Conditioned suppression of an operant response using drugs as conditioned stimuli

The possible use of a drug state as a conditioned stimulus in a classical conditioning paradigm was investigated in a series of four experiments. Suppression of an operant response served as an index of a classically conditioned response (conditioned suppression). In all the experiments drug injections were paired with a series of unavoidable shocks. Subsequently, effects of the shock-paired drug on operant response rate were compared to effects obtained in control subjects which received unpaired drug-shock experience. These experiments demonstrated that d-amphetamine (0.8mg/kg) served as a CS for conditioned suppression of a one-lever task (VI-60sec). Stimulus generalization from the shock-paired drug to cocaine (7.5mg/kg) also occurred. Reduction of external apparatus cues, by administering shocks in the operant chamber instead of a separate apparatus, produced a more durable suppression effect. Response totals recovered to a maximum of 80% of baseline responding after twelve days of testing. In one experiment animals were trained on a d-amphetamine vs. cocaine discrimination prior to shocks paired with one of the two drugs. It was hypothesized that during retraining of the operant discrimination, suppression would be observed for sessions involving the shock-paired drug. Since the suppression obtained was not cue-specific, the difficulty of the d-amphetamine vs. cocaine discrimination may have minimized transfer between the operant and classical components of the study. The prior discrimination training did not reduce the generalization of suppression from d-amphetamine to cocaine. In a final experiment d-amphetamine vs. saline discrimination training preceded the drug-shock sessions in which either d-amphetamine or saline were shock-paired for each individual subject. Although discrimination was readily acquired, no cue-specific suppression occurred. The results of this experiment suggest that a saline injection cannot serve as a CS in the absence of explicit differentiation procedures. Further research is required for clarification of this interpretation. The results of the four studies suggest that, with further development, the conditioned suppression paradigm may be a useful alternative to operant discrimination in the study of drug stimulus control. Advantages of the paradigm are discussed. Two general conclusions of this series of investigations were (1) that drug states, as possible representatives of other internal stimuli, may acquire behavioral properties through classical conditioning procedures, and (2) that generalization can occur between similar internal stimuli. Results were discussed in the context of possible applications to behavioral problems such as drug abuse and psychosomatic symptoms.