After catheter implantation and recovery, mice were trained to nose-poke for infusions of nicotine (0.03 mg/kg/infusion) (A) or saline (B). The schedule of reinforcement was maintained at a fixed ratio 1 (FR1) for a period of 6 sessions, followed by a FR2 schedule for a period of 4 sessions. Data is shown as mean (±SEM) number of nose-pokes or infusions. *p<0.05, **p<0.01, ***p<0.001, a two-way ANOVA followed by Bonferroni post hoc analysis.