CNQX (FG9065) is a potent and competitive AMPA/kainate receptor antagonist with IC50s of 0.3 μM and 1.5 μM, respectively. CNQX is a competitive non-NMDA receptor antagonist. Superfusion of hippocampal slices with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 2-5 microM) reversibly blocked the Schaffer collateral and mossy fibre excitatory postsynaptic potential (EPSP), while sparing the fast and slow gamma-aminobutyric acid (GABA)-mediated inhibition. CNQX may be a useful antagonist to study excitatory amino acid-mediated synaptic transmission. CNQX (1-5 μM) produces a selective and dose-dependent reduction in the amplitude of the monosynaptic component of the DR-VRR recorded from lumbar spinal segments. The activation of NMDA receptors is sufficient to elicit and maintain fictive locomotion after blockade of non-NMDA receptors with either DNQX or CNQX.