Pavlovian-Instrumental Transfer of the Discriminative Stimulus Effects of Nicotine and Ethanol in Rats

Abstract

To date, only 1 study has evaluated the impact of a Pavlovian drug conditional stimulus (CS) on operant responding. A within-subject operant 1-lever go/no-go (across sessions) design was used to evaluate the impact of Pavlovian contingencies on the discriminative stimulus effects of nicotine (0.4 mg/kg) and ethanol (800 mg/kg) in male Sprague Dawley rats. Drugs were administered 10 min before each acquisition and test session. One drug predicted sessions of food reinforcement and the other drug predicted sessions of non reinforcement; stimulus roles were counterbalanced. In Experiment 1 (n = 7), operant lever pressing was initially maintained on a VI-30 s schedule of food reinforcement. This phase was followed by 20 (CS+ vs. CS-) Pavlovian drug discrimination training sessions without the levers present. Two extinction tests revealed significantly more operant lever pressing under the CS+ drug conditions compared to the CS- drug conditions, suggesting evidence for Pavlovian-instrumental transfer. Operant training significantly strengthened stimulus control. In Experiment 2 (n = 7), the drugs functioned as operant drug discriminative stimuli first. Next, the predictive roles of the drug S D s and S Δ S were reversed under Pavlovian CS- and CS+ contingencies, respectively. The original stimulus control was significantly undermined but was not reversed. These studies suggest that Pavlovian drug-reinforcer contingencies embedded within the operant 3-term contingency may play a partial role in mediating the discriminative stimulus effects of drugs.