JAMA Neurology [2013] 70 (2) : 241-247 (D.A.Ziegler, J.S.Wonderlick, P.Ashourian, L.A.Hansen, J.C.Young, A.J. Murphy, C.K.Koppuzha, J.H.Growdon, S.Corkin)
For many years it has been widely claimed that, in Parkinson's Disease, there is a huge loss of the dopaminergic neurons (the brain cells that produce dopamine). It is often claimed that this cell loss is the primary cause of Parkinson's Disease. However, not a single study had ever actually shown that there was massive cell loss in Parkinson's Disease. It has also been assumed that loss of the dopaminergic neurons that can cause Parkinson's Disease precedes the loss of cholinergic neurons, which can lead to dementia, as is common in later Parkinson's Disease. However, the results of a study assessing this theory did not support what had often been claimed.
Researchers assessed the volume of the brain in the area in which dopaminergic neurons are common. They found that the volume of the brain in this area was decreased in people with mild Parkinson's Disease but not in people that did not have Parkinson's Disease. However, in more severe Parkinson's Disease there was no greater loss of volume of the brain in the area affected by Parkinson's Disease as there would have been if the severity of Parkinson's Disease was due to cell loss. Research has always instead been consistent with a major reduction in cell activity rather than an actual loss of the cells involved in Parkinson's Disease.
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