DUAL ACTION OF POST-TRAINING NALOXONE ON MEMORY

Naloxone administered at a dose of 0.2 mg/kg post-training antagonizes the deleterious effect of post-training β-endorphin administration and prevents the enhancing effect of pretest β-endorphin administration, on retention of a stepdown inhibitory avoidance task in rats. Given at a higher dose (0.4 mg/kg), naloxone caused, in addition to these effects, a pronounced retrograde facilitation which was additive with that caused by post-training ACTH or epinephrine administration. These findings show that post-training naloxone has two different effects or sets of effects, each with a different dose threshold: An interference with β-endorphin induced state dependency and a true modulatory effect. © 1978 Academic Press, Inc.