The neurobiology of tobacco dependence: a commentary.

This commentary summarises the evidence that nicotine has the pharmacological properties of a psychostimulant drug of dependence. Behaviourally it serves as a reinforcer in self-administration experiments. Within the brain, acute nicotine stimulates the release of dopamine (DA) in the shell of the nucleus accumbens whereas repeated nicotine results in selective sensitization of its effects on DA overflow in the accumbal core. These effects are thought to play a central role in the acquisition of responding for nicotine and the development of associations between delivery of the drug and cues that predict its delivery. These responses, therefore, are thought to be pivotal to its ability to cause dependence. The commentary also emphasises the evidence that cigarette smoke provides a vehicle for nicotine that maximises its addictive potential since it delivers nicotine directly into the lungs and, within 10-15 s, to the brain. For habitual cigarette smokers, this process is repeated frequently and regularly and in the context of many other sensory cues within the smoke that potentially provide additional conditioned reinforcers. This, it is argued, explains the strong addiction that many smokers develop to tobacco smoke. Smoking cessation is also associated with the expression of an abstinence syndrome that can, largely, be attributed to nicotine withdrawal and is also likely to contribute to the maintenance of the habit. The commentary closes with a brief review of the pharmacological mechanisms that may contribute to the efficacy of nicotine replacement therapy and Zyban (bupropion) as aids to smoking cessation.