Health: Study: Preggers? Put Down That Joint

PREGNANT POT SMOKERS MAY HARM FETAL BRAIN

Chemicals like those in marijuana help shape the way brain cells form
connections, scientists say, suggesting one reason why slight
cognitive impairment has been observed in babies born to women who
smoked pot during pregnancy.

The substances, called endocannabinoids, occur naturally in animals,
including humans. They were discovered in the early 1990s.

Scientists examining the developing nervous system in mice found that
these chemicals block connections of neurons, or brain cells, a study
published today in the journal Science says. There are implications
for humans, the researchers say.

Previous studies showed that mothers who smoked pot during pregnancy
had children with slight impairment in high-level integration of
behaviour - the cognitive functioning that allows a person to grasp
the physical and mental tasks needed to drive a car for the first
time, for instance.

Ken Mackie, a professor of psychology at the University of Indiana in
Bloomington who is one of the authors of the study published in
Science, said the effect on mouse neurons may explain the earlier
findings about cognition in babies.

"This is gross speculation, but if the synaptic connections are a
little off, then the higher-level behaviour might be a little off,"
Dr. Mackie said.

In one of the experiments outlined in the paper, the researchers
blocked the production of endocannabinoids in gestating mice.

When dissecting the mice's brains later, they found that the mice had
more 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, San Francisco,
who was not affiliated with the new study.

Endocannabinoids act to halt overstimulated nerve cells, Dr. Kreitzer
said.

Nerve cells that are overexcited release the chemicals as an internal
braking system.

"Basically, it's a way for the cell to dampen its own input."