Many compounds are present in tobacco, but nicotine is the addictive component that confers the risk of developing dependence. Nicotine binds to nicotinic cholinergic receptors, which are widely distributed in the central and peripheral nervous system. The nicotinic cholinergic receptor is composed of 5 subunit proteins arranged around a central pore, and the receptor is involved in physiologic responses related to smoking. There are 16 different nicotinic receptor subunit genes, α 1–7,9,10, β1–4, δ, ε, γ, and different combinations of these subunit proteins result in receptors that vary in biologic function, distribution throughout the body, and other pharmacologic properties. Binding of nicotine to nicotinic cholinergic receptors forms the basis of the molecular pharmacology that leads to dependence.
