Effects of endomorphins-1 and-2, endogenous μ-opioid receptor agonists, on spontaneous alternation performance in mice

The effects of intracerebroventricular (i.c.v.) administration of endomorphins-1 and -2, endogenous mu-opioid receptor agonists, on the spontaneous alternation performance associated with spatial working memory were investigated in mice. Endomorphin-1 (10 and 17.5 mu g) and endomorphin-2 (10 mu g) produced a significant decrease in percent alternation without affecting total arm entries. beta-Funaltrexamine (5 mu g) almost completely reversed the endomorphin-1 (10 mu g) and endomorphin-2 (10 mu g)-induced decrease in percent alternation, although neither naltrindole (4 ng) nor nor-binaltorphimine (4 mu g) produced any significant effects on alternation performance. These results suggest that endomorphins impair spatial working memory through the mediation of mu-opioid receptors. (C) 2000 Elsevier Science B.V. All rights reserved.