Exposure of Goldfish (Carassius auratus) to Bluegills (Lepomis macrochirus) Enhances Expression of Stress Protein 70 mRNA in the Brains and Increases Plasma Cortisol Levels

The effect of psychological stress on HSP70 mRNA in the brains and plasma cortisol levels in goldfish was examined. Stress was induced by exposure to a predator (bluegills). HSP70 mRNA and cortisol were determined by Northern blotting and ELISA, respectively. Goldfish exposed to four predators in the same tank without a partition showed marked increases in HSP70 mRNA and cortisol levels 6 hr and 12 hr after commencement of exposure. When goldfish were separated from bluegills with a net partition, HSP70 mRNA expression was enhanced after 6 hr, and returned to the control level after 12 hr. Plasma cortisol levels increased after 2 hr, and returned to the control level after 6 hr. When goldfish were placed in a transparent tank around which bluegills were swimming, HSP70 mRNA expression and cortisol levels increased after 6 hr and 12 hr. Goldfish exposed to water circulating through a tank with bluegills showed no sign of changes in HSP70 mRNA expression or cortisol levels. These results suggest that psychological stress enhanced HSP70 mRNA expression in the brains and increased plasma cortisol levels via visual perception.     

Innate-immune responses of tilapia (Oreochromis mossambicus) exposure to acute cold stress

In this present study, Oreochromis mossambicus tilapia were transferred to cold water at 12°C for various time intervals (1, 4, 8, 24, and 48 hr) and its innate immune response was analyzed by studying cellular and humoral parameters. In vivo, alternative complement pathway activity in blood plasma was rapidly increased at 1 hr of cold water (12°C) exposure. Lysozyme activity and cortisol levels of plasma were increased at 4 and 1 hr, respectively. Surprisingly, only plasma cortisol levels remained unchanged through 24 hr of cold water transfer. Phagocytic ability, phagocytic capacity, and respiratory burst (RB) activity of head kidney (HK) leukocytes and splenocytes showed no any significant changes. In peripheral blood leukocytes, phagocytic capacity, and RB activity were increased at 24 hr of cold water exposure. The expressions of genes involved innate immunity in splenocytes and HK leukocytes of tilapia cold water exposure were analyzed, messenger RNA (mRNA) expressions of HSP70, HSP90, and immunoglobulin M failed to change upon exposure to cold stress. Major histocompatibility complex-I and II mRNAs were significantly increased in tilapia splenocytes at 1 hr of cold water transferred. Whereas myxovirus (Mx) expression was increased in splenocytes and HK leukocytes of tilapia after 1 hr of cold water exposed. Our result reveals that the exposure of tilapia to acute cold stress condition significantly enhances plasma acid phosphatase activity and both phagocytic capacity and RB activity. Furthermore, cold stress significantly stimulates Mx gene expression in splenocytes and HK leukocytes.     

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 7day, 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.     

浅水应激后黄斑蓝子鱼生理指标变化及牛磺酸的抗应激作用

研究报道黄斑蓝子鱼受到短暂（4min）浅水应激后鱼体相关应激指标的变化及应激后20、40、60、80min时的恢复情况,以及牛磺酸的抗应激作用。结果表明,浅水应激后,该鱼血清肾上腺素浓度显著升高（P0.05）,从应激前的（2.000.22）ng/mL达到应激后的（15.121.04）ng/mL,之后逐渐恢复到应激前水平;皮质醇和胆固醇浓度没有显著性变化（P0.05）;葡萄糖浓度在应激后20min达到最大值（7.100.38）mmol/L,是应激前（2.150.02）mmol/L的约3.5倍（P0.05）。应激后60min时,脑中HSP70 mRNA的表达量达到最大值,为应激前的11.54倍（P0.05）。0.02牛磺酸浸泡能够显著降低蓝子鱼应激后的血清肾上腺素和葡萄糖水平以及脑HSP70 mRNA表达量（P0.05）。结果说明,交感神经－嗜铬组织系统可能是黄斑蓝子鱼的急性应激途径之一,鱼体通过释放肾上腺素来提高血糖浓度以满足应激时的能量需求,同时通过提高细胞HSP70的表达水平来增强鱼体的保护作用;牛磺酸具有一定的抗应激作用。       

Heat shock protects cultured neurons from glutamate toxicity.

Expression of heat shock proteins (HSPs) occurs in brain after ischemia and status epilepticus. We report that induction of the heat shock response in cortical cultures protects neurons from glutamate-induced excitotoxicity. Cultures heated to 42.2 degrees C for 20 min showed an overall decrease in protein synthesis but an increase in the synthesis of approximately 72 and approximately 85 kd proteins and in the levels of HSP70 mRNA. Heat shock inhibited excitotoxicity in cells exposed to glutamate at 3 or 24 hr following heat exposure, but not when the interval between heat and glutamate exposure was shortened to 15 min or lengthened to 48 hr. Protection due to heat shock required new protein synthesis, since it did not occur when protein or RNA synthesis inhibitors were added. By ameliorating excitotoxic processes, HSPs may attenuate brain injury in certain pathologic conditions.     

Bacterial Lipopolysaccharide Augments Febrile-Range Hyperthermia-Induced Heat Shock Protein 70 Expression and Extracellular Release in Human THP1 Cells

Sepsis, a devastating and often lethal complication of severe infection, is characterized by fever and dysregulated inflammation. While infections activate the inflammatory response in part through Toll-like receptors (TLRs), fever can partially activate the heat shock response with generation of heat shock proteins (HSPs). Since extracellular HSPs, especially HSP70 (eHSP70), are proinflammatory TLR agonists, we investigated how exposure to the TLR4 agonist, bacterial lipopolysaccharide (LPS) and febrile range hyperthermia (FRH; 39.5°C) modify HSP70 expression and extracellular release. Using differentiated THP1 cells, we found that concurrent exposure to FRH and LPS as well as TLR2 and TLR3 agonists synergized to activate expression of inducible HSP72 (HSPA1A) mRNA and protein via a p38 MAP kinase-requiring mechanism. Treatment with LPS for 6 h stimulated eHSP70 release; levels of eHSP70 released at 39.5°C were higher than at 37°C roughly paralleling the increase in intracellular HSP72 in the 39.5°C cells. By contrast, 6 h exposure to FRH in the absence of LPS failed to promote eHSP70 release. Release of eHSP70 by LPS-treated THP1 cells was inhibited by glibenclamide, but not brefeldin, indicating that eHSP70 secretion occurred via a non-classical protein secretory mechanism. Analysis of eHSP70 levels in exosomes and exosome-depleted culture supernatants from LPS-treated THP1 cells using ELISA demonstrated similar eHSP70 levels in unfractionated and exosome-depleted culture supernatants, indicating that LPS-stimulated eHSP70 release did not occur via the exosome pathway. Immunoblot analysis of the exosome fraction of culture supernatants from these cells showed constitutive HSC70 (HSPA8) to be the predominant HSP70 family member present in exosomes. In summary, we have shown that LPS stimulates macrophages to secrete inducible HSP72 via a non-classical non-exosomal pathway while synergizing with FRH exposure to increase both intracellular and secreted levels of inducible HSP72. The impact of increased macrophage intracellular HSP70 levels and augmented secretion of proinflammatory eHSP70 in the febrile, infected patient remains to be elucidated.     

Interactive effect of ammonia and crowding stress on ion-regulation and expression of immune-related genes in juvenile turbot (Scophthalmus maximus)

The present study was to investigate the interactive effect of ammonia and crowding stress on ion-regulation and expression of immune-related genes in juvenile turbot (Scophthalmus maximus). The fish were exposed to four total ammonia nitrogen (0, 5, 20, 40 mg/L TAN) and two stocking density. After 96 h of exposure, blood, gill, and liver samples were collected to measure biochemical parameters and mRNA levels of immune-related genes. The results showed that co-exposure to high TAN (20 and 40 mg/L) and high density significantly increased plasma sodium (Na⁺), gill Na⁺/K⁺-ATPase activity and mRNA levels. Following individual and combined exposure to high TAN and high density, the heat shock protein 70 (HSP 70), HSP 90, tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) genes expression were obviously higher than their control. Conversely, the lysozyme (LZM) and hepcidin mRNA levels were down-regulated in liver of fish exposed to high TAN alone and combination of high TAN-density. Moreover, glutathione S-transferase (GST) mRNA levels significantly increased in treatments with individual high TAN and high density, but decreased in high TAN-density co-exposed fish. Overall, ion homeostasis and immune status were adversely influenced in high exposed turbot under high density.     

Quantitative RT-PCR analysis and immunohistochemical localization of HSP70 in sea bass Dicentrarchus labrax exposed to transport stress

In aquaculture, fish are exposed to stressful conditions, which cause an increased synthesis of heat shock proteins (HSPs) at the cellular level. In this work we considered the expression of the constitutive and inducible forms of HSP70 as an indicator of stress caused by transport, during development of the sea bass (Dicentrarchus labrax), a teleost fish of high value for aquaculture. Qualitative RT-PCR analysis revealed expression of inducible HSP70 gene in larvae and fry (25, 40 and 80 days) as well as in adult tissues (liver, brain, muscle, gills, kidney, gonads, heart, spleen and skin) of both control and stressed animals. Expression of inducible HSP70 mRNA examined in different adult tissues by Real-Time PCR, was significantly higher in skin and skeletal muscle of stressed animals than in controls. Immunolocalization of inducible and constitutive forms of heat shock protein 70 (HSP70 and HSC70), reported here for the first time, demonstrated an ubiquitous distribution of HSC70 protein in several tissues of both stressed and control animals (at all stages), while inducible HSP70 protein was found only in skeletal muscle of stressed animals. In all stressed animals, regardless of their developmental stage, cortisol levels were higher than in control animals.     

Impairment of the stress response in matrinxã juveniles (Brycon amazonicus) exposed to low concentrations of phenol

In this study we measured plasma cortisol, plasma glucose, plasma sodium and potassium, and liver and gill hsp70 levels in juvenile matrinxã (Brycon amazonicus) subjected to a 96 h exposure to phenol (0, 0.2, and 2.0 ppm), and the effect of this exposure on their ability to respond to a subsequent handling stress. Fish were sampled prior to initiation of exposure and 96 h, and at 1, 6, 12, and 24 h post-handling stress. During the 96 h exposure, plasma cortisol and glucose levels remained unchanged in all treatments. While plasma sodium levels were significantly reduced in all groups, plasma potassium levels only decreased in fish exposed to 0 and 0.2 ppm of phenol. Liver hsp70 levels decreased significantly at 96 h in fish exposed to 2.0 ppm of phenol. All groups, except fish exposed to 0.2 ppm of phenol, were able to increase plasma cortisol and glucose levels after handling stress. Fish exposed to 2.0 ppm of phenol showed decreased gill and liver hsp70 levels after the handling stress. Our data suggest that exposure to phenol may compromise the ability of matrinxã to elicit physiological responses to a subsequent stressor.     

The expression of heat shock protein 70 in rat brain after +Gz exposure

To investigate the effect of +Gz exposure on the expression and distribution of heat shock protein 70 (HSP70) in rat brain. Methods: One hundred rats were randomly divided into control group, +2 Gz, +6 Gz and +10 Gz exposures groups. The +Gz group rats were exposed to +2 Gz, +4 Gz, +6 Gz and +10 Gz for 3 minute respectively. The expression of HSP70 in rat brain was measured by immunohistochemistry and West blot methods after +Gz exposure. Results: There was no HSP70 expression in the brains of control rats. In +2, +4. and +6 Gz groups, HSP70 was obviously expressed in cortex, hippocampus and pyriform cortex 6 h after exposures, and strongly expressed 1 d after exposure, and then had a tendency to decrease 2 d after exposure, and returned to control level 6 d after exposure. The expression of HSP70 after +6 Gz exposure was the strongest in all +Gz groups. In +10 GZ group, HSP70 protein was only weakly expressed in pyriform cortex after exposure. Conclusions: +Gz exposures may cause time-dependent HSP70 expression in rat brain.     

Expression of warm temperature acclimation-related protein 65-kDa (Wap65) mRNA, and physiological changes with increasing water temperature in black porgy, Acanthopagrus schlegeli

We isolated the warm temperature acclimation-related protein 65-kDa (Wap65) cDNA from the liver of black porgy and investigated the expression by increasing water temperature in black porgy, Acanthopagrus schlegeli. Black porgy Wap65 full-length cDNA consists of 1,338 nucleotides, including an open reading frame, predicted to encode a protein of 425 amino acids and showed high homology to pufferfish (79%), Medaka (73%), carp (70%), and goldfish (68%) Wap65. Increase in water temperature (20 degrees C --> 30 degrees C; 1 degrees C/day) induced the rise of Wap65 mRNA expression in liver of black porgy. Also, the levels of cortisol and glucose in plasma were significantly higher at 30 degrees C than at 20 degrees C. To determine the high water temperature stressor specificity of the induction of Wap65, black porgy were transferred from seawater (SW) to freshwater (FW) for 24 hr. Wap65 expression was not detected when the fish were transferred from SW to FW (in fish transferred from SW to FW), although the levels of cortisol and glucose in plasma were increased. These results suggest that increase in Wap65 gene is related to high water temperature stress and play important roles in high water temperature environment of black porgy.     

Exogenous heat shock protein-70 inhibits cigarette smoke-induced intimal thickening

Cigarette smoke is associated with increased carotid intimal thickening or stroke. Preliminary work showed that exposure to smoke resulted in a 4.5-fold reduction of heat shock protein-70 (HSP70) expression in spleens of mice using gene microarray analysis. In the current study, we investigated the role of extracellular HSP70 in carotid intimal thickening of mice exposed to cigarette smoke. Intimal thickening was induced by placement of a cuff around the right carotid artery of mice. Cuff injury resulted in increased HSP70 mRNA expression in carotid arteries that persisted for 21 days. Cigarette smoke exposure decreased arterial HSP70 expression and significantly increased intimal thickening compared with mice exposed to air. Treatment of mice exposed to cigarette smoke with intravenous recombinant HSP70 attenuated intimal thickening through reduced phosphorylated extracellular signal-regulated kinase (pERK) expression in the arterial wall. In vitro experiments with rat aortic smooth muscle cells confirmed that recombinant HSP70 decreases pERK and proliferating cell nuclear antigen (PCNA) expression in cells exposed to cigarette smoke extract and H(2)O(2). Our study suggests that decreased expression of arterial HSP70 is an important mechanism by which exposure to cigarette smoke augments intimal thickening. The effects of recombinant HSP70 suggest a role for extracellular HSP70.     

Temporal changes in stress and tissue-specific metabolic responses to municipal wastewater effluent exposure in rainbow trout

Sub-chronic exposure to municipal wastewater effluent (MWWE) in situ was recently shown to impact the acute response to a secondary stressor in rainbow trout (Oncorhynchus mykiss). However, little is known about whether MWWE exposure in itself is stressful to the animal. To address this, we carried out a laboratory study to examine the organismal and cellular stress responses and tissue-specific metabolic capacity in trout exposed to MWWE. Juvenile rainbow trout were exposed to 0, 20 and 90% MWWE (from a tertiary wastewater treatment plant), that was replenished every 2d, for 14 d. Fish were sampled 2, 8 or 14 d post-exposure. Plasma cortisol, glucose and lactate levels were measured as indicators of organismal stress response, while inducible heat shock protein 70 (hsp70), constitutive heat shock protein 70 (hsc70) and hsp90 expression in the liver were used as markers of cellular stress response. Impact of MWWE on cortisol signaling was ascertained by determining glucocorticoid receptor protein (GR) expression in the liver, brain and, heart, and metabolic capacity was evaluated by measuring liver glycogen content and tissue-specific activities of key enzymes in intermediary metabolism. Plasma glucose and lactate levels were unaffected by exposure to MWWEs, whereas cortisol showed a transient increase in the 20% group at 8d. Liver hsc70 and hsp90, but not hsp70 expression, were higher in the 90% MWWE group after 8d. There was a temporal change in GR expression in the liver and heart, but not brain of trout exposed to MWWE. Liver glycogen content and activities liver gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK), and alanine aminotransferase (AlaAT) were significantly affected by MWWE exposure. The glycolytic enzymes pyruvate kinase (PK) and hexokinase (HK) activities were significantly higher temporally by MWWE exposure in the gill and heart, but not in the liver and brain. Overall, a 14 d exposure to MWWE evokes a cellular stress response and perturbs the cortisol stress response in rainbow trout. The tissue-specific temporal changes in the metabolic capacity suggest enhanced energy demand in fish exposed to MWWE, which may eventually lead to reduced fitness.     

Differences in Susceptibility to Heat Stress along the Chicken Intestine and the Protective Effects of Galacto-Oligosaccharides

High ambient temperatures negatively affect the human well-being as well as animal welfare and production. The gastrointestinal tract is predominantly responsive to heat stress. The currently available information about the multifaceted response to heat stress within different parts of the intestine is limited, especially in avian species. Hence, this study aims to evaluate the heat stress-induced sequence of events in the intestines of chickens. Furthermore, the gut health-promoting effect of dietary galacto-oligosaccharides (GOS) was investigated in these heat stress-exposed chickens. Chickens were fed a control diet or diet supplemented with 1% or 2.5% GOS (6 days) prior to and during a temperature challenge for 5 days (38–39°C, 8h per day). The parameters measured in different parts of the intestines included the genes (qPCR) HSF1, HSF3, HSP70, HSP90, E-cadherin, claudin-1, claudin-5, ZO-1, occludin, TLR-2, TLR-4, IL-6, IL-8, HO-1, HIF-1α) and their associated proteins HSP70, HSP90 and pan-cadherin (western blots). In addition, IL-6 and IL-8 plasma concentrations were measured by ELISA. In the jejunum, HSF3, HSP70, HSP90, E-cadherin, claudin-5, ZO-1, TLR-4, IL-6 and IL-8 mRNA expression and HSP70 protein expression were increased after heat stress exposure and a more pronounced increase in gene expression was observed in ileum after heat stress exposure, and in addition HSF1, claudin-1 and HIF-1α mRNA levels were upregulated. Furthermore, the IL-8 plasma levels were decreased in chickens exposed to heat stress. Interestingly, the heat stress-related effects in the jejunum were prevented in chickens fed a GOS diet, while dietary GOS did not alter these effects in ileum. In conclusion, our results demonstrate the differences in susceptibility to heat stress along the intestine, where the most obvious modification in gene expression is observed in ileum, while dietary GOS only prevent the heat stress-related changes in jejunum.     

Discordant expression of heat shock protein mRNAs in tissues of heat-stressed rats.

Although the induction of heat shock proteins (HSP) has been studied extensively in cultured cells, comparatively few studies have examined their expression in vivo. In this report, mRNA expression of two HSP families, HSP70 and HSP27, was investigated in brain, liver, lung, and skin of rats exposed to elevated ambient temperatures. The time course and relative magnitude of the heat-induced expression for these two HSP differed between tissues of the same animal. Even within the same tissue, HSP70 and HSP27 displayed differential kinetics of induction. In brain, lung, and skin, induction of HSP70 was dependent on the duration and temperature of the heat stress. This induction was transient with maximal HSP70 expression occurring at 1 h and returning to baseline 3 h after removal of the animals from heat stress. In liver, HSP70 expression did not show a direct relationship with temperature conditions and maximal induction did not occur until 6 h after heat stress. Heat-induced HSP27 expression was dependent on time and temperature of exposure in lung and skin but not in brain and liver. These findings demonstrate that the heat shock response in vivo lacks much of the coordinate control of expression characteristic of cultured cell populations and suggest that mechanisms controlling this cellular stress response are influenced by physiologic factors that cannot be studied in vitro.     

Activation of a stress-induced gene by insecticides in the midge, Chironomus yoshimatsui

Stress proteins (heat shock proteins, HSPs) have been proposed as general biomarkers for environmental monitoring. In the present study, we evaluated the environmental stress-burden on the aquatic midge Chironomus yoshimatsui using hsp70 expression. Larvae collected from streams receiving polluted runoff (field strain) were resistant to the organophosphorus insecticide, fenitrothion (F), and the synthetic pyrethroid, ethofenprox (E), whereas a strain originally collected from an unpolluted area (susceptible strain) showed low resistance to insecticide exposure. To examine the expression of an HSP70 gene in C. yoshimatsui, an hsp70 cDNA probe was prepared using RNA obtained from the field strain larvae and used for Northern blot analyses. The expression of this HSP70 gene in larvae collected from two field sites in May about 1 week after insecticide spraying in the fields was 2.3 (p = 0.018) to 3.3 fold higher than that in the susceptible strain and was also 4.6 and 1.4 (p = 0.033) fold higher than those collected in November 3 months after the cessation of insecticide spraying. In order to identify potential inducers of the HSP70 gene of the field strain, larvae of the susceptible strain were exposed to F or E for 24 h and hsp70 mRNA levels determined. Exposures to F at 0.4 microg/L and E at 1.1 microg/L increased hsp70 mRNA levels 2.7 (p = 0.049) and 4.4 (p = 0.043) fold over controls, respectively. These results suggest that larvae collected from polluted areas are burdened by environmental stressors and the tested insecticides are potential inducers of HSP70. The results also support the suggestion that HSP70 gene expression is a sensitive indicator of low level (nonlethal) exposures to certain insecticides.     

Expression of c-fos, c-jun and HSP70 mRNA in rat brain following high acceleration stress

Rats exposed to high +Gz forces in a small animal centrifuge (SAC) exhibit loss of neuronal function (isoelectric EEG), termed G-induced loss of consciousness (G-LOC). This phenomenon is presumably due to a reduction in cerebral blood flow (CBF) or ischemia. Ischemia induces various metabolic and physiologic changes including expression of immediate early genes (IEGs) in the brain. Expression of IEGs have been suggested to be reliable markers for neuronal response to external stimuli or stress. In the present study expression of IEGs c-fos, c-jun and stress response gene HSP70 were measured in the brains of rats subjected to six 30 s exposures of +22.5Gz in a small animal centrifuge. The level of c-fos, HSP70 and beta-actin mRNA were measured by both Northern blot and RT-PCR. Expression of c-jun was measured only by RT-PCR. Expression of c-fos and c-jun was significantly stimulated at 0.5, 15, 30 and 60 min post-centrifugation. The level of HSP70 mRNA was significantly higher only at 60 and 180 min post-centrifugation. Measurement of metabolities showed a significant increase in lactate and a decrease in Cr-P level at 30 s and 15 min post-centrifugation, respectively. Lactate, but not Cr-P and ATP levels were restored to control levels by 60 min post-centrifugation. It is concluded that the transient expression of c-fos, c-jun and HSP70 mRNA is stimulated by repeated ischemic/reperfusion episodes induced by high acceleration stress.     

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.