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Study: Marijuana may affect brain wiring

NEW YORK -- Chemicals like those in marijuana help shape the way brain cells form connections, scientists said, suggesting why pregnant women who smoke pot may harm fetuses.

The substances, called endocannabinoids, occur naturally in animals, including humans.

Scientists, examining the developing nervous system in mice, found that the chemicals block connections of neurons, or brain cells, according to a paper in today's issue of the journal Science. There are implications for humans, the researchers said.

Previous studies have shown that mothers who smoke pot during pregnancy have children with slight impairment in so-called high-level integration of behavior -- the cognitive functioning that allows, for example, a person to grasp the physical and mental tasks needed to drive a car for the first time.

"The obvious implication is that prenatal exposure to marijuana can change patterns of connectivity in the developing brain," said Anatol Kreitzer, an assistant professor at the Gladstone Institute of Neurological Disease at the University of California, San Francisco, who wasn't involved in the new study.

Endocannabinoids were discovered in the early 1990s, said one of the study's authors, Ken Mackie, a professor of psychology at the University of Indiana in Bloomington.