Smoking marijuana during pregnancy raises the risk of fetal brain damage, new research suggests.

Bloomberg News reported May 25 that researcher Ken Mackie of the University of Indiana led a team that studied the effects of marijuana on neurons in mouse brains. They found that the drug helps determine how brain cells make connections -- a fact that could have some bearing on fetal brain development.

Previous studies have shown that babies born to marijuana-smoking mothers experience some cognitive impairment. "This is gross speculation, but if the synaptic connections are a little off, then the higher-level behavior might be a little off," said Mackie.

Endocannabinoids are part of the brain system acted upon by marijuana; when researchers blocked the chemicals in gestating mice, it seemed to increase the formation of neural connections. "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 at San Francisco.

The research was published in the May 25, 2007 issue of the journal Science.