Figure 3.
Ribbon synapse exocytosis evoked spikes with variable latency. A, Histogram of EPSP maximum slopes for IHC-evoked spikes (mean, 148 ± 75 mV/ms; n = 333). Successful EPSPs are color coded from slowest (blue) to fastest (red). Four slow EPSPs failed to evoke a spike (black). B, Histogram of spike onset latencies measured from EPSP onset (mean, 0.59 ± 0.3 ms; n = 333). C, Scatter plot of spike onset latency versus EPSP maximum slope for IHC-evoked spikes (crosses), color-coded as in A. The larger crosses correspond to the short-latency (red) and long-latency (blue) IHC-evoked spikes in D. The large circles are the CC-evoked spikes in D. D, Comparison of IHC-evoked spikes (solid lines) and CC-evoked spikes (dashed lines). Left, Similar IHC-evoked and CC-evoked spikes with long latencies (1.09 and 1.16 ms) and small EPSP maximum slopes (34 and 46 mV/ms). Right, Similar IHC-evoked and CC-evoked spikes with short latencies (0.36 and 0.34 ms) and large EPSP maximum slopes (230 and 228 mV/ms). Short-latency IHC-evoked spikes were smaller in height and thinner at the peak when overshooting 0 mV, consistent with the presence of greater synaptic conductance compared with long-latency IHC-evoked spikes. Bottom, The stimuli for CC-evoked spikes. E, Membrane potential slope versus membrane potential for IHC-evoked spikes (n = 161). The asterisks mark the onset of the spike segments for one fast and one slow EPSP. Each trace is color-coded according to its EPSP maximum slope (as in A and C). The bold traces correspond to the IHC-evoked spikes (solid) and CC-evoked spikes (dashed) in D. Smaller EPSP maximum slopes were associated with larger spike slopes and vice versa. Data are from one SGN aged P19.