NEW YORK (Reuters Health) - Stem cells from embryos--cells that can give rise to various specialized types of cells--could help repair damage to the fatty sheaths that surround nerve cells, according to results of a new animal study.

The technique holds promise for the treatment of spinal cord injuries and diseases such as multiple sclerosis and Alzheimer's disease, researchers report.

Earlier research had shown that stem cells taken from rat embryos can be coaxed into forming nerve cells called oligodendrocytes. These cells are essential for the formation of myelin, the fatty material which lines the body's network of axons. Without this lining to protect the axons, the brain cannot communicate properly with the rest of the body. Several diseases, including multiple sclerosis, as well as spinal cord injuries can damage myelin.

In the study, Dr. John W. McDonald, of Washington University School of Medicine in St. Louis, Missouri, and colleagues took embryonic stem cells and transformed them into oligodendrocytes. Laboratory testing showed that these cells were able to form myelin within a little over a week, the researchers report in the Proceedings of the National Academy of Sciences. In earlier experiments, mature nerve cells taken from rat brains or spinal cords had taken 4 to 6 weeks to form the myelin.

Success in the lab does not always necessarily translate into success in living animals, but the nerve cells formed from stem cells were just as effective at producing myelin in live rats, according to the report. Within a week after the cells were injected into rats whose myelin had been destroyed, the cells had begun to restore myelin. In addition, experiments in mice lacking a gene necessary to produce myelin also showed that the transplanted cells can restore myelin.

The researchers conclude that their study holds out hope that transplants of myelin-producing cells may offer a way of repairing damaged nerves in the spinal cord, and restoring nerve and muscle function lost to such injuries.

"This is paving the way to demonstrate the usefulness and safety of this type of cells so they can be used in humans," McDonald told Reuters Health in an interview. Although federal regulations prohibit the use of federal funds for research involving human embryonic cells, McDonald said he expects that this ban will be lifted eventually. Hopefully, stem cells will be used to repair human myelin within the next 5 years, he said.