ACQUISITION OF NICOTINE SELF-ADMINISTRATION IN RATS - THE EFFECTS OF DOSE, FEEDING SCHEDULE, AND DRUG CONTINGENCY

The studies presented here were designed to further clarify the nature of nicotine self-administration (SA) based on a limited access model in which rats are food restricted, receive operant training using food reinforcement, and are then tested in daily l-h drug sessions. We exa mined the effects of dose, feeding schedule, and contingency of drug d elivery on acquisition of nicotine SA. Two doses of nicotine bitartrat e, 0.03 and 0.06 mg/kg per infusion (free base), supported the transit ion from food-reinforced to drug-reinforced responding, although the p attern of behavior differed between these doses. In contrast, 0.01 mg/ kg per infusion failed to maintain nicotine SA. In a second study, ani mals were divided into three groups according to feeding schedule. Rat s that were both weight restricted and food deprived showed the highes t level of SA behavior, although nei ther food deprivation nor weight restriction was necessary to establish SA. In the third experiment, ra ts that were switched from food to nicotine as the response-dependent reinforcer maintained higher response rates throughout a 9-day period than animals switched to response-independent (i.e., yoked) nicotine w hich showed minimal responding after day 1. Furthermore, the differenc es between self-administering and yoked animals emerged during the fir st session, suggesting that nicotine may serve as a reinforcer during the first drug exposure in naive animals. These results indicate that acquisition of nicotine SA can be influenced by both dose of nicotine and feeding schedule and that, in animals previously trained on a food -reinforced operant, active lever pressing is maintained only when nic otine delivery is contingent upon responding.