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The thyroid gland of the tropical amphibian Chthonerpeton is markedly stimulated when the animal is exposed for two days to relatively high temperatures (36° C). Control animals were kept at 20° C. The stimulated gland exhibits collapsed follicles and a very tall follicular epithelium. At the ultrastructural level the activated epithelial cells were characterized by an increased number of apical microvilli, increased amounts of rough endoplasmic reticulum, an extended Golgi apparatus and a high number of various granular and vesicular inclusions. These differences in histology and fine structure were not paralleled by quantitative results, which were approximately the same in both groups of animals. The values of these determinations were relatively high. [ABSTRACT FROM AUTHOR]

The functional status of organ systems involved into the processing of exogenous food is critical for the survival and growth of fish early life stages. The present study on laboratory-reared larval turbot, Scophthalmus maximus, provides an overview on the ontogeny of structure and functions involved in digestion, absorption and metabolism of nutrients. At start of exogenous feeding the intestine of larval turbot is anatomically differentiated, with enterocytes displaying an adult-type ultrastructure and being able to process lipids. At the microvillous border of the enterocytes, enzymes of contact digestion such as aminopeptidase are found. The ultrastructure of the exocrine pancreatic cells is fully differentiated from hatching onwards. Likewise, substantial activities of trypsin-type proteases are present. A stomach anlage exists in first-feeding larvae; however, the stomach becomes functional (appearance of gastric glands and pepsin secretion) only during metamorphosis. Liver parenchymal cells already display a functional ultrastructure during the endotrophic phase; with onset of exogenous feeding they develop pronounced diet-related changes of their energy stores. Larval respiration is not executed by the gills since respiratory surface of these structures develops only towards metamorphosis. The energy generation of larval muscle tissue depends on aerobic metabolism, whereas glycolytic activities start to increase at metamorphosis. In conclusion, two important patterns can be recognized in the development of turbot larvae: (1) The structure/function is differentiated at hatching or at the onset of exogenous feeding (afterwards it experiences mainly quantitative but not qualitative growth, i.e., intestine, exocrine pancreas, liver); or (2) the structure/function is absent in larvae and develops only during metamorphosis (i.e., gills, glycolytic muscle metabolism, stomach). [ABSTRACT FROM AUTHOR]

Spermiogenesis and sperm cells of the meiobenthic priapulid Tubiluchus were described by means of the transmission electron microscope. The sperm cells are completely different from the male gametes of Priapulus, being elongated and thus indicating a different mode of sperm transfer. The anterior portion of the sperm head is characterised by a corkscrew configuration of nucleus and acrosome, both components being wrapped around each other. This kind of sperm cell has never been reported in other animal phyla. [ABSTRACT FROM AUTHOR]

Electron microscopic investigation of young Pleurobrachia pileus has shown that the colloblasts develop from ciliated cells containing rich endoplasmic reticulum. The cilium is connected with the cell-body by means of a thin strand of cytoplasm; the cilium grows spirally around the basal part of the cell and undergoes several modifications; its rootlet forms the star-shaped body; an electron-dense cylinder arises outside the microtubules, the microtubules then degenerate. Basally, the cilium exhibits special anchoring structures. [ABSTRACT FROM AUTHOR]

For the first time, the site of biosynthesis of a well characterized invertebrate digestive enzyme is localized. The enzyme chosen, Astacus protease, is a zinc-metalfoenzyme occuring in high concentration in the gastric fluid of the freshwater crayfish Astacus astacus. Enzyme production was stimulated in adult crayfish either by feeding or by removal of the gastric fluid. Immunohistochemistry, cytology and investigation with radioactive tracers demonstrate that in the hours following stimulation, new enzyme was produced in the F-cells of the midgut gland and subsequently discharged into the midgut gland lumen. The enzyme was then accumulated and stored extracellularly in the cardiac stomach in active form. The mechanism of enzyme production observed in Astacus differs considerably from vertebrates suggesting an alternative model for synthesis and storage of digestive enzymes. [ABSTRACT FROM AUTHOR]

The morphology and ultrastructure of the digestive gland of Bithynia siamensis goniomphalus and its alteration by infection with Opisthorchis viverrini were investigated by light and electron microscopy. The digestive gland of B. s. goniomphalus was composed of three different cell types: digestive cells, excretory cells, and narrow cells. In infected animals the number of excretory cells increased dramatically. Cellular injury in digestive cells as well as in excretory cells following the infection could be observed at the ultrastructural level. [ABSTRACT FROM AUTHOR]

Changes in the hepatocytes of male hamsters ( Mesocricetus auratus) and jirds ( Meriones unguiculatus) at 220 days after experimental infection with the liver fluke Opisthorchis viverrini were studied by light and electron microscopy. The hepatocytes of the control group were characterized by an intracellular compartmentation. A globular nucleus was located centrally. The main features of the perinuclear zone were the cisternae of the rough endoplasmic reticulum (RER) and interjacent mitochondria, lysosomes, and peroxisomes. The peripheral cell region was dominated by glycogen fields and scattered lipid droplets, which were surrounded by anastomosing tubules of the smooth endoplasmic reticulum (SER). An immense proliferation of the SER was striking in the hepatocytes of animals infected with O. viverrini. Coincidentally, the intracellular compartmentation disappeared. Glycogen rosettes, RER, lysosomes, and lipid droplets were distributed irregularly all over the cell, the latter being observed more frequently than in control animals. The nuclei showed lobe-like protrusions and were enlarged. The mitochondria were often dumbbell-shaped and showed pathologic degenerations up to lysis. Our results resemble those of numerous investigations concerning hepatocellular alterations caused by N-nitroso compounds. Therefore, these observations suggest a synergistic effect for trematode infection and N-nitroso compounds in the pathogenesis of opisthorchiasis. The cellular alterations observed in the hepatocytes of Opisthorchis-infected animals together with the accumulation of intermediate filaments seen in the adjacent bile-duct epithelia and in the epithelium of the gallbladder seem to indicate a disturbance of the cell metabolism and might be related to a neoplastic transformation. [ABSTRACT FROM AUTHOR]

The anterior head region of Reighardia sternae is equipped with different groups of sensilla. They have been investigated using scanning and transmission electron microscopy. According to their ultrastructure they exhibit certain features in common with true arthropods. Each sensory cell bears one apical cilium and is surrounded by two sheath cells. [ABSTRACT FROM AUTHOR]

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In several metasomal blood vessels of Phoronis muelleri myofilament-containing podocytes are the predominant cell-type. In some regions the podocytes can build a labyrinth resembling e.g. the glomerular epithelium of Enteropneusta and the axial organ of Asteroidea. [ABSTRACT FROM AUTHOR]

In order to evaluate the suitability of isolated fish hepatocytes for toxicological studies, hepatocytes were isolated from rainbow trout ( Oncorhynchus mykiss) by liver collagenase perfusion. Isolated hepatocytes were investigated for seven days in primary culture on uncoated petri dishes using light and electron microscopy. Viability of isolated hepatocytes, as estimated from trypan blue exclusion, declined from >90% at the beginning of the incubation to ⩽80% after eight days of primary culture. Survival of hepatocytes was best at an incubation temperature of 14°C, and addition of fetal calf serum failed to improve cell performance. Freshly isolated hepatocytes appeared as solitary spherical cells with numerous microvilli at the outer surface. Except for a 30% reduction in cell size due to stress-induced glycogen reduction, the ultrastructure of freshly isolated hepatocytes closely resembled that of rainbow trout hepatocytes in vivo, which is characterized by distinct cytoplasmic segregation into a perinuclear portion containing rough endoplasmic reticulum (RER) arranged in extensive stacks, mitochondria, peroxisomes and the peribiliary complex (dictyosomes, lysosomes), and large peripheral glycogen fields occasionally interspersed with small lipid inclusions. Within one day of culture, about 60-80% of the isolated hepatocytes sedimented to form a monolayer attached to the culture dishes, whereas up to 20% remained in suspension forming hepatocyte aggregates. Cell adhesion was weak, and during prolonged culture increasing amounts of cell detached, whereas the floating cell accumulations grew to aggregates of more than 100 cells. Cell viability and ultrastructure was similar in monolayers and spheroids, and only from the fifth day in culture, did hepatocytes in the centre of floating aggregates become necrotic. From day 1 to day 5, hepatocytes in primary culture displayed only minor cytological alterations. Excellent cytoplasmic compartmentation, restoration of hepatocytic glycogen stores, high secretion rates of very low density lipoproteins by dictyosomes, establishment of cell-to-cell contacts, restitution of cellular polarity and the epithelial character of the cells, as well as formation of bile canaliculi documented recovery of the hepatocytes in primary culture. From day 5 in culture, an increasing number of cells detached from the substratum, and cell senescence was indicated by a marked increase in ultrastructural heterogeneity, with progressive vesiculation and fractionation of the RER, transformation of RER stacks into huge membrane whorls, aggregation and proliferation of peroxisomes and SER, lack of dictyosomal VLDL production, drastic accumulation of lysosomes, myelinated bodies and autophagic vacuoles, as well as successive exhaustion of cellular glycogen deposits. Whereas with conventional methods for assessing cell viability, most hepatocytes appeared intact for up to ten days in culture, cytological investigations revealed severe deterioration of cellular integrity from day 7. However, for incubation periods of up to five days, isolated rainbow trout hepatocytes can be recommended as an excellent model for physiological and toxicological studies. [ABSTRACT FROM AUTHOR]

Internal fertilization is demonstrated in the priapulid worm Tubiluchus philippinensis by the electron microscopic observation of sperm in the urogenital duct of female animals. This finding is of interest in that all other members of this group thus far examined have exhibited external fertilization. [ABSTRACT FROM AUTHOR]

Under conditions of food deprivation, the hindgut epithelium of the experimental animals ( Mesidotea entomon, Oniscus asellus, Porcellio scaber) undergoes ultrastructural changes. After the application of different diets it was demonstrated that this part of the alimentary canal contains nutrients, though it is lined by a cuticle. Experimental evidence for the formation of glycogen from glucose offered as the only diet comes from autoradiographic experiments. Amino acids, too, were detected in the hindgut cells soon after refeeding. Lipids, on the other hand, which are first absorbed by the large cells of the midgut glands, were not found in the hindgut epithelium. The existence of lipid inclusions in the hindgut epithelium some weeks after refeeding, however, supports the hypothesis that lipids reach the epithelial cells of the hindgut via midgut glands and hemolymph. [ABSTRACT FROM AUTHOR]

The gills of several polychaete species belonging to 9 families were studied by scanning and transmission electron microscopy. The surface epithelium is covered by a thin cuticle which is invaded by microvilli penetrating the epicuticle in certain species. Some epithelial cells bear cilia, others are mucus-producing cells. The ciliary cells may be arranged in rows and maintain a constant flow of water over the gills. The distance between external water and blood stream differs considerably according to the species investigated. In Malacoceros the gills are characterized by closed afferent and efferent subepithelial vessels, which correspond to tubular invaginations of the coelomic wall. These vessels are lined by the basement lamina of the coelothelial cells, which are of the epitheliomuscular type. The vessels are open in the gills of other polychaetes and release the blood stream into a system of spaces immediately below the epidermis (e.g. in the branchial lamellae of Pectinaria and Terebellides). In several species the blood comes into very intimate contact with the cuticle (e.g. in the gill filaments of Dendronereides), but also in these animals both are separated by a very small epidermal layer. [ABSTRACT FROM AUTHOR]

The integument of S.E. Asian air-breathing polychaetes exhibits a variable ultrastructure with regard to cuticle and epithelial cells. The cuticle varies in thickness, contents of regularly arranged collagen fibrils, and structure of the epicuticle. The basal portion of the epithelium is either of smooth outline, or consists of slender processes of the epidermal cells separated by wide intercellular spaces which are invaded by a loose system of glia cells and nerve fibres. Extracellular spaces within the epidermis of the gills of Dendronereides heteropoda are transformed into blood lacunae. The enzyme content of the epithelial cells is relatively low. [ABSTRACT FROM AUTHOR]

Electron microscopic investigation of the scalids of the kinorhynch Trachydemus giganteus Zelinka has shown that they are receptor organs, the ultrastructure of which resembles that of arthropod chemoreceptors. On the basis of the ultrastructure of their cuticle, two types of scalids (Stachelskaliden) can be distinguished. The cilia of the scalids (Stachelskaliden) communicate directly with the surface by cuticular pores. This communication is lacking in the trichoscalids. [ABSTRACT FROM AUTHOR]

The epidermal mucous cells of various nemerteans, polychaetes and gastropods exhibit a highly heterogeneous fine structure, which is not correlated to systematic position or way of living. Formation and extrusion of the mucus secretory substances also follow different patterns. In the majority of species investigated, the mucus inclusions originate in the Golgi area, in Pomatias they form in the rough endoplasmic reticulum. The mucus droplets either coalesce in the cytoplasm or retain their individuality before being extruded. [ABSTRACT FROM AUTHOR]

Various enzyme activities have been demonstrated in the pharynx, midgut, and caeca of the polychaetes Aphrodita aculeata, Lepidonotus squamatus, and Nephtys ciliata; these activities, together with ultrastructural characteristics, indicate both secretory and absorptive abilities. [ABSTRACT FROM AUTHOR]

The nerve fibre layer and the neurocord of the Enteropneusts Saccoglossus horsti, Harrimania kupfferi and Ptychodera flava have been examined with the electron microscope. The nerve fibres vary in diameter between 0.15 to 10 μm. The majority of the fibres are of the smaller diameters. The nerve fibre layer is intraepidermal, and is divided by processes running radially from the epithelial cells to the basement membrane that separates the nerve fibre layer from the muscle cells. The cells of origin of these nerve fibres are situated mainly in the innermost layers of the epidermal cells. The nerve fibre profiles contain numerous vesicles of very varied diameter and contents, together with larger granular inclusions that are also found in the nerve cell bodies. Morphologically recognisable synapses are rare, but the majority of fibres are in intimate contact with one another. Sometimes the mass of fibres is divided into bundles by the epithelial cell processes. The majority of giant fibres are situated near to the basement membrane of the neurocord. The giant fibres also have a varied content of vesicles as well as neurofilaments and neurotubules. The central canal in Ptychodera flava and the remnants of the central canal in Saccoglossus horsti are both lined by columnar cells that bear microvilli as well as cilia with the typical 9 + 2 pattern of tubules. Scattered amongst these cells are mucus secreting cells which open into the cavity of the canal. [ABSTRACT FROM AUTHOR]

In the epidermis of turbellarians septate junctions of the pleated sheet type have been demonstrated in conventional thin sections and freeze fractured preparations. The structure of these junctions entirely agrees with that found in molluscs and arthropods. [ABSTRACT FROM AUTHOR]

Epitheliomuscular cells largely corresponding to those of cnidarians have been found in the mesenteria of Lingula and in various coelomic channels of Branchiostoma. They are characterized by basal extensions containing thin and thick myofilaments. In Lingula they also bear an apical cilium. [ABSTRACT FROM AUTHOR]

Ultrastructural alterations in liver and gills of embryonic and larval zebrafish (Danio rerio) following prolonged exposure to waterborne0.05, 0.5, and 5 mg/L 4-chloroaniline for up to 31 days as well as after a 14-day regeneration period were investigated by means of lightand electron microscopy. Acute toxicity was also tested at 25 and 50mg/L. Survival of zebrafish embryos and larvae was only impaired from 25 mg/L 4-chloroaniline, but -- after a transient stimulation following exposure to 0.5 mg/L -- 4-chloroaniline hatching was retarded after exposure to =/> 5 mg/L, and fish displayed increasing rates of abnormal development and pigmentation. In contrast, hepatocytes displayed a time- and dose-dependent response from 0.05 mg/L 4-chloroaniline, including changes in nuclei, mitochondria, peroxisomes, endoplasmicreticulum, Golgi fields, lysosomes, and hepatic glycogen and lipid stores, as well as invasion of macrophages. In gills, dose-dependent effects were evident from 0.5 mg/L 4-chloroaniline and included deformation of secondary lamellae due to vacuolization and desquamation of respiratory epithelial cells in conjunction with dilation of intercellular spaces. Respiratory epithelial cells displayed progressive mitochondrial changes, induction of cytoplasmic myelinated structures, augmentation of lysosomes, and modifications of Golgi fields. Erythrocytes were severely deformed. A 14-day regeneration period was sufficient for almost complete recovery of pathological symptoms in both liver and gills. Only minor volumetric changes in hepatocellular organelles and a limited number of myelinated bodies, lysosomes, and cytoplasmic vacuoles were reminiscent of prior 4-chloroaniline exposure. In both qualitative and quantitative terms, most effects in hepatocytes after exposure of embryonic and larval zebrafish to waterborne 4-chloroaniline are comparable to the reaction of hepatocytes in adult zebrafish liver after prolonged sublethal exposure as well as in larval zebraf [ABSTRACT FROM AUTHOR]