Quantification of CtBP2-labeled ribbons revealed a number of approximately 14-15 ribbon synapses per IHC in all groups, that remained comparable across all genotypes (Wt n = 12/ N = 9; 1-SKO n = 6/ N = 4; 1/3-DKO n = 8/ N = 6; one-way ANOVA, p = 0.717). 