Development of neuroepithelial bodies in pre- and postnatal mouse lungs: scanning electron microscopic study.

The development of pulmonary neuroepithelial bodies (NEBs) in pre- and postnatal mice were studied with scanning electron microscope. In the fetuses, at 17 days' gestation, the NEBs were recognized as slight epithelial elevations covered by developing Clara cells. At 18 days, the small apical surfaces of the specialized cells began to be exposed to the bronchiolar lumen. At 19 days (full term), numerous microvilli-covered surfaces of the specialized cells were located between the dome-shaped Clara cells. At this stage, the boundary of the NEBs was well outlined by the developing ciliated cells. In the postnatal animals, the surface structure of the specialized cells remained the same as that of the 19-day fetuses, but the modified Clara cells gradually became wide and flat. In older mice, some NEBs formed obvious spherical mounds projecting into the bronchiolar lumen. The rapid differentiation of the microvillar projections on the surfaces of the specialized cells shortly before birth should provide the animals ample surface area to make contact with the airway contents.