Analgesia induced by localized injection of opiate peptides into the brain of infant rats

Background Stimulation of a variety of brain sites electrically or by opiates activates descending inhibitory pathways to attenuate noxious input to the spinal cord dorsal horn and produce analgesia. Analgesia induced by electrical stimulation of the periaqueductal gray of the midbrain (PAG) or medial rostral ventral medulla (RVM) matures late, towards the end or past the preweaning period. Descending facilitation takes precedence over inhibition. Yet opiates injected ICV or directly into the PAG induce analgesia relatively early in development. Our goal was to reexamine the role of opiates specific to individual receptor types in analgesia at several supraspinal sites.