[Central mechanism of an extensive analgesic effect due to strong electroacupuncture of acupoint on spinal dorsal horn neurons].

Experiments were performed on male rats. The responses of dorsal horn convergent neurons in spinal cord (T12-L1) to noxious stimulation of hind paw were recorded extracellularly with glass microelectrode. When low intensity (2 V) electroacupuncture (EA) was used, the nociceptive responses of convergent neurons were inhibited by EA at "Zusanli" near noxious stimulation area, but not at "Xiaguan" far from the area. When intensity (18 V) high than the threshold of C fibers EA was applied at the far acupoint "Xiaguan", obvious analgesic effects on convergent neurons were also produced, showing an extensive analgesic effect of strong EA at acupoint. This extensive analgesic effect was abdicated by lesion of nucleus raphe magnus (NRM), but still persisted to some extent by EA at the same segment acupoint "Zusanli" with 18 V or 2 V intensity. The results suggest that, the extensive analgesia of strong EA at far segment acupoint may be mainly mediated by noxious stimulation through NRM, a negative feedback mechanism modulating pain of supraspinal cord. The analgesia due to 2 V EA at the same segment acupoint may be mainly produced by gate control in spinal cord, but also to some extend by supraspinal cord mechanism.