Morphological analysis of the GER in R75W + transgenic mice. (A-D) Hematoxylin and eosin staining of cochlear sections from R75W + and non-transgenic (non-Tg) mice. Apical turns in the cochlear were observed using microscopy. At P8, a fraction of the GER cells showed apoptotic characteristics (e.g., chromatin condensation) in both non-Tg and R75W + mice (A, B, arrows). IHC and OHC were detected in both non-Tg and R75W + mice (A, B). TC was detected in non-Tg (A), but not in R75W + (B). At P12, the GER of non-Tg mice had 5–9 cells per section and no apoptosis (C). In contrast, the GER (dotted line in D) of R75W + mice had 12–24 cells per section and had condensed nuclei indicative of apoptosis (D, arrow). TC is widely opened in non-Tg (C), but is not detected in R75W + (D). (E, F) TEM images at P12 revealed no degenerative changes in non-Tg mice (E), but nuclei with highly condensed chromatin were present in the enlarged GER of R75W + mice (F, arrow). The dotted line for C-E indicates the area of the GER. IHC, inner hair cell; OHC, outer hair cell; TC, tunnel of Corti. Scale bars = 25 μm (A–D) or 10 μm (E, F).