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

The effects of intracerebroventricular (i.c.v.) administration of endomorph ins-1 and -2, endogenous mu-opioid receptor agonists, on the spontaneous al ternation performance associated with spatial working memory were investiga ted in mice. Endomorphin-1 (10 and 17.5 mu g) and endomorphin-2 (10 mu g) p roduced a significant decrease in percent alternation without affecting tot al 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 pe rcent alternation, although neither naltrindole (4 ng) nor nor-binaltorphim ine (4 mu g) produced any significant effects on alternation performance. T hese results suggest that endomorphins impair spatial working memory throug h the mediation of mu-opioid receptors. (C) 2000 Elsevier Science B.V. All rights reserved.