Naloxone and beta-endorphin alter the effects of post-training epinephrine on memory.
These experiments examined the involvement of opioid peptides in the memory-modulating effects of post-training epinephrine (Epi). Mice were trained on inhibitory avoidance (IA) and Y-maze discrimination (YMD) tasks and given post-training injections followed by retention tests 24 h later. In the IA task retention was enhanced by low doses of Epi and impaired by high doses. In both tasks, naloxone facilitated retention and blocked the memory-impairing effects of Epi. These findings are consistent with other evidence suggesting that the memory-impairing effects of beta-endorphin are mediated by the release of opioid peptides. Previous studies have shown that a novel exploratory experience given 1 h prior to training blocks the release of brain beta-endorphin and blocks the memory-enhancing effects of post-training naloxone. In the present study we found that a novel experience given 1 h prior to training blocked the memory-impairing effect of post-training Epi otherwise obtained in both tasks. The effects of a low, memory-enhancing dose of Epi appear not to involve the release of opioid peptides: a low dose of Epi blocked the memory-impairing effect of beta-endorphin. Further, low doses of Epi and naloxone, which were ineffective when administered alone, significantly enhanced retention when administered together. We interpret these findings as indicating that the memory-enhancing and memory-impairing effects of Epi are mediated by different mechanisms.
D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects; D004192:Discrimination, Psychological / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004723:Endorphins / Q000494:pharmacology*; D004837:Epinephrine / Q000494:pharmacology*; D008297:Male; D008568:Memory / Q000187:drug effects*; D051379:Mice; D009270:Naloxone / Q000494:pharmacology*
D004723:Endorphins; D009270:Naloxone; D004837:Epinephrine