CONDITIONED TASTE AVERSIONS IN RATS AS A BEHAVIORAL BASELINE TO ASSESS THE DISCRIMINATIVE STIMULUS PROPERTIES OF PHENCYCLIDINE

Typically, drug discrimination is examined within the context of operant conditioning (cf. Stolerman & Shine, 1985). In such designs, one behavior is reinforced during sessions preceded by an injection of a drug and a second behavior is reinforced by an injection of the drug vehicle. The discrimination is evidenced by differential responding in the presence and absence of the drug stimulus. In the present series of experiments, an alternative procedure for assessment of drug-discrimination learning was examined, i.e., conditioned-taste aversion learning (cf. Riley & Tuck, 1985). In conditioned taste-aversion learning, an animal is injected with a toxin following consumption of a novel taste. In such a design, animals avoid consumption of that taste on subsequent exposures. The question posed in the present series of experiments was whether an aversion to a taste would be acquired and displayed in one specific drug state, while the same taste would be consumed in another drug condition. Prior to assessing drug-discrimination learning within the taste-aversion design, a dose of a drug had to be chosen that had no potential for supporting conditioning itself (Experiment 1), no unconditioned suppressant effects on consumption (Experiment 2), and was able to serve as a discriminative stimulus in an operant paradigm (Experiment 3). Based on the results of the first three experiments, a dose of 1.8 mg/kg of phencyclidine was chosen to determine if the taste-aversion design could serve as a baseline for drug-discrimination learning. In Experiment 4, different groups of rats were trained in a conditioned taste-aversion paradigm with either the presence or absence of PCP as a signal for a saccharin-LiCl pairing. Specifically, for Group P-L on days when PCP was injected 10 min prior to saccharin presentation, LiCl was injected immediately following saccharin access. On days when distilled water was injected 10 min prior to saccharin presentation, however, no LiCl was injected. For Group W-L, these conditions were reversed. Differential consumption in the presence or absence of the drug stimulus emerged after three conditioning trials. In addition, substituting different doses of PCP produced a generalization gradient around the training dose. The rapid control acquired by the drug stimulus in this procedure and the absence of any other confounding stimuli, e.g., a reinforcing stimulus, suggest that the conditioned taste-aversion design may be an efficient method for classifying drugs on the basis of their discriminative stimulus properties.