Individual differences in response to novelty and the conditioned locomotor effects of nicotine.

Rats' locomotor reactivity to an inescapable novel environment has been shown to be correlated with the psychomotor response to many stimulant drugs. However, the effects of nicotine on rats categorized as high responder (HR) or low responder (LR) has yielded inconclusive results. This study examined the effects of nicotine ditartrate in HR and LR rats using both a high (0.8 mg/kg; freebase) and a low dose (0.2 mg/kg; freebase). Male Sprague-Dawley rats were trained for the acquisition of nicotine-induced conditioned hyperactivity. After conditioned-hyperactivity testing, rats underwent extinction training to decrease hyperactivity by administering saline as a substitution for nicotine. Hyperactivity was then reinstated with a nicotine challenge (0.8 or 0.2 mg/kg). Pretreatment with nicotine during acquisition training significantly increased locomotor activity. Similarly, rats that had nicotine repeatedly paired with a distinct environment displayed significant conditioned hyperactivity and reinstatement of nicotine-induced hyperactivity. However, nicotine treatment was not found to differentially affect HR and LR rats. These data suggest that individual differences in response to an inescapable novel environment do not predict nicotine-induced locomotor sensitivity or sensitivity to nicotine-associated drug cues.