Figure 4.

Figure 4. Decreased phase locking to mechanical stimuli at hair-cell ribbon synapses in nsfa^I209N/st53 mutants at 60 Hz (A) Schematic of the recording paradigm. Hair cells were mechanically stimulated after establishing a loose-patch recording from the innervating afferent neuron (5 dpf). (B and C) Evoked spike rates and phase locking during a lower-frequency stimulus.

(B) Representative traces from WT (upper) and nsfa^I209N/st53 mutants (middle) during 20-Hz stimulation (bottom). Shown are 60 overlaid sweeps of spiking resulting in 546 spikes in WT and 559 spikes in nsfa^I209N/st53 mutants.

(C) Average spike latency histograms from all spikes during 60 continuous seconds of 20-Hz stimulation. WT latency values (black bars) and nsfa^I209N/st53 mutant values (gray bars) were fit by a Gaussian distribution (black and gray line, mean fraction of 20-Hz period 0.158 ± 0.002 and 0.159 ± 0.003 s, respectively).

(D and E) The timing of evoked spikes is less tightly coupled to a higher-frequency stimulus in the nsfa^I209N/st53 mutant. (D) Representative traces from WT (upper) and nsfa^I209N/st53 mutants (middle) during 60-Hz stimulation (bottom). Shown are 60 overlaid sweeps of spiking resulting in 219 spikes in WT and 217 spikes in nsfa^I209N/st53 mutants. (E) Average latency histograms from all spikes during 60 continuous seconds of 60-Hz stimulation. WT latency values (black bars) and nsfa^I209N/st53 values (gray bars) were fit by a Gaussian distribution (black and gray line, mean fraction of 60-Hz period 0.258 ± 0.003 and 0.298 ± 0.003 s, respectively). The peak of activity in mutant neurons is shifted to a later time point of the 60-Hz cycle (4.28 versus 4.95 ms) in comparison.

(F) Spike rate comparison between WT and nsfa^I209N/st53 mutants at both 20 Hz (WT, 12 ± 3 spikes/s, n = 4; nsfa^I209N/st53, 13 ± 3 spikes/s, n = 4, p = 0.80) and 60 Hz (WT, 19 ± 3 spikes/s, n = 7; nsfa^I209N/st53, 16 ± 1 spikes/s, n = 7, p = 0.32). Center lines represent the mean.

(G) Vector strength (r) of the coupling between stimulus and response (phase locking) between WT and nsfa^I209N/st53 mutants at 20 Hz (WT, r = 0.96 ± 0.02, n = 4;

nsfa^I209N/st53 mutants, r = 0.96 ± 0.02, n = 4) and 60 Hz (from C: WT, r = 0.91 ± 0.01, n = 6; nsfa^I209N/st53 mutants, r = 0.81 ± 0.02, n = 7, p = 0.001). p values are determined by unpaired Student’s two-tailed t test. ns, not significant; *p < 0.05, **p < 0.01, ***p < 0.001.