Parkinson's disease, which afflicts one million people in the United States, kills a class of brain cells that produce dopamine, one of the brain's chemical messengers. Drug therapy helps for a while, but it provokes side effects and ultimately can't keep up with the progressive disease. Testing an alternative, clinicians have implanted fetal neurons into the brains of dozens of Parkinson's patients. In many cases, this procedure has produced long-lived dopamine-producing cells and reversed symptoms of the disease, such as rigidity, slowness, and tremor. But fetal tissue is scarce, and research in the past several years suggests that stem cells, which can be mass produced in a test tube, can also replace damaged brain tissue.
Now, a team led by neurotransplant researcher Ole Isacson of Harvard Medical School in Boston reports that stem cells can compensate for some Parkinson's-like damage in animals. The researchers implanted stem cells from mouse embryos into the brains of rats and mice whose dopamine-producing neurons had been obliterated by a toxin. Once there, the immature cells develop into neurons that make dopamine-producing enzymes; furthermore, they connect with nearby brain cells.
Neuroscientist Ron McKay, of the National Institutes of Neurological Disorders and Stroke in Bethesda, Maryland, and other researchers have figured out how to grow dopamine-producing cells from embryonic stem cells in culture dishes, but with Isacson's method, "you just take cells and put them in the brain," says McKay. "You don't need to purify them, you just shove them in. This is interesting because it implies that all the instructive mechanisms [for these cells' fate] are present in the adult brain."