CELLS RESEMBLING HAIR-CELLS IN DEVELOPING RAT OLFACTORY AND NASAL RESPIRATORY EPITHELIA

A hitherto ignored microvillous cell type, distinct from microvillous supporting cells and other microvillous cell types, was encountered in olfactory and respiratory epithelia of nasal turbinates of rat fetuse s, near the transition between these two epithelia. The apex of the ce ll resembles the apices of vestibular hair cells. The cell has a cone- shaped bundle of microvilli, resembling the complex bundle of hair-cel l stereocilia, accompanied by a cilium, Therefore we called this cell type the nasal hair cell, Cilium and microvilli seemed adhered. Cell n umbers were very low, up to about 5 per turbinate. The cell's appearan ce is precocious compared to that of olfactory receptor and supporting cells. Also, while the apices of olfactory receptor and supporting ce lls and of ciliated respiratory cells underwent major morphological ma turation during the developmental period from embryonic day 16 to day 21, the apical structures of the nasal hair cell only changed marginal ly from embryonic day 16, when they were first seen, through to at lea st embryonic day 21. The cell's location and precociously mature appea rance suggests that it plays a special role in the development of nasa l epithelia.