Reversal of extinction by scopolamine.
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.
Prado-Alcalá
R A
RA
Physiology Department, Faculty of Medicine, National University of Mexico, D.F. Mexico.
Haiek
M
M
Rivas
S
S
Roldan-Roldan
G
G
Quirarte
G L
GL
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*
D011950:Receptors, Cholinergic; D012601:Scopolamine; D000109:Acetylcholine