title: Reversal of extinction by scopolamine.
abstract: The aim of this experiment was to determine the effects of muscarinic blockade on extinction of passive avoidance conditioning. Rats were trained with a foot shock of 2.5, 3.0, or 6.0 mA and were tested for retention for 8 weeks (once weekly). Five minutes before the seventh test they were injected with 8 mg/kg scopolamine. The groups that had been trained with 2.5 and 3.0 mA showed extinction, which was reversed by the scopolamine; the overreinforced group (6.0 mA) did not show extinction and the scopolamine did not alter the conditioned response. The data support the hypothesis that extinction represents the learning of a new response sustained by a set of cholinergic neurons, different from that which mediated original passive avoidance learning.
authors.affiliation: Physiology Department, Faculty of Medicine, National University of Mexico, D.F. Mexico.
authors.forename: R A
authors.initials: RA
authors.lastname: Prado-Alcalá
authors.forename: M
authors.initials: M
authors.lastname: Haiek
authors.forename: S
authors.initials: S
authors.lastname: Rivas
authors.forename: G
authors.initials: G
authors.lastname: Roldan-Roldan
authors.forename: G L
authors.initials: GL
authors.lastname: Quirarte
mesh_terms: D000109:Acetylcholine / Q000502:physiology; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000187:drug effects / Q000502:physiology; D004924:Escape Reaction / Q000187:drug effects / Q000502:physiology; D005108:Extinction, Psychological / Q000187:drug effects* / Q000502:physiology; D005239:Fear / Q000187:drug effects / Q000502:physiology; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D011950:Receptors, Cholinergic / Q000187:drug effects / Q000502:physiology; D012153:Retention, Psychology / Q000187:drug effects / Q000502:physiology; D012601:Scopolamine / Q000494:pharmacology*
chemical_list: D011950:Receptors, Cholinergic; D012601:Scopolamine; D000109:Acetylcholine