NEUROEPITHELIAL ENDOCRINE AND NERVOUS-SYSTEM IN THE RESPIRATORY-TRACTOF CYNOPS-PYRRHOGASTER WITH SPECIAL REFERENCE TO THE DISTRIBUTION OF NITRIC-OXIDE SYNTHASE AND SEROTONIN

The respiratory tract of urodeles harbours an intramural nerve network comprising an innervated system of neuroepithelial endocrine (NEE) ce lls. However, striking differences have been noted between phylogeneti cally closely related species. Zamboni- or formaldehyde-fixed whole-mo unt preparations and sections of the saclike lungs of a Japanese salam ander, Cynops pyrrhogaster, have been investigated for the immunocytoc hemical detection of nitric oxide synthase (NOS), serotonin (5-HT), VI P, somatostatin, calcitonin, and bombesin; for the enzyme-cytochemical demonstration of NADPH diaphorase (NADPHd); and for formaldehyde-indu ced fluorescence. In addition, the ultrastructural morphology has been examined by using glutaraldehyde/osmium tetroxide fixed lung tissues. Ovoid 5-HT-immunoreactive (IR) NEE cells occur singly or grouped in t he ciliomucous epithelium of the trachea and lungs of Cynops, and a fe w somatostatin-, calcitonin-, and bombesin-like IR NEE cells are also observed. These cells exhibit a characteristic neuroendocrine morpholo gy as seen with the electron microscope. In addition, large numbers of 5-HT-IR interstitial cells, with round to oval cell bodies and two or three long, slender, sometimes branching processes, are located prefe rentially along large blood vessels in the connective tissue capsule o f the lung and trachea. Immunoelectronmicroscopy shows that 5-HT is lo calized over large dense granules in the cell bodies and processes of these interstitial cells. NOS-like immunoreactivity occurs in a nerve plexus composed of thick nerve bundles and nerve cells, and in a fine varicose nerve network that originates at least partly from intrapulmo nary NOS-containing nerve cells. VIP-like immunoreactivity appears to be colocalized with NOS in the latter network. All NOS-positive nerve fibres in the lungs of Cynops pyrrhogaster and Ambystoma mexicanum sta in for NADPHd. It is concluded that the pulmonary NEE cells observed i n Cynops pyrrhogaster are similar to those described in other vertebra te species and that the 5-HT-IR interstitial cells resemble mast cells . In addition, nitric oxide is likely to be a bioactive substance invo lved in nonadrenergic, noncholinergic inhibitory neurotransmission in the pulmonary nervous system of urodeles, where it may be colocalized with VIP. (C) 1994 Wiley-Liss, Inc.