Nicotine causes opposite effects on alcohol intake: Evidence in an animal experimental model of abstinence and relapse from alcohol.

INTRODUCTION: Tobacco and alcohol are frequently co-abused, but the mechanism underlying this interaction is not well understood. Experimental data on the influence of nicotine upon alcohol consumption are not conclusive.
METHODS: To elucidate the role of nicotine in alcohol consumption, alcohol-experienced rats were submitted to consecutive phases of forced abstinence from alcohol, followed by relapses, in which their alcohol consumption was measured in a 2-bottle choice test. Rats were assigned to one of 4 groups: (a) "Control," which received daily saline injections during both the abstinence and relapse phases, (b) "Nic. All," which received nicotine injections during both phases, (c) "Nic. Abst.," which received nicotine during the abstinence phase only, and (d) "Nic. Rel.," which received nicotine during the relapse phase only. The nicotine doses (0.4, 0.6, and 0.8 mg/kg) were administered in an escalating fashion. Alcohol consumption was measured 3 times per day.
RESULTS: Overall, the rats treated daily with nicotine during both the abstinence and relapse phases (Nic. All) significantly increased their alcohol intake compared with the rats treated daily with vehicle alone (Control). Similarly, rats treated with nicotine during the alcohol abstinence phase only (Nic. Abst.) also increased their alcohol consumption. However, rats treated with nicotine during the alcohol relapse phase only (Nic. Rel.) decreased their alcohol intake. In addition, a more exhaustive analysis showed critical differences in patterns of alcohol consumption during the first hour and the first day of alcohol access. DISCUSSION: Taken together, we provide evidence that depending on the timing of exposure, the same dose of nicotine can have opposite effects on alcohol consumption.