Naloxone eliminates passive avoidance retention deficits produced by pretest exposure to novelty in rats.
Pretest exposure to novelty or injections of beta-endorphin can enhance passive avoidance (PA) retention (e.g., Izquierdo & McGaugh, 1985). Enhanced retention may result from a "state-dependent" match between the CNS state during test and the novelty-induced beta-endorphin state that is obtained during training in a novel apparatus. Our Experiment 1 suggests that, unlike PA, Pavlovian fear conditioning in a conditioned lick suppression (CLS) paradigm may be beta-endorphin "state-independent." Rats were given one tone-shock pairing in a novel environment. Baseline lick rates and CLS tested 48 h later in a familiar environment were not affected by pretest exposure to novelty and/or injections of 3.33 mg/kg naloxone HCl. In Experiment 2, the same rats were PA trained/tested in a new apparatus. Saline or naloxone injections and various exposure (novel, familiar, none) conditions preceded (1h) the 24-h retention test. Pretest exposure to novelty reduced retention and naloxone eliminated that deficit. In Experiment 3, naive rats given pretest exposure to novelty also showed a PA retention deficit. The results of Experiments 2 and 3 may complement rather than contradict previous findings. Pretest induction of a beta-endorphin state by novelty may either enhance state-dependent retrieval of a "weak" memory trace or make a "strong/well consolidated" training memory more vulnerable to retroactive interference from "new learning" during the pretest exposure period.
Pinheiro
A D
AD
Department of Psychology, University of Missouri, Columbia 65211.
Wright
D C
DC
D000818:Animals; D001070:Appetitive Behavior / Q000187:drug effects; D001143:Arousal / Q000187:drug effects*; D001245:Association Learning / Q000187:drug effects; D001288:Attention / Q000187:drug effects*; D001362:Avoidance Learning / Q000187:drug effects*; D001921:Brain / Q000187:drug effects; D003214:Conditioning, Classical / Q000187:drug effects; D004326:Drinking / Q000187:drug effects; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects; D012153:Retention, Psychology / Q000187:drug effects*; D012931:Social Environment; D001615:beta-Endorphin / Q000502:physiology
D011957:Receptors, Opioid; D009270:Naloxone; D001615:beta-Endorphin