Alteration of the behavioral effects of nicotine by chronic caffeine exposure

The prevalence of tobacco smoking and coffee drinking place nicotine and ca ffeine among the most used licit drugs in many societies and their consumpt ion is often characterised by concurrent use. The pharmacological basis for any putative interaction between these drugs remains unclear. Some epidemi ological reports support anecdotal evidence, which suggests that smokers co nsume caffeine to enhance the effects of nicotine. This paper reviews vario us aspects of the pharmacology of caffeine and nicotine, in humans and expe rimental animals, important for the understanding of the interactions betwe en these drugs. In particular, recent experiments are reviewed in which chr onic exposure to caffeine in the drinking water of rats facilitated acquisi tion of self-adminstration behavior, enhanced nicotine-induced increases in dopamine levels in the shelf of the nucleus accumbens and altered the dopa minergic component of a nicotine discrimination. These studies provide evid ence that the rewarding and subjective properties of nicotine can be change d by chronic caffeine exposure and indicate that caffeine exposure may be a n important environmental factor in shaping and maintaining tobacco smoking . (C) 2000 Elsevier Science Inc.