鞘内注射右美托咪定对神经病理性疼痛大鼠DRG神经元GABA_A受体激活电流的影响

THE EFFECT OF INTRATHECAL INJECTION OF DEXMEDETOMIDINE ON GABA_A RECEPTOR-ACTIVATED CURRENTS IN DRG NEURONS IN RATS WITH NEUROPATHIC PAIN

目的:观察鞘内注射右美托咪定对神经病理性疼痛大鼠背根神经节(dorsal root ganglion, DRG)神经元GABA_A受体激活电流的影响。方法 :鞘内置管成功的雄性SD大鼠36只,体重180～220g,采用随机数字表法随机分为3组(n=12):假手术组(S组)、神经病理性疼痛组(CCI组)、右美托咪定+神经病理性疼痛组(D组)。S组和CCI组鞘内注射生理盐水每日10μl/次,D组鞘内注射右美托咪定2μg/kg,生理盐水稀释至10μl,每日1次,持续至术后14 d。各组于术前1 d (T0),术后3、5、7、10、14 d(T1-5)时测试热缩足潜伏期(thermal withdrawal latency, TWL)。于术后T5时测试完TWL后处死大鼠,在急性分离的DRG细胞上,运用全细胞膜片钳技术,记录不同浓度药物作用下各组背根神经节细胞GABA_A受体激活电流的变化。结果 :(1)与S组比较,CCI组和D组T1-5时TWL均缩短(P <0.05);与D组比较,CCI组T1-5时TWL均缩短(P <0.05)。(2)GABA (0.1～1000.0μmol/L)可以使85.7%(102/119)的DRG神经元产生浓度依赖性的内向电流,而且这种内向电流能被GABA_A受体选择性拮抗剂荷包牡丹碱(100μmol/L)所阻断。(3)CCI组在不同浓度(0.1～1000.0μmol/L) GABA激活电流幅值均小于S组和D组(P <0.05);D组在不同浓度(0.1～1000.0μmol/L) GABA激活电流幅度小于S组(P <0.05)。结论:右美托咪定通过增强GABA_A受体介导的突触前抑制作用,可能是其缓解神经病理性疼痛的机制之一。

Objective:To observe the effect of dexmedetomidine on GABAA receptor-activated currents in dorsal root ganglion(DRG)neurons in rats with neuropathic pain.Methods:36 male adult Sprague-Dawley rats,weighing(180-220 g),were randomly allocated into 3 groups(n=12):Sham group(S),chronic constrictive injury group(C),dexmedetomidine plus chronic constrictive injury group(D).D group intrathecal injection of dexmedetomidine 2μg/kg evry day for 14 days,diluted with saline to 10μl,while group S and group CCI received equal volumes of saline.Thermal withdrawal threshold(TWT)was assayed on 1 day before surgery,and 3,5,7,10,14 d after operation using radiant heat.The rats were sacrificed on 14 d(T5)after TWT tests.Whole cell patch clamp technique was used to record the effect of different concentrations of GABA on GABAA receptor-activated currents in DRG neurons.Results:(1)Compared with group S,TWT values were reduced on T1-5 in group CCI and D(P<0.05);The TWT values were also reduced in group CCI as compared to group D.(2)GABA(0.1-1000.0μmol/L)produced concentration-dependent inward current in 85.7%DRG neurons,and this kind of inward current could be blocked by bicuculline,a selective blocker for GABAA receptors.(3)The currents of group CCI were decreased compared with group S and D(GABA,0.1-1000.0μmol/L).Contrast with group S,the currents of D decreased significantly(GABA,0.1-1000.0μmol/L).Conclusion:Dexmedetomidine potentiates the presynaptic inhibitory effect of GABAA receptors,which may be one of its pharmacological mechanisms to relieve neuropathic pain in rats.