The course of the decrease of hypothalamic beta-endorphin induced by training, and the development of the effect of beta-endorphin on the retrieval of inhibitory avoidance in rats.
Step-down inhibitory avoidance training or the simple exposure of rats to the training apparatus is followed by a decrease of hypothalamic beta-endorphin immunoreactivity at 0.1, 1.0 or 2.0 h after training. Immunoreactivity returns to normal at 6.0 h. The ip administration of 1.0 microgram/kg of human beta-endorphin 6 min prior to training produces an inhibition of the retrieval of the step-down task at 6.0 h, but not at 0, 1.0 or 2.0 h after training. This effect is reversed by a second injection of the substance immediately before testing. The possible physiological significance of this parallel development of the effect of beta-endorphin on retrieval and the depletion of the substance caused by training is discussed. The data indicate that retrieval is insensitive to the peptide when its hypothalamic stores are depleted.
D000818:Animals; D001362:Avoidance Learning / Q000502:physiology*; D004723:Endorphins / Q000032:analysis / Q000502:physiology*; D005260:Female; D007031:Hypothalamus / Q000032:analysis; D008568:Memory / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D001615:beta-Endorphin
D004723:Endorphins; D001615:beta-Endorphin