Scanning electron microscopy of the auditory teeth along the mouse cochlear duct

The auditory teeth in the spiral limbus of the cochlear duct are located under the limbal portion of the tectorial membrane and separated by furrows lodging the interdental cells. In this study, the shape, arrangement and distribution of the auditory teeth in the cochlear duct of adult mice were examined by scanning electron microscopy after removing the tectorial membrane and the interdental cells with chemical maceration methods. The auditory teeth appeared on the top face of the spiral limbus between the edge of the vestibular lip and the Reissner membrane. The teeth on the vestibular lip side possessed elongated upper plates and formed a continuous row resembling the keyboard of a piano; the teeth were separated by radially oriented parallel slits. The elongated teeth decreased in length from the base to the apex of the cochlear duct. The teeth on the Reissner membrane side showed star-shaped upper plates separated by slits and gaps. The population density of the star-shaped teeth decreased from the base to the apex, widening the gaps to hold the interdental cells. The upper plates of the teeth occupied about 75% of an extent of the tooth zone in the hook and first basal half turn, and about 55% in the apical turn. The regional differences of the auditory teeth are considered to be closely related to local functions of the tectorial membrane and the interdental cells.