Fig. 1: Threshold and amplitude of dendritic spikes are controlled by N-methyl-D-aspartate receptor (NMDAR) co-agonist levels.

a Schematic of experiments. Whole-cell patch clamp recordings (ip, intracellular pipette, current clamp, CA1 pyramidal cells), iontophoretic glutamate application (ep, extracellular pipette), two-photon excitation (2PE) imaging of patched cell and iontophoresis pipette filled with Alexa Fluor 594 (40 µM and 50 µM, respectively). b Example of a typical recording (left panel: scale bar 20 µm; right panel: zoom in on dashed box in left panel, scale bar 5 µm). c Sample dependence of the somatic depolarizations on the iontophoretic current (left panel, filled circles: maximum amplitude, black below dendritic spike threshold and yellow above, empty circles: slow component amplitude). Right panels: corresponding sample traces. Upper right panel: scale bars 2 mV and 20 ms. Lower right panel: dV/dt, scale bars 5 mV/ms and 2 ms. In dV/dt the first two deflections represent the stimulus artifact. d NMDAR blockade (D-APV, 50 µM) increased the threshold stimulus (left panel, smallest iontophoretic current eliciting a dendritic spike, 0.31 ± 0.03 µA vs. 0.45 ± 0.05 µA, n = 16, p = 0.000077) and reduced the slow component (middle panel, 14.36 ± 1.23 mV vs. 9.42 ± 0.90 mV, n = 16, p = 0.00000022). Right top panel: sample traces recorded with the baseline threshold stimulus. Right bottom panel: sample traces recorded with the threshold stimulus in D-APV (baseline: black traces; D-APV: red traces; scale bars 2 mV and 10 ms; insets: dV/dt, scale bars 5 mV/ms and 2 ms). e D-serine (10 µM) significantly decreased the threshold stimulus (left panel, 0.40 ± 0.04 µA vs. 0.34 ± 0.04 µA, n = 16, p = 0.00011) and increased the slow component (middle panel, 13.77 ± 1.73 mV vs. 16.87 ± 2.05 mV, n = 14, p = 0.00024). Right panels: sample traces of somatic voltage and dV/dt (insets) as before (upper traces with threshold stimulus during baseline; lower traces with threshold stimulus in D-serine, scale bars for voltage 2 mV and 10 ms and for insets 5 mV/ms and 2 ms). Two-sided paired Student’s t tests throughout. Data are expressed and displayed as mean ± s.e.m. Source data are provided as a Source Data file.