Prolonged prenatal exposure to nicotine decreases the number of newborn cells in the hippocampus, a brain area important in learning and memory, according to preliminary research presented at Neuroscience 2010, the annual meeting of the Society for Neuroscience, held in San Diego. The study offers a neurobiological explanation for why the children of women who smoke during pregnancy are at an increased risk of developing learning disabilities.

"Previous research has shown that nicotine, cocaine, and other addictive drugs decrease the number of newborn cells in adults. Our research suggests that these effects may be even more dramatic in newborn animals," said Robin Lester, PhD, of the University of Alabama at Birmingham, who directed the study. "These findings provide further warnings to expectant mothers that they should seek help in refraining from smoking during pregnancy," Lester said.
To mimic the conditions of moderate to heavy smoking in a pregnant mother, Lester and his colleagues treated pregnant rats with nicotine through an implanted mini-pump, which acts similarly to a nicotine patch. The researchers then counted the number of newborn cells in the offsprings' dentate gyrus, a section of the hippocampus known to contain neuronal stem cells. They also monitored synaptic plasticity -- the reorganization of neural pathways considered essential to learning.

"We found a reduced number of dividing stem cells and altered plasticity in the newborn animals exposed to nicotine," Lester said. These findings may lead to new approaches to treating learning disabilities and other behavior deficits associated with prenatal nicotine exposure.

Research was supported by a United States Public Service Grant and the Evelyn F. McKnight Brain Institute.

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