Abstract
Adolescence is a critical period for the initiation of drug use, starting with tobacco and alcohol and progressing to marijuana and other illicit drugs. These findings have led to the suggestion that tobacco and alcohol are ‘gateway’ drugs that sensitize maturing reward pathways to the effects of illicit substances such as cocaine. To test this hypothesis, we have examined whether low-dose nicotine pretreatment alters acquisition of cocaine self-administration in adolescents more than in adults. Male and female Sprague-Dawley rats, aged postnatal day (P) 28 or P86, were given two daily intravenous injections of nicotine (0.03 mg/kg/0.1 ml) or saline for four days. At P32 and P90, rats were placed in self-administration chambers and tested for acquisition of cocaine (0.2 or 0.5 mg/kg/inj) for five days. Data were collapsed across cocaine dose and sex since there was no significant effect of these variables. Adolescent rats pretreated with nicotine exhibited significantly greater cocaine-reinforced responding as compared to saline controls or adults (p < 0.01). This effect was evident as early as the first day, suggesting that nicotine sensitizes adolescent rats to the rewarding effects of cocaine. In addition, this drug pretreatment effect did not generalize to all rewards, since nicotine did not increase responding for sucrose pellets in adolescents. Additional behavioral and neurochemical studies are currently being conducted to determine the underlying mechanisms. These findings provide evidence that the adolescent brain is uniquely vulnerable to the effects of nicotine and support the ‘gateway’ hypothesis of teenage drug use. This study is supported by DA19138 and DA07318.
Published Version
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