Subepithelial fiber components of the round window membrane of the guinea pig: an ultrastructural and immunohistochemical study.

Subepithelial fiber components of the round window membrane (RWM) of the guinea pig were studied by the following methods: transmission electron microscopy (TEM), scanning electron microscopy (SEM) with NaOH treatment, high-voltage electron microscopy (HVEM) and immunohistochemical staining. SEM observation revealed intersecting collagen fibers and a vascular network in the middle layer. TEM observation showed that at the attachment region to the bone fibroblasts, collagen fibers and elastic fibers were intermingled with each other, and mesenchymal cells (bone-lining cells) were scattered on the surface of the bone. The cytoplasmic processes of fibroblasts and bone-lining cells were connected by interdigitations. HVEM demonstrated that collagen fibers of the RWM were directly linked to the fibers of the bone matrix. Immunohistochemically, the middle layer was positive for antibody to type I collagen. Immunoreaction for fibronectin was also positive at the middle layer and most intense in the region attached to the bone. Thus, the RWM is securely attached to the bone by type I collagen fibers together with the bone-lining cells and fibroblasts.