NICOTINE
The behavioral effects of
nicotine have been defined as both stimulant and depressant, effects that are
influ-enced by the present mental status and expectations of the smoker.
Smokers may feel alert and relaxed. Nicotine produces myriad effects on the
central nervous system (CNS), almost all of which appear to be medi-ated
through nicotinic receptors. Additionally, nicotine influences multiple
neuronal systems. One of its most prominent effects is stimulated release of
dopamine, particularly in the nucleus accumbens, which is a major component of
the reward system. Nicotine also stimu-lates the release of endogenous opioids
and glucocorti-coids.
Tolerance to nicotine’s
effects develops rapidly and most likely involves multiple processes, although
the pattern and extent of tolerance development is not identical for all of
nicotine’s effects. It has been pro-posed that rapid tolerance or desensitization
occurs to the behavioral or reinforcing effects of nicotine. These effects are
of such a short duration that a smoker con-tinually cycles between a sensitized
and desensitized state. This notion is consistent with the fact that drugs with
high abuse liability have a rapid onset and short duration of action.
Regardless of the mechanism
of tolerance, nicotine is a highly addicting drug. Even though most individuals
are unaware of nicotine’s reinforcing properties when smoking, many individuals
feel intense, long-lasting craving when attempting to stop. Although most
smok-ers wish to quit, only about one-third attempt to do so each year.
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