Neuroepithelial Bodies in Vertebrate Lungs

Abstract

The pulmonary epithelial lining of humans and of all vertebrate species studied so far has been shown to harbor a system of neuroendocrine cells, composed of solitary cells and innervated organoid cell groups called neuroepithelial bodies (NEBs). The system was first described more than 45 years ago, but data were limited for many years because NEBs are low in number and diffusely localized, and because of the lack of reliable methods to visualize them. This contribution provides an overview of the current state of knowledge of the microscopic morphology of pulmonary NEBs. Some of the most important techniques on hand to study the system, e.g., silver staining, formaldehyde-induced fluorescence, immunocytochemistry, electron microscopy and confocal laser scanning microscopy, will be touched upon briefly. Extensive comparative studies revealed the presence of a wide range of bioactive substances in pulmonary NEBs of all vertebrate classes, suggesting an essential role in the respiratory system. Structurally, NEBs are conceived as receptor-effector units and resemble known chemoreceptors in other organs. Many hypotheses have been proposed about their function, but so far, the exact role played by the NEBs in any given physiological process remains to be elucidated. Experimental data suggest that the complex innervation of NEBs, which has given rise to conflicting interpretations in the literature, may play an important role in their reaction to stimuli. It may be concluded that, even making use of the great possibilities provided by modern histological techniques, the investigation of pulmonary NEBs cells remains a challenge.