Figure 1.

Anomalous recovery of NMDAR-mediated evoked EPSCs from MK-801 block. A, Representative traces show progressive block of AMPAR- and NMDAR-mediated components in an averaged evoked EPSC trace administrated with NBQX (5 μm) and MK-801 (10 μm), respectively. All the recordings were conducted in whole-cell configuration in low-Mg²⁺ (0.25 mm) ACSF with the GABA_A antagonist BMI (10 μm). B, Paired-pulse stimuli (100 ms interpulse interval) evoked NMDAR-mediated EPSCs. The recording was conducted in low-Mg²⁺ ACSF with both GABA_A and AMPA receptor antagonists. In our recording, the second evoked EPSCs were always bigger than the first ones. The paired-pulse ratio was measured as the ratio of the second current amplitude over the first current amplitude. C, Selective block of synaptic NMDAR-mediated EPSCs. Because paired-pulse stimuli could facilitate presynaptic release of glutamate, which in turn facilitates the activation of synaptic NMDAR currents, 50 paired-pulse stimuli were delivered at 0.125 Hz with simultaneous MK-801 perfusion, which could selectively block opened synaptic NMDAR channels. However, during 30 min washout period, we observed a progressive gradual EPSC recovery and finally recovered up to ∼35% of the control. D, Agonist-evoked block of NMDAR-mediated EPSCs. Whole-cell application of NMDA (1 mm) through puffer in the presence of the noncompetitive NMDA receptor open channel blocker MK-801 (10 μm) almost completely abolish evoked EPSCs. After a 30 min washout period, no significant recovery was observed. Circle in the inset refers to the boundary between synaptic and extrasynaptic region. The cylinder refers to the effective blocking area by MK-801.