity EA before administration were respectively （9.02±2.59）%, （19.91±3.35）%, （28.20±1.91）% and （34.00±2.11）%, and those after administration were （11.03 ±2.71）% , （17.13 ±2.54）% , （26.75±2.28）% and （29.68±2.06）%. There were no significant differences before and after administration （P 〈 0.05）. There were no remarkable effects on the inhibition effect of low-intensity EA by injection of normal saline into the inferior central nucleus of bilateral thalamus. CONCLUSION： The EA stimulus of different intensity may be imported by fibers of different size, and the analgesic effect may yield through different central mechanism, The analgesic effect elicited by activation of small afferent fibers with high-intensity EA is mediated, at least in part, by the activation of inhibitory system of inferior central nucleus of thalamus.