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I don't know. But I do know this: George Andes wrote: >>Our PD is caused by a progressive loss of dopamine producing cells in our substantia nigra. By the time PD becomes clinically diagnosable, on the average 80% of the substantia nigra is gone. This is not a trivial loss. (Why Nature has provided us with such a great excess or redundancy in substantia nigra capacity is an interesting but unanswered question.)<< Elizabeth Abecrombie at the Center for Molecular and Behavioral Neuroscience at Rutgers University's Newark Campus has done important work in this area. If I understand it correctly, the main reason there are no symptoms in PD until 80% of dopamine neurons are lost goes as follows. As dopamine neurons die in the substantia nigra the system not only loses the ability to release dopamine, it also loses the capacity to re-uptake dopamine that is floating around between cells. Intracellular dopamine is normaly absorbed and recycled by these cells. The net result is that the amount of dopamine available to receptors remains pretty much the same as cells are dying until a critical level is reached. This damages the theory that in presymptomatic PD remaining dopamine cells work so hard to keep levels up that they end up dying of exhaustion. If your intreacellular dopamine level is a bit low and your dopamine neurons are just plain exhausted why not go for a walk - a Parkinson's Unity Walk. Next Sunday at Riverside Park in New York City. (Sorry I couldn't resist) Come meet Bill Langston, Earl Ubell and Anne Meara of Stiller & Meara and have some fun. If it rains you can meet us under the tent at Grant's Memorial. We'll even have cookies! (Dress Informal. Party Hats - Optional) Fund the Research. Find the Cure. Call Newt.