Nicotine

Nicotine is a potent parasympathomimetic stimulant and an alkaloid found in the nightshade family of plants. Nicotine acts as an agonist at most nicotinic acetylcholine receptors (nAChRs), except at two nicotinic receptor subunits (nAChRα9 and nAChRα10) where it acts as a receptor antagonist.

Nicotine is found in the leaves of Nicotiana rustica, in concentrations of 2–14%; in the tobacco plant, Nicotiana tabacum; in Duboisia hopwoodii; and in Asclepias syriaca.

Nicotine desensitization is associated with suppression of tonic release of dopamine (DA) in both the striatum and nucleus accumbens (NAc) shell that may occur via the α4β2 subtype of nicotinic acetylcholine receptor (nAChR), whereas phasic frequency-dependent augmentation and high-frequency stimulation (HFS)-related gating release is more pronounced in the striatum than in the NAc shell. Differences between phasic and tonic release associated with nicotine desensitization may underlie processing of reward signals in the NAc shell, and this may have major implications for addictive behavior ¹⁾.