Study in mice sheds light on Ambien side effects

* Sleep drug can shut down important brain circuit

* Some people may be predisposed to rare side effects

By Julie Steenhuysen

CHICAGO, June 29 (Reuters) - A new study in mice may help explain some of the rare but strange side effects in people taking the sleep drug Ambien, including sleep walking, midnight binges and even driving while not fully awake.

Ambien, made by Sanofi-Aventis (SASY.PA), can shut down powerful brain circuits responsible for inhibiting brain activity under certain circumstances, leaving other brain circuits unchecked, researchers at Georgetown University Medical Center in Washington said.

"You are kind of releasing the brakes," said Molly Huntsman of Georgetown, who worked on the study that appears in the Proceedings of the National Academy of Sciences.

This may stimulate brain circuits that would normally be silenced. "In a way, Ambien is awakening other circuits because the brakes are not in place," Huntsman said.

To study the effects of the drug, known generically as zolpidem, Huntsman and colleagues conducted a series of experiments in mice.

The team wanted to see how mice on the drug would respond when the researchers trimmed their whiskers, which rodents use as their primary sensory system -- much like humans rely on vision to take in information about the world.