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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.

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: α-D-glucose, α-D-mannose, α-L-fucose, α-D-1,3-N-acetyl-galactosamine and α-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.

The oocytes of the abyssal Teleost, Hoplostethus mediterraneus were studied. Four stages of growth were observed and the oocytes of all the stages were surrounded by follicular cells and had several nucleoli in the nucleus. In the oocytes of the II degrees stage, vacuoles without contents, in oocytes of the III degrees stage several vacuoles with a basophilic contents and small yolk globules were identified. General and basic proteins, ribonucleoproteins, acid proteoglycans with -COOH groups were recognized in the cytoplasm, in the nucleoli of oocytes in the II degrees stage and in the vacuolar contents of oocytes in the III degrees stage. In the follicular cells, in the pellucid zone, in the yolk globules, from their beginning, glycoproteins were present. Positivity, for all lectins used, was revealed in the follicular cells and in the four stages of oocytes growth. alpha-D-glucose and alpha-D-mannose binding sites were in the pellucid zone and in the initial yolk globules. In the lather galactose and beta-N-acetyl glucosamine were present too. nNOS and VIP immunopositivity revealed at the periphery of the cytoplasm and at network of nerve fibres between oocytes, suggests NO is involved in a mechanism of regulation of the gametogenesis and of the spawning.

The phylogeny and functional roles of many bioactive compounds in the invertebrate integument are still unclear. In order to deal with this issue, we performed an immunohistochemical investigation of the integument of the mussel, Mytilus galloprovincialis, to demonstrate the presence of nNOS- and VIP-positive nerve fibers in subepidermal connective tissue of the mantle. Positive nerve cell bodies were detected in this tissue as well as in cortex of sperm follicles, and adjacent to maturating oocytes and spermatocytes located in the thickness of the mantle. These results indicate involvement of a local inhibitory non-adrenergic-non-cholinergic (NANC) regulatory mechanism of epidermal functions, such as mucous secretion and ciliary beating. At the gonadic level, this mechanism probably regulates the cycle of maturation and release of the gametes in both sexes. [ABSTRACT FROM AUTHOR]