Middle ear mucosa in rats and humans.

The purposes of the study were to review thoroughly the literature and summarize it in a standardized fashion; to study the mucosa, including the distribution of mast cells, in all parts of the middle ear cavity in rats; and to compare the experimental findings with those known in humans. Adult, healthy rats were studied by light, scanning electron, and transmission electron microscopic techniques. The ciliated and secretory cells of the rat tympanic cavity are confined to two tracts, one anterior and one inferoposterior to the promontory. The tracts connect the epitympanum with the eustachian tube. The pars flaccida exhibits the highest density of mast cells, but mast cells are also distributed in the subepithelial layer of the tracts and in the floor of the tympanic bulla. The structure of the rat mucosa shows striking similarities to that of humans. Thus, from a morphological point of view, the rat seems to be a suitable model for middle ear studies. However, to be able to compare results obtained in different species and/or different laboratories, the areas of the middle ear from which the specimens have been taken must be carefully defined and presented in a standardized manner.