Exposure to some insecticides may cause a cascade of chemical events in the brain that could lead to Parkinson's Disease, researchers have found.
Permethrin repels mosquitoes
A team from Virginia Polytechnic Institute studied levels of key chemicals in the brain of mice exposed to various levels of the insecticide permethrin.
They found that the insecticide stimulated a reduction in levels of an important transmitter chemical called dopamine.
Parkinson's symptoms such as the muscle rigidity, shuffling gait, and a rhythmic tremor have been linked to the loss of dopamine production in the brain.
The researches also found that exposure to permethrin was linked to increased production of a protein called alpha-synuclein.
This protein is a major component of fibrous tangles called Lewy bodies, which are found in the brain of patients with Parkinson's.
Exposure to low levels of the insecticide seemed to have a more immediate effect than exposure to higher doses.
But the researchers believe this could be because high levels simply overwhelm the delicate systems within the brain, which takes time to come to terms with and react accordingly.
Researcher Dr Jeffrey Bloomquist said a tiny dose - less than one thousandth of that needed to kill a mouse - was enough to produce effects on the brain.
However, he said that while mice exposed to permethrin had shown Parkinson's-like symptoms, they had not developed the full blown disease.
The researchers now plan to examine the effects of longer term exposure permethrin, and of exposure to another widely used pesticide, chlorpyrifos.
Permethrin is used to treat clothes to repel and kill ticks and mosquitoes.
It acts in a similar way to DDT by strongly exciting the nervous systems of insects.
The chemical is toxic at high levels and classified as a possible carcinogen by the US Environmental Protection Agency.
A spokeswoman for the UK Department for Environment Food and Rural Affairs said the use of permethrin was due to be phased out under an ongoing European Union review.
She told BBC News Online: "DEFRA is sponsoring research into a possible link between Parkinson's disease and pesticides.
"This was not one of the pesticides that was being looked at, but we are interested in these results and will pass them on to the research team."
The results of the research were presented at a meeting of the American Chemical Society.