Zacopride, a 5-HT3 receptor antagonist, reduces voluntary ethanol consumption in rats.

The effect of the selective 5-HT3 receptor antagonist, zacopride, was assessed in male Sprague-Dawley rats in free choice (6% ethanol and water) experiments. In Experiment 1, single zacopride (0.01-10 mg/kg, IP) injections failed to alter ethanol (ET) consumption during 1-h restricted ET access. In Experiment 2, zacopride (5.0 and 10 mg/kg, IP) injected twice daily for 5 days significantly reduced ET intake and ET preference during 24-h free access to 6% ET and water without altering the total volume of fluid consumed. Thus, the schedule of ET access (i.e., free vs. restricted) and/or the duration of drug treatment may determine the efficacy of pharmacological agents in altering ET preference. 5-HT3 receptor blockade may reduce serotonin/dopamine-mediated maintenance of ET preference; a process that may proceed via extinction mechanisms.