Aurelio Licata

PARANEURONS IN THE GILLS AND AIRWAYS OF FISHES

This chapter describes the distributional patterns of the neuroendocrine cells in the respiratory surfaces of fishes and their bioactive secretions which are compared with similar elements in higher vertebrates. The neuroendocrine cells in the airways of fishes differentiate as solitary and clustered cells, but the clusters are not converted into neuroepithelial bodies which are reported in terrestrial vertebrates. The dipnoan fish Protopterus has innervated neuroendocrine cells in the pneumatic duct region. In Polypterus and Amia the lungs have neuroendocrine cells that are apparently not innervated. Two types of neuroendocrine cells are found in the gill of teleost fishes. These cells are very different by their location, structure and immunohistochemistry. Advanced studies on functional morphology of neuroendocrine cells in fish airways are still necessary to increase our understanding of their multifunctional role in the gill area. Microsc. Res. Tech. 37:4–12, 1997.

Neuronal nitric oxide synthase (nNOS) expression in the epithelial neuroendocrine cell system and nerve fibers in the gill of the catfish, Heteropneustes fossilis.

We studied immunohistochemically the localization of neuronal nitric oxide synthase (nNOS) in gills of an Indian catfish species, Heteropneustes fossilis. It is shown that most of the epithelial neuroendocrine cells that are present in gill filaments and lamellae stained positively. Co-localization of nNOS and endothelin was also shown in neuroendocrine cells. A dense plexus of nNOS-containing nerve fibers was present beneath the gill epithelium, associated with efferent filament arteries and the basal side of neuroendocrine cells. nNOS immunopositive neurons were not found in gill areas. nNOS immunopositive neuroendocrine cells appeared to differ from neuroepithelial cells in gills of various teleost species, which are considered as oxygen-sensitive receptors and are present in the distal halves of gill filaments. Other types of neuroendocrine cells have been identified previously in other areas of gills using antibodies to serotonin and endothelin peptides. These cell types are likely to be involved in chemical regulation of the physiology of gill cells. In relation to the function of the other cell types, our data on nNOS localization suggest that NO is a wide-spread transmitter in the gill of the Indian catfish. It may play a role both in the local regulation of vascular tone and in inhibitory innervation of the gill.

The effect of an anionic detergent on complex carbohydrates and enzyme activities in the epidermis of the catfishHeteropneustes fossilis (Bloch)

SummaryThe histochemistry of various oxidative enzymes and complex carbohydrates in the epidermis of the catfishHeteropneustes fossilis was investigated after exposure to sublethal concentrations of the detergent sodium alkulbenzenesulphonate.It was found that the detergent treatment was accompanied by a marked increase in the number of mucous cells which produce histochemically detectable amounts of acidic glycoproteins with a shift towards the production ofO-acetylated sialic acids. The activities of mitochondrial enzymes were lost in the superficial cell layers. In contrast the activities of glucose-6-phosphate and lactate dehydrogenase increased considerably. The rise in glucose-6-phosphate dehydrogenase was correlated with the metabolic requirements for the enhanced production of mucus under stress.The changes in both enzyme activities and in the chemical composition of mucus may provide a suitable experimental model for histochemical investigations of the effect of stress induced by pollulants on aquatic organisms.

Enzyme cytochemical and immunocytochemical studies of flask cells in the amphibian epidermis

SummaryThe localization of oxidoreductases and transport enzymes in flask cells of the amphibian epidermis was studied at the light-microscopic level. In these cells, the deposition of cytochemical reaction products was very similar to that found in fish epidermal ionocytes, thus demonstrating histochemical similarities between these two types of cells. The present histochemical results revealed high levels of activity of alkaline phosphatase (ALPase), potassium-dependent nitrophenylphosphatase (K+-p-NPPase) and carbonic-anhydrase isozymes (CA-I and CA-II) in the apical region of the flask cells, indicating that enzyme zonation may be the main site of the ion pumping.

Localization of calbindin D28K-like immunoreactivity in fish gill: a light microscopic and immunoelectron histochemical study

The presence of calbindin D28K in fish (Heteropneustes fossilis) gill was studied by use of specific antibodies raised against chick duodenal 28 kDa calbindin in immunoperoxidase and electron-microscopic labelling experiments. Immunoreactivity for calbindin D28K, which has been observed in the intestine of a number of avian and mammalian species, is reported for the first time in the gill. It was primarily located in neuroendocrine (NE) cells. Some immunoreactivity was also located in the glycocalyx of the non-endocrine cells, i.e., the pavement cells, which have ultrastructural characteristics quite different from those of endocrine cells. The calbindin-immunopositive NE cells were ascertained in both gill filamental and lamellar epithelium. All the NE cells contained secretory granules as the most distinctive feature of these cells. Ultrastructurally, two types of NE cells were distinguished according to the morphology of their secretory granules. The calbindin immunoreactivity in the NE cells was stimulated when the calcium concentration of the ambient water was reduced. The present findings suggest that NE cells exert some as yet unidentified function related to calcium-mediated processes involving the expression of calbindin.

Immunohistochemical localization of nNOS in the skin and nerve fibers of the earthworm Lumbricus terrestris L. (Annelida Oligochaeta)

The epidermis of the earthworm Lumbricus terrestris is a multifunctional tissue. It is composed of supporting, mucous, neuroendocrine-like, sensory and basal cells. NO is considered to be a molecule that regulates numerous functional activities (also in non-neuronal cells) in vertebrates. In the earthworm epidermis, we found neuronal NO synthase immunopositivity in orthochromatic and metachromatic mucous cells, neuroendocrine-like cells and in epidermal and subepidermal nerve fibers and striated muscle fibers. It is suggested that NO has a multitude of biological actions, affecting functional activities of the epidermis such as tissue homeostasis, control of secretion, proliferation, respiration, defense, water-salt balance, as well as regulation of tonus in vascular and striated muscles.

5-Hydroxytryptamine immunoreactivity in the epidermal sacciform gland cells of the clingfish Lepadogaster candollei Risso

SummarySerotonin has been demonstrated in the epidermal sacciform glandular cells of the clingfish Lepadogaster candollei by use of immunocytochemistry.Serotonin immunoreactivity is found both in the peripheral cytoplasm of the glandular cells and their luminal secretion. The presence of serotonin in the sacciform glandular cells parallels that located by both biochemical and immunocytochemical procedures in the cutaneous glands of many amphibian species.

Lectin-binding pattern on the surface epidermis of Ambystoma tigrinum larvae

SummaryThe surface epidermis of Ambystoma tigrinum larvae was examined at the light- and electron-microscope levels using five different lectin conjugates as probes for the detection of sugar residues on the cell membranes. Concanavalin A (Con-A), wheat-germ agglutinin (WGA), Ricinus communis agglutinin I (RCA-I), Dolichos biflorus agglutinin and soybean agglutinin (SBA) conjugates clearly labelled the surface cells, especially their apical surfaces. At electron microscopy, the labelling on plasma membranes was found to exhibit regional differences. Among the lectins tested WGA displayed a particularly characteristic binding pattern. WGA also bound to basolateral cell surfaces, including the tight-junction zone wich was also stained by the RCA-I conjugate. The different labelling intensity and staining patterns obtained with the conjugates indicated the polarity of the cell surfaces. It is also assumed that the WGA staining of the basolateral membranes and intercellular spaces reflected transcellular transport, which is facilitated by acidic glycoconjugates. Other functional aspects of the polarized distribution of the lectin conjugates were also correlated with the receptor sites of certain sugar residues.

Patterns of enzyme activities in the gills of the catfish Heteropneustes fossilis (Bloch) exposed to the anionactive detergent Na-alkyl-benzenesulphonate (LAS)

SummaryThe effect of sodium-alkyl-benzenesulphonate (LAS) on the activity of the respiratory enzymes of the gills of Heteropneustes fossilis (Bloch) was investigated. After 48 h exposure, the main injury to gills was the progressive separation of the lamellae from their vascular components. The enzymes of the aerobic part of the metabolism showed a decrease in activity, whereas the activity of lactate dehydrogenase was strongly increased, thus indicating that LAS has a high potential to interfere with aerobic mechanisms; however, the mode of action of it has yet to be clearly defined.

Immunohistochemical localization of nNOS and VIP in the mantle integument of the mussel, Mytilus galloprovincialis

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.