Endorphins alter acquisition and consolidation of an inhibitory avoidance response in rats.
Peripheral i.p. administration of 1.0 microgram/kg gamma-endorphin to rats, 30 min prior to training in a 1-trial inhibitory avoidance task, enhanced retention performance measured 72 h later. A much smaller dose of 0.1 microgram/kg beta-endorphin administered immediately following training produced a retention deficit. Both of these endorphin effects were time dependent, since gamma-endorphin given 90 min prior to, and beta-endorphin given 90 min after training produced no effect on retention performance. A wide dose range of either gamma-endorphin (0.1-10 micrograms/kg) administered after training or beta-endorphin (0.1-10 micrograms/kg) administered before training had no effect. These results suggest that the behavioral actions of beta-endorphin and smaller beta-lipotropin sequences such as gamma-endorphin, are distinct. We also found that 0.1-100 micrograms/kg of either alpha-endorphin or Met-enkephalin given before or after training was without effect on retention of the response.
D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004723:Endorphins / Q000494:pharmacology*; D004744:Enkephalin, Methionine / Q000494:pharmacology; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000187:drug effects; D012153:Retention, Psychology / Q000187:drug effects; D018822:alpha-Endorphin; D001615:beta-Endorphin; D018823:gamma-Endorphin
D004723:Endorphins; D004744:Enkephalin, Methionine; D001615:beta-Endorphin; D018822:alpha-Endorphin; D018823:gamma-Endorphin