Adolescent nicotine expo-sure produces less affective measures of withdrawal relative to adult nicotine exposure in male rats

Vulnerability to nicotine addiction is significantly increased in individuals who begin smoking during adolescence; however, the underlying mechanisms of this phenomenon remain unclear. This study examined the motivational effects of nicotine withdrawal in adolescent (PND 27-42) and adult (PND 60-75) rats using the conditioned place aversion paradigm. Male Wistar rats were tested for their initial preference for either of two distinct compartments of our conditioning apparatus. Rats were then implanted with subcutaneous (sc) pumps that produce equivalent blood plasma levels of nicotine for 14 days. Conditioning was conducted over the last 8 days of nicotine exposure. Rats received the nicotinic antagonist mecamylamine (1.5 or 3.0 mg/kg, sc) to precipitate withdrawal in their initially preferred compartment, and on alternate days they received saline in their non-preferred compartment. Following conditioning, rats were re-tested for their preference for each compartment. A subsequent study was conducted to examine potential developmental differences in learning place aversion produced by another aversive stimulus, lithium chloride (LiCl). Rats received LiCl (0, 10, 30, or 100 mg/kg, sc) in their initially preferred side using similar conditioning procedures. Adults displayed robust place aversion produced by nicotine withdrawal. This effect was lower in adolescent rats even in a group of young rats that received 7 additional days of nicotine exposure prior to conditioning. This developmental difference was specific to nicotine withdrawal since there were no differences between adolescents and adults in learning place aversion with LiCl. Our findings demonstrating reduced effects of nicotine withdrawal constitute a powerful basis for the increased vulnerability to nicotine dependence during adolescence. (c) 2006 Elsevier Inc. All rights reserved.