Mouse spiral ganglion neurons display aberrant central projections in the absence of Fzd3. Lipophilic dyes were placed into the base (red) and apex (green) of Fzd3+/− control cochlea (A,C,E) and Fzd3 null mutants (B,D,F) at E18.5. A two dimensional rendering of a stack of images taken through the cochlear nuclei complex (A,B) shows more overlap of base and apex projection in the mutant compared to control. Yellow arrows indicate nerve entry points. (C,D) Single optical sections showing normal divergence to the AVCN and DCN as well as segregation between afferents from the base and apex in controls and a more profound projection to the PVCN of the apex of Fzd3 mutant mice. (E,F) Higher magnification of a single optical section showing fibers running parallel to each other in a single direction in the AVCN in a control. In contrast, there was aberrant trajectory of afferents in the AVCN in Fzd3 mutants and single fibers can be observed projecting across multiple other afferents (D,F). Magenta arrows show the course of a single fiber as it projects. White arrows show fibers projecting in the wrong direction (ventrally) (F). AVCN, anteroventral cochlear nucleus; DCN, dorsal cochlear nucleus; PVCN, posteroventral cochlear nucleus; VAS, ventral acoustic stria; D, dorsal; A, anterior. Orientation for all panels as in (A) Scale bars represent 100 µm. Two control and Four mutant animals were examined.