Here is a new news report, followed by the underlying scientific article. Researchers from the Scripps Research Institute in La Jolla, California, found that rats suddenly deprived of nicotine had to be given much more of a pleasurable reward stimulus to get the same buzz they had before. Addiction is a reflection of a physical demand by those receptors for more of the chemical. In the experiment, nicotine withdrawal produced a decrease in brain reward function - meaning that for the same stimulation, the nerve centres experienced a smaller buzz. The effects lasted four days, during which the rats showed the classic signs of withdrawal such as anxiety, irritability and craving.
Tobacco smoking is a worldwide public health problem.
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. The authors 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. 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.