Adolescent-onset nicotine self-administration modeled in female rats

Rationale. Although the great majority of tobacco addiction begins during adolescence, little is known about differential nicotine effects in adolescents versus adults. Objectives. A rat model was used to determine the impact of the age of onset on nicotine self-administration. Methods. In expt 1, nicotine self-administration of female Sprague-Dawley rats over a range of acute doses (0.01-0.08 mg/kg per infusion) was determined in adolescent (beginning at 54-62 days) versus adult (beginning at 84-90 days). In expt 2, chronic nicotine self-administration over 4 weeks from adolescence into adulthood was compared with the chronic self-administration beginning in adulthood. In expt 3, adolescent-adult differences in nicotine effects on body temperature and locomotor responses were determined. Results. Adolescent-onset rats showed a significant main effect of increased nicotine intake compared with adult-onset rats in an eight-fold range of acute unit doses/infusion. Significant age differences were also seen in the chronic level of nicotine self-administration. Over 4 weeks, the adolescent-onset group had nearly double the rate of nicotine self-administration of the benchmark nicotine dose (0.03 mg/kg per infusion) compared to the adult-onset group. This increased nicotine intake persisted into adulthood. Adolescent rats had significantly greater response than adults to the hypothermic effects of nicotine, but had significantly less response than adults to the reduction in locomotor activity seen after nicotine. Conclusions. Adolescent-onset nicotine self-administration in female rats was associated with significantly higher levels of nicotine self-administration versus rats, which began nicotine self-administration in adulthood. This greater self-administration persists into adulthood and may underlie greater propensity of adolescents to nicotine addiction.