Which neurotransmitter serves to inhibit the central nervous system (CNS)?

GABA, or gamma-aminobutyric acid, serves as the primary inhibitory neurotransmitter in the central nervous system (CNS). Its main role is to reduce neuronal excitability throughout the brain and the rest of the nervous system. When GABA binds to its receptors on neurons, it typically causes an influx of chloride ions into the cell, leading to hyperpolarization and making it less likely for an action potential to occur. This inhibitory action is crucial for balancing excitatory signals in the brain, helping to regulate mood, anxiety, and overall neuronal firing.

In contrast, other neurotransmitters listed play different roles. Serotonin, primarily known for its role in mood regulation, can have both inhibitory and excitatory effects, depending on the receptor type it binds to, but it is not primarily classified as an inhibitory neurotransmitter. Glutamate is the main excitatory neurotransmitter in the CNS, facilitating synaptic transmission and playing a key role in learning and memory. Endorphins, while they do have inhibitory effects related to pain and stress responses, are mainly involved in the modulation of pain and are classified as peptides that act on opioid receptors, rather than serving as the primary inhibitor in the CNS.