All results are presented as group means (± SEM). For experiments comparing only two conditions, Student's t-test was performed. Self-administration and reinstatement data were analyzed with Proc Mixed (SAS Institute, Cary NC) with Tukey-Kramer comparisons. For self-administration, the dependent variable was injections/session and the independent variables were pretreatment (dose) and session type (baseline sessions vs. pretreatment sessions), allowing each pretreatment condition to be compared to the most recent baseline. For selected conditions where consecutive sessions are illustrated (Figures 1B, 2B, and 2C), additional analyses were performed using session as a factor. For reinstatement in rats, the factors were nose-poke hole (active vs. inactive), prime (saline vs. nicotine), and pretreatment (dose of WY14643); for monkeys, separate one-way ANOVAs were conducted for the three doses of WY14643. Electrophysiology and microdialysis data were analyzed using analysis of variance (ANOVA) with Dunnett or Student-Newman-Keuls comparison procedures, respectively. Experiment-wise significance levels of 0.05 were maintained in all analyses.
