Ultrastructural changes in the coronet cells of the saccus vasculosus from rainbow trout,Salmo gairdneri (Richardson), kept in sea water

Summary The coronet cells of saccus vasculosus of fresh-water living and sea-water adapted rainbow trout were studied with the electron microscope, with special regard to changes in the latter group. Only quantitative differences were observed, namely a raised number of mitochondria in the apical region and the head and also a concentration of the agranular endoplasmic reticulum with a higher amount of electron-dense material and vesicles around the Golgi saccules. Together, these findings suggest a secretory function for the coronet cell. A supposed transport of vesicles from the head region of the coronet cell out into the globules is suggested. Interrelation between primary and secondary vesicles is discussed.This work was supported by grants from the Royal Physiographical Society of Lund and the Faculty of Natural Sciences at the University of Lund.—I am greatly indebted to Mrs. Lena Svenre and Miss Inger Norling for excellent technical assistance.     

Studies on the histomorphology and histochemistry of the saccus vasculosus of Cyprinion macrostomus.

The saccus vasculosus of Cyprinion macrostomus is made up of coronet and supporting cells. Neurones are not observed. The luminal surface of the coronet cells exhibits hair-like protrusions. The saccus vasculosus is mainly concerned with a secretory function. Plenty of secretory material is seen in the lumen. PAS and alcian blue tests are positive for the secretory material in the lumen and the apical protrusions of the coronet cells. Some cells also exhibit small PAS- and alcian blue-positive granules. The possibility of the elaboration of glycogen by the coronet cells is ruled out. The toluidine blue test is also positive for the secretory material in the lumen and the apical protrusions. Small metachromatic granules are also seen in some of the coronet cells. The acetone-Sudan black B and Sudan black B tests point to lipid moiety of the coronet cells, the apical protrusions and the secretory material in the lumen. The acrolein-Schiff and ninhydrin-Schiff tests point to a protein moiety of the coronet cells and the secretory material in the lumen. The performic acid-alcian blue test showed cystine to be present in small amount.     

Light microscopic and ultrastructural study of the development of the saccus vasculosus in the rainbow trout,Oncorhynchus mykiss

This study using light and electron microscopy indicates that the saccus vasculosus is distinguishable in 9-mm embryos and grows continuously throughout embryonic development to the adult stage. In the saccus vasculosus, epithelial mitoses are observed in all stages studied. Phases of centriologenesis, ciliogenesis, and globule formation have been characterized in developing coronet cells. During the phase of centriologenesis, new centrioles appear in association with pre-existing centrioles and not on deuterosomes. After ciliogenesis, each cilium differentiates to a globule almost at the same time as the other cilia of the coronet cell. The inner membrane system of the globules seems to derive from the ciliary plasma membrane. This membrane system often produces membrane whorls during the development. The different phases of coronet cell development have been found in the same individual and in all the stages studied except the 9-mm embryo. Cerebrospinal fluid-contacting neurons are observed in the saccus epithelium from the 12-mm embryos on and are distinguishable from coronet cells in their early formative stages. The three cell types of the saccus vasculosus increase continuously in number during development. Nerve processes are found in the saccus vasculosus of embryos, whereas differentiated synapses appear later in the fry. The significance of continued coronet cell formation is discussed in relation to a putative coronet cell and/or a globule renewal cycle in the adult.     

Relationships between the tubular system in the globules of the coronet cells of the saccus vasculosus and the cerebrospinal fluid in Gasterosteus aculeatus form leiurus (Teleostei)

Summary In the stickleback, Gasterosteus aculeatus, the globules of the coronet cells in the saccus vasculosus contain a tubular system that most probably communicates permanently with the lumen of the saccus. Only very few openings were found in random ultrathin sections. Injecting peroxidase into the cerebrospinal fluid revealed the communication between this tubular system and the cerebrospinal fluid. As early as 1 h after peroxidase injection the tracer was detected in the tubular system. This system increases the potential exchange surface between the coronet cells and the content of the saccular lumen, and may also facilitate the access of components of the cerebrospinal fluid (CSF), even of high molecular weight, into the globules. It remains to be determined whether the intratubular condensations (granules) are, as often believed, of secretory origin or are formed by accumulation of components of the CSF.With the technical collaboration of Melle A. Meunier     

Further investigations on the structure and function of the saccus vasculosus of the rainbow trout,Salmo gairdneri Richardson

Alkaline phosphatase activity in coronet cells of the saccus vasculosus of the rainbow trout was localized ultracytochemically. Deposits of reaction product were found in varying amounts on the membranes of primary vesicles in the globules. This observation is discussed in relation to other morphological data and the possible resorptive function of the coronet cells in the homeostasis of the CSF.     

Changes in the Saccus Vasculosus Epithelium During the Smoltification Process in Atlantic Salmon (Salmo salar)

The changes that take place in the saccus vasculosus epithelium during smoltification of Atlantic salmon (Salmo salar) are described. The major cell type of the epithelium, the coronet cells, have a number (mean = 32) of spherical protrusions connected with a non-motile cilium to the apical part of the cell. The protrusions extend into the saccus lumen. In parr the protrusions become more spherical during the spring season, while in smolt the opposite process takes place. Parr coronet cells have most of the mitochondria in the apical part of the cell, while in smolt they are concentrated basally. The relative areal fraction of heterochromatin in the nuclei increase from 23 to 29 during the smoltification process. The results are consistent with the view that the coronet cells take an active part in the smoltification process.     

Fine structural localization of adenosine triphosphatase activities in the saccus vasculosus of the rainbow trout,Salmo gairdneri Richardson

The following characteristics of the adenosine triphosphatases (ATPase) in the saccus vasculosus were studied in Salmo gairdneri Richardson: 1) distributional pattern, 2) cytochemical properties in relation to different substrates, inhibitors, pH and bivalent metal ions, and 3) ultrastructural localization. Ultracytochemical studies using modifications of the Washstein-Meisel technique showed that within the pH range 7.1-8.0 several Mg++ or Ca++-activated ATPase are localized on the intracellular surface of membranes and in the cytoplasm of ependymal coronet cells and tanycytes ("supporting cells", "Zwischenzellen", glial cells"). The high ATPase activity at the level of the specialized luminal plasma membranes of coronet cell globules and of tanycyte microvilli is discussed in relation to phenomena of active transport and a possible resulting transfer of low-molecular weight substances into and/or from the cerebrospinal fluid (CSF). The localization of ATPase on the specialized membranes of primary vesicles is considered in connection with available structural and enzyme-cytochemical data on a possible function of these cell organelles in storage and release of substances (including Ca++ ions?). The cytoplasmic ATPase activity in coronet cells is ascribed to microtubules and/or possible existing contractile proteins/filaments, presumably concerned with internal transport or motility processes. In tanycytes ATPase activity is believed to be associated with the characteristic microfilamentous system of still unknown function. The ATPase activity in the (9 + 0) ciliary apparatus of globules could not be interpreted in terms of motility. The present study provides further support to the proposed hypothesis of the transport function of the saccus vasculosus, and an extension of the concept in the sense that not only the principal coronet cells, but also the tanycytes of this circumventricular organ are involved in CSF-homeostasis.     

Histophysiology of the saccus vasculosus of the Indian freshwater goby Glossogobius giuris Ham. (Teleostei)

The author studied the structure and functions of the saccus vasculosus of the Indian freshwater goby Glossogobius giuris (Ham.). The saccus is ovoid, is localized on the ventral surface of the brain and is lodged between the inferior lobes. It consist of several loculi lined with coronet cells and is bathed with blood from surrounding sinusoids. The coronet cells are variably shaped and have a conspicous central nucleus. It is suggested that the purpose of the saccus vasculosus is to act as a storage site for carbohydrates to the brain. By converting glycogen to acid mucopolysaccharides, the coronet cells are involved in glycogen metabolism.     

A histoenzymological study of the saccus vasculosus of the freshwater teleost, Clarias batrachus (L.).

The saccus vasculosus (SV) of C. batrachus is comparatively small and situated latero-dorsal to the pituitary in between the lobi inferiores. It is in open communication with the third ventricle and is made up of coronet and supporting glial cells with interspersed liquor contacting neurons. These cellular constituents are arranged in one to three layers which are not thrown into folds. The PAS positive nature of the apical part of some coronet cells and their continuation with the PAS and AF positive material present in the lumen strongly suggest their secretory role. The coronet cells exhibited strong NADH diaphorase, NADPH diaphorase, cytochrome oxidase and MAO activity. AChE activity was comparatively weak. These enzyme histochemical studies show that SV has a dual function of transport and secretion. The strong MAO activity suggests the probable aminergic control of this organ.     

Possible Ascidian Counterpart to the Vertebrate Saccus Vasculosus with Reference to Pyura tessellata (Forbes) and Boltenia echinata (L.)

The morphology of the hitherto unknown larva of Pyura tessellata (Forbes) is described and the discovery of an auxiliary brain vesicle is presented. The vesicle was also found in another pyurid species Boltenia echinata (L.). The auxiliary vesicle communicates with the sensory vesicle at the level of the statocyte and is lined with cubodial epithelial cells carrying a 2 μm globular structure projecting into the lumen. These cells very closely resemble primitive tunicate coronet cells previously reported and coronet cells typical for the saccus vasculosus found in elasmobranchs and many ganoids and teleosts.     

On the presence and localization of glycogen accumulations inside coronet cells of the saccus vasculosus of the dogfish (Scylliorhinus caniculus)

Summary In several coronet cells of the saccus vasculosus of Scylliorhinus large quantities of glycogen occur, as shown by light and electron microscopy. The significance of glycogen as an energy storage necessary for a transcellular ion transport process taking place in the coronet cells is discussed.The authors thank Dr. F.C.G. van de Veerdonk, W. F. Jansen and W. F. G. Flight for reading the manuscipt and for their critical remarks. They are also indebted to Mr. H. van Kooten and his staff for their valuable photographic assistance.     

Histochemische Beobachtungen am Saccus vasculosus der Forelle

Summary The saccus vasculosus of rainbow trout and brown trout, the latter caught in the wild, has been investigated by histochemical means. Isolated coronet cells and groups of them were found to be rather strongly but unspecifically stainable by alcian blue. A performic acid-aniline-aldehyde-thionine reaction demonstrated that such cells contain more disulfide groups than their nonstaining neighbours. This higher disulfide content and the stainability by alcian blue do not necessarily coincide with the presence of acid mucopolysaccharide, which was found in the cytoplasm of coronet cells in some cases. The hypothesis is discussed that cystine may be stored and used by coronet cells as a precursor of the acid mucopolysaccharide, which has been shown in the lumen of the organ.     

Morphogenesis of the saccus vasculosus of turbot Scophthalmus maximus: assessment of cell proliferation and distribution of parvalbumin and calretinin during ontogeny

The ontogenesis of the saccus vasculosus (SV) of turbot Scophthalmus maximus is described using histological and immunohistochemical methods to assess the general morphology, as well as the distribution of proliferative cells and several calcium‐binding proteins (CaBP). The results reveal that the SV begins to differentiate on hatching, when immature coronet cells are morphologically distinguishable. Further morphogenesis involves the formation of a tubular avascular SV, which remains until premetamorphic larval stages. Folding and vascularization of the SV occurs mostly during metamorphosis, when S. maximus settle down on the bottom. Proliferative cells were placed within the SV itself and in the neighbouring infundibular hypothalamus. Their putative relationship with the growth of the SV is discussed. The CaBPs analysed are expressed in coronet cells. Parvalbumin is expressed in these cells from the beginning of their differentiation, while calretinin expression arises in the tubular SV and becomes more widespread over time. These data emphasize the importance of calcium buffering in the function of coronet cells.     

Postnatal development of the Mongolian gerbil uterine glands

The development of gerbil uterine glands has been described. Gland formation starts about day 6 postnatally (p.n.). At day 10 p.n. the glandular lumen contains already some fluid, and the glandular cells are in an activated state. The apical shape of the glandular cells depends mainly on the width of the lumen. Secretory vesicles in early developmental stages are electron-lucent. As sexual maturity is reached, secretory granules become electron-dense. This change in secretory granular structure indicates a change in the quality of uterine gland fluid.     

Ultrastructural Observations on the Development of the Microsporidian Protozoon Plistophora hyphessobryconis Schaperclaus*

SYNOPSIS. A sequence of developmental stages of Plistophora hyphessobryconis Schaperclaus, a microsporidian protozoan parasite of the muscular tissue of several species of freshwater fishes, was studied with the electron microscope. The youngest stages observed, ca. 4 × 2 μ, have a single nucleus and their plasm contains only ergastoplasmic lamellae and ribosomes. They are surrounded by a halo of lysed host tissue. They increase in volume to become large sporonts with a great number of nuclei and a thick, 2-layered membrane. Thru schizogony, a corresponding number of sporoblasts is produced within this pansporoblast membrane. Sporoblasts start to develop a thick spore membrane, and a number of smooth-membraned vesicles appear in the plasm. These vesicles fuse to make the outer membrane of the filament. Later, its inner structures originate—the axial electron-dense substance, filling the hollow lumen of the filament, and a middle, electron-transparent layer. The structure of the filament is discussed in relation to its function and with regard to the findings of other authors. The polaroplast is a laminated structure, originating possibly by transformation of endoplasmic reticulum; the polar cap forms its apical part. The cap is also lamellar; its substance reaches into the lumen of the filament for a certain distance. No micropyle was discovered in the shell; the filament is fastened to the polar cap. These observations on microsporidian development and on the structure of their spores are compared with similar data on myxosporidian species. Such a comparison speaks clearly in favor of the complete taxonomic separation of the Microsporidea from the Myxosporidea, the latter being quite different also from other sporozoa sensu lato.     

Über Aktivitätsphasen im Epithel des Saccus vasculosus von Etmopterus spinax

Summary The coronet cells in the saccus vasculosus of Etmopterus spinax L. were investigated histologically and histochemically. Inclusions of granula in the coronet cells were observed in 8 specimens. The granules react positivly as lipid and protein containing substances. They are attached to the Einschlußkörper in the cell base and accumulate around the nuclei or in the inner fibre apparatus of the cell apex. The diameter of the granules reaches 2,5 in the cell base and diminishes to less than 1 in the apical structures. These granula are interpreted as a sign of secretion into the third ventricle.This secretory activity is high in gravid females (31,4–54,7 % of the cells) and low in juvenile females or specimens in which no ovulation could be stated (0–4,7 %). Gravid females show differences in the distribution pattern of the granula within the cells, thus indicating a phasic activity.The coronet cells in the saccus vasculosus of Etmopterus seem to be involved in the secretory phenomena related to gravidity.

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Die Untersuchungen wurden mit dankenswerter Unterstützung durch die Deutsche Forschungsgemeinschaft durchgeführt.     

Light and electron microscopy studies of the oesophagus and crop epithelium in Aplysia depilans (Mollusca, Opisthobranchia)

The oesophagus and crop epithelium of Aplysia depilans consist in a single layer of columnar cells with apical microvilli, and some of them also possess cilia. Cell membrane invaginations, small vesicles, multivesicular bodies and many dense lysosomes were observed in the apical region of the cytoplasm. In most cells, a very large lipid droplet was observed above the nucleus and a smaller one was frequently found below the nucleus; glycogen granules are also present. Considering these ultrastructural features, it seems that these cells collect nutritive substances from the lumen by endocytosis, digest them in the apical lysosomes and store the resulting products. The cell bodies of mucus secreting flask-shaped cells are subepithelial in the oesophagus and intraepithelial in the crop. Histochemistry methods showed that the secretion stored in these cells contains acidic polysaccharides. Secretory vesicles with thin electron-dense filaments scattered in an electron-lucent background fill most of these cells, and the basal nucleus is surrounded by dilated rough endoplasmic reticulum cisternae containing small tubular structures. Considering the relatively low number of secretory cells, mucus production cannot be high. Moreover, since protein secreting cells were not observed in either oesophagus or crop, extracellular digestion in the lumen of these anterior segments of the digestive tract most probably depend on the enzymes secreted by the salivary and digestive glands.     

Morphometric and ultrastructural features of the mare oviduct epithelium during oestrus

Morphometric, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations have displayed regional differences in the mare oviductal epithelium. The entire mucosa of the oviduct was lined with a pseudostratified epithelium, which consisted of two distinct cell types, ciliated and non-ciliated. Ciliated cells were predominant in the three different segments of the oviduct and their percentage increased from fimbriae to ampulla and significantly decreased in the isthmus. SEM revealed in the infundibulum finger-like mucosal folds, some of them interconnected, in the ampulla numerous and elaborated branched folds of the mucosa, whereas the isthmus displayed a narrow lumen, short and non-branched mucosal folds. In the ampulla and isthmus the majority of non-ciliated cells showed apical blebs provided or not of short microvilli. TEM displayed different ultrastructural features of ciliated and non-ciliated cells along the oviduct. Isthmus ciliated cells presented a more electron-dense cytoplasm than in infundibulum and ampulla cells and its cilia were enclosed in an amorphous matrix. The non-ciliated cells of infundibulum did not contain secretory granules but some apical endocytic vesicles and microvilli coated by a well developed glycocalyx. Non-ciliated cells of ampulla and isthmus contained secretory granules. Apical protrusions of ampulla displayed two types of secretory granules as well as occasional electron-lucent vesicles. Isthmus non-ciliated cells showed either electron-lucent or electron-dense cytoplasm and not all contained apical protrusions. The electron-dense non-ciliated cells displayed microvilli coated with a well developed glycocalyx. Three types of granules were observed in the isthmus non-ciliated cells. The regional differences observed along the epithelium lining the mare oviduct suggest that the epithelium of the each segment is involved in the production of a distinctive microenvironment with a unique biochemical milieu related to its functional role.     

Mitochondria-rich (chloride) cells in the gill epithelia from four species of stenohaline fresh water teleosts

Summary The mitochondria-rich (chloride) cells have been found to be present in the gill epithelia of four species of stenohaline fresh water teleosts. The cytoplasm of these chloride cells contains an extensive network of cytoplasmic tubules which communicate with intercellular spaces bordering the lateral and basal cell surfaces. Numerous vesicles with fairly electron-dense interiors are also present in the apical cytoplasm of chloride cells. The apical surface of a chloride cell forms an apical pit, but the lumen of the pit does not appear to be in continuity with the interior of the apical vesicles and tubules inside the cell.When Carassius auratus were kept in 100, 200, 300, and 400 mOsm-diluted sea water for a month, no appreciable changes occurred in the number and fine structure of the chloride cells, except for a dilation of the apical vesicles and a slight decrease in diameter of the cytoplasmic tubules in these cells in the fishes kept in 300 and 400 mOsm.These results suggest that chloride cells may be a rather common occurrence in the gill epithelia of stenohaline fresh water teleosts, and may function in ion-transport in these fishes in fresh water environments.