Glutamate is excitatory or inhibitory?

• A. GABA inhibitory
• B. Both
• C. Excitatory
• D. Neither

Answer: (C)

Glutamate is the primary excitatory neurotransmitter in the brain. When it binds to ionotropic receptors (NMDA, AMPA, kainate) on the postsynaptic neuron, these channels open and allow Na+ (and often Ca2+) to enter while K+ leaves. This inward positive current depolarizes the neuron, creating excitatory postsynaptic potentials and increasing the likelihood of firing an action potential. Some metabotropic glutamate receptors can modulate activity in more complex ways, but the overall effect of glutamate signaling is excitatory. For contrast, GABA is the main inhibitory neurotransmitter, producing hyperpolarization and reducing firing. Excessive glutamate activity can lead to excitotoxicity due to calcium overload.