Previous research has determined that depressed people are more likely to smoke and more resistant to quitting. For this study, lead author Dr. Gregory A. Ordway and collaborator Dr. Violetta Klimek examined the locus coeruleus, a portion of the brain associated with depression. The researchers compared brain tissue samples from long-term smokers to samples from nonsmokers.

The researchers found that the brains of the heavy smokers had fewer alpha-2 adrenoceptors and significantly less of the enzyme tyrosine hydroxylase, which helps to manufacture the brain chemicals noradrenaline and dopamine. These neurochemical abnormalities are similar to the brains of animals treated with antidepressant drugs.

"This is the first time someone demonstrated that chronic smoking produced biological effects in the brain that are associated with antidepressive effects in the brain," Ordway said.

"Chronic smoking produces 'antidepressant-like' effects on the human brain," concluded Ordway, a professor of psychiatry at the University of Mississippi Medical Center. "This may contribute to the high incidence of smoking and difficulty to quit in those who are depressed."

Ordway plans to conduct additional animal studies to determine whether smoking caused this effect or those with this brain chemistry were more at risk to becoming smokers.

The report is published in the September issue of the Archives of General Psychiatry.

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