Which neurotransmitter is the major inhibitory neurotransmitter in the central nervous system?

• A. Dopamine
• B. Gamma-aminobutyric acid (GABA)
• C. Serotonin
• D. Norepinephrine

Answer: (B)

GABA is the major inhibitory neurotransmitter in the central nervous system. When released, it binds to GABA receptors, mainly GABA_A (ionotropic) and GABA_B (metabotropic). Activation of GABA_A opens chloride channels, causing hyperpolarization of the neuron and making it less likely to fire. This widespread inhibition helps balance excitation in neural networks and prevent runaway activity. In contrast, dopamine, serotonin, and norepinephrine can have either excitatory or inhibitory effects depending on receptor type and brain region, so they’re not the primary inhibitory system in the CNS. Drugs that enhance GABA activity (like benzodiazepines) illustrate how boosting this inhibitory system dampens neural activity for anxiolytic or anticonvulsant effects.