Аннотация:The influence of enkephalin on the processes of elaboration and preservation of the defensive conditioned reflexes of bilateral avoidance (CRBA) and conditioned reflexes of passive avoidance (CRPA) in intact rats and animals with changed functional state of serotoninergic system of the brain was examined. Injection of enkephalin in a dose of 10 mg to intact animals accelerated the elaboration of CRBA not influencing in this case their preservation, but deeply disturbed the CRPA preservation. The excess of serotonin [5-hydroxytryptamine, 5-HT] in the brain created by means of 5-oxytryptophan fully prevented the acceleration of CRBA elaboration by enkephalin under the usual conditions. Injection of enkephalin at the background of 5-HT lowering and raising in the brain favored CRBA preservation. Under the enkephalin influence the inclusion of [3H]tyrosine and [14C]lysine in water-soluble and water-insoluble proteins of different cerebral structures lowered. The obtained data testify to participation of serotoninergic system and brain proteins in the mechanisms of enkephalin action to the processes of learning and memory.