ULTRASTRUCTURE AND INNERVATION OF NEUROEPITHELIAL BODIES IN THE LUNGSOF NEWBORN CATS

Neuroepithelial bodies (NEB) occur throughout the airway mucosa and al veolar parenchyma of kitten lungs. In the bronchi, they are often situ ated on top of a cartilage plate. They form compact corpuscles contain ing 10-20 corpuscular cells and appear covered with a layer of flatten ed Clara cells. Kitten NEB are occasionally observed to display mitosi s of the corpuscular epithelial cells. A prominent blood capillary lie s at their basal pole. The corpuscular cells contain numerous dense co re 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 th e corpuscular cells and sometimes run in clusters, so that they contac t each other. Many nerve endings undergo spontaneous degeneration. We conclude that kitten NEB are well adapted to function as chemoreceptor s and as endocrine or paracrine organs. Their chemoreceptor activity c ould 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, kitt en NEB innervation appears to involute rapidly soon after birth. This may indicate that their chemoreceptor function is only of primary impo rtance 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.