Rapid induction of Pavlovian approach to an ethanol-paired visual cue in mice

Abstract

Although many studies have shown Pavlovian conditioned approach to cues paired with natural reinforcers, it has been quite difficult to induce such behavior with drug reinforcers. This experiment tested a novel Pavlovian procedure for inducing approach to a conditioned stimulus (CS) paired with ethanol. Mice (NZB/B1NJ, DBA/2J) received intraperitoneal injections of ethanol (2 g/kg) immediately before 10-min exposure to a rectangular chamber that contained a distinctive visual cue (star) at one end (Paired group, CS+ trials). On alternate days, saline injection preceded apparatus exposure with no distinctive cues (CS- trials). Unpaired control mice received ethanol in the home cage 60-75 min after each CS+ trial. NZB/B1NJ Paired group mice spent increasing amounts of time (>85% of the session) in proximity to the star, whereas Unpaired group mice did not. DBA/2J Paired group mice spent slightly more time on the star side than Unpaired group mice but did not show an acquisition curve. Postconditioning tests showed a strong preference for the star side in Paired groups from both strains after saline injection. However, only NZB/B1NJ mice showed a preference after ethanol. This study provides the first unambiguous demonstration of Pavlovian conditioned approach to an ethanol-paired visual stimulus in the absence of any contingency between the animal's behavior and drug exposure. This effect, which is remarkable both in terms of its magnitude and the rapidity with which it was produced (within 2-3 trials), may be related to the cue-associated craving that accompanies alcohol and drug addiction.