Effects of training dose on discrimination and cross-generalization of chlordiazepoxide, pentobarbital and ethanol in the rat

Abstract

Six groups of rats (N=8), trained to discriminate chlordiazepoxide (5 or 20 mg/kg), pentobarbital (5 or 15 mg/kg) or ethanol (750 or 1500 mg/kg) from saline in a two-lever food-reinforced procedure, were tested for stimulus generalization with the three drugs. Training drug, but not training dose, affected the extent of generalization to a test drug; symmetrical generalization between chlordiazepoxide and pentobarbital and asymmetrical generalization between chlordiazepoxide and ethanol and between pentobarbital and ethanol was observed. Training dose level affected (1) slope and ED₅₀ of the generalization gradients of training drugs and substitution drugs, (2) discriminative performance, (3) response bias and (4) threshold dose for response suppression. Indices of lever selection and percentage drug-appropriate lever responses yielded similar generalization maxima, slopes and ED₅₀s. The potency of chlordiazepoxide relative to the potency of pentobarbital to induce drug stimulus generalization varied across the experimental groups. The results indicate differences between the discriminative effects of chlordiazepoxide, pentobarbital and ethanol. It is suggested that the discriminative effects of chlordiazepoxide, pentobarbital and ethanol are not based on their response rate modulating effects and that training dose is not a determinant for the extent of cross-generalization between these compounds.