Individual mEPSC bursts in high K_o. (A) Individual mEPSC bursts (dotted boxes) were identified as explained in Materials and methods in recordings obtained in 1.5 Ca_o/20 K_o (upper trace) and in 3 Ca_o/20 K_o (lower trace). (B) Comparison of burst frequency (number of bursts per minute: upper panels) and burst occurrence (the percentage of recording time when a burst was observed: lower panel) in 2.5 K_o and in 20 K_o solutions (left: 1.5 Ca_o; right: 3 Ca_o). Dashed lines link results of individual experiments together. (C) A plot of the number of mEPSCs inside a burst as a function of burst duration (blue: 1.5 Ca_o/20 K_o; brown: 3 Ca_o/20 K_o) reveals a linear relationship. The slope of the regression line corresponds to an intraburst mEPSC frequency of 28.6 Hz. It intersects the ordinate axis at an initial value of 4.6 events. The relation shown is for all blue and brown points; separate regression lines for blue and brown points were almost identical to the line shown. (D) Comparison of mEPSC IEIs for the first four events in a burst (purple), for the entire burst (blue), and for the last four events in a burst (green). Mean values between the three groups are significantly different, showing a gradual frequency adaptation during a burst. P values represent the results of Wilcoxon signed-rank tests in B, and of paired t tests in D. Number of independent experiments: n = 8 cells from 6 animals in B, left; n = 6 cells from 5 animals in B, right; n = 14 bursts from 7 cells taken from 6 animals in D.