Scientists have been able to produce nerve cells in the lab by using stem cells drawn from bone marrow, a breakthrough that could help people with Alzheimer's disease, Parkinson's disease or spinal-cord injuries.

If the findings are borne out, they might one day enable doctors to take cells from a patient's bone marrow, turn them into nerve cells and then inject them into patients' brains and spinal cords, replacing injured cells.

The research, conducted at the University of Medicine and Dentistry of New Jersey and MCP Hahnemann University in Philadelphia, was funded in part by the Christopher Reeve Paralysis Foundation. An account of the research was published Monday in the Journal of Neuroscience Research, based in Los Angeles.

It could be years before the technique is tested in humans, however, since studies and tests in animals will be needed first. Still, other researchers were excited by the possibilities.

``Clearly it is important to generate neurons from other tissues,'' neuroscientist Ronald McKay told The Philadelphia Inquirer in Tuesday's editions.

``We have to demonstrate that these cells will perform ... specific functions'' in the brain and spinal cord, and not behave like stem cells only in the lab, said McKay, of the National Institutes of Health.

``It's really beautiful,'' Dr. William Greenough, a neuroscientist at the University of Illinois in Urbana-Champaign, told The New York Times. ``I see this as a truly significant step along the way toward developing new technologies for the repair of the damaged brain.''

Stem cells are stored in various organs and grow naturally into the specific types of cells needed by those organs. Stem cells from fetal tissue can grow into any type of cell; the latest study suggests that the same might be true for adult stem cells.

Dr. Ira Black of the University of Medicine and Dentistry of New Jersey reported the stem cells, treated with growth factors and antioxidants in tissue culture experiments, quickly divided into two cells - another stem cell and a nerve cell.

By tinkering with the chemical signals he used to stimulate the conversion, Black and his colleagues were able to turn 80 percent of the bone marrow cells taken from rats and humans into nerve cells. He said he transplanted rat nerve cells to the brains and spinal cords of rats and found that they formed connections with other neurons and survived.

Stem cells could be drawn from the patient being treated, eliminating the problem of adding tissue the immune system might attack, said Darwin Prockop, of Tulane University's medical school, who co-authored the research.

Susan Howley, director of research at the Christopher Reeve Paralysis Foundation, cautioned that many questions still surround the new technique.

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