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[Reduction of effects of stimulating SmI and electroacupuncture produced by intraperitoneal injecting atropine in the adjuvant-induced acute arthritic rat].

Using the adjuvant-induced acute arthritic rat as a pain model, we have previously shown that the SmI area is implicated in the inhibitory effect of acupuncture on the afferent nociceptive information of parafascicular nuclei (Pf). The purpose of this study was to determine whether acetylcholine (ACh) participates in this modulatory process. Experiments were conducted with adjuvant-induced acute arthritic rats and extracellular recordings from pf were obtained through microelectrodes stereotaxically. The results showed that: (1) After intraperitoneal-injecting atropine (5mg/kg), the effect of stimulating SmI on nociceptive responses of Pf neurons was decreased, while it was not decreased if saline was administered. Compared in the same neurons, the difference of nociceptive responses at 0' to 15' after cessation of stimulating SmI was statistically significant. This finding indicated that ACh was involved in descending modulation of SmI. (2) The effect of acupuncture was decreased after intraperitoneal-injecting atropine (5mg/kg), while it was not decreased if saline was administered. The difference of nociceptive response was statistically significant at 0' to 10' and 20' to 40' after cessation of EA in comparison between the background of atropine and saline. It indicated that ACh was involved in acupuncture analgesia. These results suggest that ACh may be participated in acupuncture analgesia as a neurotransmitter of the corticofugal modulation of pain.