Figure 1.

MK-801 block of NMDA-mEPSCs in hippocampal cultures. A, NMDA-mEPSCs measured from 20 DIV hippocampal cultures by whole-cell voltage clamp during constant perfusion with extracellular solution containing (in mm) 2 Ca²⁺, 0 Mg²⁺, 0.05 picrotoxin, 0.01 CNQX, 0.015 glycine, 0.001 strychnine, and 0.001 TTX. The panel depicts application of 50 μm AP-5 during a representative recording. B, NMDA-mEPSCs recorded in the same setting as in A. The panel depicts application of 10 μm MK-801 during a representative recording. C, D, Traces show gradual MK-801 block of NMDA-mEPSCs in 12 DIV (C) and 20 DIV (D) cultures (n = 10 for each). E, The time constant for MK-801 block was faster in 20 DIV (τ = 9 s) cultures compared with 12 DIV (τ = 24 s) cultures (down to 20%). In these experiments, NMDA-mEPSC activity was quantified by calculating cumulative charge (Q) transfer in 10 s intervals. F, Charge transfer quantified by summation of area below baseline (noise plus events). Before MK-801, 1091 ± 269 pC; after 10 min in MK-801, 337 ± 55 pC; after AP-5, 319 ± 72 pC (p = 0.016 before and after MK-801, p = 0.84 before and after AP-5). G, The effect of elevated extracellular Ca²⁺ (switch from 2 mm Ca²⁺ to 8 mm Ca²⁺) on NMDA-mEPSCs (top) and AMPA mEPSCs (bottom) at 12 DIV cultures. AMPA mEPSCs are recorded in 2 mm Mg²⁺, 50 μm picrotoxin, 1 μm TTX. H, Fold increase in mEPSC activity as measured by Q transfer. I, The time constant of MK-801 block decreases to 13 s (from 24 s) at 8 mm Ca²⁺ (n = 9). NMDA-mEPSC traces are superimposed before and after 2 min of MK-801 application. J, K, Averaged traces for selected clearly identifiable spontaneous events are superimposed before and 2 min after MK-801 treatment; note the faster decay kinetics of MK-801-exposed miniature events. L, M, Comparison of rise and decay times of NMDA-mEPSCs before and 2 min after MK-801 treatment. Both rise and decay times are decreased (10–90% rise times: before MK-801, 11.2 ± 0.85 ms, n = 7 experiments; after MK-801 treatment, 8.05 ± 0.2 ms, n = 7 experiments; decay times before MK-801, τ = 43.9 ± 6.5 ms, n = 7 experiments; after MK-801 treatment, τ = 18.8 ± 0.9 ms, n = 7 experiments). *p < 0.05; **p < 0.01.