Primary neural disorders in the deaf white cat cochlea.

Eleven white kittens were investigated from 2 days after birth up to an age of 4 months. After their hearing ability or deafness had been tested electrophysiologically, electron microscopic work was done at the level of the cochlea. Previous histological data indicated that the hereditary process of degeneration begins at the epithelial and sensory elements of the cochlea, and that the neural degeneration is only a secondary and very slow process. Results presented here indicate that, at least in some white cats, this assumption needs to be modified. Early failure in the myelination of the lamina spiralis fibres was noticed in most of the white kittens. Furthermore, two kittens (7 and 16 days old) presented a complete degeneration of the spiral ganglion neurons, and signs of anterograde degeneration of their fibres going to the organ of Corti. These primary neural defects indicate that hereditary hearing defects may directly affect both epithelio-sensory and neural structures.