Endomorphins 1 and 2, endogenous mu-opioid receptor agonists, impair passive avoidance learning in mice.
The effects of intracerebroventricular administration of endomorphin-1 and endomorphin-2, endogenous mu-opioid receptor agonists, on passive avoidance learning associated with long-term memory were investigated in mice. Endomorphin-1 (10 and 17.5 microg) and endomorphin-2 (17.5 microg) produced a significant decrease in step-down latency in a passive avoidance learning task. beta-Funaltrexamine (5 microg) almost completely reversed the endomorphin-1 (17.5 microg)- and endomorphin-2 (17.5 microg)-induced shortening of step-down latency, although neither naltrindole (4 ng) nor nor-binaltorphimine (4 microg) produced any significant effects on the effects of endomorphins 1 and 2. These results suggest that endomorphins 1 and 2 impair long-term memory through the mediation of mu-opioid receptors in the brain.
Ukai
M
M
Department of Chemical Pharmacology, Faculty of Pharmacy, Meijo University, 468-8503, Nagoya, Japan. ukai@meijo-u.ac.jp
Watanabe
Y
Y
Kameyama
T
T
D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D001522:Behavior, Animal / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D008297:Male; D051379:Mice; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology*; D017450:Receptors, Opioid, mu / Q000819:agonists
D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D009842:Oligopeptides; D017450:Receptors, Opioid, mu; C105293:endomorphin 1; C051844:norbinaltorphimine; C105294:endomorphin 2; D009271:Naltrexone; C024524:beta-funaltrexamine; C055382:naltrindole