Noxious stimuli and Met-enkephalin release from nucleus reticularis gigantocellularis.

The nucleus reticularis gigantocellularis of the rat medulla oblongata was perfused in situ, and effects of noxious stimuli on the release of immunoreactive Met-enkephalin were examined. Formalin-induced and thermal but not mechanical stimuli increased the "tonic" release of immunoreactive Met-enkephalin from this nucleus. No "phasic" increase was observed following the three forms of stimulation. A topical application of dibucaine abolished the formalin-induced increase in the release of immunoreactive Met-enkephalin. Therefore, the possibility that persistent noxious stimuli may activate the Met-enkephalin-containing fibers in the nucleus reticularis gigantocellularis has to be given consideration.