It is already known that nicotine stimulates the release of dopamine causing a high and often leading to addiction.
But now there is evidence suggesting that nicotine might not be the only factor that hooks people on tobacco.
Take a puff of tobacco, and a blast of 4,000 chemicals fills your lungs, blood, and brain. The smoke delivers a
strong hit - about 2 mg in each cigarette - of nicotine, a compound the U.S. Surgeon General in 1988 deemed an
addictive drug. But is nicotine alone what hooks people on tobacco? Apparently not. According to a new report,
smoking may exert yet another powerful addictive influence, one that enhances the effect of nicotine in what a
leading researcher calls a "diabolical synergism."
In the new research, published in the journal Nature, scientists ran brain scans on smokers had 40% less of a
brain enzyme known as monoamine oxidase B, or MAO B. The enzyme breaks down dopamine, a chemical
messenger in the brain associated with feelings of pleasure. Because of its exquisitely satisfying effects, says
Joanna Fowler, a chemist at Brookhaven National Laboratory and one of the study's authors, "dopamine is
crucially important in reinforcing and motivating behavior."
Thus smoking appears to create a self-perpetuating cycle: less MAO B leads to more dopamine, leads to more
pleasure, leads to more smoking, leads to less MAO B and so on.
Scientists have not yet identified what factor in smoke lowers levels of MAO B, but Fowler speculates that it may
be working synergistically with nicotine to boost dopamine levels. Earlier research showed that nicotine also
increases dopamine levels by gripping like Velcro to receptors clustered in the forebrain.
There may be an even more dangerous synergy at work, according to Alan Leshner, director of the National
Institute on Drug Abuse. "Every substance that is addicting leads to an increase in dopamine levels in the brain,"
he says. That may help to explain why people who abuse another. Fowler likens the effect to creating a
biochemical pathway or channel: "A drug may leave an imprint in the brain, so that the next drug becomes more
pleasurable than it would otherwise." In short, the brain gets into a rut that just grows deeper and deeper.
