An addictive chemical stimulant that occurs naturally in tobacco. For nearly a century doctors have noticed that people with Parkinson’s disease who use tobacco (primarily by cigarette smoking) report that their symptoms seem to improve shortly after tobacco use. Researchers also noticed that Parkinson’s disease is less likely to develop in people who smoke. This finding has given rise to the theory that cigarette smoking can protect against Parkinson’s disease.
Nicotine, the key active ingredient that enters the body with tobacco use, appears to have several actions in the brain. One is that it blocks certain cholinergic receptors, called nicotinic acetyl-choline receptors, preventing them from binding with ACETYLCHOLINE, a NEUROTRANSMITTER important to motor function. Acetylcholine is one of the monoamine neurotransmitters that, in health, exist in balance in the brain. dopamine is also a monoamine neurotransmitter. When dopamine levels drop in Parkinson’s disease, the ratio of dopamine to other monoamine neurotransmitters such as acetylcholine changes. Acetylcholine becomes more active, overstimulating cholinergic receptors. Nicotine’s mild anticholinergic effect helps to slow cholinergic transmissions to the muscles, easing symptoms such as tremors (although in some people with Parkinson’s disease, nicotine has the opposite effect and causes tremors to worsen).
Nicotine also blocks monoamine oxidase B (MAO-B), an enzyme that aids the metabolism of dopamine. This effect extends the availability of dopamine in the basal ganglia and other areas of the brain involved with motor function. For the person with Parkinson’s, this effect helps to mitigate neuromuscular symptoms such as bradyki-nesia (slowed movements). This MAO-B blocking effect also extends the availability of dopamine in the cerebrum, where it affects brain centers related to mood and pleasure. Researchers believe this effect of nicotine accounts for its addictive qualities, as dopamine stimulates those centers. Nicotine also activates receptors in areas of cognitive function, improving focus, concentration, and memory.
Although research shows that nicotine administration, such as through the common “stop smoking” patches and gums, can relieve some of the symptoms of Parkinson’s disease, there is not yet adequate evidence to support its use as a therapeutic approach. The health risks and consequences of cigarette smoking and other forms of tobacco use are too high to offset any potential benefit from nicotine. The cardiac and vascular complications of smoking (for example heart attack, stroke, and hypertension) appear to be due to the effects of nicotine itself, hence nicotine patches are hardly any safer for long-term use than smoking.
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