Periadolescent and adult rats respond differently in tests measuring the rewarding and aversive effects of nicotine

Rationale: Initiation of tobacco use typically begins during adolescence, and the nature of these first experiences with nicotine may affect the probability of continued use. In rodents, a number of studies suggest that periadolescents are more responsive to the rewarding effects of nicotine compared to adults. Objectives: This study was designed to determine if there are age differences in the rewarding and aversive effects of nicotine by using the conditioned place preference (CPP) and conditioned taste avoidance (CTA) paradigms, respectively. We also examined age differences in locomotor responses to nicotine. Methods: In the CPP paradigm, male periadolescent and adult Wistar rats received nicotine (0.2, 0.4, or 0.8 mg/kg, s.c.) or vehicle prior to place conditioning trials. In the CTA paradigm, in separate groups of rats, periadolescents and adults were exposed to a 0.1% saccharin solution, followed by the administration of nicotine (0.2, 0.4, or 0.8 mg/kg, s.c.) or vehicle. Four saccharin nicotine pairings were followed by a preference test and three extinction sessions. Results: In the CPP paradigm, nicotine produced a dose-dependent place preference in periadolescent, but not in adult, rats. In the CTA paradigm, adult rats expressed a dose-dependent avoidance of saccharin after pairings with nicotine, whereas periadolescents were resistant to CTA formation. With regard to locomotor activity, adults and periadolescents showed comparable locomotor responses to nicotine. Conclusions: These results suggest that periadolescent rats find nicotine more rewarding and less aversive, compared to adult rats. This shift in the balance between the rewarding and aversive effects of nicotine may make adolescents more susceptible to continued nicotine use.