Enkephalin-induced myoclonic twitches blocked by ergometrine and potentiated by haloperidol.

Myoclonic twitches (MT) in the submandibular muscles induced by intraventricular administration of D-ala2-met-enkephalinamide (DALA) were studied electromyographically in the rat. Measurement of MT activity was selected since it permits parallel study of the effect of enkephalin on both dopaminergic and serotonergic transmitter systems. The twitches induced by enkephalin were blocked by naloxone, gamma-hydroxybutyrate, and ergometrine, but potentiated by haloperidol. Methysergide did not alter the stimulatory effect of DALA. These results were interpreted as a possibility for a specific enkephalin-induced activation of the so-called inhibition-mediating dopaminergic system, which is sensitive to the blocking action of ergometrine, but resistant to the blocking action of haloperidol.