Effects of Adolescent Nicotine Exposure on Adult Cocaine Reward, Aversion and Self‐Administration

Abstract

These studies examined adolescent nicotine preexposure effects on the rewarding and aversive effects of adult cocaine use and the relationship of these changes to self‐administration. In Experiment 1, rats on postnatal day (PND) 28 were divided into two groups and given daily 0.6 mg/kg injections of nicotine or vehicle until PND 42. Rats were given locomotor tests to examine nicotine‐induced sensitization. They were allowed to age untreated to PND 76, implanted with jugular catheters and allowed to recover for at least 5 days. On PND 90, cocaine self‐administration (0.25 or 0.75 mg/kg), progressive ratio (PR) responding, extinction and cue‐induced reinstatement testing began. Experiment 2 explored nicotine's impact on the balance of cocaine's affective properties. Rats (PND 28‐ 75) were treated as described above. On PND 76, they were tested for the aversive and rewarding effects of cocaine in a combined conditioned taste avoidance (CTA)/place preference (CPP) procedure. Rats were given access to a novel saccharin solution, injected with cocaine (5.6, 10 or 18 mg/kg) then placed in CPP chambers. In Experiment 1, the nicotine group showed sensitized locomotor activity over trials compared to controls, showing that the nicotine was behaviorally active. All rats in Experiment 1 showed clear, dose dependent responding during acquisition, PR, extinction and reinstatement, with no nicotine preexposure effect. In Experiment 2, rats showed a significant CTA trial x Drug effect (p = .012) with cocaine groups consuming less saccharin over trials with no preexposure or dose group differences. There was no significant CPP or interaction with preexposure. These studies suggest that adolescent nicotine preexposure does not have an impact on adult cocaine self‐administration or its affective properties under these parametric conditions.