Final answer:
Parkinson's disease is associated with decreased GABA and substance P. The degeneration of dopaminergic neurons in Parkinson's disease leads to an imbalance in neurotransmitters in the basal ganglia circuitry.
Step-by-step explanation:
Parkinson's disease is a diagnosis you should think of when you encounter decreased GABA (gamma-aminobutyric acid) and substance P. In Parkinson's disease, the degeneration of dopaminergic neurons and loss of dopamine in the basal ganglia circuitry leads to an imbalance in glutamate and GABA neurotransmission. This imbalance results in increased excitation and cell death. Additionally, dysfunctional GABAergic transmission is present in the altered function of the reward system that underlies addictive behavior.