Which neurotransmitter is primarily inhibitory in the CNS?

Which neurotransmitter is primarily inhibitory in the CNS?

• A. Dopamine
• B. Glutamate
• C. GABA
• D. Acetylcholine

Answer: (C)

GABA is the main inhibitory neurotransmitter in the CNS. When released, it binds to GABA_A receptors, which are ligand-gated chloride channels; opening these channels allows Cl− to flow into the neuron, hyperpolarizing the membrane and producing fast inhibitory postsynaptic potentials that make firing less likely. GABA_B receptors, a separate metabotropic type, activate potassium channels and reduce calcium influx, giving longer-lasting inhibition. This inhibitory signaling is essential for balancing excitation and preventing network hyperactivity. Glutamate, in contrast, is the primary excitatory transmitter in the CNS, activating receptors that let positively charged ions enter and depolarize neurons. Dopamine mostly serves as a modulatory signal with effects that depend on receptor subtype and circuit, not primarily inhibitory. Acetylcholine can be excitatory in many CNS pathways (via nicotinic receptors) and can have inhibitory roles in some circuits (via muscarinic receptors), but it is not the principal inhibitory transmitter.

GABA is the main inhibitory neurotransmitter in the CNS. When released, it binds to GABA_A receptors, which are ligand-gated chloride channels; opening these channels allows Cl− to flow into the neuron, hyperpolarizing the membrane and producing fast inhibitory postsynaptic potentials that make firing less likely. GABA_B receptors, a separate metabotropic type, activate potassium channels and reduce calcium influx, giving longer-lasting inhibition. This inhibitory signaling is essential for balancing excitation and preventing network hyperactivity.

Glutamate, in contrast, is the primary excitatory transmitter in the CNS, activating receptors that let positively charged ions enter and depolarize neurons. Dopamine mostly serves as a modulatory signal with effects that depend on receptor subtype and circuit, not primarily inhibitory. Acetylcholine can be excitatory in many CNS pathways (via nicotinic receptors) and can have inhibitory roles in some circuits (via muscarinic receptors), but it is not the principal inhibitory transmitter.