Ultrastructure and immunohistochemical identification of the extracellularmatrix of the chinchilla cochlea

The molecular composition and three-dimensional organization of the extrace llular matrix (ECM) was studied by immunofluorescent microscopy, transmissi on and scanning electron microscopy in three connective tissue structures o f the cochlea: the spiral limbus, basilar membrane and spiral ligament. Typ e II collagen, fibronectin, tenascin, chondroitin sulfate proteoglycans, al pha(v) and beta(1) integrins were immunolocalized in the ECM of these conne ctive tissue structures. Electron micrographs showed a continuum of cross-s triated collagen fibrils having a similar diameter and axial periodicity th at spread from the spiral limbus via the basilar membrane and into the spir al ligament. Some of collagen fibrils were aggregated laterally into bundle s. Bundle images, and their digital Fourier transformations, showed a major 67-nm axial D-repeat characteristic for collagen fibrils. Transmission ele ctron microscopy showed numerous proteoglycans associated with the collagen fibrils. The spiral limbus, basilar membrane and spiral ligament demonstra ted regional differences in molecular composition and structural organizati on of their ECM. The glycoproteins fibronectin, tenascin and alpha(v) integ rin were immunolocalized mainly in the basilar membrane. Collagen fibrils o f the spiral limbus and spiral ligament did not appear to be strongly orien ted. However, most of the collagen fibrils in the basilar membrane were arr anged into radially directed bundles. Collagen fibrils in the basilar membr ane were also surrounded by a homogeneous matrix, which was immunoreactive to fibronectin and tenascin antibodies. A more complete understanding of th e composition and structural organization of the ECM in these connective ti ssue structures in the cochlea provides a foundation upon which micromechan ical models of cochlear function can be constructed. (C) 1999 Elsevier Scie nce B.V. All rights reserved.