Smoking linked to breakdown of brain's 'reward system'


Scientists have found that smoking tends to reduce levels of a key enzyme in the brain that is important to the "reward system" linked by scientists to addiction.

The enzyme, called MAO-B or monoamine oxidase-B, breaks down dopamine, a brain chemical that acts as a messenger between nerve cells. Dopamine is one of several chemicals that have been linked by scientists to emotion and arousal, the brain's reward system.

Dopamine is also linked to controlling movement, scientists say. When dopamine levels drop in Parkinson's disease, for instance, a patient's symptoms of muscle tremor and rigidity worsen. This link, researchers at Brookhaven National Laboratory in New York said yesterday, may be important because it could lead others to study the effectiveness of MAO-B inhibitors (the same ones used to treat Parkinson's) in treating addictions like smoking.

The new findings are to be reported today in the journal Nature by Joanna Fowler, director of the positron emission tomography imaging program at Brookhaven, and her colleagues.

"If we want to develop effective treatments for addictions, we need to better understand the changes that are occurring in the brain," Ms. Fowler said.

The researchers used positron emission tomography, known as PET, to scan the brains of eight smokers, four former smokers and eight nonsmokers. As it turned out, the patients with lower MAO-B levels were the smokers.

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