Which neurotransmitter is low in the brains of individuals with Huntington's disease?

In Huntington's disease, there is a notable reduction in levels of GABA (gamma-aminobutyric acid), which is an inhibitory neurotransmitter. This deficiency is significant because GABA plays a crucial role in modulating neuronal excitability throughout the nervous system. In the context of Huntington's disease, the degeneration of specific neuronal populations, particularly those in the striatum that utilize GABA, leads to an imbalance of neurotransmission. This can contribute to the motor symptoms, cognitive decline, and psychiatric symptoms associated with the disease.

The loss of GABA-producing neurons leads to increased excitatory activity in other pathways, which manifests as the characteristic involuntary movements (chorea) and disturbances in behavior and cognition seen in individuals with this condition. Thus, the low levels of GABA are pivotal in understanding the pathophysiology of Huntington's disease, making it the correct answer to the question.