Effect of atropine and propranolol on retrieval enhancement by a novel experience or by injection of beta-endorphin prior to testing in rats.
Wistar rats were trained in step-down inhibitory avoidance and tested 24 h later. One h prior to testing they were exposed to an open field or to an open field with flashing light (OFL) for 2 min. The OFL-exposed group showed retrieval enhancement for the avoidance task. This effect was mimicked by an injection of beta-endorphin (2.0 micrograms/kg) 1 h prior to testing, and both effects were blocked by the concomitant administration of naloxone (0.8 mg/kg, ip). Propranolol (2.0 mg/kg, ip) and atropine (0.5 mg/kg, ip) injected 6 min before the test completely blocked the retrieval-enhancing effect of both beta-endorphin and OFL. These results suggest that: 1) in rats, novel experiences may induce retrieval enhancement provided they are alerting; 2) the retrieval-enhancing effect of pre-testing exposure to OFL is probably due to activation of the brain beta-endorphin system which triggers late beta-noradrenergic and cholinergic mechanisms acting at the moment of retrieval.
Netto
C A
CA
Departamento de Bioquímica, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brasil.
Oliveira
C B
CB
Gianlupi
A
A
Quillfeldt
J
J
D000704:Analysis of Variance; D000818:Animals; D001285:Atropine / Q000494:pharmacology*; D001362:Avoidance Learning / Q000187:drug effects*; D005260:Female; D008568:Memory / Q000187:drug effects*; D009270:Naloxone / Q000494:pharmacology*; D010775:Photic Stimulation; D011433:Propranolol / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012153:Retention, Psychology / Q000187:drug effects*; D001615:beta-Endorphin / Q000494:pharmacology*
D009270:Naloxone; D001615:beta-Endorphin; D001285:Atropine; D011433:Propranolol