The give and take of Parkinson's treatment.

Two surgical treatments for Parkinson's disease--one that transplants cells into a patient's brain and another that destroys some brain tissue--show promise in recent studies. However, the first operation is controversial, and the second poses clear risks to the patient.

In Parkinson's disease, the brain lacks dopamine, a vital neurotransmitter. Its absence leads to tremors, muscle rigidity, and other problems in motor control. Brain surgery for Parkinson's was tried in the 1950s and early 1960s but was shelved in 1967. That year physicians began prescribing the drug levodopa, which the body processes into dopamine. Unfortunately, levodopa's beneficial effects diminish over years of use.

In the late 1980s, doctors took the radical step of transplanting healthy neurons into the brains of Parkinson's patients. The surgery, intended to spur dopamine production, drew criticism because it uses human embryo cells.

In a study started in 1995, doctors at the University of Colorado Health Sciences Center in Denver injected fetal cells into 20 Parkinson's patients, one of whom later died in an unrelated accident. The surgeons injected an inert substance into 20 others. A year after surgery, dopamine production had risen in 13 of the 19 treated patients. Among those 13, the patients under age 60 scored better in movement tests than they had before surgery.

The 20 untreated patients showed no increase in dopamine production, Curt R. Freed, a neuroscientist at Colorado, reported last month at a meeting of the Society for Neuroscience in Miami Beach, Fla. After the year-long test concluded, 14 of the untreated patients elected to have surgery, Freed says. He continues to track all the patients' progress.

Meanwhile, Swedish and British scientists report that after 10 years, a 69-year-old Parkinson's patient is still showing benefits from surgery that implanted embryonic cells into one side of his brain. The transplanted cells are still making dopamine and haven't succumbed to whatever destroyed his original cells, the team reports in the December NATURE NEUROSCIENCE.

Moreover, the scientists ascertained for the first time in a Parkinson's patient that dopamine made by the transplanted cells is being released and used, as researchers had assumed, says study co-author Paola Piccini of the Imperial College School of Medicine in London.

In Parkinson's patients, dopamine-starved brain cells make extra receptor molecules to capture what dopamine is available. To test for this overabundance, Piccini and her colleagues injected the patient with radioactive chemicals that highlight such receptors. They found that the side of the brain that had received the cell implants had appropriate amounts of receptors-indicating that the implanted neurons were sending dopamine across synapses to host neurons.

The Europeans "have done an excellent job following a few patients very closely" and showing dopamine release, Freed says.

An opposite surgical approach inserts a hot needle into one side of the brain to destroy a small portion of the globus pallidus, an area that's hyperactive in many Parkinson's patients. The technique was discovered 4 decades ago, when surgery accidentally damaged the globus pallidus in a Parkinson's patient--whose motor control subsequently improved.

In a new study in the Netherlands, 18 patients who underwent the surgery raised their scores significantly on standardized movement tests during the following 6 months, says Rob M.A. de Bie of the University of Amsterdam.

The operation carries risks, however. Two patients showed serious adverse reactions, such as psychosis, and seven others had milder effects including facial paralysis, the scientists report in the Nov. 13 LANCET.

Still, this kind of surgery is "the most important therapeutic advance in Parkinson's disease" since levodopa, says Niall Quinn of the Institute of Neurology in London, writing in the same journal.