In Parkinson's disease, which neurotransmitter deficiency is associated?

• A. Acetylcholine deficiency.
• B. Norepinephrine deficiency.
• C. GABA deficiency.
• D. Dopamine deficiency.

Answer: (D)

Parkinson disease centers on a loss of dopamine-producing neurons in the substantia nigra, which lowers dopamine in the nigrostriatal pathway to the striatum. This dopamine deficiency disrupts the balance between the basal ganglia circuits that facilitate and inhibit movement, making it hard to start and coordinate movements and producing tremor, rigidity, and bradykinesia. Because dopamine normally keeps acetylcholine activity in check, its loss leads to relatively increased cholinergic activity in the striatum, which is why anticholinergic meds can help some patients. Norepinephrine and GABA are involved in other aspects of brain function and disease, but the defining association with Parkinson disease’s motor symptoms is dopamine deficiency.