Changes in cytochemistry of sensory and nonsensory cells in gentamicin-treated cochleas.

Effects of a single local dose of gentamicin upon sensory and nonsensory cells throughout the cochlea were assessed by changes in immunostaining patterns for a broad array of functionally important proteins. Cytochemical changes in hair cells, spiral ganglion cells, and cells of the stria vascularis, spiral ligament, and spiral limbus were found beginning 4 days post administration. The extent of changes in immunostaining varied with survival time and with cell type and was not always commensurate with the degree to which individual cell types accumulated gentamicin. Outer hair cells, types I and II fibrocytes of the spiral ligament, and fibrocytes in the spiral limbus showed marked decreases in immunostaining for a number of constituents. In contrast, inner hair cells, type III fibrocytes and root cells of the spiral ligament, cells of the stria vascularis, and interdental cells in the spiral limbus showed less dramatic decreases, and in some cases they showed increases in immunostaining. Results indicate that, in addition to damaging sensory cells, local application of gentamicin results in widespread and disparate disruptions of a variety of cochlear cell types. Only in the case of ganglion cells was it apparent that the changes in nonsensory cells were secondary to loss or damage of hair cells. These results indicate that malfunction of the ear following gentamicin treatment is widespread and far more complex than simple loss of sensory elements. The results have implications for efforts directed toward detecting, preventing, and treating toxic effects of aminoglycosides upon the inner ear.

[Marginal cells of the stria vascularis in vitro]. / Marginalzellen der Stria vascularis in vitro.

Explants of stria vascularis and spiral ligament of the guinea pig cochlea were cultivated and after 2 days fibroblast-like cells were found growing around the explant. Marginal cells advanced at 15 microns/day to the border of the explant, and after 2 weeks they proliferated on top of a thin layer of fibroblast-like cells outside the explant, replacing several layers of fibroblast-like cells. Tight junctions and interdigitations of the lateral membranes were found between all neighbouring marginal cells. Their apical surface was covered by microvillus-like membrane extensions. The basal membrane of the new marginal cells did not interdigitate with the underlying membranes of fibroblast-like cells; there was always a gap between the two cell types. The results demonstrate that marginal cells of the stria vascularis are capable of repairing damage to the epithelium, such as may be caused by endolymphatic hydrops, even if the luminal side contains perilymph-like fluid. Furthermore, the cell culture allows living, clearly identified marginal cells to be studied in vivo.

Microanatomy of the mouse osseous cochlea: a scanning electron microscopic study.

This is the first scanning electron microscopic demonstration of the three-dimensional architecture and detailed surface structures of the entire osseous labyrinth of the cochlea. Mouse cochleae were observed after dissolving the soft tissues with KOH and NaOCl solutions. The precise shapes, surface structures, and orientations of the primary osseous spiral lamina and secondary osseous spiral lamina in the cochlea were observed along their entire course from the hook at the base to the helicotrema at the apex. The primary osseous spiral lamina showed three half turns after the hook; the lengths of the hook and each half turn and the slope angle of the spiral were obtained. The widths of the primary and secondary spiral laminae and the spiral fissure for the basilar membrane between the free edges of the two spiral laminae were measured along the course of the cochlear duct. The surface of the lateral wall under the stria vascularis was also viewed. Scanning electron microscopy can provide more precise microanatomical data than has been previously available for the osseous cochlea, giving a better understanding of hearing mechanisms with regard to the width, support, and movement of the basilar membrane and the functions of various components of the cochlea.