Endomorphin-1 improves scopolamine-induced impairment of short-term memoryvia mu(1)-opioid receptor in mice

The effects of intracerebroventricular injection of endomorphin-1 and 2, en dogenous mu -opioid receptor agonists, on the scopolamine-induced impairmen t of spontaneous alternation performance associated with short-term memory were investigated in mice. Endomorphin-1 (0.03 mug) inhibited scopolamine ( 1 mg/kg)-induced impairment of spontaneous alternation performance without affecting total arm entries, while endomorphin-2 (0.01-10 mug) failed to si gnificantly influence the scopolamine (1 mg/kg)-induced impairment. Endomor phin-1 (0.03 mug) itself had no marked effects on spontaneous alternation p erformance in intact mice. Although beta -funaltrexamine (5 mug), a mu -opi oid receptor antagonist, did not significantly affect the inhibitory effect s of endomorphin-1 (0.03 pg) on the scopolamine (1 mg/kg)-induced impairmen t, naloxonazine (35 mg/kg), a mu (1)-opioid receptor antagonist, significan tly reversed the inhibitory effects of endomorphin-1 (0.03 mug) on the impa irment. Naloxonazine (35 mg/kg) unlike beta -funaltrexamine (5 mug) did not significantly influence the scopolamine (1 mg/kg)-induced impairment of sp ontaneous alternation performance. These results suggest that endomorphin-1 improves the disturbance of short-term memory resulting from cholinergic d ysfunction through the mediation of mu (1)-opioid receptors. NeuroReport 12 :3723-3727 (C) 2001 Lippincott Williams & Wilkins.