Interactions between enkephalin and dopamine in the control of locomotor activity in the rat: a new hypothesis.

D-ala2-met5-enkephalinamide (DALA) was found to be without effect on motility when injected in doses from 10 to 40 micrograms. When ICV injection of DALA was combined with IP injection of amphetamine, DALA markedly enhanced the stimulatory effect of amphetamine. The effects of DALA + amphetamine could be partially antagonized by naloxone. The locomotion-reducing effect of the dopamine antagonist pimozide was not affected by concurrent administration of DALA. These data suggest a complex interaction between opiates and dopamine. It is suggested that the effects of DALA are best explained assuming that the opiate inhibits GABAergic neurotransmission.