Distribution of different collagen types in the rat's tympanic membrane and its suspending structures

Background: The objective of the study was to investigate the histological distribution of collagens in the healthy rat's tympanic membrane. Methods: Immunohistochemical analysis of collagen type I, II, III, and IV in the tympanic membranes in healthy adult female Sprague-Dawley rats. The staining was semiquantified using light microscopy in a blinded fashion, not knowing what type of collagen the slide had been stained for. Results: The pars tensa of the tympanic membrane was mainly stained for collagen type II and IV. The fibrous annulus could on immunohistochemistry be subdivided into an inner and an outer portion. The inner portion of the fibrous annulus was mainly stained for collagen type It, whereas the outer portion was most strongly stained for collagen type III and collagen type IV. The test-retest reliability of the semiquantative method was 81%. Conclusion: Collagen type II and IV are the major collagen constituents of the pars tensa of the tympanic membrane. The outer portion of the fibrous annulus has collagen type III and IV as its major constituents, whereas the inner portion is made up of collagen type II.