LI Deaf White Mink: Electron Microscopic Study of the Inner Ear

Publisher Website
Google Scholar
Abstract
At every stage of develop -ment Hedlund white mink appear to be deaf. Mink normally are born with a fetal-type inner ear which slowly matures during the first weeks of life. Autidory startle responses begin about 14 days after birth in normal mink. Saunders previously described the light microscopic appearance of the adult white mink cochlea with collapse of scala media, degeneration of the organ of Corti, curled tectorial membrane, and changes in the stria vascularis. The saccule was collapsed with a degenerated sensory epithelium in adults which means that Hedlund mink are another example of cochleosaccular degeneration and may be added to the many other known examples among deaf animals as well as humans. Deafness in Hedlung mink is probably not primarily due to effective development of the organ of Corti, its innervation or vascular supply. Although hearing loss was evident at 2 weeks by comparison with normals, the cochlear hair cells and their nerve endings were normal in appearance by electron microscopy. The spiral vessel beneath the organ of Corti was widely patent at the stage. Hair cells are present in adults. Those of the basal turn are swollen, and lack hairs or nerve endings. Apical turn hair cells are better preserved. In each hair cell a number of Freidmann-type cross-striated bodies were found. The tectorial membrane lies curled within the inner sulcus. It was squeezed on its outer edge by the dropping of Reissner''s membrane and forced into the inner sulcus. Electron microscopy revealed absence of mitochondria in the marginal cells of the stria vascularis at 2 weeks after birth. Because of the vital role played in all cells normally by mitochondria, their lack may explain why endolymph is lacking. Reissner''s membrane drops, and scala media collapse. Absence of mitochondria in marginal cells of the stria was the earliest cytological abnormality in Hedlund mink. The stria becomes more degenerated as maturation progress. Some day the most important factor causing deafness in Hedlund mink may be inability of the stria vascularis to produce endolymph. Hedlund white mink are different from Shaker-1 mice with respect to the development of their cochleosaccular degeneration and deafness. Shaker mice have a fairly normal stria vascularis with normal filling of scala media but show early electron microscopic abnormalities of the organ of Corti. Hedlund white mink have early changes of the stria that progress to severe degeneration. Abnormalities of the organ of Corti do not appear until later. The electron microscope showed that these 2 kinds of animals follow different pathways to develop a similar final degeneration of the inner ear.