Fig. 6: Spontaneous activity in postsynaptic afferent terminals.
From: In vivo spontaneous Ca2+ activity in the pre-hearing mammalian cochlea
a Average intensity projection displaying GCaMP6 expression in vivo from a P4 mouse (top: Snap25-GCaMP6s) and segmentation mask highlighting ROIs (bottom) for identified SGN terminals colour-matched to their associated IHC. Fluorescence signals from individual ROIs in (a) shown as average traces per IHC (b) and individually (c: rasterplot, 38 SGN terminals). Colour labels on the right of the rasterplot indicate the SGN terminals belonging to the colour-matched IHC in (a) and (b). d Average Ca2+ transient frequency in SGN terminals per IHC as a function of age (IHCs from left to right: 97, 63, 76, 149, 67, 105, 20 mice, P4-P9). e Frequency of spontaneous Ca2+ transients in SGNs from wild-type (WT, grey), heterozygous (HET, blue) and knockout (KO, magenta) P7-P8 otoferlin (Otof) mice transduced in vivo with AAV-syn-jGCaMP8f. The frequency of Ca2+ transients is about 1/10th of that measured in mice that constitutively express GCaMP6 (a), which is due to the lower expression of GCaMP, reducing signal-to-noise and hampering the detection of smaller events. Calcium signals were present in SGN terminals from 57 wild-type IHCs (out of 125, 5 mice), 91 heterozygous IHCs (out of 203, 5 mice), but only in 9 Otof-/- IHCs (out of 214, 6 mice). f Calcium activity of individual ROIs placed on 105 SGN terminals recorded ex vivo (P8 GCaMP6ffl/flNeuroD-Cre+/-). g Distribution of the full duration at half maximum of Ca2+ transients from P7-P9 SGN terminals recorded in vivo (blue, 1652 terminals, 11 mice) and ex vivo (green, 283 terminals, 11 mice). Correlation matrices computed from the in vivo (h) and ex vivo (i) recordings in panels (c) and (f), respectively. Each matrix element represents the Pearson correlation coefficient of one pair of SGN terminals. j Average correlation coefficient among SGN terminal Ca2+ signals recorded in vivo (34 recordings, 10 mice) and ex vivo (20 recordings, 11 mice) from P7-P9 mice expressing GCaMP. Average data: mean ± SD (median: red lines). Statistics: Kruskal-Wallis with Dunn’s post-test (e); two-sided Mann-Whitney U-test (j).
