By Merritt McKinney

NEW YORK (Reuters Health) - New research in mice raises hopes that stem cells may one day be used to treat brain injuries. Mice that had neural stem cells injected into their brains shortly after a brain injury experienced significant improvement in motor skills, researchers report.

Since there is currently no treatment for traumatic brain injury, the results of the study provide "a great deal of renewed hope," the study's senior author, Dr. Tracy K. McIntosh of the Head Injury Center at the University of Pennsylvania in Philadelphia, told Reuters Health in an interview.

Stem cells are immature "master" cells capable of maturing into different types of body tissue. These cells are most abundant in embryos, but there are also stem cells in some adult tissues, such as bone marrow.

In the interview, McIntosh explained that another set of researchers had developed a line of neural stem cells from mouse fetal tissue. When injected into mice that had a cerebral palsy-like disorder, the cells had traveled toward the damaged area of the brain, so McIntosh and his colleagues decided to see whether neural stem cells might be useful for treating brain injury. The hope for the cells, he said, was that they would be able to differentiate to replace nerve cells that had died.

That is exactly what happened when the researchers injected neural stem cells into the brains of mice with brain injury.

"These cells are very, very clever," McIntosh said. They "appeared to travel directly toward the site of injury." Not only did the cells differentiate to form neurons, but they also formed the glial cells that support neurons.

Besides surviving and differentiating, the stem cells seemed to help the mice recover somewhat, the researchers report in the October issue of the journal Neurosurgery. Though the cognitive, or mental, abilities of the mice did not improve after treatment, their motor skills did get better.

"When we see behavioral improvement, we say hooray," McIntosh said.

The next step, according to the Pennsylvania researcher, is to follow mice longer than the 3-month study to monitor the long-term effects of treatment. Noting that mice in the study were treated a few days after brain injury, McIntosh said he would like to see how long the "window of opportunity" for treatment lasts after injury, to determine if the cells could help people who suffered traumatic brain injuries months or years ago.

SOURCE: Neurosurgery 2002;51.