Which neurotransmitter is known for its inhibitory effect and is then considered a major inhibitory neurotransmitter in the brain?

GABA, or gamma-aminobutyric acid, is recognized as the primary inhibitory neurotransmitter in the brain. It plays a crucial role in reducing neuronal excitability throughout the nervous system. By binding to its receptors, mainly GABA_A and GABA_B, it induces a hyperpolarization of the neuron, making it less likely to fire an action potential. This inhibitory effect is essential for maintaining the balance between excitation and inhibition in neural circuits, which is vital for normal brain function, including the regulation of anxiety, mood, and overall brain activity.

In contrast, other neurotransmitters mentioned, such as acetylcholine, serotonin, and dopamine, are primarily associated with excitatory processes or modulatory roles rather than direct inhibition. Acetylcholine can have both excitatory and inhibitory effects depending on the type of receptor it binds to, while serotonin is mainly involved in mood regulation and various other functions but is not primarily categorized as inhibitory. Dopamine, involved mainly in reward and motivation pathways, also does not have a primary inhibitory role in the same way that GABA does. Thus, GABA is distinctly positioned as the major player in providing inhibitory signaling in the brain.