Introduced in 1988 by Tage Honore and colleagues, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) provided the first potent, competitive non-NMDA glutamate receptor antagonist capable of resolving AMPA/kainate transmission from NMDA receptor currents.
In retinal and brain-slice electrophysiology, CNQX blocks fast AMPA-mediated excitatory postsynaptic currents (EPSCs) and hyperpolarizing OFF-bipolar cell responses without blocking voltage-gated sodium channels.
Pairing CNQX with an NMDA receptor blocker (such as APV or MK-801) completely abolishes fast ionotropic glutamatergic transmission while leaving inhibitory GABAergic or metabotropic signaling intact.