Relative contributions of NR2B and NR2A subunits to isolated NMDA-EPSPs. (A) Isolated NMDA-EPSPs obtained in a low Mg2+ solution (0.1 mM; n = 5). (i) After recording baseline responses, defining the 100% level (1), applying NR2A inhibitor NVP-AAM077 (0.4 μM) leads to a substantial reduction of the isolated NMDA response (2). Adding NR2B inhibitor Ro25-6981 (0.5 μM) further depresses the responses down to near zero (3). Subsequent perfusion with AP5 (50 μM) fully blocks the synaptic responses and values obtained in this solution are taken as zero level (4). (ii) Traces 1–3 plotted together after subtraction of the zero level. (iii) Bar diagram quantifying the reductions of NMDA-EPSPs after sequentially adding the two subunit-specific blockers, NVP-AAM077 and Ro25-6981. (B) Similar plots for another set of experiments where the two blockers were applied in a different order (n = 6). The bar diagrams show data as mean ± S.E.M. Calibrations: 0.1 mV, 20 ms.