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WASHINGTON (Reuters) - Reuters [OL] via NewsEdge Corporation : Researchers said Monday they had created a possible new source for treating Parkinson's patients -- the brain cells of cloned cattle. Brain cells from cattle fetuses were genetically engineered, then cloned and injected into rats with Parkinson's disease. The treatment seemed to reduce the symptoms in the rats, the researchers reported in the journal Nature Medicine. They said they hoped the technique could one day be used in people. The scientists' approach combined three new and controversial technologies -- cloning, genetic engineering, and the use of fetal brain cells to treat Parkinson's. Dr. Curt Freed at the University of Colorado School of Medicine, Dr. Steven Stice of the University of Massachusetts at Amherst and colleagues said they had been intrigued by reports about brain cell transplants for Parkinson's patients. There is no cure for Parkinson's, a common brain disorder that causes tremors and progresses to total muscle failure and death. It afflicts 1 percent of people over the age of 50. Victims have a shortage of dopamine -- an important brain chemical that plays a role in muscular movement. Research has shown that their dopamine-producing brain cells have somehow been destroyed. But some experiments have shown Parkinson's patients might be helped with injections of these brain cells from human fetuses. Aborted or miscarried fetuses have been the source, but using them is highly controversial. ``A major problem for this emerging therapy is the limited and variable supply of human fetal tissue,'' the researchers wrote in their report. Earlier this year Stice's team reported they had cloned a small herd of cattle using fetal cells -- not the difficult technique that produced Dolly the sheep, cloned from an adult cell, but nonetheless a hard task. They teamed up with Freed's group to see if such cloned fetuses might help Parkinson's patients. ``Their study highlights some of the potential benefits of this technology and will inevitably rekindle many of the debates about cloning,'' Keith Campbell of Scotland-based PPL Therapeutics, the company that cloned Dolly, said in a commentary. The researchers cloned cattle fetuses, genetically engineered them, grew them until their brain cells were at a certain stage, and removed the brain cells. These brain cells -- neurons that produce dopamine -- were injected into the brains of rats. It is hard to tell with rats, but the animals displayed less ``circling behavior'' -- one of the symptoms of Parkinson's in rats. The researchers killed some of the rats and looked at their brains and saw that in many cases, the injected cells had grafted onto their brains. Using genetically engineered clones has two advantages -- genes can be added to reduce the risk that the patient's immune system will reject the cells, and scientists can produce cells that are exactly alike, with an effect thus more predictable. The researchers think cattle fetuses could have human genes added and be used as a source of brain cells. But this calls for xenotransplantation -- using animal tissues in humans -- which is another hotly debated area. Scientists point out the risk of transmitting unknown diseases, and changing some of the genes does not always do away with the risk of rejection by the patient's immune system.