NICOTINE-INDUCED ACUTE TOLERANCE - STUDIES INVOLVING SCHEDULE-CONTROLLED BEHAVIOR

The major goal of the present study was to examine acute tolerance to nicotine-induced disruption of operant behavior following a single, no ncontingent injection. Rats were trained to lever press for food reinf orcement under a fixed ratio-30 schedule. Once trained, rats were inje cted with either saline or nicotine (0.8 mg/kg) in their home cages. A fter either a 90- or 180-min delay, each rat was injected with nicotin e (0.4 mg/kg) and placed in the operant chamber for a 30-min behaviora l evaluation session. This experiment was replicated with slight modif ications 1 week later. The results of the present study suggest that 0 .8 mg/kg of nicotine produces acute tolerance to the response rate dec reasing effects of 0.4 mg/kg of nicotine. Because the tolerance-produc ing dose of nicotine was injected while rats were not in the test envi ronment, they did not have an opportunity to practice the target behav ior while under the influence of the drug. Hence, the acute tolerance observed in this study appears to be, at least partly, pharmacological (vs. behavioral) in nature, and may be related to a desensitization o f central nicotinic acetylcholinergic receptors (nAChRs).