Analgesia produced by microinjection of L-glutamate into the rostral ventromedial bulbar nuclei of the rat and its inhibition by intrathecal alpha-adrenergic blocking agents.

Definite and dose-dependent analgesia followed microinjection of L-glutamate into the nucleus reticularis paragigantocellularis (NRPG) of rats. This analgesic effect was inhibited by lumbar intrathecal pretreatment with phenoxybenzamine and phentolamine but not by propranolol, methysergide or naloxone. Microinjection of L-glutamate into the nucleus raphe magnus (NRM) also produced an analgesic effect which was reduced by intrathecal pretreatment with methysergide but not by phentolamine. These findings provide direct evidence that the NRPG and NRM function separately in descending pain-suppression systems of the spinal cord.