Postnatal maturation of neuroepithelial bodies and carotid body innervation: A quantitative investigation in the rabbit

The intrapulmonary airways contain oxygen-sensitive chemoreceptors which ma y be analogous to the arterial chemoreceptors: the neuroepithelial bodies ( NEB). While the NEB are prominent in the neonatal lung, physiological studi es indicate that the carotid bodies are still relatively inactive at birth. This points to an unequal degree of development of both during the early n eonatal period. As a reflexogenic chemoreceptor function depends on a well- developed innervation, we undertook a comparative investigation of the deve lopment of the NEB and the carotid body glomus cell innervation. Two morpho logical aspects of the innervation of NEB and carotid body glomus cells wer e quantified in rabbits of different age groups. The total sectional area o f intracorpuscular and intraglomerular nerve endings per NEB or glomus cell group, respectively, was measured and the area percentage of mitochondria and synaptic vesicles was determined. In the NEB, no significant difference in total sectional area of the nerve endings between the age groups was ob served, while in the carotid body there was a significant increase in the a dult age group. In addition, the area percentage of mitochondria and synapt ic vesicles of the nerve endings did not change significantly with age in t he NEB, while in the carotid body these increased and decreased, respective ly, with age. These observations point to a shift from morphologically effe rent nerve endings, rich in synaptic vesicles, to morphologically afferent nerve endings, rich in mitochondria. Our interpretation of these findings i s that, at birth, the NEB innervation is more mature than the carotid body glomus cell innervation and that the latter matures at a later time than th e former. These findings support the theory that the NEB may act as complem entary chemoreceptors to the carotid body during the early postnatal period .