Fig. 6. Axon misrouting in the Brn3a^-/- vestibular system. Inner ear sections from E16.5 (A-E) and E18.5 (F) Brn3a^+/+ (A) and Brn3a^-/- (B-F) embryos were immunostained with anti-NF 150 (A-C) and anti-p75^NTR (D,E) antibodies with counterstaining by Hematoxylin, or labeled by silver impregnation (F). Although in the wild type (A), vestibular ganglion (VG)-derived nerve fibers immunoreactive for NF 150 or p75^NTR invariantly follow pathways leading to innervation of only sensory epithelia of the saccule (Sac), utricule (Utr) and crista (Cri), they often form aberrant branches in the mutant that project into the outside of the inner ear (B-D), or into the cochlea (Co) (E). Tracing nerve fiber trajectories by silver impregnation reveals similar anomalous fiber branches that penetrate the temporal bone and project away from the inner ear (F). Arrows indicate abnormal nerve fiber branches. Scale bar: 50 µm in C,F; 100 µm in A,B,D,E.