Stress and cortisol treatment changed affinity and number of glucocorticoid receptors in leukocytes and gill of coho salmon

Stress circuitry: mechanisms behind nervous and immune system communication that influence behavior

Inflammatory processes are increased by stress and contribute to the pathology of mood disorders. Stress is thought to primarily induce inflammation through peripheral and central noradrenergic neurotransmission. In healthy individuals, these pro-inflammatory effects are countered by glucocorticoid signaling, which is also activated by stress. In chronically stressed individuals, the anti-inflammatory effects of glucocorticoids are impaired, allowing pro-inflammatory effects to go unchecked. Mechanisms underlying this glucocorticoid resistance are well understood, but the precise circuits and molecular mechanisms by which stress increases inflammation are not as well known. In this narrative review, we summarize the mechanisms by which chronic stress increases inflammation and contributes to the onset and development of stress-related mood disorders. We focus on the neural substrates and molecular mechanisms, especially those regulated by noradrenergic signaling, that increase inflammatory processes in stressed individuals. We also discuss key knowledge gaps in our understanding of the communication between nervous and immune systems during stress and considerations for future therapeutic strategies. Here we highlight the mechanisms by which noradrenergic signaling contributes to inflammatory processes during stress and how this inflammation can contribute to the pathology of stress-related mood disorders. Understanding the mechanisms underlying crosstalk between the nervous and immune systems may lead to novel therapeutic strategies for mood disorders and/or provide important considerations for treating immune-related diseases in individuals suffering from stress-related disorders.

Temporal variations in scale cortisol indicate consistent local-and broad-scale constraints in a wild marine teleost fish

Environmental changes can alter the nursery function of coastal areas through their impact on juveniles' growth and survival rates, an effect mediated by individuals' chronic stress response. Fish chronic stress can be quantified using scale cortisol but no study has yet been quantified the spatio-temporal variations in scale cortisol and its relationship with growth in wild nurseries. We collected wild sea bass juveniles (Dicentrarchus labrax, four years, three nurseries) and found that scale cortisol levels increased consistently with age and across cohorts in 2019 and 2020 probably due to greater stress history in older fish and/or heatwaves that occurred in summers of 2018 and 2019. Growth was impaired in fish with high scale cortisol in 2019 and 2020, confirming the usefulness of scale cortisol as a biomarker of broad and local constraints in wild fish; longer time series will enable us to identify environmental factors underpinning these temporal variations.

Effects of cortisol on female-to-male sex change in a wrasse

Sex change occurs as a usual part of the life cycle for many teleost fish and the modifications involved (behavioural, gonadal, morphological) are well studied. However, the mechanism that transduces environmental cues into the molecular cascade that underlies this transformation remains unknown. Cortisol, the main stress hormone in fish, is hypothesised to be a key factor linking environmental stimuli with sex change by initiating gene expression changes that shift steroidogenesis from oestrogens to androgens but this notion remains to be rigorously tested. Therefore, this study aimed to experimentally test the role of cortisol as an initiator of sex change in a protogynous (female-to-male) hermaphrodite, the New Zealand spotty wrasse (Notolabrus celidotus). We also sought to identify potential key regulatory factors within the head kidney that may contribute to the initiation and progression of gonadal sex change. Cortisol pellets were implanted into female spotty wrasses under inhibitory conditions (presence of a male), and outside of the optimal season for natural sex change. Histological analysis of the gonads and sex hormone analyses found no evidence of sex change after 71 days of cortisol treatment. However, expression analyses of sex and stress-associated genes in gonad and head kidney suggested that cortisol administration did have a physiological effect. In the gonad, this included upregulation of amh, a potent masculinising factor, and nr3c1, a glucocorticoid receptor. In the head kidney, hsd11b2, which converts cortisol to inactive cortisone to maintain cortisol balance, was upregulated. Overall, our results suggest cortisol administration outside of the optimal sex change window is unable to initiate gonadal restructuring. However, our expression data imply key sex and stress genes are sensitive to cortisol. This includes genes expressed in both gonad and head kidney that have been previously implicated in early sex change in several sex-changing species.

Immunomodulation and skin microbiota perturbations during an episode of chronic stress in gilthead seabream

Fish stress is a major concern in the aquaculture industry. Many stressors coming from routine practices can predispose fish to compromised growth, immunity and overall health. This study focuses on the characterization of the skin microbiota using next generation sequencing (NGS) platform by targeting a genomic marker 16S and to determine growth performance and immune status of gilthead seabream (Sparus aurata) during an episode of chronic stress. Two groups were established: control group and chronically stressed group. Stressed fish were subjected to 1 min air exposure twice a week for 4 weeks. Results showed that stress negatively affected fish growth performance. Cellular and humoral systemic immunity remained unaffected while local immunity in skin was positively stimulated (total IgM and peroxidase). Skin mucus microbial composition showed significant differences especially after 14 days. Stressed fish showed a decrease in the abundance of the genera Acinetobacter, NS3a_marine_group and Pseudomonas, while Pseudoalteromonas and Marinagarivorans increased significantly. In conclusion, air exposure stress was associated with alterations in skin mucosal immunity and microbial composition that may have been beneficial to the host favoring adaptation to stress.

Survival and gene expression responses in immune challenged larval lake sturgeon

Larval lake sturgeon, Acipenser fulvescens, reared in hatcheries for stock enhancement of wild populations may be susceptible to early opportunistic bacterial infection. Thus, we examined survival and whole-body mRNA expression of both stress- and immune-related genes (MyD88, IL-1β, StAR, GR1, and HSP70) in 30 days post fertilization larval lake sturgeon following immune challenge with lipopolysaccharides (LPS). Larval sturgeon were exposed to 0, 25, 50, 100, 150, and 200 μg ml^-1 LPS and sampled after 30 min, 4 h, and 48 h. Mortality was zero in 0 and 25 μg ml^-1 LPS; 37.5% in 50 μg ml^-1 LPS and 100% in the higher concentrations. Expression of MyD88 and StAR mRNA were positively correlated and increased with time in the 50 μg ml^-1 LPS treatment. There was an influence of both treatment and time on IL-1β mRNA, with expression 10-fold higher than controls after 4 h. Expression of HSP70 mRNA was suppressed within 30 min of 50 μg ml^-1 LPS exposure and remained so throughout the time course. Correlated mRNA expression of GR1 with MyD88, StAR and IL-1β suggests a potential relationship between the innate immune and glucocorticoid responses of larval lake sturgeon during this early developmental stage. Data presented suggest that larval lake sturgeon largely responded with predicted changes in gene expression of immune related and stress response genes following LPS challenge. This study provides a foundation for future research examining the effects of hatchery and naturally occurring stressors on the immune responses of larval lake sturgeon.

Influence of chronic stress on the mechanism of the cytotoxic system in common carp (Cyprinus carpio)

Aquaculture conditions expose fish to internal and environmental stressors that increase their susceptibility to morbidity and mortality. The brain accumulates stress signals and processes them according to the intensity, frequency duration and type of stress, recruiting several brain functions to activate the autonomic or limbic system. Triggering the autonomic system causes the rapid release of catecholamines, such as adrenaline and noradrenaline, into circulation from chromaffin cells in the head kidney. Catecholamines trigger blood cells to release proinflammatory and regulatory cytokines to cope with acute stress. Activation of the limbic axis stimulates the dorsolateral and dorsomedial pallium to process emotions, memory, behaviour and the activation of preoptic nucleus‐pituitary gland‐interrenal cells in the head kidney, releasing glucocorticoids, such as cortisol to the bloodstream. Glucocorticoids cause downregulation of various immune system functions depending on the duration, intensity and type of chronic stress. As stress persists, most immune functions, with the exception of cytotoxic functions, overcome these effects and return to homeostasis. The deterioration of cytotoxic functions during chronic stress appears to be responsible for increased morbidity and mortality.

Transcriptional Profiles of Genes Related to Stress and Immune Response in Rainbow Trout (Oncorhynchus mykiss) Symptomatically or Asymptomatically Infected With Vibrio anguillarum

Rainbow trout (Oncorhynchus mykiss) is one of the most common aquaculture fish species worldwide. Vibriosis disease outbreaks cause significant setbacks to aquaculture. The stress and immune responses are bidirectionally modulated in response to the health challenges. Therefore, an investigation into the regulatory mechanisms of the stress and immune responses in trout is invaluable for identifying potential vibriosis treatments. We investigated the transcriptional profiles of genes associated with stress and trout immune functions after Vibrio anguillarum infection. We compared the control trout (CT, 0.9% saline injection), asymptomatic trout (AT, surviving trout with minor or no symptoms after bacteria injection), and symptomatic trout (ST, moribund trout with severe symptoms after bacteria injection). Our results showed activated immunomodulatory genes in the cytokine network and downregulated glucocorticoid and mineralocorticoid receptors in both AT and ST, indicating activation of the proinflammatory cytokine cascade as a common response in AT and ST. Moreover, the AT specifically activated the complement- and TNF-associated immune defenses in response to V. anguillarum infection. However, the complement and coagulation cascades, as well as steroid hormone homeostasis in ST, were disturbed by V. anguillarum. Our studies provide new insights toward understanding regulatory mechanisms in stress and immune functions in response to diseases.

Evaluation of an in vitro assay to screen for the immunotoxic potential of chemicals to fish

A wide variety of environmental contaminants has been shown to disrupt immune functions of fish and may compromise their defense capability against pathogens. Immunotoxic effects, however, are rarely considered in ecotoxicological testing strategies. The aim of this study was to systematically evaluate the suitability of an in vitro immuno-assay using selected fish immune parameters to screen for chemicals with known immunotoxic potential and to differentiate them from non-immunotoxicants. Non-stimulated and lipopolysaccharide-stimulated head kidney leukocytes of rainbow trout (Oncorhynchus mykiss) were exposed for 3 h or 19 h to chemicals with different modes of action. As immune parameters, phagocytosis activity, oxidative burst activity and cytokine transcription (IL-1β, TNFα, IL-10) were examined, accompanied by in silico modelling. The immunotoxicants dexamethasone, benzo(a)pyrene, ethinylestradiol and bisphenol A significantly altered the immune parameters at non-cytotoxic concentrations whereas diclofenac had only weak effects. However, the two baseline chemicals with no known immunotoxic potential, butanol and ethylene glycol, caused significant effects, too. From our results it appears that the in vitro fish leukocyte assay as performed in the present study has only a limited capacity for discriminating between immunotoxicants and non-immunotoxicants.

The intersection of stress, sex and immunity in fishes

While sexual dimorphism in immune responses has been documented in other vertebrates, evidence for a similar phenomenon in fish is lacking. Here, we review the relationship between immunity, stress, spawning, and sex hormones in fish to gain a better understanding of sex-based differences in fish immune responses and its consequences for aquaculture. It is well known that there is a strong link between the stress response and immune function in fish. In addition, research to date has demonstrated that sexual dimorphism in the stress response exists in many species; yet, the relationship between the sexual dimorphic stress responses and immune function has rarely been explored together. Aside from stress, spawning is also known to trigger changes in fish immune responses. Estrogens and androgens have been shown to modulate the immune system which could account for differences between the two sexes of fish when spawning; however, evidence regarding the sexual dimorphism of these changes varies between fishes and is likely related to the spawning strategy employed by a given species. Sex hormones are also used in aquaculture practices to produce monosex populations, and exposure to these hormones early in development has been shown to impact the development of immune organs in several fishes. While female fish are generally thought to be more robust than males, aquaculture practices should also consider the role that maternal stress has on the immune function of the offspring and what role this plays in compromising the immune response of farmed fish.

Impact of Ringer's Solution Challenge Stress to Immunostimulatory Experiment, Insights From Japanese Flounder

Ringer's or phosphate buffer saline (PBS) solution buffer usually was used as dilution butter in intraperitoneal injection. Stress could activate immune response, inflammatory response and glycogen metabolic process. The impact of solution buffer as a stressor to immune system was ignored in immunostimulatory experiment. In this report, we tested the hypothesis that the innate immune response and glycogen metabolic process were altered when it were challenged with Ringer's in Japanese flounder (Paralichthys olivaceus). RNA-seq was performed after challenge with Ringer's at 8 h and 48 h. The data revealed that the expression profiles of blood, gill, and kidney were significantly changed. Differentially expressed genes (DEGs) were identified, and energy metabolic and immune-related genes were up-regulated or down-regulated obviously. GO and KEGG analyses showed that DEGs were mainly enriched in innate immune terms and pathways. Weighted gene co-expression networks analysis (WGCNA) also indicated the highest association module with stress. A total of 16 genes were detected in the gray module, which were immune-related and metabolic-related genes. These results provided fundamental information on intraperitoneal injection with solution buffer. It offered useful clues to further explore the functional mechanism of stress and immunity.

Down-regulation of corticosteroid receptor in leucocytes of stressed rainbow trout

The relationship between stress and immunosuppression was investigated in peripheral blood leucocytes (PBL) in rainbow trout, with reference to corticosteroid receptor (CR) expression and responses to cortisol- and/or lipopolysaccharide (LPS)-administration. Confinement stress in shallow water resulted in a sustained elevation of plasma cortisol, whereas lysozyme and immunoglobin levels were suppressed. Significant increases in mRNA levels of caspase-6 and insulin-like growth factor (IGF)-I were observed in PBL isolated from stressed fish. Confinement stress also suppressed proinflammatory cytokine, interleukin (IL)-1β, expression in PBL. There were decreasing tendencies for the mRNA levels of CRs in PBL of stressed fish. In-vitro treatment of cortisol and LPS on isolated PBL from unstressed trout increased both IL-1 β and CR mRNA expression. However, in PBL from stressed fish, cortisol and LPS treatment increased IL-1 β but not CR mRNA levels. Proliferative activities estimated as in-vitro incorporation of bromodeoxyuridine (BrdU) were decreased by cortisol in PBL from the unstressed and stressed fish groups; however, LPS-stimulated proliferation was observed only in the unstressed fish. Ratios of apoptotic PBL quantified as cell fragmentation using an automated cell counter were increased by cortisol in both groups; however, LPS-stimulated apoptosis was observed only in the stressed fish. Our study reveals cortisol has immune-suppressive effects in stressed fish, irrespective of CR down-regulation and desensitization. The complexity of immune-endocrine interaction is shown by the stress-induced attenuation of LPS effects.

Thermal Modulation of Monoamine Levels Influence Fish Stress and Welfare

Fish are ectotherm organisms that move through different thermal zones according to their physiological requirements and environmental availability, a behavior known as thermoregulation. Thermoregulation in ectothermic animals is influenced by their ability to effectively respond to thermal variations. While it is known that ectotherms are affected by thermal changes, it remains unknown how physiological and/or metabolic traits are impacted by modifications in the thermal environment. In captivity (land-based infrastructures or nets located in the open sea), fish are often restricted to spatially constant temperature conditions within the containment unit and cannot choose among different thermal conditions for thermoregulation. In order to understand how spatial variation of temperature may affect fish welfare and stress, we designed an experiment using either restricted or wide thermal ranges, looking for changes at hormonal and molecular levels. Also, thermal variability impact on fish behavior was measured. Our results showed that in Atlantic salmon (Salmo salar), a wide thermal range (ΔT 6.8°C) was associated with significant increases in monoamines hormone levels and in the expression of clock genes. Aggressive and territoriality behavior decreased, positively affecting parameters linked to welfare, such as growth and fin damage. In contrast, a restricted thermal range (ΔT 1.4°C) showed the opposite pattern in all the analyzed parameters, therefore, having detrimental effects on welfare. In conclusion, our results highlight the key role of thermal range amplitude on fish behavior and on interactions with major metabolism-regulating processes, such as hormone performance and molecular regulatory mechanisms that have positive effects on the welfare.

Dietary exposure to a binary mixture of polybrominated diphenyl ethers alters innate immunity and disease susceptibility in juvenile Chinook salmon (Oncorhynchus tshawytscha)

Polybrominated diphenyl ethers (PBDEs) have been used as flame retardants in consumer products and are now found in the aquatic environment. The presence of PBDEs puts the health and survival of aquatic species at risk due to the various toxic effects associated with exposure to these compounds. The effects of a binary dietary mixture of PBDEs on innate immunity and disease susceptibility of juvenile Chinook salmon (Oncorhynchus tshawytscha) were examined in the present study. Salmon were fed roughly 1:1 mixtures of two environmentally predominant PBDE congeners, BDE-47 and BDE-99. The six resulting whole body total PBDE concentrations ranged from less than the limit of quantification to 184 ng/g, wet weight (ww). The innate immune system was assessed by using two in vitro macrophage function assays. Specifically, assays that examined the ability of head kidney macrophages to: (1) engulf sheep red blood cells (SRBCs); and (2) produce a respiratory burst, as determined by the production of a reactive oxygen species, superoxide anion. Macrophages from salmon fed the BDE-47/99 mixture diets engulfed more SRBCs and produced greater superoxide anion than salmon fed the control diet. An increase in macrophage function was observed in fish with whole body total PBDE concentrations ranging from 2.81 ng/g, ww to 184 ng/g, ww. The mechanism for this increase in macrophage function due to PBDE exposure is currently unknown, but may be due to the ability of PBDEs to act as an endocrine receptor agonist and/or antagonist. Salmon exposed to the BDE-47/99 mixture diets were also challenged with the pathogenic bacteria, Vibrio (Listonella) anguillarum to determine disease susceptibility. Kaplan-Meier survival curves of fish exposed to the BDE-47/99 mixture and control diets were significantly different. The Cox proportional hazard risk ratios of disease-induced mortality in juvenile Chinook salmon with whole body concentrations of total PBDEs of 10.9, 36.8, and 184 ng/g, ww were significantly greater than the fish fed the control diet by 1.56, 1.83 and 1.50 times, respectively. Not all concentrations of the binary mixture diets had significant hazard ratios relative to the control diet, due to a non-monotonic concentration response curve. The mixture of PBDE congeners resulted in interactive effects that were generally non-additive and dependent upon the congener concentrations and metric examined. Consequently, predicting the interactive effects in juvenile Chinook salmon exposed to mixtures of PBDE congeners on innate immunity and disease susceptibility cannot be readily determined from the adverse effects of individual PBDE congeners.

Stress up-regulates oxidative burst in juvenile Chinook salmon leukocytes

When fish perceive stressful scenarios, their hypothalamus-pituitary-interrenal axis is activated resulting in the release of corticotropin releasing hormone, adrenocorticotropic hormone (ACTH), and finally cortisol. The physiologic stress response of fish has most often been linked to the reduced performance of the immune system, with a few exceptions where the immune system is activated. In this report, we tested the hypothesis that oxidative burst activity levels in juvenile Chinook salmon (Oncorhynchus tshawytscha) are altered when the fish is presented with a stressor. Fish were subjected to a stressor for 3 h and then allowed to recover for 20 h following the stressor. Plasma and spleens were collected from euthanized fish before the stressor, at the end of a 3 h stressor, and 23 h after the start of the experiment. Plasma was held at -80 °C until cortisol radioimmunoassay analysis was performed to confirm stress. Spleens were held in Dulbecco's Modified Eagle Medium overnight and analyzed the day following collection. Oxidative burst activity was measured in splenic leukocytes after being stimulated with phorbol 12-myristate 13-acetate. We found a significant increase in activated oxidative burst from fish subjected to the stressor as compared to unstressed fish. Speculation is given to ACTH being the leukocyte priming agent in this experiment rather than the cortisol itself.

Rapid acclimation of the cortisol stress response in adult turquoise killifish Nothobranchius furzeri

The turquoise killifish Nothobranchius furzeri is an increasingly popular model species for comparative vertebrate research, and the basic physiology including responses to stressful stimuli are of primary interest. We exposed adult killifish to a single or repeated periods of acute confinement followed by analysis of tissue cortisol and plasma cortisol concentrations. Individuals were also sampled for messenger RNA (mRNA) expression of corticotropin-releasing hormone (CRH), mineralocorticoid receptor (MR), and glucocorticoid receptor (GR) in the brain to examine the effects of repeated stress events on constitutive expression of these important stress axis components. Following a single 30-minute confinement stress, male plasma cortisol significantly differed from baseline (p = 0.04). Both male and female whole-body cortisol were significantly increased (p = 0.004 and p = 0.04, respectively) at 15 and 30 minutes poststress. Despite obvious dimorphic behavior and morphology, cortisol concentrations did not differ between the sexes. Exposure to daily repeated confinement for one week altered the cortisol response in both sexes. Time 0, 15, and 60 minutes poststress cortisol concentrations were depressed in repeatedly stressed males (p ≤ 0.05), and times 0, 30 and 120 minutes poststress cortisol concentrations were depressed in repeatedly stressed females (p ≤ 0.05). Constitutive expression of CRH, MR, and GR mRNA in the brain following one week of repeated stress events did not differ among treatments or sexes. This study introduces the first description of hypothalamic-pituitary-interrenal axis activity in this important model species. Reduced cortisol production in repeatedly stressed adult killifish suggests acclimation to repeated stressors. Furthermore, acclimation was rapid, and plasma cortisol concentrations altered significantly in as little as one week.

Physiological and proteomic responses to corticosteroid treatments in Eurasian perch, Perca fluviatilis: Investigation of immune-related parameters

The comparative effects of cortisol and 11-deoxycorticosterone (DOC), two major corticosteroids in fish, have yet received little attention in teleosts. We evaluated the proteomic and immune responses of Eurasian perch to chronic corticosteroid treatments. We implanted immature perch with cortisol (80mg/kg) or DOC (4mg/kg) and measured the proportions of blood leucocytes, immune indices in the plasma, spleen and liver (complement and lysozyme activity, total immunoglobulin and immune gene expression in the tissues) and differential proteome expression (corticosteroid versus control) in the liver and the spleen on days 2, 4 and 14 post-treatment. Implantation of cortisol decreased the ratio of blood leucocytes and depressed Ig levels in both organs while DOC modulated the proportion of leucocyte sub-populations (increase in lymphocytes and decrease in granulocytes). In contrast, the innate humoral immunity was not strongly influenced by any of corticosteroid implants. The only immune parameter that was significantly affected was lysozyme, after DOC treatment. A number of proteins were differentially regulated by these hormones and some were identified in the liver (21 for cortisol and 8 for DOC) and in the spleen (10 for cortisol and 10 for DOC). None of the proteins was directly linked to immunity, except the natural killer enhancing factor, which was repressed by cortisol in the spleen. Our results also confirm that the proteins involved in energetic and glucose metabolism are affected by corticosteroids. Furthermore, these corticosteroids differently regulate immune status in Eurasian perch and they primarily impact leucocytes, as opposed to innate immune function.

Characterization of two channel catfish, Ictalurus punctatus, glucocorticoid receptors and expression following an acute stressor

Two channel catfish glucocorticoid receptor genes, ipGR1 (NR3C1_1) and ipGR2 (NR3C1_2) were partially characterized. Identification and analysis of the genomic organization of two channel catfish glucocorticoid (GC) receptors (GRs) revealed differences in the lengths of exons 1 and 2 and the addition of an extra 27-bp exon inserted after exon 2 in the GR1 gene, yielding a 9-aa insert in the receptor protein. Sequence of the 9-aa insert in ipGR1 (WRARQNTHG) is unique compared to other teleost fish GRs. Amino acid sequence alignment of the two channel catfish GRs, revealed 55% sequence identity between them, with a high degree of sequence conservation (82%) in the DNA binding and ligand binding domains. Real-time PCR indicated that ipGR1 and ipGR2 were expressed in all tissues evaluated. Channel catfish GR1 was predominantly expressed in the gills, nearly 25-fold higher than in the liver. GR1 expression was higher than GR2 expression in gills, intestine, head kidney and heart (P<0.05). Channel catfish hepatic GR1 mRNA expression was significantly (P<0.05) increased from pre-stress expression 30min following removal of the acute stressor. After 30min of stress and during the 2h recovery period, ipGR1 mRNA expression was higher relative to ipGR2 expression. Hepatic ipGR2 expression was not affected (P>0.05) by the acute stress event. The present study adds to the growing body of information on GR evolution and function and further demonstrates the unique regulation of the GC/GR system in teleost fish.

Cold-induced changes in stress hormone and steroidogenic transcript levels in cunner (Tautogolabrus adspersus), a fish capable of metabolic depression

The cunner (Tautogolabrus adspersus) is a fish with a wide latitudinal distribution that is capable of going into metabolic depression during the winter months, and thus, represents a unique model to investigate the impacts of cold temperatures on the stress response. In this study, we measured resting (pre-stress) plasma cortisol levels in 10 °C and 0 °C acclimated cunner from Newfoundland, and both catecholamine and cortisol levels after they were given a standardized handling stress (i.e. 1 min air exposure). In addition, we cloned and characterized cDNAs for several key genes of the cortisol-axis [cytochrome P450scc, steroidogenic acute regulatory protein (StAR) and a glucocorticoid receptor (GR) most likely to be an ortholog of the teleost GR2], determined the tissue distribution of their transcripts, and measured their constitutive (i.e. pre-stress) transcript levels in individuals acclimated to both temperatures. In cunner acclimated to 0 °C, post-stress epinephrine and norepinephrine levels were much lower (by approximately 9- and 5-fold, respectively) compared to 10 °C acclimated fish, and these fish had relatively low resting cortisol levels (~15 ngml(-1)) and showed a typical post-stress response. In contrast, those acclimated to 10 °C had quite high resting cortisol levels (~75 ngml(-1)) that actually decreased (to ~20 ngml(-1)) post-stress before returning to pre-stress levels. Finally, fish acclimated to 10 °C had higher P450scc transcript levels in the head kidney and lower levels of GR transcript in both the head kidney and liver. Taken together, these results suggest that: (1) temperature has a profound effect on the stress response of this species; and (2) although the ancestors of this species inhabited warm waters (i.e. they are members of the family Labridae), populations of cunner from colder regions may show signs of stress at temperatures as low as 10 °C.

Differential modulation of resistance biomarkers in skin of juvenile and mature pink salmon, Oncorhynchus gorbuscha by the salmon louse, Lepeophtheirus salmonis

Juvenile pink salmon larger than 0.7 g reject the sea louse, Lepeophtheirus salmonis, and are considered resistant to the infection. Robust innate defense responses in the skin contribute to the observed resistance. In contrast adult pink salmon captured at sea or shortly before spawning carry large numbers of the parasite, suggesting inability to control the infection. The purpose of this research is to better understand these apparently contradictory conclusions by comparing a suite of genetic and cellular markers of resistance to L. salmonis in the skin of juvenile and mature pink salmon. The expression of major histocompatibility factor II, C-reactive protein, interleukin-1β, interleukin-8 and cyclooxygenase-2 was down-regulated in mature but not juvenile pink salmon. Similarly, skin at the site of parasite attachment in juvenile salmon was highly populated with MHIIβ(+) and IL-1β(+) cells that were either absent, or at reduced levels at similar sites in mature salmon. In addition, mucocyte density was relatively low in the skin of mature salmon, irrespective of louse infection. In juveniles, the higher mucocyte density decreased following louse attachment. We show that in mature pink salmon, genetic and histological responses in skin are depressed and speculate that salmonid defense against L. salmonis is modulated by maturation.

Activity of the hypothalamus-pituitary-interrenal axis (HPI axis) and immune response in carp lines with different susceptibility to disease

The stress response transmitted by the HPA axis is one of the best examples of neuroendocrine-immune interactions that are critical for survival. Analogous to the situation in mammals, the stress response in fish is characterized by the activation of the hypothalamo-pituitary-interrenal axis (HPI). Effects of cortisol on the fish immune system comply with findings in mammals and suggest that the differences in sensitivity to stress will influence the immune response and as a consequence of survival. Therefore, we studied the stress response and its immunity-related effects in four different carp lines (R3, R3xR8, K and R2) that display a differential pathogen susceptibility. Previous studies indicate that R3xR8 and R3 carp are susceptible to bacterial and parasite infection, while R2 and K are relatively resistant to infection. Interestingly, the most striking effect of stress on leukocyte composition and activity was observed in the pathogen-resistant K carp, even though no robust changes in gene expression of stress-involved factors were observed. In contrast, R3 carp showed no spectacular stress-induced changes in their immunological parameters with concurrent significant activation of the HPI axis. Upon stress, the R3 carp showed up-regulation of crf, pomc and gr2 gene expression in the hypothalamus. Furthermore in R3 carp, at all levels of the HPI axis, stress induced the highest up-regulation of il-1β gene expression. Although we are aware of the complexity of the interactions between stress and pathogen susceptibility and of the risk of interpretation based on correlations, it is noteworthy that the fish more susceptible to infection also exhibited the highest response to stress.

Manipulating glucocorticoids in wild animals: basic and applied perspectives

One of the most comprehensively studied responses to stressors in vertebrates is the endogenous production and regulation of glucocorticoids (GCs). Extensive laboratory research using experimental elevation of GCs in model species is instrumental in learning about stressor-induced physiological and behavioural mechanisms; however, such studies fail to inform our understanding of ecological and evolutionary processes in the wild. We reviewed emerging research that has used GC manipulations in wild vertebrates to assess GC-mediated effects on survival, physiology, behaviour, reproduction and offspring quality. Within and across taxa, exogenous manipulation of GCs increased, decreased or had no effect on traits examined in the reviewed studies. The notable diversity in responses to GC manipulation could be associated with variation in experimental methods, inherent differences among species, morphs, sexes and age classes, and the ecological conditions in which responses were measured. In their current form, results from experimental studies may be applied to animal conservation on a case-by-case basis in contexts such as threshold-based management. We discuss ways to integrate mechanistic explanations for changes in animal abundance in altered environments with functional applications that inform conservation practitioners of which species and traits may be most responsive to environmental change or human disturbance. Experimental GC manipulation holds promise for determining mechanisms underlying fitness impairment and population declines. Future work in this area should examine multiple life-history traits, with consideration of individual variation and, most importantly, validation of GC manipulations within naturally occurring and physiologically relevant ranges.

Seasonal changes in gene expression of corticoid receptors in anadromous and non-anadromous strains of rainbow trout Oncorhynchus mykiss

To clarify the regulation of expression of corticoid receptor (CR) genes during period of parr-smolt transformation of salmonids, seasonal changes in mRNA levels of glucocorticoid receptor (GR)-1, GR-2 and mineralocorticoid receptor (MR) were examined in gill, leucocytes, spleen and brain of anadromous and non-anadromous forms of Oncorhynchus mykiss. Increases in gill Na(+) , K(+) ATPase activity, plasma thyroxine levels and hypo-osmoregulatory ability assessed by 24 h seawater challenge test represented characteristics of smoltification in anadromous O. mykiss from May to June, whereas there was no apparent increase in the values of non-anadromous O. mykiss. Plasma cortisol levels of anadromous O. mykiss were higher than levels of non-anadromous O. mykiss from April to June. In gill of non-anadromous O. mykiss, there were significant increases in mRNA levels of three types of CR in spring. Although there were significant seasonal variations of CR mRNA levels in gill of anadromous O. mykiss, they appear to be less clear than those variations in non-anadromous O. mykiss. In anadromous O. mykiss, significant elevations in mRNA levels of the three types of CR were observed especially in the spleen. In both preoptic area and basal hypothalamus of the brain, there were tendencies to increase in CR mRNA levels from spring to summer in both anadromous and non-anadromous O. mykiss. These results showed difference in regulation of CR gene expression between the two forms of O. mykiss for osmoregulatory, immune and central nervous systems.

Effects of dietary arachidonic acid on cortisol production and gene expression in stress response in Senegalese sole (Solea senegalensis) post-larvae

Dietary fatty acids, particularly arachidonic acid (ARA), affect cortisol and may influence the expression of genes involved in stress response in fish. The involvement of ARA on stress, lipid, and eicosanoid metabolism genes, in Senegalese sole, was tested. Post-larvae were fed Artemia presenting graded ARA levels (0.1, 0.4, 0.8, 1.7, and 2.3%, dry matter basis), from 22 to 35 days after hatch. Whole-body cortisol levels were determined, before and 3 h after a 2 min air exposure, as well as the expression of phospholipase A2 (PLA 2 ), cyclooxygenase-2 (COX-2), steroidogenic acute regulatory protein (StAR), glucocorticoid receptors (GRs), phosphoenolpyruvate carboxykinase (PEPCK), and peroxisome proliferator-activated receptor alpha (PPARα). Relative growth rate (6.0-7.8% day(-1)) and survival at the end of the experiment (91-96%) and after stress (100%) were unaffected. Fish reflected dietary ARA content and post-stress cortisol increased with ARA supply up to 1.7%, whereas 2.3% ARA seemed to enhance basal cortisol slightly and alter the response to stress. Results suggested that elevating StAR transcription might not be necessary for a short-term response to acute stress. Basal cortisol and PLA 2 expression were strongly correlated, indicating a potential role for this enzyme in steroidogenesis. Under basal conditions, larval ARA was associated with GR1 expression, whereas the glucocorticoid responsive gene PEPCK was strongly related with cortisol but not GR1 mRNA levels, suggesting the latter might not reflect the amount of GR1 protein in sole. Furthermore, a possible role for PPARα in the expression of PEPCK following acute stress is proposed.

Orally administered LPS enhances head kidney macrophage activation with down-regulation of IL-6 in common carp (Cyprinus carpio)

Immunostimulants represent a promising aquaculture tool for enhancing disease and stress resistance in cultured fish. Moreover, the term and dose for acting immunostimulants is an important thing for fish farmer. This study investigated the immune parameters of common carp after oral administration of LPS (5, 10, 20 μg/kg/days) for 30 and 60 days, which is considered to be the proper time period for acting in aquaculture. Phagocytic and bactericidal activities of head kidney macrophages and serum lysozyme activities were significantly enhanced in LPS-fed carp. Orally administered LPS augmented the expression of interleukin (IL)-1β and TNF-α mRNAs but reduced the expression of IL-6 mRNA in head kidney. Although LPS was detected in the serum and liver after a high-dose (>15 mg/kg) oral administration, it was not detected by administered LPS-specific ELISA after a low-dose (<20 μg/kg) administration. It is speculated that orally administered LPS enhances the eliminating functions of head kidney macrophages with down-regulation of IL-6.

Cortisol response to waterborne 4-nonylphenol exposure leads to increased brain POMC and HSP70 mRNA expressions and reduced total antioxidant capacity in juvenile sole (Solea solea)

4-Nonylphenol (4-NP) is a breakdown product of alkylphenolpolyethoxylates and can be found in almost all environmental water matrices. 4-NP can act as environmental stressor on fish, typically causing modulation of hypothalamic-pituitary-interrenal axis (HPI). To examine the effects of the xenoestrogen 4-NP or 17β-estradiol (E2) on induction of stress response mechanisms by evaluating the levels of proopiomelanocortin (POMC) mRNA, heat shock protein 70 (HSP70) mRNA and plasma cortisol, we exposed juvenile sole (Solea solea), under static condition for 7 day, to either 10(-6) or 10(-8) M 4-NP, or 10(-8) M E2. In addition, plasma cortisol titers were correlated to the total antioxidant capacity (TAC), one of the oxidative stress parameters. 4-NP treatments resulted in high levels of POMC mRNA, HSP70 mRNA and plasma cortisol. On the contrary, E2 basically down-regulated POMC expression. Moreover, elevated cortisol levels in fish exposed to the highest dose of 4-NP were accompanied by low TAC. These results suggest that 4-NP modulates the sole HPI axis inducing a cortisol-mediated stress response. Specifically, we suggest that 4-NP affects brain POMC mRNA levels via non-estrogen receptor (ER)-mediated mechanism further supporting the ability of 4-NP to target multiple receptor systems.

Slow release cortisol implants result in impaired innate immune responses and higher infection prevalence following experimental challenge with infectious pancreatic necrosis virus in Atlantic salmon (Salmo salar) parr

Stress can affect the immune system and increase susceptibility to various diseases but knowledge of the underlying mechanisms is scarce. There is a complex interaction between the immune system and the endocrine system of vertebrates. In fish, cortisol is a key hormone regulating stress response and recent studies have also suggested that this hormone can affect the immune system, where cortisol is mainly regarded as an immunosuppressive factor. The aim of the present study was to examine the impact of chronically elevated levels of cortisol on the immune response and susceptibility to experimental infection with infectious pancreatic necrosis virus (IPNV). Further, the effect of IPNV challenge on circulating levels of cortisol was investigated. Atlantic salmon parr were implanted intraperitoneally with sustained-release implants of bovine of cortisol (50 μg cortisol g(-1) body weight in an implant based on vegetable lipids). Vehicle implants were used as control (sham-injected). At 45 days after implantation (DAI), fish were challenged with a low virulent isolate of IPNV (by immersion). Samples of plasma, liver and head kidney was taken from fish before and 24 h, 48 h, 7 days week and 21 days post infection (DPI). Cortisol level in plasma was measured using radioimmunoassay and gene expression in liver and head kidney was analyzed with real-time PCR (RT-PCR). Infection prevalence in infected fish was assessed by virus culture and RT-PCR of head kidney samples. Cortisol implantation compared with sham-implanted fish had increased levels of plasma cortisol at 45 DAI. The relative expression of Interferon alpha-1 (IFNα-1), Myxo virus-1 Mx, Heat-shock protein 70 (HSP70), Serum amyloid A (SAA), Glucocorticoid receptor (GR) and Heat-shock protein 90 (HSP90) tends to be down-regulated by cortisol implantation. There was a higher prevalence of fish with detectable levels of IPNV, as measured by cell culture and RT-PCR, in the cortisol-implanted group challenged with IPNV (0 = 0.0305) relative to the group that received a sham implantation. Further, cortisol seems to delay the induction of the antiviral IFNα-1 pathway and Mx mRNA expression. This study shows that elevated plasma cortisol level leads to an impaired innate immune response, and higher virus (IPNV) prevalence in Atlantic salmon parr.

The mRNA expression of cortisol axis related genes differs in Atlantic cod (Gadus morhua) categorized as high or low responders

Cortisol is a major stress hormone in fish and is known, under normal or stressful conditions, to affect several physiological processes including growth and immunity. Thus, efforts have been made for several cultured finfish species, including the Atlantic cod, to determine whether fish with a high or low cortisol response to stress can be identified and selected. However, we have a limited understanding of the mechanisms that determine these two phenotypes. Thus, we measured total and free plasma cortisol levels in high and low responding cod when subjected to a 30 s handling stress, and the mRNA expression of four key genes in the glucocorticoid (i.e. cortisol) stress axis both pre- and post-stress. The cortisol data is consistent with our previous findings for cod, with high responding (HR) fish having ∼3-fold higher total and free plasma cortisol levels when compared to low responding (LR) fish. Three of the transcripts studied encode key proteins involved in steroidogenesis (StAR, P450scc and 3βHSD), and the constitutive mRNA expression of all three genes was significantly higher (∼2-fold) in the head kidney of HR fish when compared to LR cod. The other gene of interest was the glucocorticoid receptor (GR). We partly cloned and characterized a cDNA from Atlantic cod likely to be this fish's ortholog of the teleost GR1, and showed that while there was no difference in hepatic constitutive GR mRNA expression between groups, HR fish had liver GR mRNA levels that were significantly (1.8-fold) higher at 3 h post-stress as compared to LR fish. Our results suggest that the different magnitude of cortisol response between LR and HR fish is at least partially determined by the capacity of the interrenal tissue to produce steroids.

Effects of elevated circulating cortisol levels on hydromineral status and gill tight junction protein abundance in the stenohaline goldfish

A role for cortisol in the regulation of hydromineral balance and gill tight junction (TJ) protein transcript abundance in the stenohaline freshwater goldfish was investigated. Intraperitoneal cortisol implants (50, 100, 200, 400 μg cortisol/g body weight) were used to dose-dependently elevate circulating cortisol levels over a 4 day period. Elevated cortisol did not significantly alter serum osmolality, serum Na(+) or muscle water content, however serum glucose and gill Na(+)-K(+)-ATPase activity were significantly increased and serum Cl(-) levels were significantly reduced when compared to control groups. Transcript levels for glucocorticoid receptor 1 (GR1) and mineralocorticoid receptor (MR) in the gill remained unchanged by cortisol treatment, however glucocorticoid receptor 2 (GR2) mRNA abundance was significantly down-regulated. Conversely, cortisol treatment significantly increased transcript and protein abundance of the TJ protein occludin in goldfish gill tissue, as well as mRNA abundance for claudin e, 7 and 8d. Goldfish tissue expression profiles demonstrated that transcripts encoding for these claudins are particularly abundant in the gill. Overall, results suggest a 'tightened' gill epithelium in response to elevated cortisol levels in goldfish. However, negative autoregulation of gill GR2 transcript suggests a lessened capacity to respond to cortisol and thus a potentially 'dampened' corticosteroid-mediated effect in the gill. Reduced systemic Cl(-) levels also suggest that sustained cortisol elevation in goldfish may have a detrimental effect on other ionoregulatory tissues.

Stress and immune modulation in fish

Stress is an event that most animals experience and that induces a number of responses involving all three regulatory systems, neural, endocrine and immune. When the stressor is acute and short-term, the response pattern is stimulatory and the fish immune response shows an activating phase that specially enhances innate responses. If the stressor is chronic the immune response shows suppressive effects and therefore the chances of an infection may be enhanced. In addition, coping with the stressor imposes an allostatic cost that may interfere with the needs of the immune response. In this paper the mechanisms behind these immunoregulatory changes are reviewed and the role of the main neuroendocrine mechanisms directly affecting the building of the immune response and their consequences are considered.

Evidence for transcriptional regulation of the urea transporter in the gill of the Gulf toadfish, Opsanus beta

Ureotelic Gulf toadfish (Opsanus beta) do not excrete urea continuously; instead, urea is accumulated internally until a branchial urea transport mechanism is activated to facilitate the excretion of urea in distinct pulses. This unusual pulsatile urea excretion pattern is regulated, in part, by permissive declines in circulating cortisol concentrations. The current study examined toadfish urea transporter (tUT) and glucocorticoid receptor (GR) transcript levels in toadfish gill following chronic (days) and acute (hours) changes in corticosteroid activity. Experimentally lowering circulating cortisol did not significantly alter tUT mRNA abundance but increased GR mRNA. On an acute timescale, a 6.2-fold upregulation of tUT mRNA occurred 12 to 18 h following a urea pulse event with no change in GR mRNA. In silico analysis of an isolated 1.2 kb fragment, upstream promoter region of the tUT gene, revealed 6 putative glucocorticoid response element (GRE) half sites. In vivo reporter assays of the tUT promoter fragment demonstrated relative luciferase activity was enhanced 3.4- and 9.8-fold following exposure to moderate (via a 48 h crowding stress) and high (via infusion for 48 h) cortisol. We conclude that a GRE-mediated upregulation of mRNA may be required to maintain tUT activity by offsetting post-transcriptional and/or post-translational changes that may be associated with chronically elevated plasma cortisol.

Reverse effect of mammalian hypocalcemic cortisol in fish: cortisol stimulates Ca2+ uptake via glucocorticoid receptor-mediated vitamin D3 metabolism

Cortisol was reported to downregulate body-fluid Ca(2+) levels in mammals but was proposed to show hypercalcemic effects in teleostean fish. Fish, unlike terrestrial vertebrates, obtain Ca(2+) from the environment mainly via the gills and skin rather than by dietary means, and have to regulate the Ca(2+) uptake functions to cope with fluctuating Ca(2+) levels in aquatic environments. Cortisol was previously found to regulate Ca(2+) uptake in fish; however, the molecular mechanism behind this is largely unclear. Zebrafish were used as a model to explore this issue. Acclimation to low-Ca(2+) fresh water stimulated Ca(2+) influx and expression of epithelial calcium channel (ecac), 11β-hydroxylase and the glucocorticoid receptor (gr). Exogenous cortisol increased Ca(2+) influx and the expressions of ecac and hydroxysteroid 11-beta dehydrogenase 2 (hsd11b2), but downregulated 11β-hydroxylase and the gr with no effects on other Ca(2+) transporters or the mineralocorticoid receptor (mr). Morpholino knockdown of the GR, but not the MR, was found to impair zebrafish Ca(2+) uptake function by inhibiting the ecac expression. To further explore the regulatory mechanism of cortisol in Ca(2+) uptake, the involvement of vitamin D(3) was analyzed. Cortisol stimulated expressions of vitamin D-25hydroxylase (cyp27a1), cyp27a1 like (cyp27a1l), 1α-OHase (cyp27b1) at 3 dpf through GR, the first time to demonstrate the relationship between cortisol and vitamin D(3) in fish. In conclusion, cortisol stimulates ecac expression to enhance Ca(2+) uptake functions, and this control pathway is suggested to be mediated by the GR. Lastly, cortisol also could mediate vitamin D(3) signaling to stimulate Ca(2+) uptake in zebrafish.

The use of the zebrafish model in stress research

The study of the causes and mechanisms underlying psychiatric disorders requires the use of non-human models for the test of scientific hypotheses as well as for use in pre-clinical drug screening and discovery. This review argues in favor of the use of zebrafish as a novel animal model to study the impact of early (stressful) experiences on the development of differential stress phenotypes in later life. This phenomenon is evolutionary conserved among several vertebrate species and has relevance to the etiology of psychiatric disorders. Why do we need novel animal models? Although significant progress has been achieved with the use of traditional mammalian models, there are major pitfalls associated with their use that impedes progress on two major fronts: 1) uncovering of the molecular mechanisms underlying aspects of compromised (stress-exposed) brain development relevant to the etiology of psychiatric disorders, and 2) ability to develop high-throughput technology for drug discovery in the field of psychiatry. The zebrafish model helps resolve these issues. Here we present a conceptual framework for the use of zebrafish in stress research and psychiatry by addressing three specific domains of application: 1) stress research, 2) human disease mechanisms, and 3) drug discovery. We also present novel methodologies associated with the development of the zebrafish stress model and discuss how such methodologies can contribute to remove the main bottleneck in the field of drug discovery.

Vinclozolin affects the interrenal system of the rare minnow (Gobiocypris rarus)

Vinclozolin, a widely used fungicide, has been characterized as a potent androgen antagonist. In this study, the effects of vinclozolin on the interrenal system of the rare minnow (Gobiocypris rarus) were evaluated. The results revealed a decline of the renal somatic index (RSI) and the presence of histopathological effects, including shrinkage of the glomerulus and expansion of the Bowman's space in the kidneys, in rare minnows exposed to vinclozolin. Elevated plasma cortisol concentrations in females exposed to ≥ 2 μg/L vinclozolin and males exposed to ≥ 10 μg/L vinclozolin (p<0.05) suggested that endocrine stress was evoked by vinclozolin exposure. Significant decreases in mRNA levels of interrenal crf, pomc, gr, and nka in females and gr and nka in males were observed after exposure to ≥ 0.5 μg/L and 2 μg/L vinclozolin (p<0.05), respectively; however, no changes in expression of these genes were observed in the brain of males (p ≥ 0.159) or females (p ≥ 0.053) compared with the control. The results indicated that female rare minnows were more sensitive than males to vinclozolin exposure. In conclusion, vinclozolin exposure evoked endocrine stress on the hypothalamic-pituitary-interrenal axis in the rare minnow, and the interrenal tissue was more sensitive than the brain tissue to stress caused by vinclozolin exposure. These results provide additional data about the modes of toxicological action of vinclozolin.

Diel variations in the selected serum immune parameters in Oreochromis mossambicus

Almost all metabolic processes in an organism alternate through high and low activity phases with a regular periodicity of nearly 24h. These daily/diel variations are governed by factors such as light, weather conditions, availability of food or predator activity. The immune system in fish is expected to follow the same routine based on external cues from the environment which it lives. The present study was carried out to investigate such daily/diel variations in selected immune parameters such as serum lysozyme and peroxidases activity, total serum globulin level and peripheral blood leukocyte count in Oreochromis mossambicus. The fish were maintained in semi natural condition (i.e.12L:12D). The results showed significant rise in serum peroxidases and lysozyme between 0200 h and 0600 h of the day and serum cortisol exhibited elevated level between 2200 h and 0600 h. Total serum globulin exhibited peak concentration from 1400 h to 1800 h. Thus suggesting the possibility of rhythmic functioning of immune system in O. mossambicus.

Stress-related hormones modulate cytokine expression in the head kidney of gilthead seabream (Sparus aurata)

Neuro-endocrine and immune systems closely interact in fish, and their regulation is crucial for the maintenance of good health of cultured fish. We have used the seabream head kidney to study whether stress-related hormones can modulate the immune response. For this purpose, the effects of adrenaline, adrenocorticotropic hormone (ACTH) and cortisol on the expression of pro-inflammatory cytokines (TNF-alpha, IL-1beta, IL-6) and the anti-inflammatory cytokine TGF-beta1 were determined by means of quantitative real-time PCR on isolated head kidney cells. ACTH (150 ng mL(-1)) caused an acute increase of TNF-alpha and IL-6 mRNA levels as well as an inhibition of IL-1beta expression. The expression of the anti-inflammatory cytokine TGF-beta1 was also increased, although in a lower extent. Adrenaline (1 muM) early effects were only clear inhibiting IL-1beta expression but not TNF-alpha, IL-6 or TGF-beta1 mRNA levels, while a longer exposure to the hormone inhibited all cytokines. Moreover, cortisol (50 and 100 ng mL(-1)) reduced the expression of all cytokines in a dose-dependent manner. Bacterial lipopolysaccharide (LPS) stimulated IL-1beta expression and inhibited that of the anti-inflammatory TGF-beta1, although it was ineffective on TNF-alpha and IL-6. In addition, adrenaline and cortisol decreased the LPS-stimulated IL-1beta expression, further demonstrating their previously reported anti-inflammatory effects. The combination of ACTH and LPS, on the other hand, did not affect LPS-stimulated IL-1beta expression but was effective increasing TNF-alpha expression. Taking all these results in consideration, we conclude that the expression of pro- and anti-inflammatory cytokines in the seabream head kidney is highly influenced by stress-related hormones, thus indicating an important role for the endocrine system in the modulation of the immune response in teleost fish.

Stress and innate immunity in carp: corticosteroid receptors and pro-inflammatory cytokines

The stress hormone cortisol is deeply involved in immune regulation in all vertebrates. Common carp (Cyprinus carpio L.) express four corticoid receptors that may modulate immune responses: three glucocorticoid receptors (GR); GR1, with two splice variants (GR1a and GR1b), GR2 and a single mineralocorticoid receptor (MR). All receptors are expressed as of 4 days post-fertilization and may thus play a critical role in development and functioning of the adult immune system. Immune tissues and cells predominantly express mRNA for GRs compared to mRNA for the MR. Three-dimensional protein structure modeling predicts, and transfection assays confirm that alternative splicing of GR1 does not influence the capacity to induce transcription of effector genes. When tested for cortisol activation, GR2 is the most sensitive corticoid receptor in carp, followed by the MR and GR1a and GR1b. Lipopolysacharide (LPS) treatment of head kidney phagocytes quickly induces GR1 expression and inhibits GR2 expression. Cortisol treatment in vivo enhances GR1a and MR mRNA expression, but only mildly, and cortisol treatment in vitro does not affect receptor expression of phagocytes. Cortisol has no direct effect on the LPS-induced receptor profile. Therefore, an immune rather than a stress stimulus regulates GR expression. Cortisol administered at stress levels to phagocytes in vitro significantly inhibits LPS-induced expression of the pro-inflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin-12 (IL-12) (subunit p35) and of inducible nitric oxide synthase (iNOS) expression. A physiologically differential function for GR1 and GR2 in the immune response of fish to infection is indicated.

Cloning of sole proopiomelanocortin (POMC) cDNA and the effects of stocking density on POMC mRNA and growth rate in sole, Solea solea

Proopiomelanocortin (POMC) is an important gene implicated in different functions, such as the stress response of the hypothalamus-pituitary-adrenal axis. The aim of the present study was to determine whether farming conditions, such as stocking density, can be considered a powerful stressor influencing in turn the growth rate in juvenile fish. Thus, POMC cDNA expression was investigated during adaptation to farming conditions in sole (Solea solea), as a model for studying the effects of rearing densities on stress response; different stocking densities (50, 100, and 250 animals/m(2)) were applied and, after 7 and 21 days, the fishes were examined for body weight and plasma cortisol levels as indicators of stress. In addition, proopiomelanocortin was cloned and sequenced from the brain of sole, allowing semi-quantitative RT-PCR to be performed to evaluate POMC mRNA expression in brain tissue. There was a significant increase in cortisol levels in fish reared at high stocking densities of 250/m(2) compared to fish reared at control densities of 100 and 50/m(2), in both experimental times, i.e., 7 and 21 days. The high stocking densities were also found to decrease the specific growth rate of fish. Moreover, it was demonstrated that the highest stocking density induced a significant decrease in sole POMC mRNA expression. It is concluded that POMC and cortisol are both involved in the stress response due to high rearing densities, during which cortisol may serve as a negative regulator of POMC.

Susceptibility of sexually mature rainbow trout, Oncorhynchus mykiss to experimental cryptobiosis caused by Cryptobia salmositica

Sexually mature rainbow trout, Oncorhynchus mykiss, were highly susceptible to cryptobiosis caused by Cryptobia salmositica. Spawning female trout were more susceptible (higher parasitaemia and mortality) than sexually mature males. Most infected female trout (seven of nine) with eggs died before or shortly after spawning; however, none of the nine infected sexually matured males or the uninfected fish died. There was no significant difference in the severity of the anaemia between infected male and female trout. All infected males developed exophthalmia, while this clinical sign was not seen in any of the infected females nor in uninfected trout. The addition of 17 beta-estradiol (at physiological level or higher) did not enhance in vitro multiplication of the Cryptobia; however, fresh plasma from sexually mature females or males when added to cultures significantly increased in vitro multiplication of the pathogen. In addition, plasma from sexually mature females were significantly better than those from males in promoting in vitro parasite multiplication. Parasite multiplication did not increase after plasma from sexually mature fish were heat inactivated.

Multiple corticosteroid receptors in fish: from old ideas to new concepts

The effect of corticosteroid hormones in fish are mediated through intracellular receptors that act as ligand-binding transcription factors. Many studies have been devoted to cortisol binding using radiolabeled ligand in fish and allowed characterization of a single class of high affinity binding sites in various tissues. Molecular characterization of cortisol receptors has only been initiated recently by cloning the different receptor forms: Following a isolation of a first glucocorticoid receptor (GR), a mineralocorticoid receptor (MR) was described and the presence of various GR isoforms was recently reported. Sequence comparison and phylogenetic analysis of these sequences confirm that fish possess both GR and MR and that GR gene is duplicated. The importance of these various corticosteroid receptor forms is also illustrated by analysis of their transcriptional activity. When tested in human cell lines, these receptors showed functionally distinct actions on GR-sensitive promotors, thus suggesting a more complicated corticosteroid signaling system than initially anticipated from binding studies. These results also suggest that, whereas cortisol is certainly the physiological ligand for GR, this may not be the case for MR which showed high sensitivity for deoxycorticosterone (DOC) and aldosterone. As this last hormone is probably absent in fish, these results raise the question as to whether DOC could be a physiological ligand for MR in fish. Information on DOC effect in fish is very scarce and clarification of the differential osmoregulatory roles of cortisol and DOC in fish needs ellucidation. This will require analysis of all actors of the corticosteroid signaling system at pre-receptor, receptor, and post-receptor levels.

Expression of glucocorticoid receptor in the intestine of a euryhaline teleost, the Mozambique tilapia (Oreochromis mossambicus): Effect of seawater exposure and cortisol treatment

Cortisol plays an important role in controlling intestinal water and ion transport in teleosts possibly through glucocorticoid receptor (GR) and/or mineralocorticoid receptor. To better understand the role of GR in the teleost intestine, in a euryhaline tilapia, Oreochromis mossambicus, we examined (1) the intestinal localizations of GR; (2) the effects of environmental salinity challenge and cortisol treatment on GR mRNA expression. The mRNA abundance of GR in the posterior intestinal region of tilapia was found to be higher than that in the anterior and middle intestine. In the posterior intestine, GR appears to be localized in the mucosal layer. GR mRNA levels in the posterior intestine were elevated after exposure of freshwater fish to seawater for 7 days following an increase in plasma cortisol. Similarly, cortisol implantation in freshwater tilapia for 7 days elevated the intestinal GR mRNA. These results indicate that seawater acclimation is accompanied by upregulation of GR mRNA abundance in intestinal tissue, possibly as a consequence of the elevation of cortisol levels. In contrast, a single intraperitoneal injection of cortisol into freshwater tilapia decreased intestinal GR mRNA. This downregulation of the GR mRNA by cortisol suggests a dual mode of autoregulation of GR expression by cortisol.

Quantification of a glucocorticoid receptor in sea bass (Dicentrarchus labrax, L.) reared at high stocking density

To assess the effects of environmental stress conditions on fish, the examination of a suite of biomarkers, including endocrine parameters, has been suggested. In teleosts, glucocorticoids, including cortisol and corticosterone, are known to mediate stress response. Inside the cell, they bind to a high-affinity cytosolic glucocorticoid receptor (GR), which acts as ligand-dependent transcription factor to control and regulate gene expression. Receptor number or affinity may directly influence the degree of reactivity of target cells. GR transcripts have been cloned and characterized in different fish species, but no studies, to date, are available on the quantification of GR in sea bass (Dicentrarchus labrax, L.), although this is one of the most important species in Mediterranean aquaculture. These considerations prompted our interest in cloning the GR in this species and investigating the impact of long-term exposure to crowding stress on GR expression in the liver of sea bass. Our data clearly demonstrate that a high rearing density stress affects GR mRNA, whose abundance in the liver decreased inversely with blood cortisol levels.

Osmoregulatory action of 17β-estradiol in the gilthead sea breamSparus auratus

The osmoregulatory action of 17beta-estradiol (E2) was examined in the euryhaline teleost Sparus auratas. In a first set of experiments, fish were injected once with vegetable oil containing E2 (1, 2 and 5 microg/g body weight), transferred 12h after injection from sea water (SW, 38 ppt salinity) to hypersaline water (HSW, 55 ppt) or to brackish water (BW, 5 ppt salinity) and sampled 12h later (i.e. 24 h post-injection). In a second experiment, fish were injected intraperitoneally with coconut oil alone or containing E2 (10 microg/g body weight) and sampled after 5 days. In the same experiment, after 5 days of treatment, fish of each group were transferred to HSW, BW and SW and sampled 4 days later (9 days post-implant). Gill Na+,K+ -ATPase activity, plasma E2 levels, plasma osmolality, and plasma levels of ions (sodium and calcium), glucose, lactate, protein, triglyceride, and hepatosomatic index were examined. Transfer from SW to HSW produced no significant effects on any parameters assessed. E2 treatment did not affect any parameter. Transfer from SW to BW resulted in a significant decrease in plasma osmolality and plasma sodium but did not affect gill Na+,K+ -ATPase activity. A single dose of E2 attenuated the decrease in these parameters after transfer from SW to BW, but was without effect on gill Na+,K+ -ATPase activity. An implant of E2 (10 microg/g body weight) for 5 days significantly increased plasma calcium, hepatosomatic index, plasma metabolic parameters, and gill Na+,K+ -ATPase activity. In coconut oil-implanted (sham) fish, transfer from SW to HSW or BW during 4 days significantly elevated gill Na+,K+ -ATPase. Gill Na+,K+ -ATPase activity remained unaltered after transfer of E2-treated fish to HSW or BW. However, in E2-treated fish transferred from SW to SW (9 days in SW after E2-implant), gill Na+,K+ -ATPase activity decreased with respect to HSW- or BW-transferred fish. Shams transferred to HSW showed increased levels of lactate, protein, and trygliceride in plasma, while those transferred to BW only displayed increased trygliceride levels. E2-treated fish transferred to HSW showed higher protein levels without any change in other plasmatic parameters, while those transferred to BW displayed elevated plasma glucose levels but decreased osmolality and protein levels. These results substantiate a chronic stimulatory action of E2 on gill Na+,K+ -ATPase activity in the euryhaline teleost Sparus auratas.

Effects of prolactin and growth hormone on proliferation and survival of cultured trout leucocytes

The in vitro effects of prolactin (PRL) and growth hormone (GH) on the proliferation and survival of leucocytes isolated from the blood of the rainbow trout (Oncorhynchus mykiss) were examined, with special reference to the immunosuppression by cortisol. Both PRL and GH induced a mitogenic effect in trout leucocytes. Contrary, the frequencies of annexin V-positive apoptotic cells and propidium iodide-positive dead cells were decreased by the administration of PRL, but were uninfluenced by GH. Administration of cortisol suppressed the mitotic activity and induced cell death of leucocytes. PRL inhibited the decrease in mitosis and the increase in cell death due to cortisol. GH significantly assisted recovery of cortisol-suppressed mitosis but did not influence the survival of leucocytes. These results suggest that PRL and GH are involved in the maintenance of specific immune functions in fish through a prevention of immunosuppression by cortisol.

Inflammatory interactions in fish exposed to pollutants and parasites: a role for apoptosis and C reactive protein

Although previous studies have highlighted the inflammatory responses of fish infected with parasites and exposed to pollutants, very little is known about how these two stressors interact within the fish. In this review, which also contains original data, the effect of these two parameters on the fish inflammatory response is assessed and, in particular, the role of apoptosis and the acute phase protein, C reactive protein, is evaluated. InCyprinus carpioexposed to 0·5 mg NH4+l−1or 0·1 mg Cd2+l−1and experimentally infected with the blood fluke,Sanguinicola inermis, the pollutant type and the order in which the fish experiences the parasite and toxicant, significantly affects the ultrastructural appearance and cellular content of the pronephros and thymus. This is reflected in the intensity of infection where the pollutant appears to have less effect on an established infection. Both stressors, pollutant and infection, may mediate their effects via the endocrine system. Studies have revealed that cortisol at 100 ng ml−1is able to induce apoptosis in pronephric cells of carp and that an increase in apoptosis is associated with an increase in phagocytosis in this immune organ. In addition, C reactive protein, which is used as a biomarker of the inflammatory response in humans and other mammals, is evaluated as a possible indicator of physiological states in fish exposed to pathogens and pollutants.

Effects of different stressor agents on gilthead seabream natural cytotoxic activity

Several common situations in gilthead seabream (Sparus aurata L.) farming, such as air exposure, crowding and the use of anaesthetics, have been demonstrated to be stressful. In the present study, these conditions were simulated in the laboratory, after which head-kidney natural cytotoxic cell (NCC) activity was evaluated. For this, several specimens were air exposed for 2 min, returned to the aquarium and sampled from 0 to 4 days after exposure. NCC activity was significantly lower on the day following air-exposure compared with the control (rested fish) but not at any other time studied. Other fish were crowded (100 kg biomass m(-3), 2 h), returned to an aquarium with the same density as the control group (9 kg m(-3)) and sampled from 0 to 4 days after treatment. Head-kidney NCC activity was statistically increased compared with the control (resting) fish, 1 day after crowding. Anaesthesis for 1 h with 60 or 200 microl 2-phenoxyethanol l(-1)had no significant effect on NCC activity, while the use of 50 mg MS222 l(-1)for 1 h reduced such activity (by about 40%) compared with the control. In other experiments, fish were consecutively treated with crowding and anaesthetics. When treated with the lowest 2-phenoxyethanol concentration after crowding, the NCC activity inhibition was abolished compared with the activity in fish treated either with crowding or anaesthetic alone, while the use of the highest concentration increased such inhibition. The use of MS222 after crowding did not produce any differential effect compared with the fish treated with only one of the factors. In conclusion, NCC activity is affected differently according to the stress factor applied (hypoxia, crowding and/or anaesthetics). Differences in the effects provoked by these stressors on other seabream innate immune parameters are discussed.