Fig. 4.

Quantal depression is absent when transmitter release is reduced. A, No depression of mEPSCs is seen in 2 mm SrCl₂/0 mmCaCl₂. B, In the same neuron as inA, mEPSCs in 2 mm SrCl₂/3 mm CaCl₂ show depression. C, Mean mEPSC amplitude ± SEM versus time from initial rise of eEPSC from the same cell shown in A and B.Filled triangles, open circles, Mean of 20 mEPSCs in 0 mm or 3 mm Ca²⁺solutions, respectively. Filled circle, Mean of 344 control mEPSCs. D, Cumulative probability distributions of mEPSC amplitudes from the same cell demonstrate that mEPSCs within 100 msec of an eEPSC in normal Ca²⁺ (3 Ca²⁺, poststimulus) are significantly depressed as compared with events after an eEPSC in 0 Ca²⁺ (0 Ca²⁺, poststimulus), or preceding eEPSCs in 0 Ca²⁺ (0 Ca²⁺, prestimulus) or 3 Ca²⁺ (3 Ca²⁺, prestimulus; Komolgorov–Smirnov test, p < 0.0005). Calibration bar in B applies also to A.