Parkinson's disease is a syndrome in which nerve cells in mainly the substantia nigra (translates to ‘black matter’), slowly die. These cells are closely involved in the production of dopamine, a neurotransmitter (chemical messenger in the brain) that is used for several functions. One of these functions, where problems are observed in Parkinson's disease, is the regulation and initiation of motor activity. This leads to the well-known trembling, little and slow movement, stiff muscles, and so on. To a lesser but sometimes no less disturbing extent other (for example cognitive) functions suffer from the breakdown of dopamine producing cells.
The problems with motor function are related to the nigrostriatal circuit. Dopamine from the substantia nigra normally finds its way to the nearby striatum, part of the basal ganglia, which is an important brain structure for movement. As people age, the number of functioning substantia nigra cells usually decreases, but this happens more rapidly in Parkinson's patients. It seems that only when there is a substantial reduction of perhaps 60 to 70 percent of dopamine-producing cells do observable symptoms of Parkinson's disease appear. The reduced production of lost cells in the substantia nigra can nowadays be somewhat compensated for by an increased production of dopamine, for example through deep brain stimulation of the remaining cells by means of implanted electrodes.
Author: Tom de Graaf (translated by Melanie Smekal)