Individual differences in locomotion, anxiety-like behavior, and reward after nicotine and baclofen administration

Abstract

Tobacco use is a significant health problem that began in adolescence for many adult smokers. Anxiety may also be a risk factor in who develops nicotine dependence disorders. This study uses adolescent male Sprague-Dawley rats (n = 160) and splits them into a high anxiety (HA) and low anxiety (LA) group based on the results of pretest day of a conditioned place preference (CPP) protocol with a biased chamber. These rats are further divided into drug groups that receive either saline or 0.6 mg/kg baclofen (i.p.) 30 minutes before testing and then either saline or 0.5 mg/kg nicotine (s.c.) immediately before testing.

Open field testing showed a significant difference between HA and LA rats in locomotor activity, as well as significant differences between drug groups when compared to saline. Notably, baclofen administration significantly decreased locomotor behavior from saline levels in HA animals, but did not do so in LA animals. In both HA and LA groups, baclofen and nicotine co-administration significantly decreased locomotor behavior from locomotor activity levels in animals administered nicotine alone. Additionally, the open field was used to examine potential differences in anxiety-like behavior. Baclofen administration failed to produce differences in anxiety-like behavior between HA and LA groups, but nicotine administration and baclofen + nicotine co-administration had slightly more of an effect on anxiety-like behavior in LA than HA animals. Single-trial nicotine CPP testing found that HA rats formed significant CPP to nicotine and baclofen + nicotine, but LA rats did not. This study shows that innate anxiety-like behavior plays a significant factor in formation of locomotor responses to baclofen as well as later anxiety-like responses to nicotine and baclofen administration in adolescent rats. This study also serves to highlight the role that innate anxiety-like behavior plays in nicotine reward in adolescents.