Dramatic decreases in brain reward function during nicotine withdrawal.

Tobacco smoking is a worldwide public health problem. In the United States alone, over 400,000 deaths and $50 billion in medical costs annually are directly attributed to smoking. Accumulated evidence indicates that nicotine is the component of tobacco smoke that leads to addiction, but the means by which nicotine produces addiction remain unclear. Nicotine is less effective as a positive reinforcer than other drugs of abuse in non-dependent animals. Nevertheless, nicotine-withdrawal symptoms, including depressed mood, anxiety, irritability and craving in dependent subjects may contribute to the addictive liability of nicotine. We show here that spontaneous nicotine withdrawal in rats resulted in a significant decrease in brain reward function, as measured by elevations in brain reward thresholds, which persisted for four days. Further, systemic injections of a competitive nicotinic-receptor antagonist led to a dose-dependent increase in brain reward thresholds in chronic nicotine-treated rats. The decreased function in brain reward systems during nicotine withdrawal is comparable in magnitude and duration to that of other major drugs of abuse, and may constitute an important motivational factor that contributes to craving, relapse and continued tobacco consumption in humans.