1,720,972 research outputs found
Developmental Effects of Cortisol on the Stress Response and Behaviour in Zebrafish
No full textThe objective of the study was to determine whether maternal stress affects early development in zebrafish (Danio rerio). The hypothesis was that maternal stress will lead to excess cortisol deposition in the embryos, and this will compromise the larval stress response and locomotor activity. Maternal stress and the attendant rise in cortisol levels led to excess cortisol deposition, but only transiently in the embryos. This was kept in check by cortisol-induced stimulation of 11βHSD2, a cortisol-degrading enzyme, in the ovarian follicles. Excess embryo cortisol content disrupted the larval stress response, locomotor activity, and was anxiolytic. These phenotypes corresponded with increased region-specific neurogenesis. Post-hatch elevation in cortisol levels by waterborne exposure, mimicking a stress response, increased locomotor activity but did not impact anxiety behaviour. Overall, maternal stress alters larval stress and behavioural phenotypes, underpinning a distinct developmental effect associated with elevated zygotic cortisol content in zebrafish
Characterization of Rapid Nongenomic Cortisol Signalling in Rainbow Trout Liver
No full textGlucocorticoids are critical in the regulation of metabolic processes for stress adaptation. Cortisol, the primary glucocorticoid in fish, exerts physiological effects through genomic and nongenomic signalling pathways. The genomic response to cortisol is characterized by activation of the corticosteroid receptors, glucocorticoid receptor (GR) and mineralocorticoid receptor (MR), whereas the nongenomic cortisol response involves rapid changes to downstream second-messenger signalling cascades independent of gene regulation. However, nongenomic glucocorticoid signalling remains poorly characterized in teleost models and even more so in the liver, despite the importance of this tissue in regulating both metabolic and physiological adjustments in the face of a stressor. Therefore, the primary objective of this thesis was to further elucidate mechanisms of rapid cortisol signalling in rainbow trout (Oncorhynchus mykiss) liver. The hypothesis tested was that activation of secondary-signalling cascades would mediate rapid cortisol effects and glucocorticoid-membrane receptor(s) were involved in initiating this response. Indeed, stress and the attendant rise in cortisol rapidly modulated cAMP response element binding protein (CREB) phosphorylation, and reduced reactive oxygen species (ROS) generation and glutathione production in vivo. While corticosteroid receptors were identified on the plasma membrane, RU486 had no effect on CREB signalling or ROS generation in vitro, suggesting that these endpoints are GR-independent. Also, cortisol did not rapidly affect the transcript abundance of glucocorticoid-responsive genes associated with the corticosteroid receptors along with biomarkers for immune, growth, metabolic, and oxidative stress systems, suggesting a role for genomic activation in directly regulating the stress response. Furthermore, a membrane-specific cortisol receptor(s) remains unidentified in any species. Altogether, the results presented here propose a role for rapid nongenomic glucocorticoid signalling in modulating the stress-mediated metabolic responses in fish liver, and this provides a novel approach in studying the role of glucocorticoids in mediating stress coping mechanisms
The effect of maternal stress on early life history traits and performance in salmonids
No full textDuring the upstream spawning migration of Pacific salmon, circulating cortisol concentration increases to mobilize energy stores. Pacific salmon contend with a gauntlet of stressors that can further elevate cortisol concentrations in response to stressful stimuli. Consequently, plasma cortisol concentrations measured in maternal fish that have reached their spawning grounds may reflect their recent stress history. Despite studies mimicking the maternal transfer of cortisol to the eggs, how natural variation in maternal cortisol concentrations shapes offspring phenotypes is unclear. Therefore, I assessed whether stress in maternal salmonids alters the growth and stress performance of their offspring via increased cortisol deposition in the eggs. Specifically, I tested whether high concentrations of circulating cortisol in maternal fish reduced embryo survival, and fry growth and stress performance. Eggs from 101 wild coho salmon (Oncorhynchus kisutch) females were collected from three rivers in the interior Fraser River watershed, British Columbia, Canada. The eggs were fertilized and reared until the fry stage at a hatchery. High egg cortisol concentration increased offspring mortality at the eyed stage. Interestingly, the surviving free-swimming fry had enhanced growth, resulting in larger size, and heightened cortisol stress response. The corresponding increase in the transcript abundance of genes related to growth and stress axis functioning in the fry suggest that high maternal cortisol concentrations programmed offspring for faster growth and heightened stress reactivity during early development. To test whether high egg cortisol concentrations specifically causes the phenotypic variation such as that observed in coho salmon, I manipulated steroid concentrations in the eggs of 10 maternal rainbow trout (Oncorhynchus mykiss) by immersion in water-borne cortisol during fertilization. Cortisol treatments increased egg steroid concentrations; however, neither the developmental trajectory nor the stress performance of fry differed statistically among treatments. Therefore, the utility of egg cortisol concentration as a biomarker of offspring developmental performance may be dependent on the life history of the animal. Overall, maternal cortisol concentration seems to act as a cue that prepares the offspring of wild coho salmon for stressful environments
The Contribution of Skeletal Muscle Metabolism to Aerobic Scope of Rainbow Trout (Oncorhynchus mykiss)
No full textBeyond cellular maintenance, fish require additional energy to accomplish activities such as swimming, digestion, growth, and reproduction. Aerobic scope is the capacity to increase metabolic rate above the minimum (i.e. standard vs maximal metabolism) to meet the demands required for these other activities. Increasing temperatures often increase the standard metabolic rate, reducing and limiting aerobic scope, and it has been suggested this may ultimately limit heat tolerance in fishes. Many different tissues collectively contribute to metabolic rate, but we do not know if specific tissues dominate energy use in fishes, nor how they are impacted by temperature. This thesis investigated the hypothesis that red, aerobic muscle is the primary contributor to the aerobic metabolism, and thus aerobic scope, of a swimming fish. Swim tunnel respirometry using rainbow trout (Oncorhynchus mykiss) and measures of oxygen consumption on isolated, working muscle were used to determine their respective aerobic scopes, using oxygen as a proxy for aerobic metabolism across a range of temperatures, up to those approaching the critical thermal maximum of rainbow trout. Further, the mass of red muscle in fish, along with measures of metabolic rate, were used to assess the contribution of red muscle metabolism to that of the whole fish. It was found that red muscle was not a major contributor of aerobic metabolism compared to the whole fish, and thus it was not a major component of aerobic scope. However, red muscle showed similar effects of temperature on both resting and maximum metabolism as that seen in whole fish, increasing the standard metabolic rate at high temperatures but not affecting the maximum metabolic rate. Further, red muscle power output was significantly reduced at high temperatures while metabolic rate was not, potentially implicating the cost of maintenance of muscle as one contributing factor to the high mortality rate of fish at high temperatures
Ecological consequences of genetically-based thermal traits in fishes
No full textUnprecedented contemporary rates of environmental change risk irreversible loss of biodiversity and ecosystem functioning in aquatic systems, with population persistence dependent on resiliency in thermal physiology and thermoregulation. The association between thermal physiology and behavioural traits can predict population persistence, range shifts, and evolution in the face of contemporary climate change, but the mechanisms underlying these relationships are unknown. In this thesis, I characterize the impact of abiotic environmental factors on population distributions, assess the relationship between thermal tolerance and preference traits, characterize the genetic architecture of these thermal traits, and use these empirical data to construct a mechanistic species distribution model for a genetically similar cluster in a marine environment. I found that temperature and water volume are significant drivers of age- and size-class distributions within a wild marine population of Oligocottus maculosus. I also found that population and generation significantly impacted various thermal tolerance traits, and that there were significant correlations between physiological and behavioural thermal traits in Gasterosteus aculeatus across generations and populations. I also show that the thermal tolerance limits of freshwater populations of G. aculeatus are closer to observed thermal extremes in their natural environments than their marine counterparts. Using phenotypically-divergent populations of G. aculeatus, I identified four significant quantitative trait loci (QTL) that were associated with thermal tolerance traits and that many of these traits co-localized to the same two QTL. Using these genetically-based thermal traits, I predicted a conservative but northward shift in the geographic range of the marine populations of G. aculeatus. Collectively, these data demonstrate that the inclusion of both physiological and behavioural data will be important in forming more robust predictions regarding species’ responses to climate change, with an emphasis on temperature-associated behaviours when considering predictions regarding population persistence. By integrating multiple responses to climate change and facilitating collaboration across fields, we can begin to produce more accurate and robust predictions concerning the fate of populations, communities, and ecosystems under contemporary climate change
Rapid Non-genomic Actions of Cortisol in Fish
No full textCortisol, the primary glucocorticoid (GC) in teleosts signals through either the genomic pathway, by activating the intracellular glucocorticoid receptor (GR) and/or the mineralocorticoid receptor (MR), or through non-genomic pathways. However, the mechanism of action of non-genomic cortisol signalling is far from clear, and there is a complete lack of consensus as to the physiological significance of this rapid action. The major goal of this thesis was to determine the mode of action of cortisol in bringing about rapid changes in intracellular Ca2+ levels [iCa2+] as a non-genomic response, and to assess the physiological consequences of this rapid effect at the cellular and organismal level. This was tested using rainbow trout (Oncorhynchus mykiss) hepatocytes (non-excitable) and zebrafish (Danio rerio) muscle (excitable) explant as in vitro and ex vivo models, respectively. The results indicate that a direct interaction of cortisol with the calcium release-activated (CRAC) channel may be responsible for the rapid increase in [iCa2+] due to cortisol. This increase in [iCa2+] with cortisol played a key role in the translocation of intracellular GR to the plasma membrane. This was evident because inhibition of the CRAC channel abolished the colocalization of GR to the caveolin-1 on the plasma membrane of hepatocytes. Cortisol also stimulated a rapid increase in [iCa2+] in zebrafish muscle explants, underscoring a conserved non-genomic role for cortisol in rapidly increasing [iCa2+] in excitable and non-excitable cells. A zebrafish tail-fin amputation model was used to investigate the physiological role of non-genomic and genomic cortisol signalling in regulating epimorphic regeneration. Cortisol rapidly increased [iCa2+] at the amputated site, and this corresponded with an increased ORAI1 (protein subunit of CRAC) expression at the site. Also, an increase in cell proliferation of ORAI1 expressing cells and blastema formation was evident at 24 h in response to cortisol stimulation, but absent in the GR knockout and MR knockout larvae, suggesting that this CRAC channel protein may be both non-genomically and genomically regulated by cortisol. Taken together, this thesis represents a significant contribution to the mechanism of action of rapid non-genomic effects of cortisol, which is essential to our understanding of the role of cortisol in stress adaptation in vertebrates
Development of Aerobic Granular Sludge Membrane Bioreactor (AGMBR) to Mitigate Fouling
No full textIn this research, the integration of aerobic granular sludge and membrane filtration to develop aerobic granular sludge membrane bioreactor (AGMBR) was explored. The main focus was on the in-depth study of extracellular polymeric substances (EPS) in AGMBR. Firstly, the long-term stability of aerobic granules (AG) was investigated in a sequencing batch reactor (SBR). This was followed by an in-depth analysis of EPS in a continuous-flow submerged AGMBR. And, the capability of AGMBR to remove organic matter, nitrogen, and phosphorus was determined. The combined strategy of long anaerobic slow feeding, fixed 1:3 ratio of feast-famine period within each SBR cycle, and continuous wasting of mature granules controlled EPS content at a suitable level to allow for long-term AG stability. High proteins/polysaccharides (PN/PS) ratios for loosely-bound EPS (LB-EPS) and tightly-bound EPS (TB-EPS) allowed for stable reactor operation for over 240 d without AG disintegration. EPS producers - Thauera, Flavobacterium and Meganema - and slow growing bacteria - Acinetobacter and Simplicispira - contributed to AG stability. The AGMBR exhibited high PN in the TB-EPS, resulting in high PN/PS ratios of 2–16. AG trapped most of the EPS in their matrix. Low soluble EPS resulted in acceptable rise in transmembrane pressure at membrane flux of 12.5 L/m2.h. An increase in soluble EPS PN correlated with increase in membrane fouling (r = 0.581). Compared to conventional membrane bioreactor, the AGMBR achieved seven times reduction in permeability maintenance cleaning frequency of the membrane. The COD showed a significant main effect on both PN and PS components of TB-EPS at α < 0.05. Water jet easily sloughed off the developed membrane cake layer, eliminating the need for chemical cleaning. The AGMBR system achieved 98.7±1%, 99.7±0.5%, 50±30%, and 35±18% removal for organic matter, ammonia-nitrogen, total nitrogen, and phosphorus, respectively. Meganema and Thauera, responsible for organic matter degradation, were present throughout the experimental duration. Nitrosomonas and Nitrospira allowed for complete nitrification. The presence of Azoarcus and Thauera points to anoxic conditions in AG, indicating some denitrification activity. Negligible phosphorus-accumulating organisms were detected; hence, the low phosphorus removal is attributed mainly to consumption for growth, struvite and biologically induced precipitation pathways
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
