Nicotine. Tobacco (Nicotiana tabacum, Nicotiana rustica, and related
species) is a plant native to the Americas (Fig. 9.1). The genus Nico-
tiana is named after Jean Nicot (1530-1600), a diplomat who intro-
duced tobacco to the French royal court—they loved it.
The molecule nicotine was isolated from and named after the
tobacco plant by German chemists around 1828. While tobacco, being
a plant, contains hundreds of different chemicals, a number of which
may possess physiological activity, nicotine is considered the primary
psychoactive constituent. It is generally taken into the body by smok-
ing the dried leaves of the plant. It may also be absorbed through the
nasal mucosa or oral cavity, if a snuff preparation or chewing tobacco
is used.
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NicotineThe major known neurochemical effect of nicotine is to bind as an
agonist at nicotinic acetylcholine receptors (nAChRs). This produces
effects in the brain that presumably are related to the behavioral
effects of relaxation, alertness, and focused attention experienced by
users of tobacco. Although there are nAChRs at the neuromuscular
junction, they are slightly different in amino acid sequence from the
CNS nAChRs and, as a result, are less sensitive to nicotine binding.
Nicotine is a serious poison. The tobacco plant presumably makes
nicotine because its poison qualities confer some protection against
insects and other animals that might munch on its leaves. Insects,