Neither endocochlear potential nor Tegmentum vasculosum are affected in hearing impaired Belgian Waterslager canaries

We previously showed that the Belgian Waterslager canary strain is affected by a hereditary hearing loss that is associated with a reduced number of h air cells and hair cell pathologies in the basilar papilla. Since hair cell pathologies were also present in the sacculus, Weisleder et al. (1994) sug gested that these birds are afflicted by Scheibe's like dysplasia, a cochle o-saccular defect, in mammals, cochleo-saccular defects are characterized p rimarily by the lack of an endocochlear potential and abnormalities in the Stria vascularis which only secondarily lead to hair cell loss (Steel and B eck, 1983; Steel, 1994; 1995). Here we report the endocochlear potential of six ears from three non-Belgian Waterslager canaries and three ears of two Belgian Waterslager canaries to decide if Waterslager canaries are affecte d by a cochleo-saccular or by a neuroepithelial defect. The mean endocochle ar potential was 17.6 +/- 2.5 mV in the non-Waterslager canaries and 20.3 /- 0.6 mV in Waterslager canaries. In addition, and consistent with the pre sence of a normal endocochlear potential, light microscopy of the tegmentum vasculosum provided no evidence for pathology. These data show that Belgia n Waterslager canaries are affected by a neuroepithelial rather than a coch leo-saccular inner ear defect. (C) 2000 Elsevier Science B.V. All rights re served.