A, PPDA (1 μm), an NMDAR antagonist more selective for NMDAR2C- and NMDAR2D-containing receptors, inhibited a significant portion of the basal NMDAR-mediated tonic current. B, effect of PPDA (1 μm) on the peak amplitude of EPSCs evoked by the stimulation of Schaffer collaterals. C, mean percentage inhibition of PPDA (1 μm), ifenprodil (10 μm), and NVP-AAM077 (0.1 μm) on tonic and evoked synaptic NMDAR-mediated currents (normalization relative to the current blocked by 20 μm MK801 or by 50 μmd-AP5).