Researchers at Rush University in Chicago found that Parkinson's symptoms could arise suddenly in adult male mice...

Researchers at Rush University in Chicago found that Parkinson's symptoms could arise suddenly in adult male mice that were castrated. Scientists had long known that Parkinson's disease was linked to an unknown array of environmental and chemical insults, but this was the first time symptoms had been linked to testosterone (chemical structure is pictured). In their study published in the Journal of Biological Chemistry, researchers were able to reverse the Parkinson's symptoms by adding 5-alpha dihydrotestosterone to the food pellets of the mice. The scientists hypothesize that a drop in testosterone levels may lead to an increase in toxic nitric oxide (NO) in the brain, which ultimately kills neurons.

Source: http://www.rush.edu/webapps/MEDREL/servlet/NewsRelease?id=1712