Figure 7.

Tonotopic differences in extent of SGN activation at early developmental time points. A, Image of an excised basal portion of cochlea from a P0 Snap25-T2A-GCaMP6s mouse, which expresses GCaMP6s in SGNs. Dotted line indicates region shown in B. B, For analysis of time-lapse imaging, a grid of square ROIs was placed over SGNs. ROIs were numbered top to bottom, then left to right. All ROIs were analyzed, but only random ROIs were chosen to display in figures (white squares). Imaging was performed at room temperature (∼25°C). C, Individual ROI traces for SGNs (100 randomly selected). Colored boxes are examples of SGN coordinated activity that align with time-color representation in D. Black traces represent ROIs with at least one detected peak (fifth percentile value ± 5 SDs). Gray traces represent ROIs with no detected peaks. D, SGN Ca²⁺ transients colored based on time of occurrence. E, Individual ROI traces and time-color representation of Ca²⁺ transients in E16.5 apical (top) and basal (bottom) regions of the cochlea. Black traces represent ROIs with at least one detected peak (fifth percentile value ± 5 SDs). Gray traces represent ROIs with no detected peaks. F, Similar to E, but in P0 apical (top) and basal (bottom) regions of the cochlea. G, Quantification of active area (percentage of ROIs with at least one detected peak), correlation coefficient (80th percentile), and correlated events per minute in E16.5 and P0 cochleae. n = 17 E16.5 apical portions from 9 mice, n = 34 E16.5 basal portions from 17 mice, n = 16 P0 apical portions from 8 mice, and n = 32 P0 basal portions from 16 mice. ****p < 5e-5; one-way ANOVA with Tukey post hoc. H, Quantification of frequency, amplitude, and duration of Ca²⁺ transients calculated from individual active ROIs. n values are reported in G. ****p < 5e-5; ***p < 5e-4; *p < 0.05; one-way ANOVA with Tukey post hoc. All comparisons not indicated were not statistically significant.