Figure 4. Reduction of evoked neurotransmitter release at the NMJ in Syb1^lew/lew mice.

A, 10 consecutive EPP traces recorded from P14 diaphragm muscles (evoked by 0.2 Hz stimulation of the phrenic nerves) are superimposed. EPPs in the control mice were highly reproducible; the peaks of all 10 EPPs, as indicated by circles located to left of the traces, all fall within a range of 7 mV (between 20 and 27 mV). In contrast, EPPs in Syb1^lew/lew mice were highly variable, fluctuating over a range of 15 mV (between 2 and 17 mV, filled circles). An F test demonstrated that the variances in Syb1^lew/lew mice were significantly (*P < 0.05) increased compared to those of the controls. Similarly, EPP rising phases (arrowhead) and decay phases (arrow) were also highly variable in Syb1^lew/lew mice compared with control mice. B, quantification of EPP amplitudes between control and Syb1^lew/lew mice: EPP amplitudes were significantly reduced in Syb1^lew/lew mice (15.5 ± 1.2 mV), compared with those in the control mice (25.9 ± 1.3 mV). C, the EPP rise-slopes (10–90%) in Syb1^lew/lew mice (10.3 ± 0.8 mV ms⁻¹) were significantly reduced compared to those in the controls (17.3 ± 0.9 mV ms⁻¹). D, quantal contents were significantly reduced in Syb1^lew/lew mice (8.6 ± 0.7) compared to controls (16.1 ± 0.6). Syb1^lew/lew, n = 25 muscle fibres; control, n = 22 muscle fibres. ***P < 0.001, Student's t test.