Postsynaptic failure rate and IPSC amplitude vary among different nRt-VB pairs. (A, i) Recordings from a pair of neurons in which postsynaptic failures occurred. Single nRt APs evoked small amplitude IPSCs but could also result in postsynaptic failures (traces 2 and 5). (ii) Distribution of postsynaptic current (PSC) peak amplitudes (shaded bars) and noise (solid line) for 804 trials. The PSC distribution consists of two peaks; the first overlaps with the noise and indicates failures, and the second peak corresponds to evoked IPSCs. Bin size = 2 pA. (B, i) Recordings from a pair of neurons that lacked unitary IPSC failures in response to single nRt APs. (ii) Amplitude distribution of PSCs (shaded bars) and noise (solid line) for the neuron of B, i. Note the broad distribution and lack of overlap with the noise measurements. Bin size = 2 pA. (C, i) Recordings from a different “nonfailure” pair with a larger amplitude unitary IPSC than in the cell of B, i. Note the different calibration scales for amplitudes in A–C. Bin size = 10 pA. Vertical dashed lines in A, i; B, i; and C, i mark peaks of nRt APs. Numbers above bars in A, ii; B, ii; and C, ii are mean PSC amplitude.