A SCANNING AND TRANSMISSION ELECTRON-MICROSCOPIC STUDY OF THE DEVELOPMENT OF THE SURFACE-STRUCTURE OF NEUROEPITHELIAL BODIES IN THE MOUSE LUNG

Neuroepithelial bodies (NEBs) are groups of neuroepithelial (NE) cells that are localized on mounds on the bronchiolar epithelium of the lun g. The present study examined NEBs in mice ranging in age From 2 days before birth to 80 days after birth. The position and surface architec ture of NEBs was examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In foetal mice, 2 days before birth, NEBs were distinguished from the rest of the bronchiolar epith elium by a slight elevation of non-ciliated Clara-like cells arranged in a cobblestone-like pattern. The exposed surface of the NEB was iden tified by small protrusions with regular microvilli intermittently loc ated at the base of deep clefts between the Clara-like cells. The surf ace of the the Clara-like cells had fewer and smaller microvilli and c ould be easily distinguished from the apical surface of the NEB. Befor e birth, the surface of all of the apical cells was covered by regular ly placed microvilli, however after birth some of the more prominently positional apical cells revealed a bare patch at the centre of the po rtion of apical cell exposed to the lumen of the lung. As the mice age d there was an increase in the number of apical cell protrusions obser ved with centrally positioned bare patches. These two morphologically distinct surfaces of apical cells may have separate specialized functi ons. The exposed surfaces of apical cells were often observed in pairs and this feature has been observed in various sensory organs providin g support for chemoreceptive function. However small bright spheres re sembling vesicles were frequently observed on the lumenal surface of a pical cells of the centrally placed bare patch. Transmission electron microscopy confirmed the presence of vesicles on the surface of apical cells and due to their location these vesicles were thought to contai n a substance secreted into the lumen of the lung by apical cells. The significance of the bare region on the apical cells is not clear in t erms of the proposed chemoreceptive function usually attributed to NEB s. It may be possible that the morphological changes observed in apica l cells after birth are more appropriate for secretion of a substance into the lumen of the lung than for chemoreception. This is supported by the observation in the present study of vesicles lying on the lumen al surface of the bare region of the apical cell, however the mechanis m for secretion of whole vesicles is not clear and requires further in vestigation.