Can nicotine be used medicinally in Parkinson's disease?

The risk of Parkinson's disease is reduced by cigarette smoking, which raises some unanswered questions. Nicotine, a major component of tobacco smoke, could exert either nonreceptor-mediated biological effects or, more importantly, act on the different subtypes of nicotinic brain receptors, in particular those associated with the nigrostriatal dopaminergic pathway. There is now robust experimental evidence for a neuroprotective effect of nicotine upon dopaminergic neurons. By contrast, in animal models of Parkinson's disease, nicotine alone has slight or no motor effects. However, nicotine may modulate dopamine transmission and has clear motor effects when associated with L-DOPA, reducing L-DOPA-induced dyskinesias. Clinical trials have yielded inconclusive results thus far and are hampered by different designs and small cohorts. Ongoing studies address either symptomatic motor or nonmotor symptoms, or neuroprotection. There is still no agreement on the daily dosage of nicotine or the method of administration. Together, these data suggest that nicotine or nicotinic receptor drugs have therapeutic potential for Parkinson's disease, although the specific treatment regimens remain to be determined.