Adolescent nicotine exposure increases fixed-interval nicotine IVSA in adult male Sprague-Dawley rats. All data are presented as mean±standard error of mean. (a) Total infusions on an FR1, FI1 and PR schedule of reinforcement. (b) Active and inactive lever presses on an FR, FI1, and PR schedule. (c) Locomotion (number of chamber photobeam breaks) during the FR1, FI1, and PR schedules. * indicates significant difference from saline pre-exposure controls following significant interaction (p <0.05). $ indicates significant main effect of group in the absence of an interaction.