The Subunit alpha o of guanine nucleotide-binding protein (rabbit polyclonal antiserum 9120, K,J. Chang. USA), in the areas of rat spinal cord was localized by immunohistochemical PAP methods, and the changes of alpha o-immunoreactivity (alpha o-IR) in the substantia gelatinosa (SG) were observed after unilateral transection of dorsal roots and electroacupuncture. Intense alpha o-IR was presented in Rexed lamina I to III of the dorsal horn, and the highest alpha o-IR in lamina (SG), which was found than that in the normal and control animals. Iateral spinal nucleus of rat revealed higher density of alpha o-IR containing fiber networks. Following unilateral transection of dorsal roots and pain threshold increased significantly after electroacupuncture applied at the point "Huantiao", alpha o-IR was markedly decreased than that in the normal and control group in those areas. The optic density (OD) of alpha o-IR were measured, which decreased more markedly in opration and electroacupuncture group than that normal and control group. The results mentioned above indicate that Go-protein in terminals of primary nociceptive neurons of SG decreases markedly after dorsal roots transected and electroacupuncture. It was inferenced that partial Go-protein probably originates from the primary sensory neurons, and the release of "inhibitory" of Go may increase (with weaker alpha o-IR). In a work, Go might play important roles on the primary afferents informational regulation and electroacupuncture analgesia of the regulation.