ANATOMICAL BASIS OF A CONGENITAL HEARING IMPAIRMENT - BASILAR PAPILLADYSPLASIA IN THE BELGIAN WATERSLAGER CANARY

Recent investigations into the anatomy of the inner ear of Belgian Wat erslager canaries (BWC) have demonstrated myriad malformations associa ted with dysgenesis of the pars inferior of the otocyst. In those stud ies, the surface anatomy of BWC's basilar papilla and sacculus was exa mined utilizing scanning electron microscopy. In the present investiga tion, we utilized both light microscopy and transmission electron micr oscopy to describe the cross sectional anatomical pathology of the BWC 's basilar papilla. Examination of the BWC's organ of Corti revealed n umerous dysmorphologies: 1) hair cells from the tall hair cell region appeared broad and stunted, with deformed cuticular plates, abnormal s tereocilia, and recognizable microvilli; 2) quantitative analysis of t hese hair cells revealed disproportionately large nuclei and abnormall y short stereocilia; 3) hair cells from the short hair cell region of the papilla were absent, replaced by a population of large cells with electron-lucent cytoplasm; and 4) the tectorial membrane in the BWC pa pilla was narrow, covering only the area where the deformed tall hair cells were found. The malformations appeared to be more severe at the apex and midsection of the basilar papilla than at the base. These obs ervations allow us to suggest a hypothesis to account for the distinct anatomofunctional hearing deficit observed in these birds. In additio n, they further support our hypothesis that the inner ear of BWC is af flicted by a disorder similar to Scheibe's dysplasia, the most common inner ear defect associated with congenital hearing loss in humans. (C ) 1996 Wiley-Liss, Inc.