And over time, the majority of transplanted patients suffered dyskinesias, leading ethics commissions around the world to end human trials in the 1990s, he said.
In the new study, using brain imaging, Politis and his colleagues found that the dopamine neurons that decay in Parkinson's disease were restored and functioning in the two patients. But they also found abnormal levels of serotonin neurons within the transplanted tissue.
The serotonin neurons were releasing dopamine, which, when coming from the wrong source, caused the jerking movements.
When patients were given a serotonin receptor agonist, a drug that prevented the serotonin neurons from firing, the involuntary movements ceased.
"Both patients responded by a sudden and almost complete resolution of the troublesome abnormal movements, suggesting that the excess serotonergic neurons had in fact been pumping out dopamine, causing the dyskinesias," Politis said.
It's possible that removing serotonin cells during the preparation of transplanted tissue in future trials will prevent side effects from developing, he added.
"We believe the first priority is to make the whole procedure more safe," Politis said. "We need to establish patients won't have anything worse happening to them after the surgery. And this study addresses that."
European and North American researchers plan a new round of human trials with fetal cells in Parkinson's disease in 2012, Politis said.
Dr. Michael S. Okun, national medical director for the National Parkinson Foundation, said the study "offers some potentially important insights into the role of serotonin in off-medication dyskinesias that may be encountered following Parkinson's disease fetal cell grafting."
"The notion that a simple drug acting on the serotonin system, buspirone, proved useful in short, four-hour testing performed in two
All rights reserved