The effects of nicotine on neural pathways implicated in depression: A factor in nicotine addiction?

The prevalence of tobacco smoking varies considerably between different gro ups within the community, tobacco smoking being particularly prevalent in p atients with depressive disorder. This review will focus on results, derive d from animal studies, which suggest that, in addition to its primary reinf orcing properties, nicotine also exerts effects in stressful environments, which may account for its enhanced addictive potential in depressed patient s. It focuses on the evidence that depression sensitises patients to the ad verse effects of stressful stimuli, and that this can be relieved by drugs that stimulate dopamine release in the forebrain. This mechanism, it is pro posed, contributes to the increased craving to smoke in abstinent smokers e xposed to such stimuli, because they become conditioned to use this propert y of nicotine to produce rapid alleviation of the adverse effects of the st ress. The review also explores the possibility that chronic exposure to nic otine elicits changes in 5-HT formation and release in the hippocampus whic h are depressogenic. It is postulated that smokers are protected from the c onsequences of these changes, while they continue to smoke, by the antidepr essant properties of nicotine. However, they contribute to the symptoms of depression experienced by many smokers when they first quit the habit. (C) 2000 Elsevier Science Inc.