NEW YORK (Reuters Health) - Scientists have discovered that certain immature cells in the brain can be coaxed to mature into functioning nerve cells, replacing damaged ones, new study findings show.

By injecting growth factors into rat brains, Japanese researchers were able to stimulate "progenitor" cells to grow into mature neurons, according to the report published in the August 23rd issue of Cell.

"This is a way to allow the brain to use its own tools to make repairs," Ramesh Raghupathi, a research assistant professor in the department of neurosurgery at the University of Pennsylvania, told Reuters Health in an interview. "What is interesting about this study is that it is one of the first to show that endogenous progenitor cells can actually become fully mature neurons."

Other studies have used transplants of stem cells from the blood or fetal stem cells to try to repair brain damage, Raghupathi added.

For years, researchers have assumed that brain and spinal cells can't repair themselves. But the Japanese researchers suspected that progenitor cells, a kind of cell that can develop into at least three different types of nerve cell, could be coaxed to mature into neurons in a brain-injured animal.

"It has long been believed that the adult mammalian central nervous system (CNS) is incapable of significant self-repair or regeneration," the study's lead author Hirofumi Nakatomi, a researcher in the departments of neurobiology and neurosurgery at the University of Tokyo Graduate School of Medicine, wrote. "Many lines of recent evidence have revealed, however, that progenitors with the ability to produce new neurons...remain in the adult CNS."

Nakatomi and his colleagues studied rats with damage to the hippocampus, the part of the brain responsible for laying down new memories. The scientists damaged the hippocampus by briefly interrupting blood and oxygen flow to this part of the brain.

Other studies have shown that after a brain injury in rats, progenitor cells migrate to the damaged area, Nakatomi noted. So, shortly after the rats' brains were injured, Nakatomi and his colleagues infused growth factors into the some of the rats' brains.

When the researchers examined the rats days later, they found new hippocampal nerve cells in the rats treated with growth factor.

To test whether these cells had grown proper connections with the rest of the hippocampus, Nakatomi and his colleagues tested uninjured rats, injured rats with no treatment, and treated injured rats in a water maze. Normal rats quickly learn--and then remember--that there is a hidden platform they can climb onto to get out of the water.

Rats that had hippocampal damage had trouble finding the platform and remembering where it was shortly after the brain injury. But later, after the regrowth of neurons in rats that received growth factor, treated rats were able to remember where the platform was placed.

These results don't mean that we have an immediate cure for brain and spinal injuries, Raghupathi said. But, he added, "This is a good first step. Now we need to see if it works in higher animals, such a primates."