Prevalence, magnitude, and correlates of an extinction burst in drug-seeking behavior in rats trained to self-administer nicotine during unlimited access (23 h/day) sessions

Rationale: Animals trained to self-administer a variety of addictive drugs exhibit a temporary increase in response rate when saline is substituted for the drug (i.e., an "extinction burst"). However, the presence of an extinction burst in animal models of nicotine self-administration (NSA) has not been studied extensively. Objective: The objective of the study was to examine the prevalence, magnitude, and correlates of an extinction burst in nicotine-seeking behavior using data from a previously published study and recently trained animals. Materials and methods: Rats were trained to self-administer nicotine (0.03 mg/kg per infusion) during daily 23-h sessions. Saline extinction was subsequently arranged, followed by reacquisition of NSA for some animals. Results: There was no increase in the daily infusion rate on the first day of extinction. However, a significant increase (35%) in mean peak 2-h infusion rates was observed within the first extinction session, indicative of an extinction burst. Greater extinction burst magnitude was correlated with higher infusion rates during the first 2 h of baseline sessions and smaller decreases in infusion rate at the end of extinction. In addition, animals with the slowest initial rates of extinction exhibited the fastest rates of reacquisition when unlimited access to nicotine was restored. Conclusions: A modest increase in drug-seeking behavior occurred early within the first extinction session in rats trained to self-administer nicotine in unlimited access sessions. The presence of an extinction burst in nicotine-seeking behavior suggests similar mechanisms underlying extinction of NSA and self-administration of other drugs of abuse in animals and also parallels a similar phenomenon sometimes observed in smokers.