[Effect of leu- and met-enkephalins on the brain's reinforcement systems]

Experiments on rats were made to study the effects of intracerebroventricular injection of met- and leu-enkephalins (ME and LE) during the reactions of self-stimulation and active avoidance (AA) of electrical stimulation of the central gray of the midbrain. Microinjections of LE in doses of 50-100 micrograms facilitated SS of the brain. ME in doses of 50-200 micrograms inhibited SS of the central gray. Both enkephalins inhibited AA reaction but this effect was more remarkable after LE injection. The effects of the enkephalins on SS and AA were reversed by naloxon.