Outcome-specific Pavlovian-to-instrumental transfer (PIT) with alcohol cues and its extinction

Abstract

The acquired motivational impact of conditioned stimuli has been studied using the Pavlovian-to-instrumental transfer (PIT) task, where a cue paired with a reward is consistently shown to energize responses separately trained with that same reward ("specific" PIT). However, most alcohol studies have shown that alcohol-related cues elevate responses trained with either the same alcohol reward or with other non-alcoholic rewards ("general" PIT). The effects of extinction on this alcohol PIT effect have not been fully explored. We tested the hypothesis that cues signaling different-tasting alcohols might acquire specific craving reactions for those alcohols leading to specific PIT, but that these effects might be sensitive to extinction. Three experiments examined the specificity of PIT using alcohol and non-alcohol outcomes. Rats first consumed different-flavored alcohol solutions in their home cages. Then they were trained to perform two responses, each reinforced with distinctly flavored solutions, using a Polycose fading procedure. The outcomes were sweet (4% sucrose) or salty (0.9% NaCl) ethanol (10% v/v) solutions (Experiments 1 and 2) or one plain or salty alcohol vs. a non-alcoholic sweet solution (Experiment 3). Then, two cues were each differentially paired with these outcomes. In PIT tests, animals performed both responses in the presence and absence of these cues without any rewards. Experiments 1, 2, and 3 showed that a cue paired with a flavored alcohol produced a small but consistent bias toward the response trained with the same alcohol solution (specific PIT). Experiment 2 showed that extinction eliminated this effect. Experiment 3 demonstrated that specific PIT occurred when contrasting salty, or plain, alcohol to a non-alcoholic solution. These results provide evidence that alcohol-related stimuli can elicit craving for specific types of alcohol (as revealed by specific PIT), but that this effect is sensitive to extinction. This paradigm of contrasting two distinctly flavored alcohols may be an especially useful animal model of alcohol addiction.