Nicotine addiction is a worldwide problem. However, previous studies characterizing the rewarding and reinforcing effects of nicotine in animal models have reported inconsistent findings. It was observed that the addictive effects are variable on different factors (e.g. route, dose, and age). Here, we evaluated the rewarding and reinforcing effects of nicotine in different routes of administration, across a wide dose range, and in different age groups. Two of the most widely used animal models of drug addiction were employed: the conditioned place preference (CPP) and self-administration (SA) tests. Nicotine CPP was evaluated in different routes [intraperitoneal (i.p.) and subcutaneous (s.c.)], doses (0.05 to 1.0 mg/kg) and age [adolescent and adult rats]. Similarly, intravenous nicotine SA was assessed in different doses (0.01 to 0.06 mg/kg/infusion) and age (adolescent and adult rats). In the CPP test, s.c. nicotine produced greater response than i.p. The 0.2 mg/kg dose produced highest CPP response in adolescent, while 0.6 mg/kg in adult rats; which were also confirmed in 7 days pretreated rats. In the SA test, adolescent rats readily self-administer 0.03 mg/kg/infusion of nicotine. Doses that produced nicotine CPP and SA induced blood nicotine levels that corresponded well with human smokers. In conclusion, we have demonstrated that nicotine produces reliable CPP [0.2 mg/kg dose (s.c.)] in adolescents and [0.6 mg/kg dose (s.c.)] in adults, and SA [0.03 mg/kg/infusion] in adolescent rats. Both tests indicate that adolescent rats are more sensitive to the rewarding and reinforcing effects of nicotine.
Keywords: Addiction; Adolescent; Adults; Conditioned place preference; Nicotine; Self-administration.