Glycoconjugate histochemistry and nNOS immunolocalization in the mantle and foot epithelia of Tapes philippinarum (bivalve mollusc)

Glycosaminoglycans and NO synthase probably regulate mucous cell secretion in the skin of Tapes philippinarum. We have demonstrated the presence of "protein" cells, "glycogen" cells, "phenol" cells and five types of mucous cells, with different chemical composition of the mucus in the mantle epithelium of T. philippinarum. The foot epithelium contained "protein" cells and two types of mucous cells. Using biotinylated lectins, in the mantle and foot epithelia we have shown specific sites for the following oligosaccharides: alpha-D-glucose, alpha-D-mannose, alpha-L-fucose, alpha-D-1,3-N-acetyl-galactosamine and alpha-N-acetyl-glucosamine. nNOS immunoreactivity in the intraepithelial and intradermal cells and in the mucocytes suggested a regulatory role of NO in mucus secretion, as demonstrated also in other invertebrates.

Morphological, histochemical and immunohistochemical study of the gill epithelium in the abyssal teleost fish Coelorhynchus coelorhynchus

Histochemical and immunohistochemical study was carried out on nitrinergic innervation and neuroendocrine system in the gill epithelium of the abyssal fish Coelorhynchus coelorhynchus. The results showed that nNOS-positive nerve fibers, originating from the branchial arch were present in the subepithelial tissue of branchial primary filament. nNOS-positive neuroendocrine cells were also present in the primary filaments and secondary lamellae. Numerous mucous cells in the gill epithelium were AB/PAS-positive, while sialic acid was absent as confirmed by neuraminidase reaction and WGA lectin histochemistry. The mucus compounds in abyssal teleost fish are different from those found in pelagic species, being related to their living conditions. In abyssal species, greater numbers of chloride and neuroendocrine cells are involved in the movement of water and electrolytes. Neuroendocrine cells possess oxygen receptors which mediate the cardiovascular and ventilatory response to oxygen deficiency, as reported in teleost species. Besides, NO contributes through nervous stimulation to the regulation of vascular tone and blood circulation in the gill.