carmendrahl writes "Exposure to certain pesticides, including rotenone and paraquat, has been associated with a higher incidence of Parkinson's disease in population studies. But how did scientists come to think of a link between Parkinson's disease and pesticides in the first place? The answer involves the 1980s drug underworld, where criminals were synthesizing modified versions of illegal drugs such as heroin to stay one step ahead of the law. One molecule in some designer heroin cocktails, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), breaks down in the human body into 1-methyl-4-phenylpyridinium (MPP+), a nerve cell killer. Heroin addicts exposed to this molecule got Parkinson's-like symptoms. As for the connection to pesticides, MPP+ is a weed killer that was used in the 70s. It also closely resembles the structure of the pesticide paraquat. The saga, therefore, put scientists on high alert to the possibility that pesticides might play a role in developing Parkinson's."