Gamma-endorphin affects retrieval of an inhibitory avoidance task.
Rats were trained in a step-down inhibitory avoidance task and retrieval was measured during a test session conducted 24 h after training. The ip administration of a low dose of gamma-endorphin (0.2 micrograms/kg) immediately after training reduced retrieval time from 40.6 to 13.5 s (N = 15). Higher doses of gamma-endorphin given 5 min before testing (1.0 micrograms/kg) or immediately after training (5 micrograms/kg) enhanced retrieval time from 38.6 to 300 s (N = 15) and from 40.6 to 104.4 s (N = 15). All of these effects were blocked by pretreatment with naloxone (0.4 mg/kg). Alpha-endorphin (0.2, 1.0 or 5.0 micrograms/kg) administered either after training or before testing had no effect on retrieval. Since at least the amnestic effect of gamma-endorphin is similar to that of beta-endorphin, and gamma-endorphin is a possible metabolite of beta-endorphin by limited proteolysis of the carboxyl-terminal amino acid, it is suggested that at least some effects of beta-endorphin on memory may be mediated by its proteolysis product, gamma-endorphin.
Dalmaz
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Departamento de Bioquímica, Universidade Federal do Rio Grande do Sul (Centro), Porto Alegre, RS, Brasil.
Fin
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D000647:Amnesia / Q000139:chemically induced; D000704:Analysis of Variance; D000818:Animals; D001362:Avoidance Learning; D001921:Brain / Q000378:metabolism; D004723:Endorphins / Q000096:biosynthesis / Q000494:pharmacology*; D004924:Escape Reaction / Q000187:drug effects*; D008297:Male; D008568:Memory / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D012153:Retention, Psychology / Q000187:drug effects*; D018822:alpha-Endorphin; D018823:gamma-Endorphin
D004723:Endorphins; D018822:alpha-Endorphin; D018823:gamma-Endorphin