Ultrastructure and innervation of neuroepithelial bodies in the lungs of newborn cats

Abstract

Neuroepithelial bodies (NEB) occur throughout the airway mucosa and alveolar parenchyma of kitten lungs. In the bronchi, they are often situated on top of a cartilage plate. They form compact corpuscles containing 10-20 corpuscular cells and appear covered with a layer of flattened Clara cells. Kitten NEB are occasionally observed to display mitosis of the corpuscular epithelial cells. A prominent blood capillary lies at their basal pole. The corpuscular cells contain numerous dense core vesicles (DCV), whose number and diameter remain unchanged with age. Kitten NEB are innervated by nerve fibres that "loop" through the corpuscle and form morphologically afferent as well as efferent nerve endings. The nerve endings display afferent synaptic junctions with the corpuscular cells and sometimes run in clusters, so that they contact each other. Many nerve endings undergo spontaneous degeneration. We conclude that kitten NEB are well adapted to function as chemoreceptors and as endocrine or paracrine organs. Their chemoreceptor activity could be modulated by axon reflexes since their afferent nerve endings are often continuous with the efferent ones, as well as by interneural modulation since nerve endings often form clusters. In addition, kitten NEB innervation appears to involute rapidly soon after birth. This may indicate that their chemoreceptor function is only of primary importance during gestation and at birth. However, the secretory function of kitten NEB, as evidenced by the unchanged numbers and dimensions of their DCV, seems to remain steady throughout life.