Prado-Alcalá R A, Haiek M, Rivas S, Roldan-Roldan G, Quirarte G L
Physiology Department, Faculty of Medicine, National University of Mexico, D.F. Mexico.
Physiol Behav. 1994 Jul;56(1):27-30. doi: 10.1016/0031-9384(94)90257-7.
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.
