The extravascular channel system in the rostral pituitary of Mugil cephalus (Teleostei) as revealed by use of horseradish peroxidase

Summary Using the unlabeled antibody peroxidase-antiperoxidase (PAP) technique at the light microscopic level, it was demonstrated that, in the amphibian magnocellular hypothalamo-hypophysial neurosecretory system, vasotocin and mesotocin are synthesized in separate neurons. A tendency to preferential location of the two kinds of neuronal perikarya is described. The neurosecretory perikarya are the origin of separate vasotocinergic and mesotocinergic axons. In the neural lobe, the pattern of distribution of the two types of axons is different. The coarse ventricular dendrites of both kinds of neurons are hormone-containing processes. Staining with anti-bovine neurophysin I serum suggested that the vasotocinergic and the mesotocinergic neurons synthesize different neurophysins.This investigation was supported by a grant from the Belgian Nationaal Fonds voor Geneeskundig Wetenschappelijk Onderzoek     

Morphological and functional peculiarities of mesenchymal cells in the pars tuberalis of the pituitary gland

Summary Following injection of high doses of horseradish peroxidase (HRP), mesenchymal cells distributed in the perisinusoidal space of the pars tuberalis of the hypophysis in cats, rabbits and Japanese quails, sequester the exogenously administrated peroxidase intensively. These cells are designated by the authors as horseradish peroxidase-uptake cells (HRP-uptake cells or HUC). HRP-uptake cells constitute a system of macrophages in the pars tuberalis of mammals and birds, and are located around the hypophysial portal veins. HRP-uptake cells differ in morphological and functional characteristics from similar cells in other parts of hypophysis. They are thought to play a role in the hypothalamic control of adenohypophysial secretion.Supported by grants (No. 144022, 237002) from the Ministry of Education, Science and Culture, Japan     

Histological investigation of pituitary homotransplants in the marine form (trachurus) of the threespine stickleback,Gasterosteus aculeatus L.

Summary Whole pituitary glands were autotransplanted into the tail musculature of intact sticklebacks similar in size to the donors. The structure of the grafted pituitaries and of the in situ glands in the recipient and sham-operated fish was examined. The prolactin-secreting cells, thyrotrophs and possibly the gonadotrophs showed signs of being under inhibitory hypothalamic control whereas the somatotrophs appeared to be more autonomous of hypothalamic influence. The pars intermedia and corticotrophs appeared to be dependent upon the hypothalamus for maintenance of functional acitvity.I am indebted to Drs. W. S. Hoar and T. J. Lam for their help during the period of this investigation and to Mr. L. Sharman for his technical assistance.The work was supported by a grant in aid of research from the National Research Council of Canada to Dr. W. S. Hoar.     

Responses of the teleost pituitary (goldfish,eel) to deionized water

Summary The cytological responses of the pituitary gland during adaptation to deionized water (DW) were investigated in the goldfish and the eel. In both teleost species, a stimulation of the prolactin (PRL) cells could not be detected, although the levels of blood electrolytes (Na⁺,Ca²⁺,Cl^–) are reduced in the eel. PRL cells appear less active in DW-adapted eels. A striking stimulation of the PAS-positive cells of the pars intermedia occurs in both species after 3 weeks and, in the eel, is still present after 11 weeks. Cell and nuclear hypertrophy, mitoses and a well-developed endoplasmic reticulum are observed. MSH cells are partially degranulated when pigmentation is affected; a reduced activity of MSH cells is evident after 11 weeks. The amount of neurohypophysial tissue is reduced. In the goldfish and the eel, during adaptation to DW, an unknown factor secreted by the PAS-positive cells of the pars intermedia appears to play a more important role than the secretion of PRL. These two species are able to survive in fresh water without the pituitary. The control of the PAS-positive cells by external sodium or calcium is discussed.     

Reproductive cycles of Mugil cephalus, Liza ramada and Liza aurata (Teleostei: Mugilidae)

Carbohydrates in photoreceptor segments in the retina of the firemouth cichlid Thorichthys meeki are described and compared. The present periodic acid-Schiff (PAS) and lectin results revealed the occurrence of neutral carbohydrates, composed mainly of glycosamine and mannose and glucose, in the light absorbing segments in rods and cones in this species. Unlike in mammals, the retina in this teleost seems to be poor in galactose and galactose-galactosamine units in the light absorbing segments.     

Freeze-etch study of the teleostean pituitary

Summary The structure of membranes in the pituitary of several teleostean species was studied with the freeze-etching technique. Nuclear pore density is higher in hormone-secreting than in stellate cells, suggesting a higher rate of nucleo-cytoplasmic interactions in the secretory cells. The perinuclear endoplasmic reticulum (ER) in the MSH-secreting cells has a large number of fenestrae, whereas in the ER whorls of the prolactin-secreting cells the fenestration occurs only rarely. Three different types of membrane specializations are described, presumably related to exo-endocytotic events at the level of the plasmalemma.The Following Abbreviations are used in the Present Study AH adenohypophysis - ER endoplasmic reticulum - ES extravascular spaces - FE freeze-etching - HRP horseradish peroxidase - NH neurohypophysis - NS neurosecretory - SG secretory granule This work was supported by grants from the Swiss National Science Foundation Nos. 3.636.75, 3.611.75 and the Dr. Eric Slack-Gyr Stiftung in Zürich     

The gonadotropic cells in the pituitary of the black molly,Mollienisia latipinna,and other teleosts,identified by the immunofluorescence technique in normal and androgen-treated animals

Summary Using anti-carp-gonadotropic--globulin, the indirect immunofluorescence technique was applied to sections of the pituitary of 12 teleost species. From the investigated species, the Poeciliinae, and especially the black molly, showed a distinct localization of fluorescent cells in the mesoadenohypophysis. Strong fluorescence was observed in the ventralmost region, containing the presumed gonadotropic cells; weak fluorescence was observed in the dorsal region, in the presumed thyrotropic cells. The possibility of an unspecific reaction with TSH-cells in the latter region is discussed. Treatment of male black mollies for 38 days with methyltestosterone resulted in a loss of fluorescence in the ventral region of the meso-adenohypophysis, whereas there was no decrease of the fluorescence in the dorsal region. The results support the hypothesis that the ventral basophils in the mesoadenohypophysis produce gonadotropic hormone.     

Ultrastructural autoradiographic localization of serotonin in the pituitary of a teleost fish,Poecilia latipinna

Summary Light- and electron-microscopic autoradiographic studies of pituitaries of the molly Poecilia latipinna, after their incubation with tritiated serotonin, revealed the presence of labelled cells in the proximal pars distalis, together with cell processes or nerve fibres throughout all regions of the gland except the prolactin cell zone. The serotonincon-centrating cells and most of the fibres contained small dense-cored vesicles, but some labelled fibres contained larger granules similar in ultrastructure to those of vasotocinergic fibres.This work was supported by a SERC studentship to DJG and SERC grant GR/6379-06 to Professor J.N. Ball     

Somatostatin in the brain and the pituitary of some teleosts

Summary Immunocytochemical investigations show that somatostatin (SRIF)-like immunoreactive material is present in the brain and the pituitary of nine different species of teleosts. In the brain, immunoreactive perikarya and fibers are observed in the preoptic periventricular nucleus, the entopeduncular nucleus, the anterior periventricular nucleus, and the nucleus lateralis tuberis. In the pituitary, SRIF-like-immunoreactive fibers occur in the proximal pars distalis (PPD), which contains the growth hormone (GH)-secreting cells. Nerve fibers are scattered among GH cells (cyprinids), or end on the basal lamina at the neuroglandular interface of the PPD (eel, salmonids). In the eel, the proximal neurohypophysis does not penetrate deeply into the PPD that is very poorly vascularized. In some species, e.g. Myoxocephalus, SRIF-like immunoreactive fibers are also observed in the caudal neurohypophysis, and even among MSH cells of the pars intermedia.In long-term starved carps and eels, the amount of SRIF-like material in the pituitary is clearly reduced. A possible role of SRIF in the concomitant stimulation of GH cells is discussed.     

Distribution of extracutaneous melanin pigment in Sparus auratus, Mugil cephalus, and Dicertranchus labrax (Pisces, Teleostei)

The morphological and biochemical characteristics of pigment accumulations found in the kidney, liver, spleen, and mesentery of three different species of teleost fishes have been studied. There are significant differences in number, distribution, and morphology of pigment accumulations in different organs of the three species. Biochemical studies have shown the existence of tyrosinase activity in the mesentery of Mugil cephalus and in the kidney and mesentery of Sparus auratus. No tyrosinase activity was found in any internal organs of Dicertranchus labrax. That activity was assayed using three methods: tyrosine hidroxylation, dopa oxidation, and melanin formation. The morphological and biochemical observations are in agreement. In those organs in which we have demonstrated melanin synthetic activity, the pigment cells are morphologically and like melanophores, while in the organs that show no melanin synthetic activity, the pigment cells resemble macrophages.     

The blood-testis barrier in Aphanius dispar (Teleostei)

Summary Thin sections of normal testes from the cyprinodont Aphanius dispar were studied by electron microscopy after intravascular injection of live specimens with horseradish peroxidase. The intercellular space in the spermatogenic cysts is marked differently by the tracer according to the degree of differentiation of the germ cells. Spermatogonia and gonocytes undergoing meiosis are surrounded by a dark band of the marker. This band gradually disappears during spermiogenesis. In cysts containing ripe spermatozoa, the marker penetrates a short distance between the bases of adjoining Sertoli cells bordering the cysts, but is arrested by tight junctional complexes near the lumina of the cysts. The tight junctions between the Sertoli cells provide a permeability barrier between the vascular spaces of the stroma and the lumina of ripe cysts.Abbreviations BM basement membrane - BTB blood-testis barrier - HRP horseradish peroxidase This research was supported by a grant from the National Council for Research and Development, Israel, and the GKSS Geesthacht-Tesperhude, Federal Republic of Germany     

Bacilliform inclusions in cells of the proximal pars distalis in the pituitary of four species of Tilapia (Teleostei)

Summary Thin sections and replicas of freeze-etched pituitaries from six species of the teleostean family of Cichlidae were studied by electron microscopy. Four species belonging to the genus Tilapia exhibit rod-like structures, i.e., bacilliform inclusions (BI), about 1–2 m in length in cells of the proximal Pars distalis. The BI are found either isolated or fused in small groups. They are enclosed in an envelope similar to that of secretory granules. Both the BI and the secretory granules give a positive PAS-reaction.Abbreviations BI bacilliform inclusion - GTH gonadotroph hormone - STH somatotroph hormone - TSH thyrotroph hormone This research was supported by a grant from the National Council for Research and Development, Israel, and the GKSS Geesthacht-Tesperhude, Germany     

Pineal neurons projecting to the brain of the rainbow trout,Salmo gairdneri Richardson (Teleostei)

Summary The morphology of intrapineal neurons that give rise to the pineal tract and project to the brain in the rainbow trout was visualized by the use of neuronal backfilling with horseradish peroxidase (HRP). The tracing was performed on excised pineal organs under in-vitro conditions at 4° C, with filling times ranging from 6 to 24 h. Large multipolar, bipolar and unipolar neurons were visualized in the rostral tip of the pineal organ (pineal ganglion). These neurons possessed extended dendritic trees participating in the formation of a circumscribed neuropil-like area. Throughout the pineal organ small bipolar elements were the most ubiquitous type of neuron, however, with markedly smaller numbers in the proximal portion of the pineal end-vesicle. In the pineal stalk, some bipolar neurons were observed to contact the pineal lumen, which is continuous with the third ventricle, via dendritic processes of various types. It could not be established whether any of these CSF-contacting processes were identical with photoreceptor outer segments. The basal processes of the bipolar neurons sometimes possessed distally projecting collaterals. In conclusion, it has been shown that (i) different types of neurons displaying varied patterns of regional distribution contribute to the pineal tract, and (ii) certain CSF-contacting neurons in the pineal organ send axonal processes directly toward the brain.Supported by Research grant Ko 758/2-4 from the Deutsche ForschungsgemeinschaftFellow of the Alexander von Humboldt Foundation, Bonn, Federal Republic of Germany     

Histology of the pituitary gland of the grey mullet, Mugil cephalus L.

The present communication deals with a histological study of the pituitary gland of the teleost fish Mugil cephalus , found in the estuarine waters of Cochin area. Six different cell types were identified in the pituitary gland on the basis of their grouping, distribution and staining properties. The prolactin and the TSH cells (thyroid stimulating hormone producing cells or thyrotrops) were identified in the rostral pars distalis and the ACTH cells (adrenocorticotropic hormone producing cells or corticotrops) in the interphase between the neurohypophysis and the rostral pars distalis. The STH cells (somatotropic hormone producing cells or somatotrops) and the gonadotropic cells were distinguished in the proximal pars distalis and the MSH cells (melanin stimulating hormone producing cells or melanotrops) in the pars intermedia.     

Motile aeromonas infection of striped (grey) mullet Mugil cephalus

Infection of striped mullet (Mugil cephalus) with Aeromonas hydrophila results in an acute septicemic disease. The disease can be experimentally induced by intramuscular injection, skin or gill scarification or by the oral route using pellets purposely seeded with bacteria. The organism was isolated from the blood 1–2 days after infection and from all organs 24 hr or longer after infection. The disease is characterized by early inflammatory and proliferative changes and later necrotic changes. Enteritis and hepatic necrosis are constant findings in aeromonad disease of M. cephalus but surface lesions are not pathognomic for these infections in mullet. Death of infected fish may be attributed to bacterial toxins which cause necrosis of parenchymal organs and soft tissue structure.     

Ontogeny of the photoreceptors in the embryonic retina of the viviparous guppy,Poecilia reticulata P. (Teleostei)

Summary Ultrastructural analyses of retinal development in the guppy embryo show that at midgestation all types of photoreceptors are differntiated in the fundus, and at birth differentiation extends over the whole retina. Formation of discs of outer segments is more rapid in rods than in cones. Double cones differentiate simultaneously with long single cones and are formed by the adhesion of two primordial inner segments; short single cones develop last. Wherever cones are differentiated, they are arranged in an adult-type square mosaic. The rods in the embryo, as opposed to the adult, are likewise regularly arranged within the mosaic unit.These results are at variance with the generally held opinion that adult teleosts which possess duplex retinae have larvae with pure cone retinae, and that rods, double cones and mosaics appear in late larval life or only at metamorphosis.In the double cones of the guppy embryo subsurface cisternae develop along the adjoining primordial inner segments. Additionally, regularly distributed subsurface cisternae are formed in the regions of intimate contact of long single cones with double cones and rods.We suggest that the early development of rods and double cones, and a square-mosaic with regular distribution of rods and subsurface cisternae, provide the newly born with a fully functional optical apparatus, especially suited to perception of movements. This is necessary for its survival against predatory, especially maternal, attacks.This work was in part subsidized by a grant from the Medical Research Council of Ireland to Y.W.K.     

Immunocytochemical identification of prolactin cells in the pituitary gland of tilapia larvae (Oreochromis mossambicus: Teleostei)

Summary Using an antiserum to highly purified chum salmon prolactin, prolactin cells were identified in the putative rostral pars distalis of newly hatched tilapia larvae (Oreochromis mossambicus) by the immunogold method for the electron microscope. In the putative rostral pars distalis, some cells had another kind of secretory granule which was much less numerous, much smaller in size, and without immunoreactivity to salmon prolactin antiserum. Controls incubated with salmon prolactin-preabsorbed antiserum or normal serum showed no immunoreactive cells, confirming the specificity of the antiserum. The possible role of prolactin in the osmoregulation of tilapia larvae is discussed.