The mesolimbic dopamine system mediates the reinforcing effects of nicotine and other drugs of abuse. Thus the genes affecting the functionality of the mesolimbic dopamine system can be contributing factors to predisposition to nicotine abuse. These genes include dopamine receptors, signaling molecules of cAMP pathway such as adenylate cyclase, and others. Evidence put forth by a number of investigators suggests that the difference in the different biochemical profile of cAMP pathway in the mesolimbic dopamine system may result in differential predilection to abused drugs. The precise relation of up-regulated cAMP signaling pathway~y and nicotine predilection, however, remains vague. The present study seeks to bridge this gap by investigating the consequence of up-regulated cAMP pathway in transgenic mice, caused by a subtle substitution mutation in the dopamine D2 receptor, on nicotine responsiveness. Particularly, these studies seek to produce a strain of transgenic mice that express the mutant D2 receptor and to investigate whether the mutant D2 receptor will result in up-regulation of cAMP pathway in transgenic mice and therefore increased vulnerability to nicotine abusing. The availability of transgenic mice expressing the mutant D2 receptor will help establish the causal effect relationship of an up- regulated cAMP pathway and predilection to nicotine abuse. The proposed studies will also lead to an understanding of whether a subtle change in structure of dopamine D2 receptor, one of mediators for the basic neurobiological function of mesolimbic dopamine system, may affect predisposition to nicotine abuse.