Age differences in the spontaneous acquisition of nicotine self-administration in male Wistar and Long–Evans rats

Abstract

Epidemiological evidence suggests that adolescents may exhibit a unique susceptibility to the motivational effects of nicotine compared to adults. In contrast to the hypothesis of an enhanced vulnerability to nicotine during adolescence, we have observed that nicotine is less reinforcing in adolescent compared to adult rats using a progressive ratio reinforcement schedule in an operant self-administration procedure, although prior operant conditioning experience may have masked differences in initial sensitivity to nicotine. This study examined the spontaneous acquisition of nicotine self-administration in adolescent (postnatal day (PD) 31) and adult (PD87) male Wistar and Long-Evans rats. Rats self-administered nicotine (0.015 or 0.03 mg/kg/infusion, i.v.) during 2-h operant conditioning sessions under fixed-ratio-1 (FR1) and FR3 reinforcement schedules for six sessions each. A subset of rats (adolescents: PD42, adults: PD98) underwent extinction of responding and nicotine priming-induced reinstatement (0.15 mg/kg, s.c.). In a separate group of rats, saccharin self-administration (0.1 ml of 0.2% w/v) was tested to determine the specificity of our findings with nicotine. A greater proportion of adult compared to adolescent rats acquired self-administration of 0.015 mg/kg/infusion nicotine, but both age groups readily acquired self-administration of 0.03 mg/kg/infusion nicotine and saccharin. Age differences in extinction of responding for nicotine or saccharin depended upon strain, but priming-induced reinstatement was similar across age and strain. The current findings are consistent with those obtained under a more demanding progressive ratio reinforcement schedule and suggest that adolescents, compared to adults, may not be as sensitive to the reinforcing effects of nicotine.