The very idea of transplanting chunks of living human brain once raised images of Frankenstein and seemed possible only in science fiction films.

Today, it's medical reality.

Nearly 50 human patients around the world have received brain implants to treat their Parkinson's disease. Scientists predict that 100 more may be performed by the end of the year.

These experimental operations to treat advanced stages of Parkinson's disease have opened the door for transplant treatments for a number of different diseases, such as Alzheimer's and Huntington's, stroke and other brain traumas, spinal cord injuries and even, one day in the future, mental retardation, depression and schizophrenia.

"The field has just exploded," said Dr. Richard J. Wyatt, associate director for research at St. Elizabeths Hos- pital in the District and the National Institute of Mental Health in Bethesda.

But even as human trials get under way, controversy embroils the field of human brain implant surgery.

To begin with, there is confusion over the long-term effectiveness of this type of surgery. Experts who gathered recently in Rochester, N.Y., for the Schmitt Neurological Sciences Symposium on Transplantation into the Mammalian Central Nervous System could not reach a consensus on how much the brain tissue transplants actually improve the symptoms of Parkinson's disease. Nor could they agree on what impact these implants have on the inner workings of the brain.

There is also major concern over the source of brain cells to be used in transplant operations. So far, surgeons are transplanting cells from the patients' own adrenal glands to the brain to produce the chemical dopamine, which is missing in Parkinson's patients.

Animal experiments, however, suggest that the most promising cells for brain transplants are found in the embryonic brains of aborted human fetuses.

Swedish and English research teams are planning to transplant human fetal cells into Parkinson's patients within the next year. The American medical community, however, fearing the ethical implications of using tissue from aborted fetuses, is more cautious.

Yet, despite the confusion and uncertainty, the pace of this pioneering brain surgery has quickened. Surgeons in half a dozen American medical centers have decided to push ahead and implant tissue in human brains until they can prove that the technique works or they become convinced that it does not.

Researchers at the New York University School of Medicine operated on their first patient on July 8. Doctors at Tampa General Hospital in Tampa, Fla., did their first brain implant three weeks ago.

A study of 18 patients is under way at Vanderbilt University Medical Center in Nashville. Others have been treated at Rush-Presbyterian-St. Luke's Medical Center in Chicago; the Universidad Nacional Autonoma de Mexico, and the Institute of Neurology, both in Mexico City; the University of Lund in Lund, Sweden; the Institute of Neurology and Neurosurgery in Havana; and the Capital Institute of Medicine in Beijing.

"I think this is just the beginning of a new frontier," said Dr. George Allen, a Vanderbilt neurosurgeon. "It involves conflict, controversy and uncertainty, both public and scientific. If you don't have that, you don't know you are at the frontier. I love being out there." Easing Parkinson's Symptoms

People in the end stages of Parkinson's disease are often desperate for new experimental therapies. The disorder, which affects 1 million Americans, causes immobility and constant, uncontrollable tremor, among other physical symptoms, while leaving the mind alert, though trapped in a failing body. The symptoms can be lessened by oral medications, such as L-dopa, but the drugs fail to help 15 percent of patients and eventually stop working for nearly all patients after 10 to 15 years.

"There is a great push from all the patients," said Dr. Lars Olson, a pioneer in this field from the Karolinska Institute in Stockholm. He said these patients are willing to take great risks if there is some hope of improving their conditions.

The current explosion of human brain implant surgery

began late last year when reports first spread that surgeons in Mexico City were achieving impressive results with a handful of patients. They had modified a Swedish technique to treat Parkinson's disease -- an operation that had been tried in four patients in 1982. The Swedes abandoned the surgery after it failed to improve the patients' conditions.

No other research group attempted surgery in human patients until 1986, when the Mexican team, led by Dr. Rene Drucker-Colin of the Universidad Nacional Autonomade de Mexico, entered the field.

The results have been dramatic -- and controversial.

The first of their 18 patients was a 35-year-old man with severe Parkinson's disease. His symptoms were fairly classic -- severe rigidity, uncontrollable tremor of the limbs and difficulty walking or even getting out of a chair.

In February 1986, the Mexican team removed one of his adrenal glands -- there are two, one on top of each kidney -- which produce adrenalin and other hormones. Scientists speculate that when placed in the brain, the adrenal cells help make dopamine, a brain chemical essential to controlling voluntary body movement and missing in Parkinson's patients.

Using a microscope, the neurosurgeons bored into the patient's brain and carved out a small cavity on one side of the brain in an area that normally needs dopamine to function, the so-called caudate nucleus. Steel clips were used to hold the four to six fragments of adrenal gland in the cavity.

The implanted tissue was situated in such a way that the cerebral spinal fluid could bathe the tissue and distribute any chemicals from the implanted cells to other parts of the brain.

At the Rochester conference, Drucker-Colin presented results of the surgery on this man and two other patients with videotapes showing how well the individuals could move before and after surgery.

The transplant appeared to allow the first man to care for himself and a small farm at his home. The videotape showed him cleaning an animal stall and stiffly kicking a soccer ball.

"There was evident benefit . . . by the transplant," said Drucker-Colin, adding that the man had become well enough to run a small store on his farm.

Before surgery, one 56-year-old man could barely rise from a chair to walk with a slow, shuffling, unsteady gait. Five months after surgery he was able to walk stiffly, but fairly normally, stepping over a book placed in his path, and then hopping on one foot. Signs of rigidity could still be seen, but clearly the condition of the patient had improved.

The third patient had an odd form of the disease, including tremors of the trunk (tremors usually affect just the limbs). Most of the symptoms seemed to disappear after the surgery.

The Mexican results were so dramatic that a number of scientists at the conference had trouble believing them. For one thing, the Mexican patients were not typical Parkinson's cases. They were all relatively young, ranging in age from 35 to 65. Parkinson's disease is generally a disease of the elderly, more often striking people in their sixties and seventies.

Data was presented only on the first 11 patients with no information of the remaining seven in the study. What's more, one of the cases, according to a Canadian neurologist, appeared to be misdiagnosed and may not have had the disease.

Nevertheless, other scientists could not help but be impressed. "You just don't see spontaneous recovery of a Parkinson's patient," said Dr. Alan Fine of the Medical Research Council in Cambridge, England. "Something is going on here. I don't know what."

The Mexican physicians, meanwhile, strongly defended their results. "The improvement is spectacular because the patients had very bad Parkinson's disease," Drucker-Colin said. But, he added, "you cannot really refer to this as a cure. It is a procedure that improves their clinical condition. None of the patients are cured. Some are improved fast, some slow and we really don't know how long this will last."

Chinese, American Experiments

Chinese surgeons have performed brain implants on nine Parkinson's patients. Three of the cases were presented as before-and-after videotapes by Dr. Shou-Shu Jiao of the Capital Institute of Medicine in Beijing. While the three patients showed improvement, their recoveries, for the most part, were not as dramatic as those of the Mexican patients.

The exception was a 46-year-old Chinese woman who began to develop Parkinson's when she was 34. Her rigidity had advanced to the point where she was completely frozen and could not get out of bed, let alone stand or walk.

After the surgery, she still had signs of Parkinson's disease -- tremor, slow movement, a flat facial expression -- but she could stand, walk, feed herself and even climb stairs unassisted.

The dramatic results in the younger patients of both the Mexican and Chinese groups helped strengthen the notion that adrenal cell transplants were going to be most effective in younger patients, several scientists said.

The third set of human data came from Vanderbilt in Nashville, where six of a planned series of 18 patients already have received transplants. But preliminary results have been inconclusive, according to neurosurgeons.

It was not possible to tell from videotapes whether the patients were significantly better after the surgery. Some patients experienced enough benefit to stop taking medicine to control their disorder. On the other hand, some of the Vanderbilt patients seemed worse, needing more L-dopa to control their disease than before surgery.

"It is too early to make any conclusions about the cause of any improvement that might be seen," Allen said. "It could be placebo. It could be the natural cycling of the disease." Parkinson's symptoms are known to improve by themselves and then get worse again with time.

While researchers debate the effectiveness of this surgery, important scientific questions remain. Just how, for example, does the transplanted tissue ease symptoms of the disease?

In an interview, Drucker-Colin said that he doubted that the patients improved because the transplanted tissue itself was producing enough dopamine to make a difference. Several researchers suggested that the transplanted cells may stimulate remaining dopamine-producing cells to work harder and produce more of the essential chemical, leading to a positive effect on the disease.

There also was a surprising side effect from the Mexican implants that baffles neurologists. Drucker-Colin noticed that the patients did not complain of much pain after the abdominal surgery, which often tends to be painful. He discovered that the patients produced 10 to 40 times more enkephalin, the brain's natural opiate-like pain killer, than normal.

The three groups -- American, Chinese and Mexican -- all used slightly different surgical techniques. The Chinese essentially used the approach developed by the Swedes five years ago. In this technique, adrenal cells are packed in a metal, corkscrew-shaped holder and implanted deep into the brain in such a way that the brain's fluids do not bathe the transplant. That approach didn't work for the Swedes but apparently worked for the Chinese.

The Mexicans varied the technique so the tissue was implanted in a cavity within the brain that could be reached by cerebral fluids, and then clipped into place with a steel retainer. The American group at Vanderbilt used essentially the same approach -- substituting a soft, absorbable pad for the steel clip -- but but didn't get nearly the dramatic results shown by the Mexicans.

In the Mexican study, moreover, three of the 18 patients have died -- at least two of causes that seemed related to the surgery: one from an infection of the pancreas; another from a stroke 45 days after surgery. A third patient, a 55-year-old man, had a heart attack five months after the implant.

Despite these questions about the Mexican results, American researchers have been making pilgrimages to Mexico City to see the patients and talk with their physicians.

"We spent a week in Mexico and reviewed the data," said Dr. Charles Olanow, chief of the Parkinson's disease and movement disorder center at the University of South Florida. "It was exciting. It has a lot of promise. I felt there was enough enthusiasm there to try it."

Transplanting Fetal Cells

For all the controversy about the results of the adrenal cell implants, a bigger, and potentially more public, controversy looms on the horizon.

Animal studies that are now under way have begun to suggest that the adrenal cell transplants do not work very well, especially in the long run, and especially for older patients.

Instead, animal studies show that transplants of dopamine-making cells gathered from the brains of aborted fetuses will work much better, in part because the cells are younger and will be more likely to grow and secrete the needed chemicals.

Surgery began with adrenal cells, said Dr. John Sladek, chairman of neurobiology and anatomy at the University of Rochester School of Medicine and Dentistry, because they are "socially acceptable. That is why you saw the rapid leap into adrenal cell transplants."

Sladek's group has shown long-term reversal of an experimentally induced form of Parkinson's disease in 14 monkeys after transplanting monkey fetal cells. "We are getting a probable dopamine-dependent effect," said Sladek who was also chairman of the recent international brain tissue transplant conference.

A group at the University of Lund in Lund, Sweden, has taken Sladek's work a step further. Instead of transplanting monkey fetal cells, a group led by Dr. Patrick Brundin implanted brain cells taken from a nine-week old aborted human fetus, and transplanted the material into the monkeys. If the fetuses are older than nine weeks after conception, the cells do not survive, he said, probably because the nerve cells are too mature after that. The results of the human fetus-to-monkey transplant were encouraging. "The grafted human fetal dopamine neurons can release dopamine spontaneously," Brundin said.

Overall, the impression from the fetal transplant work in both rats and monkeys is that fetal cells work better than adrenal cell transplants, several researchers said.

But only the Swedes and the English are willing to say they will give it a try in humans. Although fetal cells are being used in the United States to treat insulin-dependent diabetes, American researchers at the Rochester conference did not want to be the first to suggest transplanting brain cells from an aborted human fetus.

Mood of Caution

While the fundamental research in the laboratory is exciting, it can create a real human problem. "It is giving people false hope," said Dr. Jane Taylor of the Yale University School of Medicine.

Several researchers at the Rochester conference cautioned that while it is now clear that they can now begin thinking about rebuilding damaged brains with implants, they are a long way from being able to help people with various brain diseases.

And while the exception is Parkinson's disease, transplants for these patients are still in the trial and error stage, said Dr. Roy A.E. Bakay, a neurosurgeon from Emory University in Atlanta, where their first patient could be done as early as this month.

To some researchers, the pace of experimental surgery in human patients has even been too fast. "It would have been nice if {Parkinson's transplants} had stayed in the lab longer," said Dr. James Robertson, a neurosurgeon at the University of Tennessee in Memphis who expects to begin using the technique on 10 patients sometime this year. "But it is out now, and there is no way to stop someone from doing it."

With half a dozen research centers already planning brain implant surgery -- and that number increasing rapidly -- "there is no way that human investigation will not proceed," Bakay said.

Even though transplants for Parkinson's have not been proved effective by large scale human studies, "it would be easy for 25 or 50 centers to spring up in the United States," Sladek said. "That I would caution against."

Sometimes, however, science advances only when researchers take chances. The edges of scientific appropriateness -- when the animal data is good enough to try something in humans -- blurs when ambitious researchers race to be the first with a new therapy. The danger, however, is that human lives may be lost or ruined if they are wrong.

What should the individual patient do? "You don't want to be the first person to have this {kind of} procedure done," said NIMH's Wyatt said of the Parkinson's transplants. "You want to be the hundredth. A lot of things can go wrong. If you can wait, wait."

Sometimes patients can't. As the disease becomes more and more debilitating, they often will risk anything for relief. That has helped drive the move to human trials.

And, of course, there is money: funding from governments, fees from patients. "The more exciting it {a field of research} sounds, the easier it is to get money" in the form of government grants, pointed out England's Fine. So far, this experimental surgery has been free to the patient. But once perfected, brain tissue transplants would have enormous economic potential.

Despite the practical and ethical land mines that lie ahead, there is optimism among researchers that this type of surgery will become a significant treatment for Parkinson's disease and ultimately for other disorders.

As Dr. Richard Stanley Burns of Vanderbilt University put it: "Brain transplants have come of age."