the 16th and 17th nicotine pretreatment (45 minutes prior to start of the operant session). All rats received two doses (vehicle or 2 mg/kg, s.c.) over the course of 2 days in a counterbalanced design, and thus each rat served as its own control. The varenicline doses were chosen because they have previously been shown to effectively decrease nicotine self-administration (Rollema et al., 2007) and ethanol consumption (Steensland et al., 2007). Following varenicline testing, nicotine administration was terminated for five consecutive sessions to observe ethanol intake levels in the 20% ethanol operant self-administration model. We then evaluated the effect of a lower dose of nicotine, 0.2mg/kg, in the 20% ethanol operant self-administration model. The animals were separated back into their original nicotine administration group (nicotine or vehicle) but their treatment was switched to counterbalance from previous testing. As a result, animals that previously received vehicle injections would now be receiving nicotine (0.2mg/kg) injections and vice versa.
