Abstract
Both acupuncture analgesia and dorsal periaqueductal central gray stimulation-produced analgesia (dorsal PAG-SPA) tested by tail-flick latency were completely antagonized by 1 mg/kg of opiate antagonist naloxone and showed the long lasting analgesia after termination of stimulation (after effect) and the individual variation in effectiveness of analgesia. Ventral periaqueductal central gray stimulation-produced analgesia (ventral PAG-SPA) was not antagonized by naloxone, but it was antagonized by serotonin antagonist methysergide and did not show individual variation in effectiveness of analgesia. Two mg/kg methysergide antagonised 80% of AA and 70% of the dorsal PAG-SPA. Ventral PAG lesion reduced 54% of the dorsal PAG-SPA. The different naloxone reversal of PAG-SPA is due to the stimulated regions in PAG. These data imply that PAG is involved in acupuncture analgesia as an endogenous morphine-like factor releasing mechanism and as a pain inhibitory mechanism.
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