The effects of repeated exposure on the reward-enhancing effects of nicotine.

Nicotine increases operant responding for a weakly reinforcing audiovisual stimulus in rats, but the role of repeated exposure in the development of this effect has not been explicitly investigated. This study investigated, in two experiments, whether repeated nicotine exposure is a requisite for the expression of a reward-enhancing effect in rats, using a probe design by administering nicotine acutely at a range of doses (0.03, 0.1, 0.3, 1.0, and 3.0 mg/kg) both before and after two weeks of daily administration of 0.3 mg/kg of nicotine. Nicotine did not enhance responding for an audiovisual stimulus relative to baseline at any dose when administered before repeated daily administration, but responding was enhanced at 0.1, 0.3, and 1.0 mg/kg of nicotine after daily administration. The results suggest that repeated exposure to nicotine is a requisite for the expression of reward-enhancing effects, and implicate sensitization to the effects of nicotine in this process.