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Biology 202
2000 First Web Report
On Serendip

Tobacco and the Brain


Recent surveys show that 25 % of all American adults smoke despite the fact that tobacco is the No.1 cause of death (430,000 annual) and disease in this country (1). The life of a 30-year older that smokes 15 cigarettes a day is shortened by an average of more than five years (2). Why do people smoke despite the fact that it shortens their life? Why has this practice of smoking tobacco been around for 1000 years? There must be something that the human body or mind gains in spite of the threat of an early death. I realize this craving for nicotine on a personal level because I smoke. Smoker's self-reported motives for smoking include stress reduction and improved circulation (3). That sounds like my reasons. Plus smoking is like a friend that I visit and have a good time with, something that I enjoy being with.

Smoking cigarettes produces a rapid distribution of nicotine throughout the body, and reaching the brain within 10 seconds of inhalation (4). The nicotine causes a release of dopamine, neurotransmitters that carries information across synaptic clefts, in the dopamine circuit. This circuit, known as the brain's pleasure center, is an anatomically small cluster of cells. It has evolved over millions of years and mainly seems to reward activities that increase the likelihood of survival, such as sex and eating. This cluster of cells might be small but it reaches into regions of the brain involved with a variety of tasks (4). . These dopamine-releasing pathways course from the evolutionary older part of the midbrain to the hypothalamus and trigger activity of other cells, that extend from one part of the midbrain to an area in the forebrain known as the nucleus accumbens (2). It also branches out to the emotion-associated (limbic) region and into the cortex, the seat of conscious learning (5).

Somehow this information molecule dopamine causes pleasure to be experienced. Stimulating fibers originating in the nucleus accumbens is interpreted by the brain as the neurotransmitter equivalent of "Good--let's have it again" (2). High dopamine levels result in the desire for repeated increase of dopamine (4). Activation of this pleasure/ reward circuit also causes a cascade of biochemical changes in your brain cells, creating a memory of the event and the motivation to do it again, hence the setup for addiction (1). I guess it was a human misfortune that we discovered addictive drugs like nicotine that just fit into the dopamine receptor and are rewarded with pleasure (dopamine) even though they are not survival related, worse yet deadly.

Chronic exposure to nicotine results not only in physical addiction but also in mental addiction. Cigarette fixation is a combination of nicotine dependency due to the nucleus accumbens wanting more dopamine as it is stimulated, and deeply engrained behavior habits. For some people, the feel, smell, and sight of a cigarette and the usual rituals of obtaining, handling, lighting, and smoking the cigarette are all associated with the pleasurable effects of smoking (4). Also, places and times can have traditions of smoking built into them, like after sex, after meals, driving in a car or walking to class or work. These particular rituals, times, and places associated with the pleasurable effects of smoking can cause cravings and make withdrawal worse. Research is just beginning to document all of the neurological changes that accompany behavior that helps to develop and maintain nicotine addiction. Memory and habit have their own neural pathways that are reinforcers to the addiction problem. The broad reach of dopamine into the limbic system might explain why certain emotions, smells or events stir the want for a cigarette (5).

Nicotine, one of the most frequently used addictive drugs, is only one of the more than 4,000 chemicals found in the smoke from tobacco products. Carbon monoxide another detrimental chemical reaches the brain and binds to the hemoglobin and thereby reduces the usual binder oxygen, which is necessary for cellular metabolism. Research is also beginning to show that there are other psychoactive ingredients in tobacco. Using neuroimaging technology, scientists can see the dramatic effect of cigarette smoking on the brain, and are finding a marked increase in the levels of monoamineoxidase (MAO), an important enzyme that is responsible for breaking down dopamine. This decrease in two forms of MAO results in higher dopamine levels (that results in increased desired dopamine sustainment) and may be another reason that smokers continue to smoke (4).

More than 90 percent of the people who try to quit smoking relapse or return to smoking within 1 year, with the majority relapsing within a week. There are however, an estimated 2.5 to 5 percent that do in fact succeed on their own. It has been shown that pharmacological treatments, such as nicotine replacement products - gum, patch, spray and inhaler can double the odds of their success. Although the major focus of pharmacological treatments of nicotine addiction has been nicotine replacement, other treatments are being developed for relief of nicotine withdrawal symptoms. For example, the first non-nicotine prescription drug, bupropion, an antidepressant marketed as Zyban", has been approved (1996) for use as a pharmacological treatment for nicotine addiction (4). Nicotine replacement and Zyban only alleviates the pharmacological aspects of withdrawal and so a successful release from addiction needs to incorporate behavior modification.

In general, behavioral methods are employed to (a) discover high-risk relapse situations, (b) create an aversion to smoking, (c) develop self-monitoring of smoking behavior, and (d) establish competing coping responses.

Other key factors in successful treatment include avoiding smokers and smoking environments and receiving support from family and friends. The single most important factor, however, may be the learning and use of coping skills for both short- and long-term prevention of relapse. This combination of pharmacological and behavioral treatments further improves smoke cessation success rates (4). Considering the high death rate due to smoking and the difficulty of withdrawing from this deadly addiction, it is not a good sign that America's youth cigarette usage is escalating. Smoking prevalence among adolescents has risen dramatically since 1990, with more than 3,000 additional children and adolescents becoming regular users of tobacco each day (1).

WWW Sources

1)Quick Facts about Nicotine

2)Interesting Science

3) Gleitman, H., Fridlun, A., and Reisberg, D. Psychology. Fifth Edition. New York. W.W. Norton & Company. 1999

4)U.S. Government Research Reports ,

5)MSNBC News Website ,


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