Withdrawal of d,l-APV significantly increased the frequency of mEPSC responses. A, Left, Ten representative consecutive traces recorded from a neuron after 15 min of incubation in aCSF in the presence of d,l-APV. A, Right, Ten similar traces after incubation in aCSF in the absence of d,l-APV. B, Withdrawal ofd,l-APV significantly increased the frequency of mEPSC responses (filled bars) compared with control (open bars). TTX and 0 mmCa²⁺ blocked this increase. C, Withdrawal of d,l-APV had a negligible effect on the peak amplitude (left) and the rise time and decay time (right) of EPSC responses. D, The probability of mEPSC responses over a wide range of peak amplitudes. In all, 50 consecutive sweeps were selected from each recorded neuron and pooled to calculate the probability for mEPSC responses occurring at each 1 pA interval of peak amplitude. **p < 0.01.