NEUROEPITHELIAL BODIES AND SOLITARY NEUROENDOCRINE CELLS IN THE LUNGSOF AMPHIBIA

In the lungs of 12 species of Amphibia investigated so far, solitary n euroendocrine (NE) cells, as well as groups of these cells called ''ne uroepithelial bodies'' (NEB), are observed. They occur in the position strategic to monitoring gas composition, mainly in the ciliated epith elium of the apical part of the septa. A great diversity in the struct ure of NEB is observed. The NE cells and NEB in Amphibia are predomina ntly of the ''closed type,'' separated from the air space by a thin cy toplasmic layer of ciliated cells, goblet cells or pneumocytes. In two species, Bufo marinus and Ambystoma tigrinum, the ''open type'' of NE B occurs, where NEB communicate with the air space, by apical cells in Bufo and type II NE cells in Ambystoma. Both types of cells possess s ingle atypical cilia with an 8+1 microtubule arrangement and microvill i on the free surface. Single and grouped NE cells are characterized b y small dense core vesicles (DCV) dispersed in the cytoplasm. In Salam andra and Ambystoma the second type of NE cells with large DCV are obs erved. The DCV represent sites of storage of serotonin and several neu ropeptides. The basal parts of NEB and of some solitary cells are inve sted by the intraepithelial sensory nerve terminals, both afferent and efferent morphologically. In the lungs of Amphibia, similarly to othe r vertebrates, NE cells, which act as endocrine/paracrine receptors, f orm epithelial endocrine systems. (C) 1997 Wiley-Liss, Inc.