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See detailThe onset of NPQ and Deltamu(H)+ upon illumination of tobacco plants studied through the influence of mitochondrial electron transport.
Cardol, Pierre ULg; De Paepe, Rosine; Franck, Fabrice ULg et al

in Biochimica et Biophysica Acta (2010), 1797(2), 177-88

The relationship between the development of photoprotective mechanisms (non-photochemical quenching, NPQ), the generation of the electrochemical proton gradient in the chloroplast and the capacity to ... [more ▼]

The relationship between the development of photoprotective mechanisms (non-photochemical quenching, NPQ), the generation of the electrochemical proton gradient in the chloroplast and the capacity to assimilate CO(2) was studied in tobacco dark-adapted leaves at the onset of illumination with low light. These conditions induce the generation of a transient NPQ, which relaxes in the light in parallel with the activation of the Calvin cycle. Wild-type plants were compared with a CMSII mitochondrial mutant, which lacks the respiratory complex I and shows a delayed activation of photosynthesis. In the mutant, a slower onset of photosynthesis was mirrored by a decreased capacity to develop NPQ. This correlates with a reduced efficiency to reroute electrons at the PSI reducing side towards cyclic electron flow around PSI and/or other alternative acceptor pools, and with a smaller ability to generate a proton motive force in the light. Altogether, these data illustrate the tight relationship existing between the capacity to evacuate excess electrons accumulated in the intersystem carriers and the capacity to dissipate excess photons during a dark to light transition. These data also underline the essential role of respiration in modulating the photoprotective response in dark-adapted leaves, by poising the cellular redox state. [less ▲]

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See detailThe onset of photometric variability in red giant stars.
Jorissen, A.; Mowlavi, N.; Sterken, C. et al

in Astronomy and Astrophysics (1997), 324

The onset of variability in red giant stars is studied from the data collected by the `Long-Term Photometry of Variables' project which operates at ESO (La Silla) since 1982. The differential nature of ... [more ▼]

The onset of variability in red giant stars is studied from the data collected by the `Long-Term Photometry of Variables' project which operates at ESO (La Silla) since 1982. The differential nature of the observations combined with a multi-night reduction algorithm enables to study the variability of over 50 red giants with an accuracy of the order of 2 to 3 millimagnitudes on time scales ranging from days to years. All red giants with spectral types late G to early K (i.e. b-y~0.6-0.8) are stable at the level Ï _y_<6millimag (where Ï _y_ is the standard deviation of the Stroemgren y magnitude). Red giants with later spectral types are all variable, and it is found that the minimum variability level Ï _y, min_ increases with increasing b-y, thus defining a minimum-variability boundary. The new data obtained in this paper reveal that the time scale of the associated variability increases with increasing b-y (and thus amplitude), and that the stability of this time scale improves concomitantly. More precisely, irregular variations on time scales of 5 to 10-days (and Ï _y_~7millimag) characterize red giants with b-y~1.0, whereas the variations (with Ï _y_~100millimag) become more regular with periods of the order of 50d for red giants with b-y~1.3. A radial-velocity jitter (of the order of 1.5km/s r.m.s.) is associated with this photometric variability, and suggests that stellar oscillations may be responsible for the observed variations. [less ▲]

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See detailOnset of thermal ripples at the interface of an evaporating liquid under a flow of inert gas
Scheid, B.; Margerit, J.; Iorio, C. S. et al

in Experiments in Fluids (2012), 52

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See detailOnset Time of Neuromuscular Block and Intubating Conditions: Influence of Different Stimulation Patterns
Hans, Pol ULg; Dewé, Walthère ULg; Albert, Adelin ULg

in Acta Anaesthesiologica Belgica (1997), 48(1), 15-21

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See detailOntogenesis and functional aspects of oxytocin and vasopressin gene expression in the thymus network
Hansenne, Isabelle ULg; Rasier, G.; Pequeux, Christel ULg et al

in Journal of Neuroimmunology (2005), 158(1-2), 67-75

Ontogenesis of oxytocin (OT) and vasopressin (VP) gene expression and function were investigated in murine thymus. OT and VP transcripts were detected in the thymus on embryonic days 13 and 15 ... [more ▼]

Ontogenesis of oxytocin (OT) and vasopressin (VP) gene expression and function were investigated in murine thymus. OT and VP transcripts were detected in the thymus on embryonic days 13 and 15, respectively. Corresponding messenger RNAs were evidenced in thymic epithelial cells by in situ hybridization with a neurophysin probe. From all OT and VP receptors, only OTR was expressed by all T-cell subsets, while V1bR was found in double positive and single positive CD8 cells. In fetal thymic organ cultures, OTR antagonist d[DTyr(Et)(2), Thr(4)]OVT increased early apoptosis of CD8 cells, while V1bR antagonist (Sanofi SSR 149415) inhibited T-cell differentiation, and favored CD8 T-cell commitment. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailOntogenesis of behavioral sensitization and conditioned place preference induced by psychostimulants in laboratory rodents
Tirelli, Ezio ULg; Laviola, Giovanni; Adriani, Walter

in Neuroscience & Biobehavioral Reviews (2003), 27(1-2), 163-178

The present review deals mainly with the ontogenesis of two important phenomena involved in vulnerability to several neuropsychiatric disorders, namely with drug-induced sensitization (both contextual and ... [more ▼]

The present review deals mainly with the ontogenesis of two important phenomena involved in vulnerability to several neuropsychiatric disorders, namely with drug-induced sensitization (both contextual and non-contextual) and with conditioned place preference. The term 'infancy' covers the first three postnatal weeks during development in rats and mice. Conversely, the term 'adolescence' may cover the whole postnatal period ranging from weaning (PND 21) to adulthood (at least PND 60) or specifically the period around the onset of puberty (animals aged 33-44 days). Recent studies in rats demonstrated that the establishment of a context-dependent sensitization appears during the first (for repeated drug administration) or during the second (for a single drug administration) postnatal week. However, the memory of drug-context association is transient in developing pups (lasting one or two days following the drug pretreatment). The long-term retention of drug-context associations matures progressively, and is complete by the third week of postnatal life. Finally, those mechanisms responsible for an adult-like profile of context-independent pharmacological sensitization appear later during ontogenesis, being mature by the fourth week of postnatal life. Another set of experiments extended this ontogenetic characterization by comparing adolescent and adult mice. When compared to the latter, the former subjects exhibit a greater amphetamine-induced locomotor sensitization, almost no sensitization of aversive stereotyped behaviors, and a less marked place conditioning. The strength of the drug-induced place conditioning was also directly compared with the unconditioned novelty-seeking drive. In conclusion, neonatal rats are able to show a relatively short-lasting retention of sensitized drug effects (short-term sensitization), whereas the ability to exhibit relatively long-lasting sensitized effects matures progressively during infancy (long-term sensitization). On the other hand, adolescent mice show a reduced sensitization of drug-induced psychotic symptoms, together with a more marked sensitization of arousing and euphorigenic properties of the drug and a reduced incentive memory of its hedonic effects. These age-related changes do imply very different degrees of vulnerability to drug addiction and several other neuropsychiatric disorders. (C) 2003 Elsevier Science Ltd. All rights reserved. [less ▲]

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See detailOntogenetic aspects of individual differences in behavioral responsiveness to cocaine in rats
Michel, Alexa ULg; Tirelli, Ezio ULg

in Behavioural Pharmacology (1996), 10(Suppl.), 211-212

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See detailOntogenetic determinism of colour polymorphism in a coral reef fish, Chrysiptera brownriggii (Pomacentridae)
Frederich, Bruno ULg; Brié, Christophe; Santos, Raphael et al

Poster (2008, October)

The determinism of ontogenetic colour changes induced by environmental factors is poorly understood in marine fishes, especially in coral ecosystems. The present study, conducted at the Rangiroa Atoll ... [more ▼]

The determinism of ontogenetic colour changes induced by environmental factors is poorly understood in marine fishes, especially in coral ecosystems. The present study, conducted at the Rangiroa Atoll (French Polynesia) explored the effects of fish density and brightness/darkness condition (type of background) on colour determination during the ontogeny of a territorial damselfish Chrysiptera brownriggii (Bennett 1828). In this species, larvae always colonize the reef (settlement) in a yellow morph, while juveniles and adults can display two distinct colour-patterns: yellow and dark brown. Our experiments in aquaria showed that a significant higher proportion of C. brownriggii larvae turned into the brown morph in a dark condition during a period of 5 and 15 days (70-100% of brown morph induction) just after reef settlement. A significant positive effect of fish density inducing a brown colour morph was also highlighted. After a first colour induction, reversibility experiments illustrated that juveniles can change their colour morph anew after a 5-day period. Although a shift from brown to yellow morph seemed to be more limited. In the dark condition, yellow adults did not change their colour after a 5-day period. Our results showed that the colour dimorphism in C. brownriggii should be density-dependent. The period of sensitivity seems to last throughout the post-settlement period. We suggest that the yellow morph in C. brownriggii can be viewed as a paedomorphic trait. Overall, our results reveal that a darkness/lightness environment and fish density are environmental cues related to colour determinism in the polyphenetic C. brownriggii. [less ▲]

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See detailThe ontogenetic dynamic of skull shape disparity in damselfishes (Pomacentridae)
Frederich, Bruno ULg; Vandewalle, Pierre ULg

Conference (2009, May)

Damselfishes (Pomacentridae) are among the most speciose of coral-reef fishes, with > 350 species world-wide, most of which live on coral reefs. They have a life history with two distinct phases: a ... [more ▼]

Damselfishes (Pomacentridae) are among the most speciose of coral-reef fishes, with > 350 species world-wide, most of which live on coral reefs. They have a life history with two distinct phases: a dispersive pelagic larval phase and a sedentary benthic adult phase. The larval stage ends at coral reef settlement. All larvae feed on planktonic preys whereas juveniles and adults associated to the coral reef show a higher diversity of diets: zooplanktivorous, herbivorous, coral polyp feeders and omnivorous species. Morphological disparity is a major theme in paleobiology. Most studies of disparity have focused on its temporal dynamics over a geological time scale. Surprisingly, the relationship between ontogeny and disparity has received little attention. Using landmark-based geometric morphometrics, this study aims to test the hypothesis that the ontogenetic change in diet is related to an increase of shape disparity in head skeletal units (neurocranium, suspensorium + opercle, mandible and premaxilla) during the post-settlement growth in eight species of damselfishes. At the end of the larval stage (coral reef settlement), all skeletal units are already species-specific. By comparing levels of shape disparity between species at three developmental stages (at settlement, at 60 mm SL and at maximum adult body size), we found that disparity increases significantly during ontogeny. The ontogenies of shape were also compared to identify evolutionary changes in developmental processes modifying shape disparity. The ontogenetic patterns are highly divergent among species. At least, evolutionary changes affected three parameters of ontogenetic trajectories of shape in this group: (1) the allometric patterns (the direction in which the vector representing the ontogeny of shape point), (2) the amount of change undergone during the post-settlement phase and (3) the rate of shape changes. From a functional point of view, the ontogenetic transformations enhance suction-feeding and/or algae scraping (e.g. heightening of the suspensorium and opercle, shortening of the mandible). [less ▲]

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See detailOntogenetic shape changes in Pomacentridae (Teleostei, Perciformes) and their relationships with feeding strategies: a geometric morphometric approach
Frederich, Bruno ULg; Adriaens, Dominique; Vandewalle, Pierre ULg

in Biological Journal of the Linnean Society (2008), 95

The present study explores the shape changes of cranial structures directly involved in food capturing during growth after reef settlement in two species of Pomacentridae (Dascyllus aruanus and ... [more ▼]

The present study explores the shape changes of cranial structures directly involved in food capturing during growth after reef settlement in two species of Pomacentridae (Dascyllus aruanus and Pomacentrus pavo). Landmark-based geometric morphometrics were used to study allometric patterns and related shape changes in four skeletal units: neurocranium, suspensorium and opercle, mandible and premaxilla. At settlement, the larvae of both species have a relatively similar morphology, especially with respect to the mandible. Their shapes suggest a feeding mode defined as ram/suction-feeding. Ontogenetic shape changes show a shift to a suction feeding mode of prey capture. The main transformations involved are an increase in height of the suspensorium and the opercle, an elevation of the supraoccipital crest, a relative shortening of the mandible, and a lengthening of the ascending process of the premaxilla. Shape changes of the mandible in the two studied species also reflect an increase of biting capacities. The high disparity between adult shape results from differences in the rate and in the length of ontogenetic trajectories, from divergence of the ontogenetic trajectories (neurocranium, mandible, and premaxilla) and parallel shifts of the trajectories in the size-shape space (suspensorium and opercle). In an evolutionary context, allometric heterochronies during ontogeny of different skeletal unit of the head may be considered as a basis for the explanation of the diversity of damselfishes. [less ▲]

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See detailOntogenetic variations of thermal optimum for growth, and its implication on thermolabile sex determination in blue tilapia
Baras, E.; Mpo'n'tcha, A.; Driouch, H. et al

in Journal of Fish Biology (2002), 61(3), 645-660

Knowledge of how the optimum temperature for growth (Tdegrees(opt)) varies during ontogeny, and how close it is to the temperatures that induce Phenotypic masculinization is fundamental to the ... [more ▼]

Knowledge of how the optimum temperature for growth (Tdegrees(opt)) varies during ontogeny, and how close it is to the temperatures that induce Phenotypic masculinization is fundamental to the understanding of the evolution of thermolabile sex determinism (TSD) in fishes. In blue tilapia Oreochromis aureus, Tdegrees(opt) is 32.6degrees C at the start of exogenous feeding (10 mg fish) and it decreases by c 1degrees C each time that the fish bode mass increases by an order of magnitude. Temperatures <35degrees C are not sufficient to induce complete phenotypic masculinization. Based on a multiple-regression model (r(2)=0.938) plotting growth against body mass and water temperature. genotypically female tilapia living at high temperatures during the thermosensitive period (21-28 days) and being reversed into phenotypic males should incur an initial growth disadvantage over fish living at Tdegrees(opt) but not over those living at slightly colder temperatures (27-29degrees C). This initial disadvantage would be later compensated for by faster growth because of between-sex growth dimorphism to the detriment of phenotypic females. These arguments suggest that there is no definite pressure against the selection of TSD in blue tilapia and probable other Oreochromis spp. (C) 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved. [less ▲]

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See detailOntogenic and ecological control of metamorphosis onset in a carapid fish, Carapus homei: Experimental evidence from vertebra and otolith comparisons
Parmentier, Eric ULg; Lecchini, David; Lagardere, Françoise et al

in Journal of Experimental Zoology. Part A, Comparative Experimental Biology (2004), 301A(8), 617-628

In Carapus homei, reef colonisation is associated with a penetration inside a sea cucumber followed by heavy transformations during which the length of the fish is reduced by 60%. By comparing vertebral ... [more ▼]

In Carapus homei, reef colonisation is associated with a penetration inside a sea cucumber followed by heavy transformations during which the length of the fish is reduced by 60%. By comparing vertebral axis to otolith ontogenetic changes, this study aimed (i) to specify the events linked to metamorphosis, and (ii) to establish to what extent these fish have the ability to delay it. Different larvae of C. homei were caught when settling on the reef and kept in different experimental conditions for at least 7 days and up to 21 days: darkness or natural light conditions, presence of sea cucumber or not, and food deprivation or not. Whatever the nutritional condition, a period of darkness seems sufficient to initiate metamorphosis. Twenty-one days in natural light conditions delayed metamorphosis, whereas the whole metamorphosis process is the fastest (15 days) for larvae living in sea cucumbers. Whether the metamorphosis was initiated or not, otoliths were modified with the formation of a transition zone, whose structure varied depending on the experimental conditions. At day 21, larvae maintained in darkness had an otolith transition zone with more increments (around 80), albeit wider than those (more or less 21) of individuals kept under natural lighting. These differences in otolith growth could indicate an increased incorporation rate of released metabolites by metamorphosing larvae. However, the presence of a transition zone in delayed-metamorphosis larvae suggests that these otolith changes record the endogenously-induced onset of metamorphosis, whereas body transformations seem to be modulated by the environmental conditions of settlement. (C) 2004 Wiley-Liss, Inc. [less ▲]

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See detailOntogenic development of steroid 16 alpha-hydroxylase as a tool for the study of the multiplicity of cytochrome P-450.
Pasleau, Françoise ULg; Kolodzici, Claudine; Kremers, Pierre ULg et al

in European Journal of Biochemistry (1981), 120

1. Activities of progesterone, testosterone, pregnenolone and dehydroepiandrosterone 16 alpha-hydroxylase are undetectable in the fetal rat liver. During the neonatal period, the four enzymic activities ... [more ▼]

1. Activities of progesterone, testosterone, pregnenolone and dehydroepiandrosterone 16 alpha-hydroxylase are undetectable in the fetal rat liver. During the neonatal period, the four enzymic activities increase in parallel to the concentration of cytochrome P-450. Until puberty, they develop similarly in male and female rat livers. From the 40th to the 55th day, the four steroid 16 alpha-hydroxylase activities increase rapidly in the male rat liver. The sexual differentiation of the steroid 16 alpha-hydroxylation observed in adult male and female rats takes place around the 55th day. 2. In the adult rat liver, steroid 16 alpha-hydroxylase is supported by two forms of cytochrome P-450 (form I and form II), which differ in their relative affinities for the various steroid substrates, and by their relative proportions in male and female rat livers. These two forms of cytochrome P-450 are also present in the young male and female rat livers, but are roughly equal in proportion. The transition from the immature to the adult repartition of the two forms occurs during puberty and is correlated with the sexual differentiation of the steroid 16 alpha-hydroxylase activities. 3. During the critical phases of the rat ontogenic development, the in vitro interactions between benzo[a]pyrene and steroids were compared at the level of two rat liver monooxygenases: steroid 16 alpha-hydroxylase and aryl hydrocarbon hydroxylase. (a) In the immature male and female rat livers, progesterone 16 alpha-hydroxylase, and to a lesser extent, pregnenolone 16 alpha-hydroxylase are inhibited by benzo[a]pyrene. Progesterone 16 alpha-hydroxylase is also inhibited by metyrapone. (b) In the young rat, aryl hydrocarbon hydroxylase cannot be inhibited by steroids and appears to be supported by a single form of cytochrome P-450. The transition from the immature to the adult situation occurs around the 40th day. [less ▲]

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See detailOntogeny of acute sensitization to cocaine in rats
Tirelli, Ezio ULg; Gonzalez, C.

in Behavioural Pharmacology (1998), 9

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See detailOntogeny of Aromatase and Tyrosine Hydroxylase Activity and of Aromatase-Immunoreactive Cells in the Preoptic Area of Male and Female Japanese Quail
Balthazart, Jacques ULg; Tlemcani, O.; Harada, N. et al

in Journal of Neuroendocrinology (2000), 12(9), 853-66

The aromatization of testosterone into oestrogens plays a key role in the control of many behavioural and physiological aspects of reproduction. In the quail preoptic area (POA), aromatase activity and ... [more ▼]

The aromatization of testosterone into oestrogens plays a key role in the control of many behavioural and physiological aspects of reproduction. In the quail preoptic area (POA), aromatase activity and the number of aromatase-immunoreactive (ARO-ir) cells are sexually differentiated (males > females). This sex difference is implicated in the control of the sexually dimorphic behavioural response of quail to testosterone. We analysed the ontogenetic development of this sex difference by measuring aromatase activity and counting ARO-ir cells in the POA of males and females from day 1 post hatch to sexual maturity. We investigated in parallel another enzyme: tyrosine hydroxylase, the rate limiting step in catecholamine synthesis. Between hatching and 4 weeks of age, aromatase activity levels were low and equal in males and females. Aromatase activity then markedly increased in both sexes when subjects initiated their sexual maturation but this increase was more pronounced in males so that a marked difference in aromatase activity was present in 6 and 8 week-old subjects. Tyrosine hydroxylase activity progressively increased with age starting immediately after hatching and there was no abrupt modification in the slope of this increase when birds became sexually mature. No sex difference was detected in the activity of this enzyme. The number of ARO-ir cells in the POA progressively increased with age starting at hatching. No sex difference in ARO-ir cell numbers could be detected before subjects reached full sexual maturity. The analysis of the three-dimensional organization of ARO-ir cells in the POA revealed that, with increasing ages, ARO-ir cells acquire a progressively more lateral position: they are largely periventricular in young birds but they are found at higher density in the lateral part of the medial preoptic nucleus in adults. These data indicate that aromatase activity differentiates sexually when birds reach sexual maturity presumably under the activating effects of the increased testosterone levels in males. The number of ARO-ir cells, however, begins to increase in a non sexually differentiated manner before the rise in plasma testosterone in parallel with the increased tyrosine hydroxylase activity. Whether this temporal coincidence results from a general ontogenetic pattern or from more direct causal links remains to be established. [less ▲]

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See detailOntogeny of GABA-ergic and dopaminergic mediation of gnawing behavior in the mouse
Tirelli, Ezio ULg

in Psychopharmacology (1987), 92(1), 89-95

Examined the ontogenetic course of dopaminergically mediated gnawing and the potentiation of this behavior by muscimol (a gamma-aminobutyric acid receptor agonist) in developing and young adult mice using ... [more ▼]

Examined the ontogenetic course of dopaminergically mediated gnawing and the potentiation of this behavior by muscimol (a gamma-aminobutyric acid receptor agonist) in developing and young adult mice using a time-sampling or a corrugated paper procedure. In Exp I, the older group (14-53 days), displayed a dose-dependent gnawing behavior after intraperitoneal injections of methylphenidate ([MTPD], 20, 30, 50 mg/kg). In 5-, 8-, 11-, and 14-day-old pups, MTPD (10, 20, 50 mg/kg) evoked stereotyped gnawing. Muscimol pretreatment (0.025-2.3 mg/kg) induced a clear-cut potentiation of gnawing elicited by MTPD (10 or 20 mg/kg) as early as 8 days of age. It is argued that the effectiveness of MTPD in inducing gnawing-licking among 5-day-old pups confirms the early maturation of central dopamine receptors reported in the literature. ((c) 1997 APA/PsycINFO, all rights reserved) [less ▲]

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