Self-administered ethanol as a discriminative stimulus in rats

Abstract

The neurochemical and behavioral effects produced by drugs can differ based on whether self-administered or experimenter-administered. In addition, self-administered drugs, particularly those taken orally or by inhalation, have peripheral stimulus effects that are not present following experimenter administration. One drug with highly prominent peripheral stimulus effects when taken orally is ethanol. The purpose of the present experiment was to examine whether orally self-administered (SA) ethanol would serve as a discriminative stimulus and to determine if the peripheral effects of ethanol play a major role in the discriminative stimulus of orally SA ethanol. Twelve Long-Evans rats were trained to orally self-administer 750 mg/kg of 10% (w/v) ethanol and then discriminate that dose of ethanol from SA water. Six of twelve rats were successfully trained to discriminate oral SA ethanol from water. Intraperitoneal experimenter-administered and orally SA ethanol doses of 100–1320 mg/kg were tested for substitution. SA and i.p. ethanol doses of 750, 1000, and 1320 mg/kg fully substituted for the SA training dose. SA doses of 100, 320 and 560 mg/kg partially substituted for the SA ethanol training dose, whereas the 100 and 320 mg/kg i.p. ethanol doses did not substitute for SA ethanol. The ED 50 values for SA and i.p. ethanol were not significantly different from one another. The results indicate that SA ethanol can serve as a discriminative stimulus in rats and that i.p. ethanol can substitute for SA ethanol. In addition, the results also show that the discriminative stimulus effects of SA ethanol are primarily mediated by CNS drug effects.