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G Boeuf

Publications and source records attributed to G Boeuf.

At least 37 records · Page 2Linked to original sources
PubMed1998

Short-term physiological changes in turbot and seabream juveniles exposed to exogenous ammonia.

Seabream and turbot juveniles (40-520 g) were exposed to constant exogenous NH5-N concentrations (1.27-4.27 mmol/l; pH, 8.15). In 96 hr acclimated fish, plasma TA-N (total ammonia nitrogen) contents were positively correlated to ambient ammonia concentrations. The LD50 were 2.2-2.5 mmol/l TA-N in both species. There were no marked osmoregulatory disturbances and plasma urea-N, thyroid hormones levels and gill (Na-K)-ATPase activities were only affected at the highest concentrations. Liver GOT, GPT and GIDH activity dose-response were low and species dependent. In cannulated and non-cannulated turbot exposed to half 96 hr LC50 (lethal ambient concentration for 50% of the population), there was a rapid, pronounced and prolonged increase in plasma TA-N, followed by an immediate decline when exogenous ammonia supply was stopped. Maximum loading and unloading were observed within 1-3 hr. Plasma cortisol levels indicated a stressful situation in exposed fish (150 ng/ml) and a quick recovery capacity. In dose and time response experiments, the most relevant physiological indicator of ammonia stress was blood TA-N content. Other parameters tested led either to transient or low amplitude responses except when fish approached death.

Acclimatization↗
PubMed1997

Individual diurnal plasma profiles of thyroid hormones in rainbow trout (Oncorhynchus mykiss) in relation to cortisol, growth hormone, and growth rate.

In order to characterize the individual diurnal plasma profiles of triiodothyronine (T3) and thyroxine (T4) in rainbow trout (Oncorhynchus mykiss), blood samples from 41 fish were taken every hour during a 24-hr period, through a catheter inserted into the dorsal aorta. The possible influences of day-night alternation, sex, and diet (feed intake, time of meals) on thyroid hormone (TH) profiles were analyzed. The existence of relations between diurnal plasma profiles of T3, T4, T3/T4 ratio, and those of the growth hormone (GH), cortisol (previously described in Gomez et al., J. Exp. Zool. 274, 171-180, 1996), and the growth rate was monitored. Average daily T3 and T4 concentrations were, respectively, 2.6 +/- 0.2 and 5.5 +/- 0.3 ng/ml (n = 41). Our study showed little or no variation in plasma T3 concentrations during one 24-hr period, while those of T4 fluctuated markedly. T4 peaks occurred from a baseline of 4.0 +/- 0.2 ng/ml at a frequency of 2.5 +/- 0.2 peaks/24 hr, with an amplitude of 3.0 +/- 0.4 ng/ml, and a duration of 4.3 +/- 0.4 hr. There was a significant difference between the average circulating T3 level during the day and that at night (2.4 +/- 0.2 vs 2.7 +/- 0.2 ng/ml). No influence of sex or food factors was observed on daily TH concentrations. TH peaks occurred irregularly and asynchronously without apparent influence of day-night alternation, sex, and diet. The growth rate was significantly correlated with the daily T3 concentration (r = 0.77), but not with T4. No significant relationships were found between daily concentrations of T3, T4, GH, and cortisol. The absence of a relationship between TH and GH concentrations suggests that, in salmonids, GH may have no observable short-term action on the conversion of T4 to T3.

Animals↗
PubMed1997

Distribution of ionocytes in the saccular epithelium of the inner ear of two teleosts (Oncorhynchus mykiss and Scophthalmus maximus).

The saccular membranes of trout (Oncorhynchus mykiss) and turbot (Scophthalmus maximus) were examined to characterize specialized epithelial cells that might be responsible for ion exchange. The approach for localizing cell types was new for this tissue, as observations were made with a stereomicroscope and a light microscope in order to have a general view of the epithelium. No important differences between the two species were seen. The saccular tissue is a monolayer epithelium (except for the macula neural zone) surrounded by a layer of connective tissue invaded by many blood vessels. The use of the fluorescent probe DAPSMI and zinc iodide/osmium fixation-coloration defined two areas in which ionocytes were present. In the first, large ionocytes were grouped into a nearly complete, crowned meshwork around, but separated from, the macula. In the second area, opposite the macula, the ionocytes were smaller, cubical, and grouped in patches. Cells rich in Na+, K+-ATPase and carbonic anhydrase II were present in both areas. Contrary to previous studies in mammals and fish, ionocytes were also found in the epithelium of the saccule.

Animals↗
PubMed1997

Ionic composition of endolymph in teleosts: origin and importance of endolymph alkalinity.

Ionic (Na+, K+, Cl-, PO4(3-), pH), total CO2, total calcium and protein concentrations in the plasma and endolymph of the inner ear were compared in trout Oncorhynchus mykiss and turbot Scophthalmus maximus. In both species, saccular endolymph was characterized by high levels of K+ and total CO2 and in trout by an alkaline pH. The kinetic characteristics of proton secretion across the saccular epithelium of trout were investigation using a titration technique in which isolated saccules were mounted as closed sacs. The rate of proton secretion depends strongly on the pH of the Ringer's solution and secretion stops at a pH below 7.2. Proton secretion is driven by an energy-dependent mechanism involving basolateral ouabain-sensitive Na+/K+ exchangers. Proton secretion was partially inhibited by acetazolamide and completely inhibited in Na(+)-free Ringer or in the presence of 1 mmol l-1 amiloride. A cellular model stressing the importance of proton exchange through the saccular epithelium is proposed to explain the regulation of endolymph pH, a crucial factor for the deposition of otolith calcium.

Animals↗
PubMed1996

Characterization of the insulin-like growth factor type 1 receptor messenger in two teleost species.

The insulin-like growth factor type 1 receptor (IGF-1R) is a tyrosine kinase which plays essential role in the regulation of growth and development. In this study, we have cloned cDNAs encoding the tyrosine kinase domain of the IGF-1R from two species of fish. The turbot and trout nucleotide sequences share 82% identity. Moreover, the deduced polypeptides are also highly conserved (> 90% identity) compared with the IGF-1R sequences described in other vertebrates, particularly within domains involved in the catalytic activity and in the transduction pathway. Northern blot analyses have revealed a unique 13-kb mRNA transcript. Using an RT-PCR approach, we have also shown that the polyadenylation status seems to vary according to the developmental stage in turbot: polyadenylated in oocytes and in the first larval stages, the mRNA becomes undetectable in the polyadenylated fraction in later stages or in adult somatic tissues. These results suggest that IGF-1R mRNA undergoes complex post-transcriptional regulation.

Amino Acid Sequence↗
PubMed1994

Effects of growth hormone on gill chloride cells in juvenile Atlantic salmon (Salmo salar).

Experiments were performed to investigate the effects of ovine growth hormone (oGH) on both the ultrastructural features of chloride cells and the ability of gills to extrude Na+ after transfer into seawater. February presmolts and June parrs of the Atlantic salmon (Salmo salar) were implanted with oGH. In such animals, spontaneously showing a poor ability to adapt themselves to seawater life, GH significantly increased gill Na(+)-K(+)-adenosinetriphosphatase activity as well as gill sodium efflux into seawater. When examined by electron microscope, two types of chloride cells (alpha- and beta-types) were identified in control parrs and presmolts. GH treatment induced an increase in size and number of alpha-cells that displayed an extensive tubular system, while the beta-cells, thought to be specific to freshwater life, decreased in number. There was, concomitantly, an increase in number of accessory cells associated with the apical portion of the alpha-cells and, as a result, the formation of extensive shallow junctions between these cell types. Such functional and ultrastructural modifications that mimicked those naturally occurring during the last steps of the smoltification strongly suggest that GH stimulates the differentiation of freshwater chloride cells toward a seawater type.

Animals↗
PubMed1990

Ultrastructural features of mitochondria-rich cells in stenohaline freshwater and seawater fishes.

In order to elucidate the functional significance of accessory cells in freshwater fishes, such as the rainbow trout, which displays a poor adaptability to seawater life, a search for such cells was performed in two stenohaline freshwater fishes: the loach and the gudgeon. Accessory cells were never encountered in these species; but, in contrast, two types of chloride cells were observed consistently that strikingly resembled the alpha- and beta-cells previously described in the guppy, a freshwater-adapted euryhaline fish. The alpha-cell, a pale and elongated chloride cell, was located at the base of the secondary lamellae in close contact with the arterioarterial pillar capillary. Darker, ovoid chloride cells resembling the beta-cell were found exclusively in the interlamellar region of the primary epithelium facing the central venous sinous. The latter cells frequently formed multicellular complexes linked together by deep, narrow, apical junctions. In another experiment, a stenohaline seawater fish, the turbot, was adapted to diluted 5% saltwater and to fresh water. In seawater, the gill epithelium contained only one type of chloride cell, always associated with accessory cells. Due to numerous cytoplasmic interdigitations between the accessory cells and the apical portion of the chloride cell, there was a noticeable increase in the length of the shallow apical junction, sealing off the intercellular space between the two cell types. In 5% saltwater, there was a decrease in the number of these interdigitations and a concomitant decrease in the length of the shallow apical junction. In fresh water, chloride cells were partially or completely separated from the outside medium by modified accessory cells. It is thus concluded that accessory cells are found exclusively in fish living in seawater or preadapted to seawater and that they probably are involved in the formation and modulation of paracellular pathways for ionic excretion. In contrast, the respective roles of the two types of chloride cells observed in freshwater fishes are still to be determined.

Adaptation, Physiological↗
PubMed1989

Smoltification and seawater adaptation in Atlantic salmon (Salmo salar): plasma prolactin, growth hormone, and thyroid hormones.

To obtain more information on the role of prolactin and growth hormone during the parr-smolt transformation of Atlantic salmon, a population of fish in fresh water was sampled from January to June during two consecutive years. Gill Na+,K+-ATPase activity increased steadily during smoltification and a plasma thyroxine peak was observed 2-3 weeks before the gill Na+,K+-ATPase peak. On the basis of these two parameters, smoltification was considered complete in our populations in April 1985 and May 1986. Two peaks in plasma growth hormone levels occurred in 1986, one in mid-April and the second in mid-May. In both cases, these peaks coincided with a peak in plasma triiodothyronine and preceded the thyroxine peak by 1-2 weeks. Moreover, the second peak which lasted for 1 month coincided with maximal gill Na+,K+-ATPase activity. A decrease in plasma prolactin levels was observed during smoltification of Atlantic salmon in 2 consecutive years. During this period of decreasing and low plasma prolactin levels, gill Na+,K+-ATPase activity increased to its highest values. Atlantic salmon smolts were also directly transferred into seawater. After 2 days or more in seawater, plasma prolactin levels were not significantly different from those on Day 0, whereas in fresh water they showed large fluctuations. All these data indicate that growth hormone may play an important role in the development of hypoosmoregulatory activity. Increased hypoosmoregulatory ability also appears to be associated with low prolactin levels.

Acclimatization↗
PubMed1988

Ultrastructural features of chloride cells in the gill epithelium of the Atlantic salmon, Salmo salar, and their modifications during smoltification.

To elucidate the ultrastructural modifications of the gill epithelium during smoltification, gills of the Atlantic salmon (Salmo salar) were examined by electron microscopy at three stages of this process, which were defined as follows: "parrs" were freshwater fish that had not yet started their transformation; "freshwater smolts" were freshwater fish that were ready to enter seawater; and "seawater smolts" were smolts that had been transferred from fresh water and maintained for 4 days in seawater (35%). In the gill epithelium of parrs, there were two types of chloride cells. The large chloride cells contained deeply stained mitochondria and numerous apical, irregular, dense, membrane-bound bodies that formed 77% of the chloride cell population and were distinguished easily from small chloride cells that have distinctly paler mitochondria and no dense bodies in their apical cytoplasm. In freshwater smolts, the large chloride cells formed 95% of the chloride-cell population. In contrast to the small chloride cells that were not modified, they almost doubled in size. Their tubular system developed extensively to form a tight network with regular meshes significantly smaller than those observed in parr chloride cells. Forty percent of the large chloride cells were associated with a new type of cell, the accessory cell, to which they were bound by shallow apical junctions. Half of these accessory cells were not seen to be in contact with the external medium. In seawater smolts, 80% of the large chloride cells were associated with accessory cells. Most accessory cells reached the external medium and sent numerous cytoplasmic interdigitations within the apical portion of the adjacent chloride cells. As a result, a section through the apical portion of the chloride cells and their associated accessory cells revealed a mosaic of interlocked cell processes bound together by an extended, shallow apical junction. It was concluded that the Atlantic salmon develops in fresh water most of the ultrastructural modifications of the gill epithelium which in most euryhaline fish are triggered by exposure to seawater. The effective transfer into seawater would act only as a final stimulus to achieve some adequacy between the freshwater smolt and its new environment.

Animals↗
PubMed1985

Plasma and pituitary prolactin levels in rainbow trout during adaptation to different salinities.

The development of a highly specific radioimmunoassay for salmonid prolactin (PRL) using chinook salmon PRL allowed us to study plasma and pituitary PRL profiles in large sedentary rainbow trout (Salmo gairdneri) transferred from fresh water to seawater and vice versa. Plasma osmotic pressure and chloride levels were also measured for 3 weeks following change of salinity. Within 1 day after transfer to full seawater we observed a plasma PRL decrease, which stayed significantly lower (3-5 ng/ml) than the fresh water control group (10-15 ng/ml) during the entire experiment. Pituitary PRL content showed an initial abrupt increase, but after 3 weeks in seawater pituitary PRL content had decreased to the same level as in the fresh water control group. On the contrary, transfer from seawater to fresh water was followed within 1 day by a rise in plasma PRL levels, which stayed high (10-15 ng/ml) after 3 weeks in fresh water. Simultaneously, pituitary PRL content decreased significantly. These results may indicate an important role of PRL in fresh water adaptation of sedentary rainbow trout.

Acclimatization↗