An experimental stem cell therapy reversed symptoms in rats suffering from a nerve disorder similar to Parkinson's disease, a U.S. government scientist reported yesterday.

Along with an earlier Johns Hopkins study in mice suggesting the potential of stem cells to treat Lou Gehrig's disease, the study buttressed hopes that stem cells can be harnessed to treat a variety of human illnesses.

"We are absolutely confident that we have the right kind of cell ... and we can show that these cells have very clear behavioral effects on these animals," said Dr. Ronald McKay, the government researcher who led the Parkinson's study.

Some of the rats, which had dragged one side of their bodies, began to walk normally after receiving transplants of nerve cells derived from embryonic stem cells.

The transplanted cells connected with surrounding brain cells and released dopamine, a brain chemical that regulates movement. McKay, a researcher with the National Institute of Neurological Disorders and Stroke, cautioned that it could be several years before clinical trials in humans could begin.

In another study, Dr. Catherine Verfaillie of the University of Minnesota said stem cells harvested from rodent bone marrow can transform into just about every specialized cell type - including blood, muscle and nerve.

The finding suggests that bone marrow, easily extracted from living donors, might become a ready source of stem cells for human therapies. Such therapies could overcome the moral objections of people who oppose the use of stem cells derived from human embryos or fetuses.

But Verfaillie, director of the University of Minnesota's Stem Cell Institute, said research into both types of stem cells should continue. "There may be particular diseases that may be more easily treated with one cell type vs. another," she said. "These studies should be going on in parallel."

Studies by the two scientists appear in today's issue of the journal Nature.

The ethics of stem cell research has recently come before Congress, where the Senate debated a bill that would ban the cloning of human embryos for reproductive purposes or harvesting of stem cells. The bill appears to have stalled last week.

Stem cells are the precursors of every cell type in the human body. Scientists are eagerly looking for ways to use them to regenerate tissues that have been ravaged by disease. These include neurodegenerative diseases such as Parkinson's and Lou Gehrig's disease, as well as diabetes, heart disease and spinal-cord injury.

Parkinson's, afflicting 1 1/2 million people in the United States, destroys brain cells that secrete dopamine, a chemical that regulates muscle movements. The disease causes tremors, stiffness and poor balance.

In his experiment, McKay extracted stem cells from mouse embryos and, in a laboratory dish, manipulated them to become dopamine-producing neurons. Then, he transplanted the neurons into rats afflicted with a Parkinson's-like syndrome that caused them to drag one side of their bodies and walk in circles.

Some of the rats regained normal function and walked straight. Others, which in effect were overtreated, reversed course and circled in the opposite direction. This shows that much work needs to be done to determine the treatment to be given, McKay said.

McKay said he might have overcome concerns that stem cell therapies could cause cancer. Previous experiments have shown that transplants of embryonic stem cells spur the growth of tumors. McKay said he minimized this problem by using stem cells to produce neurons in a culture dish, and then transplanting the neurons into the brain.

"The incidence of tumor formation falls drastically," McKay said. Several years of experiments on monkeys must be done to determine the safety and efficacy of the therapy before it can be tried in humans.

Dr. Ted Dawson, a neurologist at the Johns Hopkins School of Medicine, has tried to use human stem cells to correct Parkinson's in rodents. Results might be published within the next 12 months, he said. Other scientists have been working on that approach as well.

In the meantime, M-0Dawson said he is concerned that news of research progress is raising unrealistic hopes among patients. "The last time there was a major press release, all my patients were asking, 'When can you put these stem cells in me?'" he said.

In the Minnesota study, researchers experimented with a type of bone-marrow stem cell that - as far as anyone knew before - gives rise to bones, muscles tendons and a few other tissues. The study was the first to show that some of the cells have the capacity to turn into almost any type of cell.

When injected into rodent embryos, some of the stem cells incorporated themselves into just about every organ. Specialized "descendants" of these cells, for instance, turned up in the lungs, liver, uterus and kidneys.

Verfaillie said she is now trying to see whether the cells can be stimulated to make insulin-producing cells that could treat diabetics, as well as dopamine-producing cells for Parkinson's sufferers.

Dr. John Gearhart, a pioneering stem cell researcher at Johns Hopkins, cautioned that only a tiny fraction of the bone-marrow stem cells - about one in 10 million - had the capacity to grow into a wide variety of cell types.

Growing enough of them for possible therapies would require keeping them in culture for a long time so they could divide again and again, raising the risk of genetic errors.

"I don't think anyone at this point views this source of cells as a practical source for any kind of cell-based therapy," Gearhart said.