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.

Central cholinergic blockade by scopolamine and habituation, classical conditioning, and latent inhibition of the rabbit’s nictitating membrane response

“…Dishabituation by a stronger eye shock was unreliable and unaffected by the drug. These observations are consistent with the Downs et al (1972) study in suggesting that VCR mechanisms of the classically conditioned NMR in rabbits are unaffected by central cholinergic blockade.…”

“…This study is consistent with an earlier report (Downs, et al, 1972) in showing that central cholinergic blockade by a belladonna alkaloid interferes with acquisition but not the ultimate performance of a classically conditioned defensive eye reflex in rabbits. However, these studies provide few clues as to whether cholinergic blockade affects conditioning directly, by interrupting the flow of activity between the CS and CR along crucial synaptic linkages, or indirectly, either by altering tonic neuropharmacological relationships between cholinergic and other (presumably crucial) neurotransmitter systems or I1Y acting on collateral structures which normally serve to regulate or guide activity along the path(s) linking the CS with the CR.…”

“…Retarded acquisition in this case could come about either because the drug somehow disrupts the formation of the connection between the CS and the conditioned response (CR) or because the drug alters the unconditioned reflex (VCR) upon which conditioning is based. Downs et al (1972) reported that UCR amplitude was not noticeably altered by the drug. While th is observation suggests that central cholinergic blockade does not affect the VCR, the possibility remains that such disruption as may exist is subtle and obscured by an eliciting stimulus as intense as that employed in their experiment (3 rnA ac and of .5 sec duration).…”

“…Previous research (Downs, Cardozo, Schneiderman, Yehle, VanDercar, & Zwilling, 1972) has shown that central cholinergic blockade by atropine sulfate retards classical conditioning of the rabbit's NMR to a tone conditioned stimulus (CS) based on an electric shock unconditioned stimulus (VCS) to the eye. Retarded acquisition in this case could come about either because the drug somehow disrupts the formation of the connection between the CS and the conditioned response (CR) or because the drug alters the unconditioned reflex (VCR) upon which conditioning is based.…”

Disruption of trace conditioning of the nictitating membrane response in rabbits by central cholinergic blockade

“…2B). At even higher doses of anticholinergics, motor impairment has not been observed (Downs et al 1972;Moore et al 1976;Harvey et al 1983).…”