Evaluation of inner ear histology and auditory brainstem response in Wriggle Mouse Sagami

Wriggle Mouse Sagami (WMS) is a spontaneous mutant strain with neuroepithelial defects. These animals are characterized by abnormal movements linked to an autosomal recessive gene. To determine the association between inner ear histology and hearing ability, we assayed these characteristics in mice homozygous and heterozygous for the mutation, as well as in wild-type animals. In homozygotes, the cochlea and saccule degenerated 3 months after birth. Beginning at 3 months of age, and progressing in an age-dependent manner, the organ of Corti disappeared and the number of spiral ganglion cells decreased, starting at the basal turn and moving toward the apical turn. The sensory epithelium became atrophic in the saccule. Three-month-old heterozygotes demonstrated degeneration in the cochlea, not in the saccule. No obvious auditory brainstem evoked response (ABR) was observed at any frequency in homozygotes aged 1 month and older. In contrast, the heterozygotes retained some hearing acuity until the age of 1 month, after which they became deaf. These findings suggest that WMS mice may provide a good model that will be useful in identifying deafness genes in humans.