(AP) Partying with Ecstasy several times a night, a common practice among users of the illegal drug, may damage key neurons in the brain and perhaps hasten the onset of Parkinson's disease, according to a study in monkeys. But some researchers were skeptical that the results from the animal studies translate to humans and said such studies discourage research that might lead to medical uses for Ecstasy.

A Johns Hopkins University researcher injected squirrel monkeys and baboons with three shots of Ecstasy, also known as MDMA, three hours apart, mimicking dosages "often used by MDMA users at all-night dance parties." He said the drug caused enduring damage to dopamine-producing neurons in the brains of the animals. The damage was still evident two weeks to six weeks later, said Dr. George A. Recaurte, the lead author the study appearing this week in the journal Science. But he said it is not clear if the damaged neurons will repair themselves, a key factor in whether Ecstasy could cause Parkinson's disease. Parkinson's disease is a brain disorder triggered by the permanent loss of dopamine-producing nerve cells. "We already know from the literature that brain dopamine declines with age," he said. "A young individual who sustains injury to these dopamine cells and depletes their reserve may be at greater risk of Parkinsonism."

But Julie A. Holland, a psychiatrist on the faculty of the New York University School of Medicine, said earlier studies on humans have failed to show that Ecstasy causes permanent damage to dopamine neurons. "It is a big leap to extrapolate what he is seeing in these primates and what you expect to see in Parkinson's syndrome," Holland, the author of a book on the risk and recreational use of Ecstasy. She said Ricaurte's research has helped "demonize" Ecstasy and prevented studies to determine if the drug could be used to treat post-traumatic syndrome. Dr. Alan I. Leshner, former head of the National Institute on Drug Abuse, however, said the Ricaurte study shows "that even an occasional use of Ecstasy can lead to significant damage to brain systems."

Stephen Kish, a University of Toronto researcher studying Parkinson's disease and Ecstasy, said he analyzed the brain of a deceased habitual Ecstasy user two years ago and found no evidence of dopamine neuron damage. "Ricaurte's findings do raise a concern that Ecstasy may damage the dopamine neurons and potentially cause Parkinson's," said Kish. But he said the current study "might not translate to humans" and has not proven a clear connection between the drug and the brain disease. In the study, the animals were given six milligrams for every 2.2 pounds of their weight. One of five monkeys and one of five baboons used in the study died shortly after receiving the shots. The brains of the surviving animals were examined microscopically and chemically after two to eight weeks. The nerve endings where the dopamine is processed were destroyed, said Ricaurte. "There hasn't been a single animal that escaped the dopamine (cell) lesions," he said. Ricaurte said the damage was not enough to cause Parkinson's symptoms, but there is "a clinical concern" that repeated use of Ecstasy will diminish the natural reserve of brain cells and lead to early disease. Holland said Ricaurte's study in monkeys and baboons does not relate to the experience of human recreational users of Ecstasy. "The dose that he gave killed 20 percent of the animals immediately," said Holland. "Clearly these animals reacted to the drug differently than humans because not one out of five Ecstasy users drops dead."

Also, she said Ricaurte's study injected Ecstasy, while most human users take the drug orally. Drugs taken orally are less concentrated in the body than drugs that are injected, said Holland. The NYU psychiatrist said "there is a lot of politics involved" in Ricaurte's study because the government does not want to allow medical research with Ecstasy, even though it has been approved for study by the Food and Drug Administration. Ricaurte's research has been funded by the National Institute on Drug Abuse, the agency Leshner once headed. Leshner is now chief executive officer of the American Association for the Advancement of Science, the organization that publishes Science, the journal printing Ricaurte's current study on Ecstasy.