title: Identification of the opioid receptors involved in passive-avoidance learning in the day-old chick during the second wave of neuronal activity.
abstract: Long-term memory formation for passive-avoidance learning in the day-old chick is known to have two distinct time windows of protein synthesis (F.M. Freeman, S.P.R. Rose, A.B. Scholey, 1995. Two time windows of anisomycin-induced amnesia for passive-avoidance training in the day-old chick. Neurobiol. Learn. Mem. 63, 291-295). The lobus parolfactorius (LPO) is thought to be an important site for the second wave of protein synthesis which occurs 4-5 h after training. Birds received bilateral intracranial injections of agonists and antagonists for the mu-, delta-, kappa-opioid receptors and the opioid receptor-like (ORL(1)) receptor directly into the LPO at 5 h post-training and were tested for recall 24 h later. Also, 100 microM beta-funaltrexamine (beta-FAN), a mu-opioid receptor antagonist, significantly impaired memory formation (P<0.01). The delta-opioid receptor was also involved in memory formation at this time-point since antagonism of this receptor by 1 mM ICI-174,864 caused amnesia (P<0.01) which was reversed by the agonist, DPLPE. The kappa-opioid receptor appeared not to be involved during the second phase of neuronal activity since neither stimulation by dynorphin nor inhibition by nor-BIN caused amnesia for the task. The ORL(1) receptor agonist orphanin FQ also had no effect suggesting that this receptor was not involved at this 5-h time-point. Cytosolic and mitochondrial protein synthesis has been shown to be important in passive-avoidance learning in the day-old chick. Both chloramphenicol (CAP) and anisomycin (ANI), inhibitors of mitochondrial and cytosolic protein synthesis, respectively, caused disruption when injected 5 h post-training into the LPO (P<0.05). Endomorphin-2 (Endo-2), a mu-opioid receptor agonist, reversed both the ANI- and CAP-sensitivity. However, DPLPE, a delta-opioid receptor agonist, only reversed the effect due to CAP. Possible mechanisms for these effects are discussed.
authors.affiliation: Division of Biochemistry and Molecular Biology, John Curtin School of Medical Research, The Australian National University, Canberra, Australia.
authors.forename: F M
authors.initials: FM
authors.lastname: Freeman
authors.forename: I G
authors.initials: IG
authors.lastname: Young
mesh_terms: D000367:Age Factors; D000647:Amnesia / Q000139:chemically induced / Q000503:physiopathology; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D000841:Anisomycin / Q000494:pharmacology; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology*; D001923:Brain Chemistry / Q000502:physiology; D002645:Chickens; D002701:Chloramphenicol / Q000494:pharmacology; D003213:Conditioning, Psychological / Q000187:drug effects / Q000502:physiology; D004399:Dynorphins / Q000494:pharmacology; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D008297:Male; D008568:Memory / Q000502:physiology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009474:Neurons / Q000737:chemistry* / Q000502:physiology*; D009842:Oligopeptides / Q000494:pharmacology; D018847:Opioid Peptides / Q000494:pharmacology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011957:Receptors, Opioid / Q000819:agonists / Q000502:physiology*; D017465:Receptors, Opioid, delta / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology; D017473:Receptors, Opioid, kappa / Q000819:agonists / Q000502:physiology; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology; D000097629:Nociceptin
chemical_list: D000701:Analgesics, Opioid; D000841:Anisomycin; D002701:Chloramphenicol; D004399:Dynorphins; D020881:Enkephalin, D-Penicillamine (2,5)-; D004743:Enkephalin, Leucine; D009271:Naltrexone; D009292:Narcotic Antagonists; D009842:Oligopeptides; D018847:Opioid Peptides; D011500:Protein Synthesis Inhibitors; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D014665:Vasodilator Agents; D000097629:Nociceptin; C105294:endomorphin 2; C024524:beta-funaltrexamine; C040643:N,N-diallyl-tyrosyl-alpha-aminoisobutyric acid-phenylalanyl-leucine