Central effects of atropine upon aversive classical conditioning in rabbits

Abstract

Rabbits were given classical discrimination conditioning with one of two tones followed by shock. In Experiment I, 40 rabbits were trained under saline, 10, 18 or 26 mg/kg atropine sulfate or 18 mg/kg methylatropine. Six rabbits in Experiment 2 were conditioned, then given further sessions with saline, and 18, 26 and 34 mg/kg atropine sulfate and methylatropine. In Experiment 3, 18 rabbits were conditioned and then given two extinction sessions under saline or 34 mg/kg atropine sulfate or methylatropine followed by extinction under saline. Chief findings were (a) atropine sulfate but not methylatropine disrupted acquisition and maintenance of conditioned eyeblinks, (b) neither drug affected unconditioned blinks, (c) fewer blinks occurred in extinction under atropine sulfate than under methylatropine or saline, (d) rabbits extinguished under atropine sulphate showed higher percentages of eyeblinks when tested without drug. Disruptions in performance of learned eyeblink responses appeared to be due to drug interference with central cholinergic transmission.