WASHINGTON?Researchers used embryonic stem cells to relieve symptoms of Parkinson’s disease in rats, demonstrating the cells can be turned into neurons that make dopamine, a key brain chemical.

The researchers at Harvard Medical School and McLean Hospital in Belmont, Mass., showed in tests that the cells injected into rats whose brains had been chemically damaged would spontaneously convert to correct the Parkinson’s symptoms.

Some experts said the study, appearing Tuesday in the Proceedings of the National Academy of Sciences, was significant because it showed embryonic stem cells could be used to treat brain disorders. However, the experts cautioned that the cells could also cause tumors.

Dr. Ole Isacson, senior author of the study, said that if further experiments are successful, there could be human trials of the technique in about five years.