Figure 1. Strong increase in quantal content but little change in paired-pulse ratio during presynaptic compensation. A, Example traces of mEPSCs recorded by TEVC in controls (black) and GluRIIB animals (gray). Asterisks above the current trace indicate detected mEPSCs. Calibration: 100 ms, 2 nA. B, Mean mEPSC amplitude in controls (black) and GluRIIB (gray; the number of experiments, n, is indicated throughout). C, Representative traces of EPSCs evoked by stimulating the motor nerve (eEPSCs). Stimulation artifacts are blanked for clarity. Calibration: 10 ms, 20 nA. D, Mean amplitudes, rise time (10–90%), decay time constants, and quantal content of eEPSCs in controls (black) and GluRIIB animals (gray). E, Representative traces of eEPSCs of conA-treated (10 μm) controls (black) and conA-treated GluRIIB animals (gray). Calibration: 10 ms, 20 nA. F, Mean mEPSC amplitude, eEPSC amplitude, and quantal content in conA-treated GluRIIB animals (gray) and conA-treated controls (black). G, PPR versus interstimulus interval at three different extracellular Ca2+ concentrations (as indicated) for control (black) and GluRIIB animals (gray) superimposed with corresponding exponential fits (left, n = 5 and 4; middle, n = 6 and 8; right, n = 6 and 6, respectively). Insets (top), Example traces of a 30 ms interstimulus interval for control (black) and GluRIIB animals (gray). Calibration: 5, 20, and 60 nA from left to right and 20 ms. Inset (bottom), Illustration of the method for determining the amplitude (vertical gray lines) of the first and second EPSC for short interstimulus intervals (10 ms interstimulus); dashed horizontal line, baseline; solid gray line, exponential decay of the first EPSC; white line, fit to the measured EPSCs (see Eqs. 1, 2).