Neuroepithelial bodies and solitary neuroendocrine cells in the lungs of amphibia

Abstract

In the lungs of 12 species of Amphibia investigated so far, solitary neuroendocrine (NE) cells, as well as groups of these cells called "neuroepithelial bodies" (NEB), are observed. They occur in the position strategic to monitoring gas composition, mainly in the ciliated epithelium of the apical part of the septa. A great diversity in the structure of NEB is observed. The NE cells and NEB in Amphibia are predominantly of the "closed type," separated from the air space by a thin cytoplasmic layer of ciliated cells, goblet cells or pneumocytes. In two species, Bufo marinus and Ambystoma tigrinum, the "open type" of NEB occur, where NEB communicate with the air space, by apical cells in Bufo and type II NE cells in Ambystoma. Both types of cells possess single atypical cilia with an 8+1 microtubule arrangement and microvilli on the free surface. Single and grouped NE cells are characterized by small dense core vesicles (DCV) dispersed in the cytoplasm. In Salamandra and Ambystoma the second type of NE cells with large DCV are observed. The DCV represent sites of storage of serotonin and several neuropeptides. The basal parts of NEB and of some solitary cells are invested by the intraepithelial sensory nerve terminals, both afferent and efferent morphologically. In the lungs of Amphibia, similarly to other vertebrates, NE cells, which act as endocrine/paracrine receptors, form epithelial endocrine systems.