Figure 2.

Paired-pulse facilitation observed at the MOC–OHC synapse around the onset of hearing is absent in hearing mice. A, Representative traces of 10 individual responses during paired-pulse stimulation protocols at P11–P13 (top) and P20–P22 (bottom). ISIs are 12.5, 25, 50, and 100 ms, corresponding to MOC stimulation frequencies of 80, 40, 20, and 10 Hz, respectively. Individual traces are represented with different colors for clarification purposes. B, Facilitation indexes (FI = X₂/X₁) for the total average response, FI_S, the release probability, FI_P, and the amplitude of successfully evoked postsynaptic responses, FI_A plotted as a function of the ISIs tested. At the onset of hearing (P11–P13, top) at ISIs of 12.5 and 25 ms, FI_S and FI_P were >1, whereas FI_A is close to 1 for all ISIs tested (n = 6-7). Paired t test or Wilcoxon rank sum test: *p < 0.05 and **p < 0.01 for FI_S and FI_P. At P20–P22 (bottom), FI_S, FI_P, and FI_A were not significantly different from 1 within all ISIs tested (n = 5-6). See Table 3 for details.