Figure 6.

Activity-dependent recovery and desensitization both influence EPSC amplitude during ongoing activity. A, C, Representative experiments, showing the effect of the skipped stimulus in control conditions (left) and after 5 min treatment with either 100 μm EGTA-AM (right in A) or during application of 50 μm CTZ (right in C). Long trains of stimuli were applied (top traces, 50 Hz Poisson-distributed), but only EPSCs near the skipped stimulus are shown. Changes in EPSC amplitude following the skipped stimulus are smaller after EGTA-AM or CTZ treatment. B, D, Effects of EGTA-AM treatment (12 cells, B) and CTZ (6 cells, D). Closed symbols represent individual experiments. Open symbols represent overall averages. D, Blue symbols represent experiments where the preceding pause was relatively long (up to 80 ms). Red symbols had short pauses. Points falling below the dashed unity line indicate smaller effects of the skipped stimulus after treatment in individual experiments. EPSC changes in control are significantly greater than those after EGTA-AM or CTZ treatment (p < 0.05 for both). E, Desensitization is greatest after a period of recovery. Plotted is the desensitization index desens = (EPSC_ctrl^skip/EPSC_ctrl)/(EPSC_CTZ^skip/EPSC_CTZ) as a function of the preceding stimulus interval. The line shows the fit to the data, which are significantly correlated (r = 0.65, slope = 13.4, p < 0.05).