Abstract
The Eustachian tube is a small canal that connects the tympanic cavity with the nasal part of the pharynx. The epithelial lining of the Eustachian tube contains a ciliated columnar epithelium at the tympanic cavity and a pseudostratified, ciliated columnar epithelium with goblet cells near the pharynx. The tube serves to equalize air pressure across the eardrum and drains mucus away from the middle ear into the nasopharynx. Blockage of the Eustachian tube is the most common cause of all forms of otitis media, which is common in children. In the present study, we examined the epithelial lining of the Eustachian tube in neonatal and adult gerbils, with a focus on the morphological and functional development of ciliated cells in the mucosa. The length of the tube is ∼8.8 mm in adult gerbils. Scanning electron microscopy showed that the mucosal member near the pharyngeal side contains a higher density of ciliated cells and goblet cells than that near the tympanic side. The cilia beat frequency is 11 Hz. During development, the length of the Eustachian tube increased significantly between postnatal day 1 (P1) and P18. Scanning electron microscopy showed that the mucosa contained a high density of ciliated cells with a few goblet cells at P1. The density of ciliated cells decreased while the density of goblet cells increased during development. At P18, the mucosa appeared to be adult-like. Interestingly, the ciliary beat frequency measured from ciliated cells at P1 was not statistically different from that measured from adult animals. Our study suggests that the Eustachian tube undergoes significant anatomical and histological changes between P1 and P18. The tube is morphologically and functionally mature at P18, when the auditory function (sensitivity and frequency selectivity) is mature in this species.
Highlights
The Eustachian tube (ET) is a small canal that connects the tympanic cavity with the nasal part of the pharynx
We examined the histological architecture of the mucosal epithelium of the ET in the osseous portion near the tympanic opening and the cartilage portion near the pharyngeal opening from three animals using light microscopy
Previous studies using developing gerbils showed that cochlear microphonic responses were first recorded at P12, with thresholds exceeding 100 dB SPL, suggesting that the onset of hearing occurs around P12 [9]
Summary
The Eustachian tube (ET) is a small canal that connects the tympanic cavity with the nasal part of the pharynx. The ET acts as a passageway to ventilate the tympanic cavity and allows equalization of pressure between the middle ear and pharynx, which is necessary for normal hearing [1]. It drains mucus away from the middle ear into the nasopharynx. Our goal was to examine the epithelial lining of the ET in neonatal and adult gerbils, with a focus on the morphological and functional development of ciliated cells in the mucosa. Our study showed how the ET and its mucosa develop, and provides a morphological and functional basis for future animal studies concerning the pathogenesis of otitis media in earlier stages using the murine model
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