Neuroprotective and neurotoxic effects of nicotine.

The interest in the action of nicotine in the central nervous system (CNS) has significantly increased during the past 15 years. This is due in part to the growing importance of nicotine addiction and its consequences in terms of life quality and costs for public health systems in industrialized countries and, on the other hand, to the significantly higher prevalence of tobacco consumption in patients with psychiatric disorders. The actual data indicate opposite effects of nicotine in the CNS. Nicotine seems to have, at the same time, positive, neuroprotective as well as negative, neurotoxic effects. This suggests that nicotine's action is complex, probably involving different neuronal circuits influencing each other through complicated interactions. In the present review we summarize the most important results of experiments about nicotinic neuroprotection and neurotoxicity in humans and animals. Initially, we illustrate well known modifications of cholinergic transmission during physiological (normal aging) and pathological neurodegeneration. In the second part of the paper we describe neuroprotective and neurotoxic effects of nicotine also mentioning the underlying molecular mechanisms.