Fig. 2.

Incomplete blockade of NMDA receptor (NMDAR) responses by MK-801. A–C, top: examples of NMDAR excitatory postsynaptic currents (EPSCs) obtained at baseline (a₁, b₁, c₁), after 10 min of 0.1-Hz stimulation in the presence of varying concentration of MK-801 (a₂, b₂, c₂), and in the presence of 100 μM dl-2-amino-5-phosphonopentanoic acid (APV; a₃, b₃, c₃). Bottom, NMDAR EPSC peak amplitude normalized to baseline (n = 5 for each MK-801 concentration used). Stimulation was suspended for 5 min when MK-801 was added to the bath (gray shading). After 5 min, stimulation was resumed at same frequency as baseline. After 10 min, APV was added to the bath. D: enlarged example NMDAR EPSCs from C (c₁ and c₂) evoked at baseline and after 10 min of 0.1-Hz stimulation in the presence of 40 μM MK-801, normalized to the peak. Notice different amplitude scales. E: the decay in NMDAR-mediated transmission due to MK-801 blockade was fitted by a single exponential curve. NMDAR EPSC blockade is shown with 5, 10, or 40 μM MK-801. F: time constant (τ) of the MK-801 blockade of NMDAR EPSCs as a function of MK-801 concentration. G: percentage of baseline blocked by 60 stimuli (10 min at 0.1 Hz) as a function of MK-801 concentration.