Met5-enkephalin: potent contraversive rotation after microinjection in rat substantia nigra.

This study reports a novel action of Met5-enkephalin in the rat substantia nigra, i.e. potent contraversive rotation that is dose-dependent, site-specific, mimicked by morphine and blocked by naloxone. These results suggest that this pentapeptide may play an important modulatory role in the control of movement in this region of the central nervous system. Alterations in endogenous Met-enkephalin levels in the substantia nigra may be a contributive factor in Parkinson's disease, a movement disorder related to neuropathology of the substantia nigra.