Facilitation of memory retrieval by pretest morphine mediated by mu but not delta and kappa opioid receptors.
Mice were trained to avoid electric shock (0.6 mA) in a step-through type passive avoidance learning task, retention being measured 24 h after the training trial. Morphine 10 mg/kg administered 30 min before the test trial (pretest) facilitated memory retrieval, and the effect was completely antagonized by 1 mg/kg naloxone, a selective mu-opioid receptor antagonist. On the other hand, pretest administration of 0.01-10 mg/kg DTLET, a selective delta-opioid receptor agonist, did not produce the same effect as morphine. Nor-binaltorphimine, a kappa-opioid receptor antagonist, did not antagonize the effect of pretest morphine, at doses of 1 and 2 mg/kg. These results suggest that the facilitation of memory retrieval by pretest morphine is mediated through mu- but not delta- or kappa-opioid receptors.
Shiigi
Y
Y
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Nagasaki University, Japan.
Takahashi
M
M
Kaneto
H
H
D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects; D044482:Benzeneacetamides; D004597:Electroshock; D008297:Male; D008568:Memory / Q000187:drug effects*; D051379:Mice; D008815:Mice, Inbred Strains; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D011759:Pyrrolidines / Q000494:pharmacology; D011957:Receptors, Opioid / Q000187:drug effects* / Q000502:physiology; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu
D000700:Analgesics; D044482:Benzeneacetamides; D009842:Oligopeptides; D011759:Pyrrolidines; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D009270:Naloxone; D009020:Morphine; C037653:deltakephalin; C045444:U 69593