What is the pharmacological mechanism of nicotine?

Answer: Nicotine activates and rapidly desensitizes the ionotropic nicotinic acetylcholine receptors.

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Nicotine is a plant alkaloid compound that acts as a central nervous system stimulant. It is found at a high concentration in tobacco plants, and at a low concentration in certain edible plants, such as tomatoes and eggplants.

When ingested, nicotine enters the bloodstream rapidly and crosses the blood-brain barrier. Once here, the nicotine can activate the nicotinic acetylcholine receptors which result in the increased release of dopamine from the ventral tegmental area into the nucleus accumbens.

Nicotinic acetylcholine receptors (nAChRs) are excitatory cation channels. When a molecule of nicotine binds to one of these channels, the receptor changes conformation and allows cations to move into or out of the cell. Sodium ions will generally move into the cell, down its electrochemical concentration gradient. This causes the cell to depolarize, or to increase excitability. Therefore, nicotinic receptors are considered to be excitatory.

One difficulty in studying nAChRs in the laboratory setting is the rapid desensitization of the receptors. The receptors desensitize within seconds, and it takes an even longer amount of time before the receptors are able to be activated again.

Nicotine can enter the bloodstream via one of several methods of administration. The most common preparation is smoking cigarettes: burning the preserved, dried leaves of the tobacco plant followed by inhaling the smoke into the lungs. The lungs are very efficient at exchanging air from the atmosphere with the blood stream, so an effect may be felt within seconds. Other methods of administration include transbuccal such as for snuff or snus, oral for nicotine gum, or transdermal for a nicotine patch.