Morphological and cytochemical characterization of neuroepithelial bodies in fetal rabbit lung I. Studies of isolated neuroepithelial bodies

Neuroepithelial bodies (NEB) in 29-day fetal rabbit lung were examined by light microscopy and cytochemistry to demonstrate their structural and biochemical properties in situ. Longitudinal sections of NEB at airway bifurcations demonstrated their chemoreceptor-like appearance. Furthermore, the cytochemical presence of serotonin, acetylcholinesterase, formaldehyde-induced fluorescence, and silver-staining properties demonstrated the neural-like biochemical properties of NEB cells. Forty-one NEB and eight single neuroendocrine cells from whole fetal lungs were examined ultrastructurally. Juxtaluminal junctional complexes composed of tight and intermediate junctions, desmosomes, and cytoplasmic filaments were demonstrated in the corpuscular-shaped NEB. Basal bodies were apparent in NEB cell cytoplasm; cilia extended from NEB cells. Dense-core vesicles (DCV) were of at least three types: type 1, type 2, and enterochromaffin type. The majority of epithelial cells adjacent to NEB in near-term airway epithelium were undifferentiated, with large amounts of glycogen. However, ciliated cells were adjacent to some small NEB and single neuroendocrine cells; mucus or Clara-type cells were not observed. NEB isolated by collagenase treatment revealed an intact organoid structure, DCV, and desmosomes and retained their argyrophilia and formaldehyde-induced fluorescence. NEB were recovered in cell fractions separated by unit gravity that had cells in clumps of four or more. One to five NEB stained with silver in cytocentrifuge preparations of control, mixed cells, whereas up to 20 intact NEB were demonstrated in the clumpcontaining, separated fractions. We propose that isolated NEB retain certain biochemical and metabolic properties similar to those of their counterparts in situ. Serotonin and 5-hydroxyindole acetic acid were found by high-performance liquid chromatography analysis in the fractions containing NEB, and amine precursor uptake and decarboxylation (APUD) activity were demonstrated. Moreover, muscarinic cholinergic receptors were detected, consistent with the occurrence of acetylcholinesterase in NEB. The elution profile of bombesin radioimmunoactivity substantiated that isolated fetal rabbit NEB contained this neuropeptide and that NEB were enriched by unit gravity sedimentation. These studies suggest that NEB are structurally and functionally developed before other cell types in immature airway epithelium and can be isolated as intact organoids, which retain some of their structural and metabolic integrity.