Nicotine: Mental effects
Last modified: Saturday, 20. June 2009 - 1:16 pm
Nicotine has several effects that are due to its action on the brain. Beginning smokers may experience dizziness or lightheadedness and sometimes vertigo. At higher doses, nausea and vomiting may occur. These effects can also be elicited in chronic smokers with forced, rapid smoking. Most smokers learn to avoid such unpleasant effects by adjusting their inhalation patterns.
Studies have indicated that there are two major pleasurable effects of nicotine ingestion that reinforce the habit: stimulation (vigilance, wakefulness) and relaxation. Tobacco users may feel that smoking helps them concentrate and feel clear headed, and studies do show that nicotine causes an improvement in attention, recall, information processing, reaction time, and problem solving. Smokers may also feel that smoking helps them relax in stressful situations or that it lifts their mood. They may feel calm and experience less anger, tension, depression, and stress. Both stimulation and relaxation may be experienced at the same time, resulting in a state of relaxed wakefulness.
Nicotine is known to bind to acetylcholine receptors (the receiving areas on cells) that are located throughout the central nervous system as well as the peripheral nervous system. Acetylcholine is a neurotransmitter: it transmits nerve impulses from one nerve fiber to another. The pleasurable effects of nicotine are a direct result of nicotine binding to these acetylcholine receptors, which then triggers the release of other neurotransmitters and hormones. Epinephrine, dopamine, nor-epinephrine, acetylcholine, serotonin, vasopressin, and beta-endorphin are all released. Epinephrine (adrenaline) release results in a “rush” or “kick” as it stimulates the body, increasing heart rate, blood pressure, breathing rate, and blood sugar. The wide variety of chemical messengers in the following list adapted from Neal L. Benowitz (1999) may explain the diverse, and sometimes seemingly opposite effects of nicotine (stimulation and relaxation) reported by smokers:
• Dopamine causes pleasure and appetite suppression.
• Norepinephrine causes mental stimulation and appetite suppression.
• Acetylcholine causes mental stimulation and cognitive (thinking) enhancement.
• Vasopressin causes memory improvement.
• Serotonin causes mood enhancement and appetite suppression.
• Beta-endorphin causes a reduction of anxiety and tension.
Furthermore, nicotine may have different effects at different doses. Rapidly delivered, increasing doses are likely to cause a stimulating reaction, whereas slower, chronic intake has a more calming, sedating effect.
Nicotine is thought to cause addiction primarily through its action to increase the levels of dopamine, which activates the brain circuitry that regulates feelings of pleasure and motivation, the so-called reward system. Increased dopamine in this system produces pleasurable sensations, as seen in other drugs of abuse such as cocaine and heroin.
Substances in smoke other than nicotine may also affect the brain. An unknown substance in smoke causes a decrease in the level of monoamine oxidase (MAO), an important enzyme responsible for breaking down dopamine. The decrease in MAO results in higher dopamine levels, which contributes to the desire to keep smoking.
The desire to smoke can also be brought on by reinforcing factors called “external stimuli” such as the sight, taste, and smell of tobacco smoke, as well as the social setting and rituals associated with smoking. These previously neutral stimuli in the environment, or certain events, can become associated with tobacco use and thus become triggers for a desire to smoke.
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