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January 7, 2011

Smoking during pregnancy affects genes involved in brain development, study finds

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New research from the University of Virginia Health System shows that nicotine use during pregnancy affects genes important in the formation and mechanism of myelin, a fatty brain substance that insulates brain cell connections in regions of the brain associated with neurobehavioral development.

The findings, presented Sunday at the annual meeting of the Society for Neuroscience in San Diego, may explain why the children of mothers who smoke during pregnancy are more likely to develop such psychiatric disorders as attention deficit hyperactivity disorder, depression, autism and drug abuse.

Researchers found that when rodents were given nicotine during pregnancy, their offspring showed changes in myelin genes in specific regions of their brain’s limbic system – structures involved with emotion. The effect was strongest in the prefrontal cortex, a region of the brain important for decision-making.

“Our research shows that gestational treatment with nicotine significantly modifies myelin gene expression in specific brain regions that are involved in behavioral processes,” says Ming Li, PhD, professor in the UVA Department of Psychiatry and Neurobehavioral Sciences , who led the study.  “Myelin deficits have been observed in adults with various psychiatric disorders.  Our findings suggest that abnormal myelination may contribute to the psychiatric disorders associated with maternal smoking.”

Previous research has shown that maternal smoking during pregnancy has various long-lasting neurobehavioral effects on offspring, explains Li.  Many psychiatric disorders associated with smoking during pregnancy begin or change symptomology during adolescence, a period of continuous development of the central nervous system. Most of these disorders are thought to be mediated by dysfunction of the limbic system, a collection of brain nuclei that mature during adolescence.

Li’s research team also identified sex differences in nicotine’s effects. Myelin-related genes increased in the prefrontal cortex of the male offspring but decreased in the females. The opposite was observed in the hypothalamic paraventricular nucleus, a brain region involved in the regulation of stress and appetite, among other functions.

“These findings suggest that maternal smoking may affect daughters and sons differently,” says Li.

In addition, the substantial and long-lasting changes by the low dose of nicotine administered to rodents in the study imply that nicotine replacement therapy during pregnancy may carry many of the same risks to children as does smoking during pregnancy.

“While further studies are necessary to determine a direct correlation of our initial findings,” Li says, “our research lends weight to the necessity of educating women to avoid smoking during pregnancy.”

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