Ukai_2002_Behav.Brain.Res_129_197

The effects of naloxonazine a mgr;(1)-opioid receptor antagonist and physostigmine a cholinesterase inhibitor on the endomorphins-induced impairment of passive avoidance learning were investigated in mice Endomorphin-1 10 mgr;g and endomorphin-2 10 mgr;g significantly impaired passive avoidance learning while naloxonazine 35 mg/kg s.c a mgr;(1)-opioid receptor antagonist which alone failed to influence passive avoidance learning significantly inhibited the endomorphin-1 10 mgr;g but not endomorphin-2 10 mgr;g)-induced disturbance of such learning A rather nonselective higher dose 50 mg/kg s.c of naloxonazine almost completely antagonized the endomorphin-1 10 mgr;g and endomorphin-2 10 mgr;g)-induced impairment of passive avoidance learning In contrast physostigmine 0.025 and 0.05 mg/kg i.p significantly reversed the endomorphin-1 10 mgr;g and endomorphin-2 10 mgr;g)-induced disturbance of passive avoidance learning whereas physostigmine 0.025 and 0.05 mg/kg i.p alone did not influence such learning These results suggest that endomorphin-1 but not endomorphin-2 impairs learning and memory resulting from cholinergic dysfunction and from activation of mgr;(1)-opioid receptors