INTERACTING BRAIN-STEM COMPONENTS OF OPIATE-ACTIVATED, DESCENDING, PAIN-INHIBITORY SYSTEMS

This is a review of research aimed at elucidating how various opiate a nalgesia substrates in rat brain stem interact with one another to bri ng about opiate analgesia. The three substrates studied are the midbra in periaqueductal grey (PAG), the bulbar nucleus raphe magnus (RM), an d the bulbar nucleus reticularis paragigantocellularis (PGC). The meth ods used in the reviewed studies are unique in that behavioral and neu ronal responses are assessed in consequence of nanoinjecting opiates ( met-enkephalin) into subset pairs of these structures. Responses to si ngle and conjoint injections are compared. Effects on neuronal and beh avioral responses in consequence of disruption of these structures wit h tetracaine block are also discussed. It is seen that PGC cannot serv e as an opiate analgesia substrate if the functional integrity PAG is impaired. However FAG does not depend on PGC's functional integrity.