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  • Title: Gamma-endorphin affects retrieval of an inhibitory avoidance task.
    Author: Dalmaz C, Fin CA.
    Journal: Braz J Med Biol Res; 1989; 22(9):1121-5. PubMed ID: 2483981.
    Abstract:
    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.
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