Two-drug discrimination within the taste aversion baseline of drug discrimination learning

Typical drug discrimination learning (DDL) uses an operant design in which subjects are trained to respond differentially based on the presence or absence of a drug. One non-operant procedure has emerged which utilizes a modification of the conditioned taste aversion (CTA) design. Since the initial assessment of DDL, a number of studies have demonstrated the ability of drugs to serve a discriminative function within the taste aversion baseline; however, the specific discrimination acquired to date, i.e., drug vs. vehicle, may limit the conclusions that can be reached and the pharmacological questions that can be asked. Operant designs have circumvented these limitations by training one group of subjects to discriminate between two drugs. Given the rapidity and sensitivity of the CTA baseline of DDL, the present study examined whether a conditional discrimination with two drugs and two tastes could be established within the same subjects using the taste aversion baseline. Specifically, animals were initially injected with pentobarbital prior to a saccharin (Sacc)-lithium chloride (LiCl) pairing and with amphetamine prior to a sodium chloride (NaCl)-LiCl pairing to determine whether both drugs could serve as discriminative stimuli within the taste aversion procedure. Following this, conditional discrimination training was initiated in which the procedure was identical to that noted above except pentobarbital was also given prior to NaCl and amphetamine was also given prior to Sacc. On these days, no subsequent injections were given. Under these conditions, animals acquired the conditional discrimination, displaying differential levels of consumption of both fluids dependent on the drug administered prior to Sacc/NaCl access. In subsequent probes, ethanol and cocaine (drugs from the same pharmacological class as pentobarbital and amphetamine, respectively) produced drug-appropriate responding specific to pentobarbital and amphetamine, respectively. Although several issues are addressed concerning the general utility of this procedure, the present study nevertheless extends the methodological modifications of the basic taste aversion baseline and may allow for other analyses and other questions that reveal more information regarding the stimulus properties of drugs.