Immunocytochemical study of the lung of domestic fowl and pigeon: endocrine cells and nerves

An SEM and TEM study of the transition of the bronchus to the parabronchus in quail (Coturnix coturnix)

The main objective was to analyse the transition of the bronchus to the parabronchus in birds and to describe its specific structure in an integrated light microscopic, transmission electron microscopic (TEM) and scanning electron microscopic (SEM) study. Lung tissue from immature and mature quail was subjected to standard processing for paraffin light microscopy, TEM and SEM after intratracheal inflation with fixative. In transverse paraffin and Durcupan semithin sections, the partition incompletely closing the broncho-parabronchial transition has the appearance of a crest-like fold delineating the entrance to the underlying parabronchial vestibulum. The core of the entrance fold is composed of loose connective tissue with free cells, and has a well-developed blood supply and innervation. Voluminous groups of smooth muscle cells are interconnected with those of neighbouring entrance folds and the interatrial septa. On the parabronchial surface and partly on the bronchial surface the entrance fold is invested with simple cuboid epithelium consisting exclusively of granular cells with lamellar inclusions. On the bronchial surface, they pass into ciliated columnar pseudostratified epithelium. At the root of the parabronchially orientated surface, they continue into the mixed population of granular and squamous atrial cells of the parabronchus. Among the granular cells of the entrance fold, scattered epithelial neuroendocrine cells are consistently present. The three-dimensional visualization demonstrated the oval form of the entrance window with a circular field of non-ciliated cells delineating the entrance to the parabronchial labyrinthine system. The general structural pattern of the entrance fold, together with the complex system of interatrial trabecles of the parabronchi underline the multifactorial function of a complex system submitted to the skeletal, regulatory and host defense of the gas exchange tissue.

Immunocytochemical survey of the neuroepithelial endocrine system in the respiratory tract of the Tokyo salamander, Hynobius nebulosus tokyoensis TAgo

The epithelial lining of the respiratory tract of urodeles has been shown to harbor an innervated system of neuroepithelial endocrine (NEE) cells. Even between phylogenetically closely related species, large differences have been reported in the appearance and chemical coding of the NEE system. Although urodeles are well suited for the purpose, none of the prior studies have provided an immunocytochemical survey of the NEE system in all parts of the respiratory tract. In the present study, many bioactive substances and a general marker were immunocytochemically demonstrated in serial sections of the entire respiratory tract of the Tokyo salamander, Hynobius nebulosus tokyoensis, a species in which neuroepithelial bodies (NEBs) were previously characterized at the electron microscopic level. In the current study, serotonin-immunoreactive solitary NEE cells were observed in variable numbers in the larynx, in all parts of the trachea, and in areas of the lungs covered with ciliomucous epithelium. Serotonin-containing NEBs, however, were detected in small cranial areas of the lung only. Solitary NEE cells were seen in the trachea and lungs of H. nebulosus tokyoensis by immunocytochemical staining for somatostatin, calcitonin, calcitonin gene-related peptide, and bombesin, but the number, localization, and appearance of the labeled NEE cells differed considerably. Only calcitonin-like immunoreactivity was also noted in some NEB-like cell clusters in the cranial parts of the lungs. Unlike many other vertebrates, neuron specific enolase was found to be a poor marker for the NEE system in the salamander species used in this investigation. It may be concluded that the NEE system of H. nebulosus tokyoensis contains at least five different bioactive substances.(ABSTRACT TRUNCATED AT 250 WORDS)