Extrasynaptic NMDAR-mediated currents increase following D1DR stimulation. A, Time course of whole-cell NMDA (100 μm, solid black line) responses after blockade of synaptic NMDARs by MK-801 (40 μm) is expressed as a fraction of whole-cell NMDA responses measured before MK-801 application. B, Bar histograms illustrating an increase in extrasynaptic NMDAR-mediated currents in slices from cocaine-naive rats following D1DR stimulation (t(11) = 2.54; *p < 0.05 vs saline no SKF; n = 6–11 cells). C, D, Current responses to the first (P1), 20th (P20) and 40th (P40) stimulation pulses illustrate use-dependent block of NMDA eEPSCs by MK-801 across the experimental groups. Current amplitudes are normalized to the first eEPSC in the saline no-SKF group for ease of comparison. E, A summary of the time course of synaptic responses in the presence of MK-801 illustrates a slight increase in the rate of MK-801 block in the saline group. F, Bar histograms summarizing the rate of block (expressed as stimulation pulse number) by MK-801.