Dopamine and opioid regulation of the memory retrieval recovery in mice

The reactivation effects of the delta-opioid receptor blockade and D2 dopamine receptor activation on the detention-induced memory deficit in mice were investigated, in order to study possible interactions between opioid and dopamine systems in memory retrieval. Animals were trained in a one-trial passive-avoidance task. Pretesting treatment with ICI 174,864 (1, 3 or 5 mg/kg, i.p.) or quinpirole (0.5, 1 or 2 mg/kg, i.p.) facilitated retrieval of memory trace in saline-pretreated mice. Pretraining injection of the dopamine autoreceptor agonist, (+)-3PPP (2 mg/kg), having no effect alone in learning, prevented the ability of ICI 174,864 to produce the memory-enhancing effect. It is suggested that the normal functioning of the dopamine system was critical for the facilitation of retrieval by delta-antagonist. Quinpirole-induced reactivátion of memory retrieval was enhanced by pretreatment with Leu-enkephalin (0.2 mg/kg), inducing increased retention. We discuss these results in the context of an important interactions between D2 dopamine and delta-opioid receptors.