A. Response rates (responses/min) for animals trained to self-administer nicotine at a unit dose of 0.03mg/kg/infusion in 1-h/day sessions over a multiple number of 1-h nicotine-self administration (NSA1-3) and extinction (EXT1-5) sessions. *** p<0.001, Bonferroni’s multiple comparison test following significant RM one way-ANOVA, where EXT2-5 are significantly different from NSA1-3 and EXT1. B. Response rates (responses/min) for each 5-min block for the average of the last three nicotine self-administration sessions prior to extinction (nicotine self-administration) and the first extinction session. C. Response rates (responses/min) for the first 5-min interval for NSA and the EXT sessions. *p<0.05, **p<0.01, ***p<0.001 versus NSA, Bonferroni’s multiple comparison test following a significant RM two- and one- way-ANOVA (for B and C, respectively). Response rates expressed as means (±SEM) with n = 84 for all figures.