Distribution of mast cells in the tubotympanum of guinea pigs.

The distribution pattern of mast cells in the middle ear mucosa and eustachian tube was examined histologically in adult and developing guinea pigs. The aim was to better understand the role of mast cells in the middle ear defense mechanism. The density of mast cells was highest in the pharyngeal orifice of the eustachian tube, and decreased in the direction of the tympanic orifice. The density was higher in adults than in developing animals. Mast cells were also found in the tubotympanic membrane of the fetal guinea pig. Mast cells in the middle ear mucosa appeared in areas covered by ciliated epithelia or areas richly vascularized. Almost all mast cells found in the middle ear and eustachian tube mucosa were the connective tissue type. The results of this investigation suggest that mast cells distribute in the tubotympanum in response to continuous stimuli to the tubotympanic cavity.