Fig. 2. Neuronal loss, neuron size reduction and migration defects in the spiral, vestibular and geniculate ganglia of Brn3a^-/- mice. (A,B) Geniculate ganglion sections from P0 Brn3a^+/+ (A) and Brn3a^-/- (B) mice were stained with Cresyl Violet. Compared with the wild type, fewer neurons are present in the mutant geniculate ganglion and they appear to be reduced in size. (C,D) Inner ear sections from P0 Brn3a^+/+ (C) and Brn3a^-/- (D) neonates were labeled with Cresyl Violet. Spiral ganglion (SG) neurons are clustered in the modiolus of the wild-type cochlea (C), whereas they are widely scattered in the mutant (D). (E) Quantitation of neuron number in developing spiral (SG), vestibular (VG) and geniculate (GG) ganglia of wild-type, Brn3a^-/- and Brn3b^-/- mice. Each histogram represents the mean±s.d. for three to four ganglia. Wild type includes both Brn3a^+/+ and Brn3a^+/- ganglia, which are indistinguishable in neuron number. (F-H) Distributions of cross-sectional areas of neuronal profiles in Cresyl Violet-labeled vestibular ganglion (F), spiral ganglion (G), and geniculate ganglion (H) from P0 wild type and Brn3a^-/- mice. Cross-sectional areas were measured for neuron profiles using NIH Image and the data were plotted using Microsoft Excel. For all three ganglia, the mutant shows a much narrower distribution with the peak substantially shifted to the left compared to the wild type. Scale bar: 25 µm in A,B; 100 µm in C,D.