Summary of NMDA EPSP depressions during unblocking of NMDA receptors. (A1) Schematic representation of the experiment described in Fig. 1. (A2) Schematic representation of the experiment described in Fig. 2. Pathways are defined as "treated" or "naive" depending on whether stimulation was "on" (solid) or "off" (dashed) during session N1. Each number (1–10) in A1 and A2 represents a portion where measurements were taken for analysis. (B) Comparison between NMDA EPSP measurements, each bar representing an average obtained for 30 consecutive responses (5 min). Value no. 1 was chosen as 100 % for experiments depicted in A1. Since a corresponding value was lacking for experiments depicted in A2, value no. 9 was chosen as 100 %. All values are expressed as mean and S.E.M (n = 8 and n = 5, respectively, for A1 and A2 type experiments). (C) Relation between instantaneous depression in session N1 (abscissa, final value relative to peak) and persistent depression in session N2 (ordinate, interpathway comparison of peaks). Each dot represents a single experiment. The analysis revealed a significant correlation between the variables as illustrated by the superimposed regression line (n = 8). (D) Relation between early and late measurements obtained with two different time windows (initial 5 ms and 35–45 ms, respectively) plotted as a "phase trajectory" (abscissa, early measure; ordinate, late measure). The curve represents an average of 20 experiments with additional smoothing to reduce noise (5 min moving average). Samples of recorded NMDA EPSPs corresponding to locations a, b of the trajectory are overlaid. Bars above EPSPs curves indicate time windows used for early and late measurements, respectively. The curve at b is shown superimposed on a dotted copy of the curve at a.