mEPSC amplitude occlusion in CTZ. (A) Example of a burst recorded in 3 Ca_o/20 K_o in the presence of CTZ (100 μM). (B) Superimposed average recordings of mEPSCs under control condition (purple; time constant of decay 0.6 ms) and after addition of CTZ (gray) showing slower, biphasic decay in CTZ (fast component time constant 1.9 ms; slow component time constant 8.0 ms; % slow component 53%). (C) Upper: Amplitude occlusion analysis (A as a function of IEI, see insert) for a burst in CTZ, showing a drop of peak amplitudes at short IEIs. An exponential fit to the data describes the recovery kinetics of mEPSC amplitudes. Extrapolation of this exponential to an interval duration of 0 provides an estimate of 75% receptor occupancy at mEPSC peak, while the time constant of recovery is 8.5 ms. Lower: Fits of normalized A(IEI) plots as in the upper plot for seven bursts (gray), with average in black. (D) Similarity between the kinetics of receptor deactivation (given by the time constant of the second component of mEPSC decay; n = 13 mEPSCs from 5 recordings) and those of amplitude occlusion recovery (n = 7 bursts from 6 recordings) indicates that mEPSC occlusion is driven by receptor deactivation.