Figure 1. Loss of presynaptic Rac1 after hearing onset does not affect calyx of Held gross morphology or ultrastructure.

(A) Cre recombinase-expressing HdAds were injected into the cochlear nucleus of Rac1^fl/fl mice at P14, yielding Rac1^−/− calyces of Held. All experiments were performed at around four weeks of age. Cre recombinase-expressing calyces could be visually identified by simultaneous expression of EGFP. (B1) Representative reconstruction of calyx terminals of Rac1^+/+ (left) and Rac1^−/− (right) animals. (B2) Calyx morphology assessed by surface area (left) and volume (right) was not affected by the loss of Rac1. (C1) Representative EM images of the active zone (yellow) and docked SV (blue) to assess synaptic ultrastructure. (C2) AZ length and number of docked SV were comparable between Rac1^+/+ and Rac1^−/−. (C3) SV distribution as a function of distance to AZ was not different between Rac1^+/+ and Rac1^−/−. Box plot whiskers extend to the minimum/maximum within the 1.5 interquartile range; open markers indicate individual data points. For EM data, the results of three independent investigators were averaged. All data shown in the figure and the detailed results of statistical tests are part of the supplementary file.