Pesticide use linked to Parkinson's disease

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Long-term low-level exposure to a pesticide widely used in horticulture and water management could be a cause of Parkinson's disease in humans, researchers at Emory University in Georgia warned this week.

They found that rats given repeated doses of the insecticide rotenone, which is derived from plant extracts, have difficulty walking, shaky paws, and protein deposits in their brains — all tell-tale symptoms of Parkinson's disease.

The results, which appear to strengthen existing epidemiological evidence of a link between pesticide exposure and Parkinson's, were announced at a meeting of the Society for Neuroscience in New Orleans. “We've shown that exposure is sufficient to do it in rats, and presumably the same can happen in people,” says neurologist Tim Greenamyre, a member of the Emory team.

Parkinson's disease affects one or two adults in every thousand, and the risk increases tenfold beyond the age of 50. Sufferers become clumsy and move stiffly, and their muscles often spasm. These and other symptoms occur because neurons that produce dopamine, a chemical messenger that rouses the body to action, degrade. In addition, fibrous protein deposits called Lewy bodies accumulate in brain cells.

Rotenone is extracted from several plants whose juice has been used by South and Central American people for centuries to catch fish. Unlike synthetic pesticides, it breaks down quickly in the environment, and was thus thought to pose little danger.

To study the physiological effects of rotenone, the pesticide was injected into the bloodstream of laboratory rats. Like many other pesticides, it was known to block the activity of the enzyme needed to provide the dopamine neurons with energy. In the rats, rotenone killed some dopamine neurons and caused deposits resembling Lewy bodies.

Benoit Giasson, a Parkinson's disease specialist at the University of Pennsylvania, Philadelphia, points out that the doses given to the rats — and their administration through injection — are very different from the normal human exposure. But he still argues that rotenone should be used with greater caution until more is known about the risks.

Because rats injected with rotenone mirror the symptoms of Parkinson's so closely, the animals will help researchers to study the disease. The work will be published in the December issue of Nature Neuroscience.

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