Is the primitive regulation of pituitary prolactin (tPRL177 and tPRL188) secretion and gene expression in the euryhaline tilapia (Oreochromis mossambicus) hypothalamic or environmental?
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We examined the effects of environmental salinity on circulating levels of the two prolactins (tPRL177 and tPRL188) and levels of pituitary tPRL177 and tPRL188 mRNA in the euryhaline tilapia, Oreochromis mossambicus. Fish were sham-operated or hypophysectomized and the rostral pars distalis (RPD) autotransplanted onto the optic nerve. Following post-operative recovery in (1/4) seawater, tilapia were transferred to fresh water (FW), (1/4) seawater (SW) or SW. Serum tPRL177 and tPRL188 levels in sham-operated and RPD-autotransplanted fish were highest in FW and decreased as salinity was increased. tPRL177 and tPRL188 mRNA levels in RPD implants as well as in pituitaries from the sham-operated fish were also highest in FW and decreased with increasing salinity. Serum osmolality increased with salinity, with the highest levels occurring in the seawater groups. We conclude that some plasma factor (probably plasma osmolality), in the absence of hypothalamic innervation, exerts a direct regulatory action on prolactin release and gene expression in the pituitary of O. mossambicus. This regulation is in accord with the actions of the two prolactins in the freshwater osmoregulation of the tilapia. (+info)
Metallothionein response in gills of Oreochromis mossambicus exposed to copper in fresh water.
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Freshwater Oreochromis mossambicus (tilapia) were exposed to 3.2 micromol/l Cu(NO(3))(2) in the water for up to 80 days, and copper (Cu) and immunoreactive metallothionein (irMT) were localized in the branchial epithelium. Cu was demonstrated in mucous cells (MC), chloride cells (CC), pavement cells (PC), respiratory cells (RC), and basal layer cells (BLC) via autometallography combined with alcian blue staining for MC and Na(+)-K(+)-ATPase immunostaining for CC and, on the basis of their location in the epithelium of PC, RC, and BLC. In control fish (water with Cu concentration +info)
Muscle as the primary site of urea cycle enzyme activity in an alkaline lake-adapted tilapia, Oreochromis alcalicus grahami.
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The tilapia fish Oreochromis alcalicus grahami from Kenya has adapted to living in waters at pH 10.5 by excreting the end product of nitrogen metabolism as urea rather than as ammonia directly across the gills as occurs in most fish. The level of activity in liver of the first enzyme in the urea cycle pathway, carbamoyl-phosphate synthetase III (CPSase III), is too low to account for the observed high rates of urea excretion. We report here the surprising finding that CPSase III and all other urea cycle enzyme activities are present in muscle of this species at levels more than sufficient to account for the rate of urea excretion; in addition, the basic kinetic properties of the CPSase III appear to be different from those of other known type III CPSases. The sequence of the CPSase III cDNA is reported as well as the finding that glutamine synthetase activity is present in liver but not in muscle. This unusual form of adaptation may have occurred because of the apparent impossibility of packaging the needed amount of urea cycle enzymes in liver. (+info)
Temperature dependence of estrogen binding: importance of a subzone in the ligand binding domain of a novel piscine estrogen receptor.
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The full length estrogen receptor from Oreochromis aureus (OaER) was cloned and expressed in vitro and in vivo as a functional transcription factor. Amino acid residues involved in the thermal stability of the receptor are located at/near subzones beta1 and beta3, which are highly conserved in other non-piscine species but not in OaER. Hormone binding studies, however, indicate that OaER is thermally stable but exhibited a approximately 3-fold reduced affinity for estrogen at elevated temperatures. Transfection of OaER into various cell lines cultured at different temperatures displayed a significant estrogen dose-response shift compared with that of chicken ER (cER). At 37 degrees C, OaER requires approximately 80-fold more estrogen to achieve half-maximal stimulation of CAT. Lowering of the incubation temperature from 37 degrees C to 25 degrees C or 20 degrees C resulted in a 4-fold increase in its affinity for estrogen. The thermally deficient transactivation of OaER at temperatures above 25 degrees C was fully prevented by high levels of estrogen. Thus, compared to cER, the OaER exhibits reduced affinity for estrogen at elevated temperature as reflected in its deficient transactivation capability. Amino acid replacements of OaER beta3 subzones with corresponding amino acids from cER could partially rescue this temperature sensitivity. The three-dimensional structure of the OaER ligand binding domain (LBD) was modelled based on conformational similarity and sequence homology with human RXRalpha apo, RARgamma holo and ERalpha LBDs. Unliganded and 17beta-estradiol-liganded OaER LBD retained the overall folding pattern of the nuclear receptor LBDs. The residues at/near the subzone beta3 of the LBD constitute the central core of OaER structure. Thus, amino acid alteration at this region potentially alters the structure and consequently its temperature-dependent ligand binding properties. (+info)
Phosphorylation state of red and white muscle in tilapia during graded hypoxia: an in vivo (31)P-NMR study.
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The aim of this study was to measure the energetic consequences of hypoxia in different types of skeletal muscle within a single tilapia species (n = 5). To that aim, 81.0 MHz (31)P-nuclear magnetic resonance (NMR) spectra were collected, alternately, from three surface coils placed adjacent to the tissues of interest (dorsal white muscle, ventral white muscle, and lateral red muscle) during a graded hypoxia load over 6 h followed by a 5-h recovery period. The fish were contained in a flow cell, enabling us full control of the oxygen content of the bathing medium. The intracellular pH and the concentrations of ATP, phosphocreatine (PCr), and P(i) were determined from the NMR spectra. For normoxia, biochemical differences for [gamma-ATP], [PCr], and [sugar phosphates] (SP) were observed between all three locations, especially between the red and white muscle. During hypoxia stress, loss of phosphorylated compounds (PCr+P(i)+SP) was observed at all locations but was the most severe in red muscle. When the aerobic (respirometry) and anaerobic ((31)P-NMR) ATP production via an energy balance are compared, flexible metabolic depression is demonstrated during anaerobioses. It is concluded that control of the aerobic and anaerobic component of metabolism during metabolic depression is independent of each other. (+info)
Na(+)/K(+)-ATPase immunoreactivity in branchial chloride cells of Oreochromis mossambicus exposed to copper.
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Chloride cells were identified by Na(+)/K(+)-ATPase immunocytochemistry at the light and electron microscope levels in gills of freshwater tilapia Oreochromis mossambicus. Turnover of chloride cells was enhanced by exposing the fish to waterborne copper (3.2 micromol l(-)(1)) for 14 days, as indicated by a 38 % increase in cells expressing proliferating cell nuclear antigen (PCNA) relative to controls. The expression of PCNA was most marked in the central area of the filamental epithelium, from where the chloride cells are thought to originate and migrate. In control fish, chloride cells were associated exclusively with the filamental epithelium. In both controls and copper-exposed fish, two chloride cell populations were seen after Na(+)/K(+)-ATPase immunostaining. These probably represent subpopulations of newly emerged chloride cells: (1) strongly stained cells (mature chloride cells) in the filamental and lamellar epithelium and (2) weakly stained cells, identified by electron microscopy as apoptotic and necrotic chloride cells, mainly in the filamental epithelium. Absolute numbers of mature chloride cells fell, while necrotic and apoptotic chloride cell numbers increased, in copper-exposed fish. A strong correlation could be established for gill Na(+)/K(+)-ATPase specific activity and the number of strongly stained chloride cells in controls and copper-exposed fish and for Na(+)/K(+)-ATPase specific activity and total numbers of immunoreactive cells in copper-exposed fish owing to an increased incidence of weakly staining cells. (+info)
Dietary choline requirements of juvenile hybrid tilapia, Oreochromis niloticus x O. aureus.
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An 8-wk feeding trial was conducted to determine the dietary choline requirement for juvenile hybrid tilapia, Oreochromis niloticus x O. aureus. Purified basal diets were formulated using vitamin-free casein (contained 370 mg choline/kg) as the protein source. Graded levels (0, 100, 200, 400, 600, 800, 1,000 and 2,000 mg choline/kg diet) of choline chloride were added to the basal diet, resulting in eight dietary treatments in the experiment. Each diet was fed to three replicate groups of tilapia initially averaging 0.62 +/- 0.01 g/fish in a closed, recirculating rearing system. Feed efficiency, survival and blood triglyceride, cholesterol and phospholipid concentrations were generally high in fish fed choline-supplemented diets compared to fish fed the control diet. Analysis by broken-line regression of weight gain and body choline concentration and by polynomial regression of liver lipid concentration of the fish indicated that the dietary choline concentration for tilapia is about 900 mg/kg. Taking into account the choline concentration of the unsupplemented basal diet, the optimal dietary choline requirement for growing tilapia is about 1,000 mg/kg. (+info)
Comparative severity of experimentally induced mycobacteriosis in striped bass Morone saxatilis and hybrid tilapia Oreochromis spp.
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Twenty striped bass Morone saxatilis and 20 hybrid tilapia Oreochromis niloticus x O. mossambicus x O. aureus each received a single intramuscular injection of 1.6 x 10(6) colony forming units per gram body weight of Mycobacterium marinum. Striped bass manifested significantly greater clinical and microscopic disease compared to tilapia. Whereas all the striped bass had died or were clinically ill by Day 8 post-infection, there was no apparent disruption of normal behaviour, physical appearance, or growth in any of the sacrificed or surviving tilapia. Histologically, granulomas in striped bass were generally larger and less discrete, with a higher proportion of heavily vacuolated macrophages, and large cores of necrotic cells. Visceral granulomas in tilapia were smaller, with a higher proportion of epithelioid macrophages, more pigment-containing cells, more peripheral lymphocytes, and virtually no central necrosis. Visceral granulomas were 18-fold more numerous in striped bass than in tilapia. Based upon histomorphometric data, mean proportions of acid-fast bacteria within pronephros granulomas were 4-fold greater in striped bass than tilapia, and striped bass granulomas averaged more than twice as large as tilapia granulomas. In the anterior kidney of striped bass, a positive correlation existed between mean mycobacterial proportions and mean necrosis scores. In tilapia, mean mycobacterial proportions correlated negatively with mean granuloma numbers, whereas there was no correlation between these parameters in striped bass. Results suggest that intrinsic functional differences in the immunologic systems of striped bass and hybrid tilapia may contribute to inter-species variation in mycobacteriosis susceptibility. (+info)