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.     

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.     

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.     

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.     

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     

Effects of stress on carbohydrate metabolism in the teleost Notopterus notopterus (Pallas)*

The effects of different types of stre35 on carbohydrate metabolism in N. notopterus were investigated. Starvation alone brings about a signifiant increse in the glycogen content of the saccus vasculosus and a significant decrease in the brain glycogen concentration. The increased glycogen concentration in the saccus vasculosus may be a device to safeguard the brain against glucose deficiency during starvation stress. Rapid depletion of the muscle glycogen following fasting shows that the muscle glycogen IS the readily utilizable source of energy during starvation. Exposure of N. noropierus to air brought about an increaSe in the liver glycogen and blood glucose levels but did not affect other paramcters studied. Physical exhaustion of N. notopierus is noticed within 1–2 min of exercise. The readily available source of energy for exercise is the muscle glycogen. and the lactic acid produced is probably metabolized in the muscle itself. Saccus vasculosus glycogen. though inde-pendent of changes in the blood glucose levels, may possibly be controlled by variations in the brain glycogen.     

Ultrastructural development of the saccus vasculosus in rainbow trout (Salmo gairdneri)

Summary The morphology of crown cells and supporting cells of the saccus vasculosus has been described by numerous investigators. A third type of cell has been mentioned by several authors and referred to variously as undifferentiated crown cells, pseudo-coronet cells, pear-shaped cells and, most recently, as liquor-contact neurons. A developmental study of the organ was undertaken as a possible means of characterizing this third cell type and determining its origin.The epithelium of the saccus vasculosus and the ependyma of the third ventricle are different and distinguishable at the time of hatching in rainbow trout. Initially, apical protrusions from crown cells extend slightly into the lumen and a few end knobs or motile cilia project from them. Basal bodies with cross-striated rootlets occur frequently. In swim-up fry, end knobs are more numerous and heavily vacuolated, although cross-striated rootlets are less apparent.Evidence is presented that is consistent with a hypothesis of secretory activity in the crown cells. Further, portions of end knobs containing this material appear to be pinched off from the remainder of the crown cell. The possible presence of bipolar neurons is also discussed.Supported by Research Grant 5 R01 NS0627 from the National Institute of Neurological Diseases and Stroke.     

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.     

The saccus vasculosus of Anguilla anguilla (L.) from larva to adult

Summary The ultrastructure of coronet cells of the saccus vasculosus has been studied in specimens of Anguilla anguilla (L.) at different stages of its life cycle. At all the stages observed coronet cells are composed of a basal and an apical part, the latter bearing globules with primary vesicles. In the larva (a marine form) and in the fully metamorphosed small eel at the time of entry into freshwater the narrow lumen and the vesicles within the apical globules are filled with electron-dense material. In forms in which adaptation to freshwater has occurred, the saccus lumen appears expanded, the apical globules are better developed, and the electron-dense material has disappeared. It is suggested that the two situations observed represent different functional states of the organ, in relation to different conditions of environmental salinity.The authors gratefully acknowledge the contribution of Dr. G. Andreoli, of the University of Parma, who provided the Atlantic larvae for this study.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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     

A histologic survey of diencephalic circumventricular organs in teleosts with special reference to osteoglossomorphs

Diencephalic circumventricular organs of various teleosts were studied histologically. Special attention was paid to osteoglossomorphs. The neurohypophysis of osteoglossomorphs (Arapaima, Notopterus, Xenomystus, andGymnarchus) is well differentiated into the median eminence and the neural lobe. The pituitary organization of these species is an intermediate between that of holosteans and of more advanced teleosts. The saccus vasculosus is absent inPantodon andGymnarchus, but it is well developed inNotopterus andXenomystus. The light microscopically discernible pineal is absent inGymnarchus: this may be the only species that lacks the pineal among teleosts. The paraphysis is found in various species including most osteoglossomorphs and some perciforms. In advanced teleosts such as gobiids and tetraodontids, the saccus dorsalis and velum transversum are absent, but the diencephalic choroid plexus is well developed instead. Some evolutionary trends are apparent in the occurrence and organization of these circumventricular organs among teleosts.