An alkaloid which is the principal addictive agent in TOBACCO. The small amount of nicotine in a single cigarette is sufficient to stimulate mental and bodily activities. In larger quantities it acts as a depressant or narcotic – habitual smokers may find its effect sedating. Nicotine works by stimulating the production of a chemical called DOPAMINE, a neurotransmitter or chemical messenger between nerve cells. Nicotine mimics the action of a neurotransmitter called ACETYLCHOLINE. Nerve cells that produce dopamine have acetylcholine-receptor molecules on their surfaces; when these ‘nicotine-like’ receptors are occupied by acetylcholine molecules, a cell is prompted to produce dopamine. So nicotine itself can artificially stimulate dopamine production. Dopamine is part of the neuronal circuitry that plays a part in the body's perception of pleasure, which is why smoking is enjoyed by many people.