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Tech researchers to study insecticide exposure

By Stewart MacInnis

Spectrum Volume 21 Issue 13 - November 19, 1998

Thanks to a $543,000 grant from the U.S. Army, Virginia Tech researchers will investigate the possibility that troops exposed to insecticides during the Persian Gulf War could be at increased risk of developing Parkinson's Disease.
"What we'll be looking at specifically is Parkinsonism and pesticide exposure," said Jeff Bloomquist, a neurophysiologist. "Insecticides are unique among environmental pollutants because they are designed to be neuro-toxic and are deliberately placed in the environment."
The three-year project will provide information of benefit to civilians as well as military personnel, he said. Bloomquist will be joined in the study by Bradley G. Klein, an associate professor of biomedical sciences and pathobiology with the Virginia-Maryland Regional College of Veterinary Medicine.
Service members serving in the Persian Gulf could have been exposed to insecticides in several ways, Bloomquist said. Insecticides were used around field encampments and in housing areas. Uniforms were also impregnated with insecticides to protect service members from disease-carrying insects.
Bloomquist, an associate professor in Department of Entomology, became interested in the effects that pesticides have on humans because of studies showing an increased rate of Parkinson's Disease among farmers and other rural residents with a relatively high exposure to the compounds. He is conducting a separate study looking at a range of pesticides used by farmers.
The Army study will focus on two types of insecticides used by the military: chlorpyrifos, an organo-phosphorous compound, and permethrin, a pyrethroid compound.
Parkinson's Disease is a degenerative disease affecting the central nervous system. About 1 percent of the population suffers from the disease, the onset of which is thought to involve both a genetic pre-disposition and exposure to an environmental toxic trigger. Bloomquist and Klein are investigating whether insecticides can be among triggering toxins.
"Parkinsonism may be a result of long-term exposure to these compounds," Bloomquist said. "If we show this connection, it likely will be years--maybe 20 years--before any symptoms of the disease begin to appear. We know enough about the disease that there are some interventions that could be devised. We will also be looking into the extent of reversibility of the toxicant's effects."
Bloomquist is especially interested in the effects of combining several compounds. He suspects a synergistic effect--compounds that by themselves pose a small risk of triggering Parkinson's Disease may generate a large risk when they are combined.
The Virginia Tech studies, which Bloomquist described as "very basic research," will investigate the neuro-chemical changes in mice when they are exposed to insecticides in various dosages and various combinations.
"The neuro-chemistry lets us catch the disease at a very early stage," Bloomquist said.
The loss of motor skills, resulting in symptoms such as muscle rigidity, shuffling gait, and a rhythmic tremor, has been linked to loss of dopamine production in the brain. That loss of dopamine is the major neuro-chemical expression of Parkinson's Disease.
Bloomquist and Klein intend to induce Parkinson's Disease in the test mice by exposing them to a neuro-toxin called MPTP, a compound that was found in the 1980s to trigger the disease after it had been injected by drug addicts. Through the chemical processes within the brain, MPTP destroys the same dopamine-producing neurons that degenerate in idiopathic Parkinson's Disease.
The loss of dopamine caused by MPTP will mimic the loss of dopamine caused by genetic pre-disposition, which can go undetected for years in humans before the symptoms of Parkinson's Disease manifest themselves.
Different groups of mice will be exposed different amounts and combinations of pesticides and MPTP. Behavioral effects will be assessed and brain tissue will be evaluated to determine the amount of dopamine that has been lost and to see if dopamine-producing cells have been destroyed.
Bloomquist and Klein are hopeful that this study will lay the groundwork for future research into ways to detect and alter the ability of toxic substances to trigger the disease. Bloomquist said understanding of the chemical processes involved may provide a clue on how to reverse or prevent Parkinson's Disease in the future.