Adolescent exposure to nicotine results in reinforcement enhancement but does not affect adult responding in rats

Abstract: Background: Adolescence is a period of development associated with a peak in an organism''s responsiveness to reward. Epidemiological data indicate that the initiation of smoking is high during adolescence and that earlier age of onset is associated with increased incidence of dependence as adults. In rats, nicotine is known to have primary reinforcing and reinforcement enhancing effects. Although the primary reinforcing effects of nicotine have been demonstrated in adolescent rats (self-administration), less is known about its reinforcement enhancing effects during this period. Moreover, the impact of adolescent nicotine exposure on its reinforcement enhancing effects during adulthood has not yet been examined. The objectives of this study were to assess whether (1) nicotine enhances operant responding for an unconditioned visual reinforcer (VS) in adolescent rats, and (2) exposure to nicotine during adolescence affects responsiveness to the VS in adulthood. Methods: Rats were exposed to nicotine (0.32mg/kg, subcutaneous injection) or saline during adolescence (postnatal day 29–42) and adulthood. Nose-poking for the VS was assessed under fixed and progressive ratio schedules. Results: Nicotine increased responding for the VS during adolescence. Adolescent nicotine exposure failed to significantly affect adult responsiveness for the VS, regardless of adult nicotine exposure, but early exposure to the VS affected responsiveness to the VS in adulthood. Conclusions: Nicotine exhibits reinforcement enhancing effects in adolescent rats. Long-term effects of adolescent nicotine on reinforcement enhancement are minimal, but the impact of early exposure to the VS and/or the primary reinforcing effects of nicotine requires further investigation. [Copyright &y& Elsevier]