电针对三叉背角会聚神经元镇痛作用的广泛性和特异性的中枢机制研究

实验用Wistar大鼠 ,玻璃微电极细胞外记录右侧三叉神经脊束尾侧核会聚神经元对同侧面颊部伤害性刺激的反应。以 2V和 1 8V分别低和高于C纤维阈值的两种强度电针“足三里”或“下关”穴 ,观察对此会聚神经元伤害性反应的影响 ,及损毁中缝大核 (NRM )后的变化。损毁NRM后低强度 (2V)电针“下关”穴 ,对伤害性反应从针中到停针后 2 5min ,仍有明显的抑制作用(P≤ 0 .0 5～ 0 .0 0 1 ) ,与损毁NRM前相比 ,抑制幅度稍低。而低强度电针“足三里”穴 ,与NRM损毁前的电针效应相类似 ,无论是针中还是针后都无此镇痛效应。损毁NRM后高强度 (1 8V)电针“下关” ,从针中到停针后 2 0min对会聚神经元痛反应仍有明显的抑制作用 (P≤ 0 .0 0 1 ) ,但与损毁前相比抑制作用减弱。而 1 8V电针“足三里”的镇痛效应在损毁NRM后消失 ,与NRM损毁前电针此穴明显镇痛的效应相比 ,组间差异非常显著。提示近痛源部位的“下关”穴电针镇痛效应 ,可能主要是通过脊髓节段内痛抑制机制实现的。高强度 (1 8V)电针虽与NRM有一定关系 ,但并不完全依赖于NRM的完整 ,表明“下关”镇痛作用具有穴位特异性 ,而远神经节段穴位“足三里”强电针(1 8V)所引起的镇痛作用则与NRM关系密切。表明远隔穴位针刺的广泛性镇痛作用可能必须通过脊髓上NRM?

Study on the Central Mechanism of Specificity and Extensiveness of EA Action in Suppressing Nociceptive Response of Trigeminal Convergent Neurons

Experiments were carried out on Wistar rats. The nociceptive responses of convergent neurons in the right trigeminal nucleus caudalis (TNC) to noxious stimuli exerted onto the receptive field(cheek) were recorded extracellularly with glass microelectrodes. The effect of electroacupuncture (EA) of “Zusanli”(ST 36) or “Xiaguan”(ST 7) with electric current intensity of 2 V and 18 V on the nociceptive responses of TNC convergent neurons was observed, and the influence of lesion of nucleus raphe magnus (NRM)on the effect of EA was analyzed. The nociceptive responses of TNC convergent neurons could be obviously inhibited by 2 V(below the threshold of C fiber excitement)stimulation of “Xiaguan”(ST 7), but did not by stimulation of “Zusanli”(ST 36),showing a specificity of action of acupoint. After lesion of NRM, the nociceptive responses could be still inhibited obviously by EA of“Xiaguan”(ST 7) during EA and 25 minutes after stopping EA. It may be due to that “Xiaguan” (ST 7) is near the receptive field of the cheek, the nociceptive signals and the EA signals could be integrated in the same or the near spinal segments. Therefore the EA produced analgesia at the acupoint near the receptive field of the nociceptive response neurons was mainly realized by 2 V EA by activating Ⅰ and Ⅱ afferent fibers through the gate control mechanism in the spinal segment. When the high intensity (18 V) EA (exceeding the threshold of C fiber excitement)was applied, the nociceptive responses of the convergent neurons in TNC could be inhibited obviously by both “Xiaguan”(ST 7) and “Zusanli”(ST 36) stimulation far from the receptive area ,showing an analgesic extensiveness of acupoint. But after lesion of NRM, the nociceptive responses could be still inhibited clearly by 18 V EA at“Xiaguan”(ST 7) rather than “Zusanli”(ST 36). The results suggest that extensive analgesia induced by high intensity (18 V) EA at “Zusanli”(ST 36) far from the pain location in the face is closely related to NRM, in other words, the supraspinal negative feedback mechanism including NRM's activation by exciting Ⅲ and Ⅳ(C) afferent fibers may contribute to the extensive analgesia of EA.