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.     

Secretion by ependymal cells of the neurohypophysis and saccus vasculosus of Polypterus ornatipinnis (Osteichthyes)

Electron microscopic studies of the neurohypophysis and saccus vasculosus of the bichir (Polypterus ornatipinnis) reveal an apocrine release of secretory material by ependymal cells (e.g., crown cells). The secretory material appears to migrate along the microtubular apparatus and the ciliary filaments to the cell buds. It is postulated that the formation of the buds and their release is mediated by cilial action. Secretion buds are noted in the cerebrospinal fluid and vascular sinusoids. Bulbous projections of neurohypophyseal secretory tracts extend into the ependymal lumen which also contains elementary secretion granules. Specialized “liquorkontaktneurone” are interspersed with ependymal cells. An interrelation between the hypothalamus, neurohypophysis, saccus vasculosus, and the meta-adenohypophysis is postulated.     

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.     

Immunocytochemical localization of S-100 protein in the hypophysis and saccus vasculosus of the elasmobranchs Mustelus manazo and Scyliorhinus torazame

Summary S-100 protein-immunoreactive cells were demonstrated by immunocytochemical procedures in the hypophysis and saccus vasculosus of two species of elasmobranchs (Mustelus manazo and Scyliorhinus torazame). In the saccus vasculosus of M. manazo, immunoreactivity was detectable exclusively in the fibrous portions interposed between the epithelial layer and the blood vessels. In the neurohypophysis, tanycytes and astrocytes of the median eminence were immunostained, but only a few labeled cells were found in the neurointermediate lobe. In S. torazame, the neurohypophysis displayed a similar distribution of immunoreactivity, but there were no labeled cells in the saccus vasculosus. In both species, none of the glandular cells of the hypophysis displayed immunoreactivity. Electron-microscopic examination showed that the immunostained cells in the saccus vasculosus correspond to astrocytes.     

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.     

The Development of Saccus vasculosus in Two Teleosts

The development and differentiation of the ventro-caudal part of the diencephalon, the saccus infundibuli, has been examined in salmon, Salmo salar L., and in pike, Esox lucius L. In salmon, the saccus infundibuli becomes the saccus vasculosus; but in pike, this does not occur. The question of saccus vasculosus and part of the neural lobe of the tetrapod pituitary being homologous is dealt with.     

The neuronal system of the saccus vasculosus of trout (Salmo trutta fario and Oncorhynchus mykiss): an immunocytochemical and nerve tracing study

The neuronal system of the saccus vasculosus of two species of trout was studied with immunocytochemical methods and carboindocyanine-dye (DiI) tract-tracing. The cerebrospinal-fluid-contacting neurons of the saccus were immunoreactive for gamma-aminobutyric acid (GABA), glutamic acid decarboxylase (GAD), and neuropeptide Y (NPY). Immunostaining of alternate sections of the saccus vasculosus of fry with anti-GAD and anti-NPY indicated that these substances were colocalized. The tractus sacci vasculosi and the neuropil of the nucleus sacci vasculosi were also immunoreactive to these substances. The GABA, GAD, and neuropeptide Y immunoreactivity of the saccus vasculosus system appeared early in trout ontogeny. After applying DiI to various levels of the tractus sacci vasculosi of adult trout, we observed massive bilateral saccular projections to the nucleus sacci vasculosi and could follow the course of the sacco-thalamic tract. This tract extended in the subependymal region of the thalamus rostral to the nucleus sacci vasculosi and split into two small tracts that reached the subhabenular-preoptic region. Sacco-thalamic fibers formed extensive periependymal plexuses along their trajectory. Interestingly, no clear evidence of the existence of a saccopetal system was obtained. On the basis of these results, we postulate that the saccus vasculosus system modulates the function of centers of the posterior tubercle and periventricular thalamus. Received: 5 August 1996 / Accepted: 4 January 1997     

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.     

Metabolic activity in the saccus vasculosus of the rainbow trout,salmo gairdneri (richardson)

Summary Labelling experiments to test mucopolysaccharide synthesis in the saccus vasculosus of the rainbow trout gave negative results and provoked analysis of succinic dehydrogenase activity in the coronet cells. Such activity was almost absent in the fresh-water living rainbow trout but was intense in sea water adapted individuals as well as in a sea water teleost, the flounder. Conversely, in sea water adapted rainbow trout which had been transferred back to fresh-water, activity had again decreased. In the sea water adapted rainbow trout high succinic dehydrogenase activity was paralleled by strongly positive staining with alcian blue, indicating the presence of mucopolysaccharides. The latter fishes also showed incorporation of N-acetyl-³H-glucosamine. Our findings indicate a role for saccus vasculosus in adaptation for osmoregulation in sea water and favour the hypothesis of a secretory function for the coronet cells.This work has been supported by grants from the Royal Physiographical Society of Lund and the Faculty of Natural Sciences at the University of Lund. We are greatly indebted to Mrs. Lena Eriksson, Mrs. Kristine Fogelström and Mrs. Lena Svenre for excellent technical assistance.     

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.     

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.     

The development of a saccus vasculosus in Tilapia mossambica Peters and other cichlids

Observations are made on the development and the presence of a Saccus Vasculosus in Tilapia mossambica and other cichlids.
In those cichlids that do not possess a saccus vasculosus the development of this organ is apparently suppressed in a very early stage of life.
A saccus vasculosus is present in all those American and Indian cichlids that were investigated, but this organ was not found in cichlids indigenous to the African continent.     

Receptor cells of the catfish olfactory mucosa

In the present study, it has been demonstrated that catfisholfactory cells, having knobs characterized by a crown of longmicrovilli, are bipolar neurons. These cells, found almost exclusivelyon the dorso-medial half of the sensory area of the olfactorylamellae, most probably function as olfactory receptor cells.They appear to be different from microvillous tufted cells describedin several other fishes as well as in the catfish.     

The hypothalamo-hypophysial vascular relationship in Indian fresh-water goby, Glossogobius giuris (Ham.).920u.

The hypothalamo-hypophysial vascular relationship and intra-hypophysial vasculatisation have been described in order to understand the regulatory mechanism of hypothalamic control over the functions of the pituitary gland. In Glossogobius giuris, the disposition of the blood vessels in the head region is on typical teleostean pattern with certain modifications. The nucleus preopticus is supplied through the nucleus preopticus artery, a small blood vessel arising from the anterior branch of the posterior cerebral artery, whereas the pituitary gland receives blood through a pair of hypophysial arteries. The blood from the pituitary is drained off by the pituitary veins whch pour their blood into the supra-orbital sinus. The anterior cerebral vein after taking the blood from anterior part of the brain including the hypothalamus and the nucleus preopticus joins with the supra-orbital sinus. The hypothalamo-hypophysial portal system is absent in this fish. The saccus vasculosus receives blood from the posterior cerebral artery through a small blood vessel and is collected by a prominent saccus vasculosus vein which pours blood into the supra-orbital sinus before it joins the infra-orbital sinus to form the heat vein. There seems to be no physological connection between the saccus vasculosus and pituitary gland. The highly vascularised neurohypophysis interdigitate with the pars intermedia and extends upto the proximal pars distalis. The blood vessels are restricted to the neurohypophysial extensions only. However, in the rostral pars distalis the blood vessels are present but the neurohypophysis does not extend to this part. The blood capillaries enter the rostral pars distalis from the capillary network on the surface of pituitary gland along with the connected tissue covering of the pituitary. The neurohypophysis shows a greater vascularisation in comparison to that of the other glandular part of the pituitary gland. In the present study of Glossogobius giuris, though an extensive ramification of neurohypophysis occurs with the pars intermedia and the proximal pars distalis, the neurosecretory axons do not innervate the endocrine cells of the pituitary gland and the blood vessels are found restricted to the neurohypophysial extensions except that of the rostral pars distalis. The neuro-vascular way of hypothalamic control over the functions of the pituitary gland seems to be justified as the neurosecretory fibres have been found associated with the blood vessels.     

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.     

Ultrastructural Peculiarities of the Embryogenesis of the Brittle Star Amphipholis kochii (Lutken, 1972)

This paper addresses morphogenetic processes and cell differentiation during embryogenesis of the brittle star Amphipholis kochii at the ultrastructural level. The radial cleavage is not strictly determined. Embryos are covered with a thick hyaline envelope and contain numerous yolk granules and small lipid drops. Blastulae feature a thick blastoderm with extensive intercellular cavities, which are retained in the crest epithelium of late gastrulae. Embryonic cells have single cilia with long cross-striated rootlets associated with the Golgi apparatus. Depolarized cells of the primary mesenchyme with a well-developed rough endoplasmic reticulum differentiate into sclerenchyme syncytium. Gastrulation occurs by invagination. Secondary mesenchymal cells emigrate from the archenteron tip to differentiate into amebocytes, which contain a well-developed Golgi apparatus and numerous mitochondria. The endoderm is formed of cubic cells with numerous yolk granules and rare microvilli. Flattened cells of the dorsal and ventral ectoderm contain a small amount of yolk. Yolk utilization during embryogenesis occurs by intracellular lysosomal digestion with selective exocytosis of toposomes.Original Russian Text Copyright © 2005 by Biologiya Morya, Gliznutsa, Dautov.     

The ciliated epidermis of Xenoturbella bocki (Platyhelminthes, Xenoturbellida) with some phylogenetic considerations

The epidermis of Xenoturbella bocki Westblad was studied by scanning and transmission electron microscopy. Two cell types predominate in the epidermis: multiciliated epidermal cells and non-ciliated or monociliated gland cells. A conspicuous feature is the dense ciliary coverage and the numerous gland cell openings. Xenoturbella has a characteristic pattern of axonemal filament termination in the distal tips of their cilia. Each epidermal cilium has the typical 9 + 2 patten through the major part of its shaft. Near the tip there is a shelf at which doublets 4–7 terminate. Doublets 1, 2, 3, 8 and 9 continue into the thinner distal part of the cilium. A similar shelf in cilia is known only from the turbellarian orders Nemertodermatida and Acoela, and hence may be an apomorphic feature which indicates a close relationship between Xenoturbellida, Nemertoder-matida and Acoela. The basal body is provided with a so-called basal foot which has a cross-striated appearance and an expanded distal plate that seems to act as a microtubule organizing center. Approximately 15–25 microtubuli radiate from the endplate of the basal foot to the basal bodies caudally. The arrangement of basal foot and ciliary rootlets in Xenoturbella differs from that of Acoela and related orders in that there are two striated rootlets only (an anterior and a posterior one), rather than one main rootlet and two lateral rootlets.     

"Blood-contacting neurons" in the brain of the Japanese eel Anguilla japonica

To discriminate "blood-contacting neurons" within the brain of the eel, Evans blue (EB) was injected intraperitoneally. After five days, six brain areas were externally stained blue with the dye; the saccus dorsalis (SD), the epiphysis (E), the area postrema (AP), the posterior part of the magnocellular preoptic nucleus (PM), the pituitary (Pit), and the saccus vasculosus (SV). Among the EB-positive area, some cells in the PM, the anterior tuberal nucleus (NAT) and the AP were discriminated as the "blood-contacting neurons" histologically, whereas EB-positive neurons were not detected in the SD, the E, the Pit and the SV regions. In the PM, most EB-positive neurons (90 %) were immunoreactive to vasotocin (AVT) antibody, indicating that these neurons are vasotocinergic. The remaining EB-positive neurons (10 %) were not immunoreactive to ANG II and tyrosine hydroxylase (TH) antibodies. Although some neurons in the PM were immunoreactive to ANG II antibody, they were EB-negative. In contrast, almost all EB-positive neurons in the AP showed TH-like immunoreactivity (-lir), indicating that these neurons utilize catecholamine(s) as a neurotransmitter. The EB-positive neurons in the NAT were not immunoreactive to AVT, ANG II and TH antibodies, whereas some neurons without EB-staining showed ANG II-lir. Possible roles of these neurons in regulating drinking behavior in eels are discussed.     

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.

---

---

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