The spiral ganglion and cochlear nuclei of deafness mice.

Deafness mice (dn/dn) never develop hearing, but, except for the associated physical defects, have no other known abnormalities. For this study, cochleas and brains of five adult homozygotes (dn/dn) and five adult heterozygotes (+/dn), matched by weight and sex, were prepared for serial section light microscopy. In the homozygotes, the organ of Corti was totally degenerated basally, gradually improving toward the apex where supporting cells, border cells and pillar cells were present; however, the stria vascularis was dystrophic in the apex. The saccular macula was atrophied or dystrophic in seven of the ten homozygote ears. The homozygotes had only 23% of the number of spiral ganglion cells found in the heterozygotes, but they appeared robust. In six of the ears of each group there was clumping of apical spiral ganglion neurons. In the homozygotes, the volume of Rosenthal's canal was 121%, that of the dorsal nuclei was 90%, and that of the ventral cochlear nuclei was 63% of the comparable volumes in heterozygotes. The globular cells of the homozygote ventral cochlear nucleus were 72% of the size of those of heterozygotes. These quantitative morphological abnormalities of the homozygote spiral ganglion and cochlear nuclei may result from organ of Corti atrophy.