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Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
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In which of the following diseases decrease in levels of single neurotransmitter was first identified?
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The correct answer is  Neurons of the substantia nigra communicate with neurons of the basal ganglia by liberating the neurotransmitter dopamine (DA). In Parkinson's disease, neurons of the substantia nigra progressively degeneration; as a result, the amount of DA available for neurotransmission in the corpus striatum is lowered. Ref Harrison20th edition pg 2456