Researchers have shown that master cells from rodent embryos can be used to repair nerves in the spinal cord and brain, a step toward new treatment for nerve disorders, such as Parkinson's disease and multiple sclerosis.

In laboratory studies, researchers guided the evolution of embryonic stem cells from mice into mature nerve cells that were transplanted into rats where they produced a nerve-insulating material the rats lacked.

Ronald D.G. McKay, of the National Institutes of Health, and colleagues put cells called olgiodendrocytes and astrocytes grown from stem cells into rats with a genetic disease that blocks formation of the nerve-insulating material called myelin. The rats' disorder is the rodent equivalent of the human myelin disorder called Pelizaeus-Merzbacher disease.

The researchers found that the transplanted cells caused myelin to grow around the nerve fibers in the rats, the researchers report in today's issue of Science.

The loss of myelin is a key part of several neurological diseases, particular multiple sclerosis. In MS, the body attacks and destroys myelin, causing a crippling loss of nerve function.

Stem cells arise early after conception and are the ancestral cells for all of the body's tissue, such as muscle, bone, nerves, skin and blood.

Experts believe if researchers can learn how to direct stem cells to make specific types of cells then it may be possible to replace diseased tissue with new growth.