Aryl hydrocarbon receptor activation impairs cortisol response to stress in rainbow trout by disrupting the rate-limiting steps in steroidogenesis

Screening and Identification of the Biomarkers Applied for the Evaluation of Acute and Chronic Thermal Tolerance Ability in Largemouth Bass (Micropterus salmoides)

Affected by the continuously rising temperature, thermal stress leads to a delinked growth rate and resistance to stress in cultured largemouth bass (Micropterus salmoides, LMB) in China. Identification of LMB with better thermal resistance will benefit the breeding of new varieties. However, there has been limited reporting on the evaluation to identify LMB with better thermal resistance. LMB consists of the northern LMB (Micropterus salmoides salmoides, NLMB) and the Florida LMB (Micropterus salmoides floridanus, FLMB). Due to their different geographical distributions, it has been suggested that FLMB exhibit better thermal resistance compared to NLMB. In this study, NLMB and FLMB were subjected to thermal stress for 3 h (acute) and 60 d (chronic) at 33 °C, respectively. Subsequently, the variations of 12 candidate biomarkers between NLMB and FLMB were analyzed. Exposure to acute thermal stress significantly increased plasma cortisol, blood glucose, and lactate levels; activities of superoxide dismutase (SOD), glutathione peroxidase (GPX), catalase (CAT), glucose kinase (GK), pyruvate kinase (PK), lactate dehydrogenase (LDH), and glucose 6 phosphatase (G6Pase); and the expressions of hsp70 and hsp90 in both NLMB and FLMB (p < 0.05). Compared to NLMB, FLMB exhibited a lower plasma cortisol level and a higher expression of hsp90 under acute thermal stress (p < 0.05). Exposure to chronic thermal stress significantly increased plasma cortisol and blood glucose levels, as well as activities of GK, PK, LDH, and G6Pase, as well as expressions of hsp70 and hsp90 in both NLMB and FLMB (p < 0.05). Additionally, FLMB showed a lower expression of hsp70 compared to NLMB (p < 0.05). In conclusion, our results showed that LMB with lower plasma cortisol level and higher expression of hsp90 under acute thermal stress, as well as lower expression of hsp70 under chronic thermal stress were suggested to have better thermal resistance. Our study provides valuable information for identifying and breeding LMB varieties with better thermal resistance in the future.

Endocrine disruptors, aryl hydrocarbon receptor and cortisol secretion

PURPOSE

Endocrine disruptors exert a plethora of effects in endocrine tissues, from altered function to carcinogenesis. Given its lipophilic nature, the adrenal cortex represents an ideal target for endocrine disruptors and thus, possibly, xenobiotic-induced adrenocortical dysfunction. However, there is no clear understanding of the effect of endocrine disruptors on adrenal steroidogenesis, in particular as regards the aryl hydrocarbon receptor (AHR) pathway, one of the key mediators.

METHODS

The present review recapitulates available evidence on the effects of AHR ligands on adrenal steroidogenesis, with focus on cortisol secretion.

RESULTS

Short-term exposure to AHR ligands most often induced a stress-like corticosteroid response followed by decreased responsiveness to stressors with long-term exposure. This was observed in several experimental models across species as well as in animals and humans in real-life settings. Prenatal exposure led to different effects according to sex of the offspring, as observed in murine models and in children from mothers in several countries. In vitro findings proved highly dependent on the experimental setting, with reduced cortisol response and steroidogenic enzyme synthesis mostly observed in fish and increased cortisol synthesis and secretion observed in murine and human adrenal cell lines. Of note, no AHR-binding element was detected in steroidogenic enzyme promoters, suggesting the involvement of additional factors.

CONCLUSION

Our review provides evidence for the impact of AHR ligands on adrenocortical function and indicates further avenues of research to better clarify its effects.

Lingering Effects of Legacy Industrial Pollution on Yellow Perch of the Detroit River

We used yellow perch (Perca flavescens) captured at four sites differing in legacy industrial pollution in the Lake St. Clair-Detroit River system to evaluate the lingering sublethal effects of industrial pollution. We emphasized bioindicators of direct (toxicity) and indirect (chronic stress, impoverished food web) effects on somatic and organ-specific growth (brain, gut, liver, heart ventricle, gonad). Our results show that higher sediment levels of industrial contaminants at the most downstream Detroit River site (Trenton Channel) are associated with increased perch liver detoxification activity and liver size, reduced brain size, and reduced scale cortisol content. Trenton Channel also displayed food web disruption, where adult perch occupied lower trophic positions than forage fish. Somatic growth and relative gut size were lower in perch sampled at the reference site in Lake St. Clair (Mitchell's Bay), possibly because of increased competition for resources. Models used to determine the factors contributing to site differences in organ growth suggest that the lingering effects of industrial pollution are best explained by trophic disruption. Thus, bioindicators of fish trophic ecology may prove advantageous to assess the health of aquatic ecosystems. Environ Toxicol Chem 2023;42:2158-2170. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

A multi-targeted investigation of Deepwater Horizon crude oil exposure impacts on the marine teleost stress axis

The toxicity of the polycyclic aromatic hydrocarbons (PAHs) in Deepwater Horizon (DWH) oil is well-established, but a knowledge gap exists regarding how this combination of PAHs affects the vertebrate stress axis. We hypothesized that (1) marine vertebrates exposed to DWH PAHs experience stress axis impairment, and co-exposure to an additional chronic stressor may exacerbate these effects, (2) serotonin (5-hydroxytryptamine; 5-HT) may act as a secondary cortisol secretagogue in DWH PAH-exposed fish to compensate for impairment, and (3) the mechanism of stress axis impairment may involve downregulation of cyclic adenosine monophosphate (cAMP; as proxy for melanocortin 2 receptor (MC2R) functionality), total cholesterol, and/or mRNA expression of CYP1A and steroidogenic proteins StAR, P450scc, and 11β-h at the level of the kidney. We found that in vivo plasma cortisol and plasma adrenocorticotropic hormone (ACTH) concentrations in Gulf toadfish exposed to an environmentally relevant DWH PAH concentration (ΣPAH₅₀= 4.6 ± 1.6 μg/L) for 7 days were not significantly different from controls, whether fish were chronically stressed or not. However, the rate of cortisol secretion by isolated kidneys after acute stimulation with ACTH was significantly lower in PAH-exposed toadfish compared to clean seawater (SW) controls. 5-HT does not appear to be acting as a secondary cortisol secretagogue, rather, PAH-exposed + stressed toadfish exhibited significantly lower plasma 5-HT concentrations than clean SW + stressed fish as well as a reduced sensitivity to 5-HT at the level of the kidney. There was a tendency for kidney cAMP concentrations to be lower in PAH-exposed fish (p = 0.069); however, mRNA expression of steroidogenic proteins between control and PAH-exposed toadfish were not significantly different and a significant elevation in total cholesterol concentration in PAH-exposed toadfish compared to controls was measured. Future work is needed to establish whether the slower cortisol secretion rate by isolated kidneys of PAH-exposed fish is detrimental, to determine the potential role of other secretagogues in compensating for the impaired kidney interrenal cell function, and to determine whether there is a reduction in MC2R mRNA expression or an impairment in the function of steroidogenic proteins.

Potential biomarker of phenol toxicity in freshwater fish C. mrigala: Serum cortisol, enzyme acetylcholine esterase and survival organ gill

In this modern industrialized era of large-scale production of agrochemicals, various emerging contaminants form the main components of waste water and sludge in most of the developing countries of the world. In this concern, phenol- an inevitable and alarming chemical pollutant in aquatic ecosystem, gains a speedy access into the water bodies as an industrial by-product. Though the detrimental effects of phenol have been studied in various aspects of aquatic life, current study is an initiative to unravel the toxic effects of phenol at molecular level in Cirrhinus mrigala. Plasma cortisol level and acetylcholine esterase activity in fish was estimated by Chemiluminescent immunoassay technique and Ellman assay respectively. Scanning electron microscopic studies were carried out to unravel the gill histopathological alterations in exposed fish. It was observed that phenol (22.32 mg/l) inhibits 50 % of acetylcholine esterase activity in brain thereby affecting the locomotion of the targeted carp. Cortisol elevated during the 7th day in exposed fish, but declined progressively on the forthcoming 21st and 28th days. Manifestations in gill encompass curling, fusion, aberrations, sloughing of gill epithelium, wider inter filamentary space and mucus coating in the primary gill filament. It concludes that the discernable deviations produced in both biochemical parameters and key organ gill can be used as a biomarker and bio-indicator respectively for assessing the existence of emerging toxicants in aquatic ecosystem.

Regulation of cortisol production during chronic social stress in rainbow trout

Chronic stress resulting from social interactions impacts the endocrine stress response in many vertebrates, including teleost fishes. Juvenile rainbow trout held in pairs form a dominance hierarchy with the subordinate individual exhibiting chronic elevation of plasma cortisol and an attenuated cortisol response to an additional acute stressor. The current study investigated the mechanisms underlying this apparent dichotomy in cortisol production at the level of the head kidney (adrenal homolog). Following four days of chronic social stress, subordinate rainbow trout exhibited elevated plasma cortisol levels that correlated with basal cortisol production by the head kidney in vitro. Subordinate trout had higher transcript abundances of steroidogenic acute regulatory protein and cytochrome p450 side chain cleavage enzyme, which facilitate key steps in steroidogenesis, as well as two paralogs of steroidogenic factor 1. Despite elevation of basal steroidogenesis, acute cortisol production in response to ACTH (in vivo and in vitro) was lower in subordinate trout. Transcript abundances of the ACTH receptor accessory proteins were elevated in subordinate fish, but head kidney cortisol production in response to a cAMP analogue was lower than in dominant fish. Together, the data suggest that the attenuated acute cortisol response of subordinate trout reflects limitations on cortisol production downstream of cAMP signalling in steroidogenic cells of the head kidney, despite the increased basal abundance of key components of the steroidogenic pathway.

Diluted bitumen-induced alterations in aerobic capacity, swimming performance, and post-exercise recovery in juvenile sockeye salmon (Oncorhynchus nerka)

The transportation of heavy crudes such as diluted bitumen (dilbit) sourced from Canadian oil sands through freshwater habitat requires the generation of information that will contribute to risk assessments, spill modelling, management, and remediation for the protection of aquatic organisms. Juvenile sockeye salmon (Oncorhynchus nerka) were exposed acutely (96 h) or subchronically (28 d) to the water-soluble fraction (WSFd) of Cold Lake Blend dilbit at initial total polycyclic aromatic compound (TPAC) concentrations of 0, 13.7, 34.7, and 124.5 µg/L. A significant induction (>3-fold) of hepatic liver ethoxyresorufin-O-deethylase (EROD) activity was induced by 96 h in fish exposed to [TPAC] ≥ 34.7 µg/L and at ≥13.7 µg/L for a 28 d exposure. Exposure resulted in a typical physiological stress response and disturbance of ion homeostasis; this included elevations in plasma [cortisol], [lactate], [Na⁺], and [Cl^-], and significant reductions in muscle [glycogen]. Critical swimming speed (U_crit) was significantly reduced (28.4%) in the acute exposure at [TPAC] 124.5 µg/L; reductions of 14.2% and 35.4% were seen in fish subchronically exposed at the two highest concentrations. Reductions in U_crit were related to significant reductions in aerobic scope (24.3-46.6%) at [TPAC]s of 34.7 and 124.5 µg/L, respectively. Exposure did not impair the ability to mount a secondary stress response following burst exercise, however, the time required for biochemical parameters to return to baseline values was prolonged. Alterations in critical systems supporting swimming, exercise recovery and the physiological stress response could result in decreased salmonid fitness and contribute to population declines if a dilbit spill occurs.

Kynurenine to tryptophan ratio as a biomarker of acute stress in fish

The aim of this study was to determine the kynurenine (KYN) to tryptophan (TRP) ratio (KTR) in fish tissue to assess its usefulness as a biomarker of acute stress. Laboratory held rainbow trout (Oncorhynchus mykiss) were subjected to an acute stressor and KYN, TRP and cortisol were measured in liver and brain tissues at 4- and 48-h post-stress. The analytical method used to determine our analytes was based on lyophilization, and liquid-solid extraction followed by isotope dilution high-performance liquid chromatography positive ion electrospray tandem mass spectrometry. The [KYN]/[TRP] ratio (KTR) was greater in fish liver and brain in the 48-h post-stress exposure group (n = 8) relative to controls (n = 8, p < 0.05); a similar increase was not observed in fish in the 4-h post-stress exposure group. Hepatic and brain cortisol levels were also elevated in fish from both stress-induced groups relative to their respective controls implying that cortisol responded more quickly to the stressful stimulus than KYN and TRP. Our results suggest that the KTR is a promising acute stress diagnostic biomarker in fish. Efforts are ongoing to assess whether the KTR can be used as a biomarker for chronic stress in fish exposed to aquatic contaminants and other environmental stressors and if similar assessments can be made on tissues collected via non-lethal approaches.

Long-term exposure to cyprodinil causes abnormal zebrafish aggressive and antipredator behavior through the hypothalamic-pituitary-interrenal axis

Cyprodinil, one of the main pyrimidinamine fungicides, has been used to control fungal diseases in plants and vegetables worldwide. Previous studies have investigated the influences of cyprodinil on the developmental and reproductive toxicity of fish. However, it remains unknown whether it affects fish behaviors and the underlying mechanisms. In our current study, zebrafish, an ideal model animal for behavioral studies, were exposed to cyprodinil from fertilization to 240 days postfertilization at 0.1 μg/L (environmentally relevant concentration) and 1, 10 μg/L. Firstly, we observed that aggressive behavior of zebrafish was significantly enhanced after exposure to 0.1-10 μg/L cyprodinil and antipredator behavior was decreased after exposure. Cyprodinil exposure altered the adrenocorticotropic hormone and cortisol levels, which regulate cortisol homeostasis and were significantly reduced in all exposure groups (0.1-10 μg/L). In addition, most of the key genes in the hypothalamic-pituitary-interrenal gland axis, such as corticotropin-releasing hormone and melanocortin 2 receptor, were downregulated significantly in all exposure groups, which was consistent with the hormone levels. In addition, in the hypothalamus, the number of apoptotic cells increased in a dose-dependent manner in the cyprodinil exposure groups. Moreover, these changes were potentially responsible for the increased aggression of zebrafish during the mirror-like aggressive test and for the reduced antipredator behavior during the predator avoidance test. Overall, the data provided herein further our understanding of cyprodinil toxicity and can be used to assess the ecological effects of cyprodinil on the induction of abnormal behaviors at the environmental level.

DNA methylome perturbations: an epigenetic basis for the emergingly heritable neurodevelopmental abnormalities associated with maternal smoking and maternal nicotine exposure†

Maternal smoking during pregnancy is associated with an ensemble of neurodevelopmental consequences in children and therefore constitutes a pressing public health concern. Adding to this burden, contemporary epidemiological and especially animal model research suggests that grandmaternal smoking is similarly associated with neurodevelopmental abnormalities in grandchildren, indicative of intergenerational transmission of the neurodevelopmental impacts of maternal smoking. Probing the mechanistic bases of neurodevelopmental anomalies in the children of maternal smokers and the intergenerational transmission thereof, emerging research intimates that epigenetic changes, namely DNA methylome perturbations, are key factors. Altogether, these findings warrant future research to fully elucidate the etiology of neurodevelopmental impairments in the children and grandchildren of maternal smokers and underscore the clear potential thereof to benefit public health by informing the development and implementation of preventative measures, prophylactics, and treatments. To this end, the present review aims to encapsulate the burgeoning evidence linking maternal smoking to intergenerational epigenetic inheritance of neurodevelopmental abnormalities, to identify the strengths and weaknesses thereof, and to highlight areas of emphasis for future human and animal model research therein.

Exposure and Recovery from Environmentally Relevant Levels of Waterborne Polycyclic Aromatic Hydrocarbons from Deepwater Horizon Oil: Effects on the Gulf Toadfish Stress Axis

There is evidence that the combination of polycyclic aromatic hydrocarbons (PAHs) released in the Deepwater Horizon oil spill impairs the glucocorticoid stress response of vertebrates in the Gulf of Mexico, but the mechanisms are unclear. We hypothesized that inhibition of cortisol release may be due to 1) overstimulation of the hypothalamic-pituitary-inter-renal (HPI) axis, or 2) an inhibition of cortisol biosynthesis through PAH activation of the aryl hydrocarbon receptor (AhR). Using a flow-through system, Gulf toadfish (Opsanus beta) were continuously exposed to control conditions or one of 3 environmentally relevant concentrations of PAHs from Deepwater Horizon oil (∑PAH₅₀  = 0-3 μg L^-1 ) for up to 7 d. One group of toadfish was then exposed to a recovery period for up to 7 d. No changes in corticotrophin-releasing factor mRNA expression, adrenocorticotropic hormone (ACTH), or pituitary mass suggested that overstimulation of the HPI axis was not a factor. The AhR activation was measured by an elevation of cytochrome P4501A1 (CYP1A) mRNA expression within the HPI axis in fish exposed to high PAH concentrations; however, CYP1A was no longer induced after 3 d of recovery in any of the tissues. At 7 d of recovery, there was an impairment of cortisol release in response to an additional simulated predator chase that does not appear to be due to changes in the mRNA expression of the kidney steroidogenic pathway proteins steroidogenic acute regulatory protein, cytochrome P450 side chain cleavage, and 11β-hydroxylase. Future analyses are needed to determine whether the stress response impairment is due to cholesterol availability and/or down-regulation of the melanocortin 2 receptor. Environ Toxicol Chem 2021;40:1062-1074. © 2020 SETAC.

Physiological Responses of Fish to Oil Spills

Millions of tons of oil are spilled in aquatic environments every decade, and this oil has the potential to greatly impact fish populations. Here, we review available information on the physiological effects of oil and polycyclic aromatic hydrocarbons on fish. Oil toxicity affects multiple biological systems, including cardiac function, cholesterol biosynthesis, peripheral and central nervous system function, the stress response, and osmoregulatory and acid-base balance processes. We propose that cholesterol depletion may be a significant contributor to impacts on cardiac, neuronal, and synaptic function as well as reduced cortisol production and release. Furthermore, it is possible that intracellular calcium homeostasis-a part of cardiotoxic and neuronal function that is affected by oil exposure-may be related to cholesterol depletion. A detailed understanding of oil impacts and affected physiological processes is emerging, but knowledge of their combined effects on fish in natural habitats is largely lacking. We identify key areas deserving attention in future research.

Long-term exposure of zebrafish to bisphenol S impairs stress function of hypothalamic-pituitary-interrenal axis and causes anxiety-like behavioral responses to novelty

Bisphenol S (BPS), a main substitute of bisphenol A, has been reported to induce multiple endocrine disrupting effects on animals, however, whether it can interfere with the corticosteroid-endocrine system still remains unknown. Furthermore, previous studies mainly investigated the influences of environmental pollutants on corticosteroid levels and gene expressions of hypothalamic-pituitary-interrenal/adrenal (HPI/A) axis, while the downstream toxic effects caused thereafter have not yet been fully elucidated. Considering the key role of cortisol, a primary corticosteroid hormone in teleost, in mediating stress adaptation and the highly positive correlation between cortisol level and anxious phenotype in the novel environment, we hypothesized that an imbalanced cortisol homeostasis due to environmental pollutant exposure may further affect the behavioral responses to novelty stress. In the present study, zebrafish, a valuable model in studying human stress physiology and anxiety behavior, were exposed to BPS from embryos to adults (120 days) at environmentally relevant concentrations (1 and 10 μg/L) and 100 μg/L. Results found that long-term exposure to BPS increased whole-body cortisol levels and caused abnormal expressions of HPI axis genes. Moreover, the excessive cortisol levels may be due to the inhibition of cortisol catabolism and excretion, as evidenced by the down-regulated expressions of hydroxysteroid 11-beta dehydrogenase 2 and hydroxysteroid 20-beta dehydrogenase 2 genes. More importantly, as we speculated, excessive cortisol levels may be responsible for the occurrence of anxiety-like behavioral responses indicated by longer latency, fewer time spent in the upper half, and more erratic movements in a 6-min novel tank test. Overall, our study provides basic data for the comprehensive understanding of BPS toxicity, and emphasizes environmental health risks of BPS in inducing anxiety syndrome at environmentally realistic concentrations.

Effects of diluted bitumen exposure and recovery on the seawater acclimation response of Atlantic salmon smolts

Petrogenic chemicals are common and widespread contaminants in the aquatic environment. In Canada, increased extraction of bitumen from the oil sands and transport of the major crude oil export product, diluted bitumen (dilbit), amplifies the risk of a spill and contamination of Canadian waterways. Fish exposed to sublethal concentrations of crude oil can experience a variety of adverse physiological effects including osmoregulatory dysfunction. As regulation of water and ion balance is crucial during the seawater transition of anadromous fish, the hypothesis that dilbit impairs seawater acclimation in Atlantic salmon smolts (a fish at risk of exposure in Canada) was tested. Smolts were exposed for 24 d to the water-soluble fraction of dilbit in freshwater, and then transferred directly to seawater or allowed a 1 wk depuration period in uncontaminated freshwater prior to seawater transfer. The seawater acclimation response was quantified at 1 and 7 d post-transfer using established hematological, tissue, and molecular endpoints including gill Na⁺/K⁺-ATPase gene expression (nka). All smolts, irrespective of dilbit exposure, increased serum Na⁺ concentrations and osmolality within 1 d of seawater transfer. The recovery of these parameters to freshwater values by 7 d post-transfer was likely driven by the increased expression and activity of Na⁺/K⁺-ATPase in the gill. Histopathological changes in the gill were not observed; however, CYP1A-like immunoreactivity was detected in the pillar cells of gill lamellae of fish exposed to 67.9 μg/L PAC. Concentration-specific changes in kidney expression of a transmembrane water channel, aquaporin 3, occurred during seawater acclimation, but were resolved with 1 wk of depuration and were not associated with histopathological changes. In conclusion, apart from a robust CYP response in the gill, dilbit exposure did not greatly impact common measures of seawater acclimation, suggesting that significant osmoregulatory dysfunction is unlikely to occur if Atlantic salmon smolts are exposed sub-chronically to dilbit.

Physiological disturbances in juvenile sockeye salmon (Oncorhynchus nerka) exposed to the water-soluble fraction of diluted bitumen

Current and proposed transcontinental pipelines for the transport of diluted bitumen (dilbit) from the Canadian oil sands traverse the coastal watersheds of British Columbia, habitat essential to Pacific salmonids. To determine the potential risks posed to these keystone species, juvenile sockeye (Oncorhynchus nerka; 1+ parr) were acutely (24-96 h) or subchronically (21-42 d) exposed to 4 concentrations of the water-soluble fraction (WSF) of unweathered Cold Lake Blend dilbit (initial total PAC concentrations: 0, 13.7, 34.7 and 124.5 μg/L) in a flow-through system. Dilbit effects on iono-osmoregulation, the physiological stress response, and the immune system were assessed by both biochemical and functional assays. Hydrocarbon bioavailability was evidenced by a significant induction of liver ethoxyresorufin-O-deethylase (EROD) activity in exposed fish. Acute and subchronic exposure significantly reduced gill Na⁺-K⁺-ATPase activity and resulted in lower plasma osmolality, Cl^-, and Na⁺ concentrations. Acute exposure to dilbit resulted in a classic physiological stress response, however at 21 d of exposure, plasma cortisol remained elevated while other measured parameters had returned to baseline values. A compromised immune system was demonstrated by a 29.5 % higher mortality in fish challenged with Vibrio (Listonella) anguillarum following dilbit exposure compared to unexposed controls. Exposure of juvenile salmonids to the WSF of dilbit (at TPAC concentrations at the ppb level) resulted in sublethal effects that included a classic physiological stress response, and alterations in iono-osmoregulatory homeostasis and immunological performance.

Impacts of deepwater horizon oil on fish

An explosion on the Deepwater Horizon (DWH) oil rig in 2010 lead to the largest marine oil spill to occur in US history, resulting in significant impacts to the ecosystems and organisms in the Northern Gulf of Mexico (GoM). The present review sought to summarize and discuss findings from the 50+ peer-reviewed publications reporting effects of DWH oil exposure on teleost fish, and concludes that oil toxicity is a multi-target, multi-organ syndrome with substantial species-specific sensitivity differences. Of the 15 species tested with characterized exposures, 20% show effects at concentrations <1 μg l^-1 while 50% display effects at <8.6 μg l^-1 ΣPAH₅₀, concentrations well within the range of reported environmental levels during the spill. Cardiotoxic effects are among the most frequently reported endpoints in DWH oil exposure studies and are thought to have significant downstream effects on fitness and survival. However, additional and possibly cardio-toxic independent impacts on sensory function and behavior are reported at very low exposure concentrations (< 1 μg l^-1 ∑PAH₅₀) and are clearly deserving of further study. Available information about modes of action leading to different categories of effects are summarized in the present review. An overview of the literature illustrates that early life stages (ELS) are approximately 1-order of magnitude more sensitive than corresponding later life stages, but also illustrates that adults can be impacted at concentrations as low as 4 μg l^-1 ΣPAH₅₀. The majority of studies exploring DWH oil toxicity in fish are performed using acute exposures (1-2 days), mid-range test temperatures (26-28 °C) and measure effects at the molecular to organismal levels, leaving a pressing need for more long-term exposures, exposures at the upper and lower levels of GoM relevant temperatures, and studies investigating population level impacts.

Transcriptome analysis of juvenile genetically improved farmed tilapia (Oreochromis niloticus) livers by dietary resveratrol supplementation

Here we used RNA-Seq to explore the transcriptomic response and specific involvement of hepatic mRNA of juvenile Oreochromis niloticus (GIFT) as a result of dietary resveratrol supplementation (0.05 g/kg RES). More than 24,513,018 clean reads were reference genome guided assembly into 23,417 unigenes. 12,596 unigenes (29.64%) were annotated to GO database. There were 5, 179 and 1526 genes significantly differentially expressed genes at 15, 30 and 45 d respectively, and 8 KEGG pathways were enriched associated with this immune response. Hyperemia and compressed hepatic sinusoid, fibrosis of liver cell and abnormal hepatic epidermal cell revealed by H&E and SEM analysis respectively. Genes related with cytokine production (il12rb2, scfr), immune system (ig8l, hlfl, cd226, prf1l), autophagy regulation (atg4b), foxo signaling (ccnb2), steroid hormone biosynthesis (cyp3a40), fatty acid metabolism (scd1), metabolism (cacna1b) have been significantly decreased, while genes associated with such pathways above (leap-2, prdx4, mb, homer1, mif, sat1, cytbc1_8) and the pathway of protein processing in endoplasmic reticulum (cne1, tram1) have been significantly increased. These findings suggested RES activated some immune and biological process-related genes to enhance GIFT's innate immunity. It also suggested high concentration addition or long-time administration may bring negative effect in tilapia liver.

Legacy environmental polychlorinated biphenyl contamination attenuates the acute stress response in a cartilaginous fish, the Round Stingray

In a population of Round Stingrays (Urobatis halleri) sampled from mainland California (polychlorinated biphenyl [PCB] exposed site, n = 46), relative to a nearby offshore island (reference site, n = 34), we tested the hypothesis that stingrays from the PCB-exposed site would have a compromised stress response. Adult male and pregnant female (pregnancy = matrotrophic histotrophy), stingrays were captured via hook and line at both locations over a breeding season and plasma was sampled either immediately (Baseline, males = 10, females = 31), or after ∼5 min of struggle on the line followed by a 15 min confinement stressor (Stressed, males = 16, females = 23). Biomarkers of the primary stress response (1α-OH-corticosterone) and the secondary response (energy mobilization; glucose, glycogen, and lactate in liver and muscle) were assessed. Females from both sites demonstrated the expected primary stress response of 1α-OH-corticosterone elevation, but the contaminant-exposed males did not. PCB-exposed stingrays, regardless of sex, failed to produce a plasma glucose increase in response to the applied stress, even though the stressor increased liver glucose as expected. This suggests a dysfunction in glucose transport due to PCB exposure. The Round Stingray accumulates lower PCB loads than other, predatory elasmobranchs, and by extension, the stress axis effects could be more severely impacted in those species as well. Lay summary Legacy polychlorinated biphenyl (PCB) contamination continues to adversely affect marine life. We show that PCB-exposure interferes with the ability of pregnant female and adult male stingrays to mobilize the energy necessary to respond appropriately to an acute stress like capture. Other cartilaginous fish species, such as sharks, accumulate considerably more PCB as a result of their predatory diet, and are likely to be more adversely impacted.

Endocrine-disrupting chemicals: Effects on neuroendocrine systems and the neurobiology of social behavior

A contribution to SBN/ICN special issue. Endocrine-disrupting chemicals (EDCs) are pervasive in the environment. They are found in plastics and plasticizers (bisphenol A (BPA) and phthalates), in industrial chemicals such as polychlorinated biphenyls (PCBs), and include some pesticides and fungicides such as vinclozolin. These chemicals act on hormone receptors and their downstream signaling pathways, and can interfere with hormone synthesis, metabolism, and actions. Because the developing brain is particularly sensitive to endogenous hormones, disruptions by EDCs can change neural circuits that form during periods of brain organization. Here, we review the evidence that EDCs affect developing hypothalamic neuroendocrine systems, and change behavioral outcomes in juvenile, adolescent, and adult life in exposed individuals, and even in their descendants. Our focus is on social, communicative and sociosexual behaviors, as how an individual behaves with a same- or opposite-sex conspecific determines that individual's ability to exist in a community, be selected as a mate, and reproduce successfully.

Comparative study of stress and immune-related transcript outcomes triggered by Vibrio anguillarum bacterin and air exposure stress in liver and spleen of gilthead seabream (Sparus aurata), zebrafish (Danio rerio) and rainbow trout (Oncorhynchus mykiss)

The stress and immune-related effects of short-term (1, 6 and 24 h) air exposure stress (1 min), bath vaccination with Vibrio anguillarum bacterin, and both stressors combined were evaluated in liver and spleen of Sparus aurata, Danio rerio and Onchorhynchus mykiss. Expression profiles of immune (interleukin 1 beta: il1β; tumor necrosis factor alpha: tnfα; interleukin 10: il10; tumor growth factor beta: tgfβ1; immunoglobulin M: igm; lysozyme: lys; complement protein c3: c3) and stress-related genes (glucocorticoid receptor: gr; heat shock protein 70: hsp70; and enolase) were analysed by RT-qPCR. Cortisol level was assessed by radioimmunoassay. The gene expression patterns in liver and spleen were found to be differentially regulated in a time- and organ-dependent manner among species. In seabream, a higher il1β-driven inflammatory response was recorded. In zebrafish, air exposure stress but not bath vaccination alone modulated most of the changes in liver and spleen immune transcripts. Stressed and vaccinated trout showed an intermediate pattern of gene expression, with a lower upregulation of immune-related genes in liver and the absence of changes in the expression of hsp70 and enolase in spleen (as it was observed in seabream but not in zebrafish). Following air exposure, cortisol levels increased in plasma 1 h post-stress (hps) and then decreased at 6 hps in O. mykiss and D. rerio. By contrast, in S.aurata the cortisol level remained higher at 6 hps suggesting a greater degree of responsiveness to this stressor. When fish were exposed to combined air exposure plus bath vaccination cortisol levels were also augmented at 1 and 6 hps in O. mykiss and S.aurata and restored to basal level at 24 hps, whereas in D. rerio the response was higher in response to the combination of both stressors. In addition, V. anguillarum bacterin vaccination triggered cortisol secretion only in D. rerio, suggesting a greater responsiveness of D. rerio hypothalamic-pituitary-interrenal axis. Overall, comparing the tissue transcription responsiveness, liver was found to be more implicated in the response to handling stress compared to spleen. These results also indicate that a species-specific response accounts for the deviations of stress and immune onset in the liver and spleen in these fish species.

Intracellular toxicity exerted by PCBs and role of VBNC bacterial strains in biodegradation

Polychlorinated biphenyls (PCBs) are xenobiotic compounds that persists in the environment for long-term, though its productivity is banned. Abatement of the pollutants have become laborious due to it's recalcitrant nature in the environment leading to toxic effects in humans and other living beings. Biphenyl degrading bacteria co-metabolically degrade low chlorinated PCBs using the active metabolic pathway. bph operon possess different genetic arrangements in gram positive and gram negative bacteria. The binding ability of the genes and the active sites were determined by PCB docking studies. The active site of bphA gene with conserved amino acid residues determines the substrate specificity and biodegradability. Accumulation of toxic intermediates alters cellular behaviour, biomass production and downturn the metabolic activity. Several bacteria in the environment attain unculturable state which is viable and metabolically active but not cultivable (VBNC). Resuscitation-promoting factor (Rpf) and Rpf homologous protein retrieve the culturability of the so far uncultured bacteria. Recovery of this adaptive mechanism against various physical and chemical stressors make a headway in understanding the functionality of both environmental and medically important unculturable bacteria. Thus, this paper review about the general aspects of PCBs, cellular toxicity exerted by PCBs, role of unculturable bacterial strains in biodegradation, genes involved and degradation pathways. It is suggested to extrapolate the research findings on extracellular organic matters produced in culture supernatant of VBNC thus transforming VBNC to culturable state.

Effects of dietary inclusions of red beet and betaine on the acute stress response and muscle lipid peroxidation in rainbow trout

This study evaluates the effects of red beet (RB) and betaine on rainbow trout submitted to an acute stress challenge. A control diet was compared with four experimental diets in which red beet (14 and 28%) and betaine (0.9 and 1.63%) were incorporated in different concentrations according to a factorial design. Cortisol in plasma and fin, glucose and lactate plasma levels, and malondialdehide (MDA) in muscle were all measured before the stress challenge and 30 min and 6 and 12 h after the stress challenge as parameters to determine the diet effects. RB and betaine had no effect on cortisol, glucose, and MDA basal levels. However, lactate basal levels were significantly lower on fish fed with RB and betaine. Thirty minutes after the stress challenge, there was a significant increase in plasma and fin cortisol, glucose and lactate concentrations, although fish fed with diets containing RB and betaine showed significantly higher plasma cortisol values. MDA values of fish fed with 14% RB and 0.9% betaine were significantly higher than MDA values from fish fed with 28% RB and 1.63% betaine. After 6 and 12 h, plasma and fin cortisol and lactate levels recovered in a similar trend. Glucose plasma levels recovered in almost all groups 12 h after the stress. Also, MDA values recovered basal levels after 6 and 12 h. RB and betaine did not enhance the tolerance to the stress challenge compared to the control group, although the presence of these ingredients had no negative effect on any of the stress indicators.

Growth and Stress Axis Responses to Dietary Cholesterol in Nile Tilapia (Oreochromis niloticus) in Brackish Water

Six isonitrogenous and isocaloric diets were formulated to contain 0% (control), 0.4, 0.8, 1.2, 1.6, or 2.4% dietary cholesterol and fed to juvenile Nile tilapia (Oreochromis niloticus) (2.20 ± 0.12 g) twice daily to apparent satiation for 8 weeks in triplicate at a salinity of 16. Fish fed 0.4% cholesterol showed a higher weight gain and specific growth rate and a lower feed coefficient ratio than fish fed other diets. No difference was found in the survival of Nile tilapia fed various levels of cholesterol. Cholesterol in the serum and liver and low-density lipoprotein cholesterol in the serum increased with the increase in the dietary cholesterol content. Relative to the control, no significant difference was found in the expression of head kidney P450scc mRNA between treatment groups. The expression of head kidney 11β-HSD2 mRNA was the highest in the control group, and it decreased significantly with increasing levels of diet cholesterol. Fish fed 0.4 or 1.2% cholesterol had a higher 20β-HSD2 mRNA expression in the head kidney than those fed other diets. Fish fed 0.8% cholesterol had higher expressions of GR1 and GR2B mRNA in the liver than other groups. Fish fed 0.4% cholesterol had the highest activity of gill Na⁺/K⁺-ATPase. Fish fed 0.8 to 2.4% cholesterol had higher serum cortisol contents than the fish in the control group and the fish fed 0.4% cholesterol. This study suggests that dietary cholesterol is not essential for Nile tilapia survival in brackish water, but 0.4% cholesterol supplementation in the Nile tilapia diet contributes to the improvement of hyperosmotic adaptation and increases in gill Na⁺/K⁺-ATPase activity and serum cortisol content by regulating the hypothalamic-pituitary-interrenal stress axis.

Effects of cortisol and lipopolysaccharide on expression of select growth-, stress- and immune-related genes in rainbow trout liver

Many studies have shown that stress-induced cortisol levels negatively influence growth and immunity in finfish. Despite this knowledge, few studies have assessed the direct effects of cortisol on liver immune function. Using real-time PCR, the expression of three cortisol-responsive genes (GR: glucocorticoid receptor, IGF-1: insulin-like growth factor-I and SOCS-1: suppressor of cytokine signaling-I), genes involved with innate and adaptive immunity (IL-1β: interleukin-1 beta, IgM: immunoglobin-M and Lyz: lysozyme), and liver-specific antimicrobial peptides (hepcidin and LEAP-2A: liver-expressed antimicrobial peptide-2A) was studied in vitro using rainbow trout liver slices. The abundances of GR, SOCS-1 and IGF-1 mRNAs were suppressed by cortisol treatment. Abundance of IL-1β mRNA was upregulated by LPS and suppressed by cortisol treatment in a time-dependent manner. While abundance of IgM mRNA was suppressed by cortisol treatment and stimulated by LPS, there were no effects of cortisol or LPS on abundance of Lyz mRNA. Abundance of hepcidin and LEAP-2A mRNA levels were suppressed by cortisol treatment and stimulated by LPS. These results demonstrate that cortisol directly suppresses abundance of GR, IGF-1, IL-1β, IgM, hepcidin, LEAP-2A and SOCS-1 mRNA transcripts in the rainbow trout liver. We report for the first time, a suppressive effect of cortisol (within 8 h of treatment) on hepcidin and LEAP-2A mRNAs in rainbow trout liver, which suggests that acute stress may negatively affect liver immune function in rainbow trout.

Hepatic transcriptome analysis of juvenile GIFT tilapia (Oreochromis niloticus), fed diets supplemented with different concentrations of resveratrol

The GIFT (Genetically Improved Farmed Tilapia) tilapia, Oreochromis niloticus, is cultured widely for the production of freshwater fish in China. Streptococcosis, which is related to pathogenic infections, occurs frequently in juvenile and adult female GIFT individuals. Resveratrol (RES) has been used in feed to control these infections in freshwater tilapia. To address the effects of RES on tilapia, we used high-throughput RNA sequencing technology (RNA-Seq, HiSeq. 2500) to explore the global transcriptomic response and specific involvement of hepatic mRNA of juvenile O. niloticus fed with diets containing different concentrations of (0, 0.025, 0.05, and 0.1g/kg) RES. A total of > 24,513,018 clean reads were generated and then assembled into 23,244 unigenes. The unigenes were annotated by comparing them against non-redundant protein sequence (Nr), non-redundant nucleotide (Nt), Swiss-Prot, Pfam, Gene Ontology database (GO), Clusters of Orthologous Groups (COG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, and 12,578 unigenes were annotated to the GO database. A total of 1444 (0.025g/kg RES), 1526 (0.05g/kg RES), and 3135 (0.1g/kg RES) genes were detected as significant differentially expressed genes (DEGs), when compared with the controls. A total of 6 (0.025 vs 0.05g/kg RES), 19 (0.025 vs 0.1g/kg RES), and 124 (0.05 vs 0.1g/kg RES) genes were detected as significant DEGs. Six genes, including dnah7x1, sox4, fam46a, hsp90a, ddit4, and nmrk2, were associated with an immune response. These findings provide information on the innate immunity of GIFT and might contribute to the development of strategies for the effective management of diseases and long-term sustainability of O. niloticus culture.

The impact of acute PAH exposure on the toadfish glucocorticoid stress response

The objective of the present study was to determine whether the polycyclic aromatic hydrocarbons (PAHs) associated with the Deepwater Horizon (DWH) oil spill impacted the stress response of teleost fish. The hypothesis was that intraperitoneal (IP) treatment with PAHs associated with the DWH oil spill or waterborne exposure to DWH oil high energy water-accommodated fraction (HEWAF) would result in the downregulation of the stress response of Gulf toadfish, Opsanus beta, a benthic marine teleost fish that resides in the Gulf of Mexico. In vivo plasma cortisol levels and adrenocorticotropic hormone (ACTH)-mediated cortisol secretion by in vitro isolated kidney tissue were measured. Toadfish at rest IP-treated with naphthalene had higher plasma cortisol compared to fluorene-treated and control fish; phenanthrene-treated fish tended to have higher plasma cortisol levels that fluorene-treated and controls. When subjected to an additional crowding stress, naphthalene and phenanthrene-treated fish were no longer able to mount a stress response compared to fluorene-treated and control fish, suggesting exhaustion of the stress response. Supporting this in vivo data, there tended to be less cortisol released by the kidney in vitro from naphthalene and phenanthrene-treated fish in response to ACTH compared to controls. In contrast, toadfish at rest exposed to 3% Slick A HEWAF did not have significantly different plasma cortisol levels compared to controls. But, exposed fish did have significantly less cortisol released by the kidney in vitro in response to ACTH. When toadfish were subjected to an additional stress, there were no significant differences in plasma cortisol or ACTH, suggesting the action of a secondary secretagogue to maintain plasma cortisol in vivo. Combined, these data suggest that in response to acute PAH exposure, there may be internalization or downregulation of the melanocortin 2 receptor (MC2R) that mediates the action of ACTH.

Fatty Acid Profile Is Modulated by Dietary Resveratrol in Rainbow Trout (Oncorhynchus mykiss)

To produce fish of a high quality that are rich in omega-3 fatty acids (n-3 FA) and simultaneously generate more sustainable aquaculture, the combined use of phytochemicals and vegetable oils in fish feed seems to be a promising approach. Resveratrol (RV) potentially induces endogenous fatty acid synthesis, resulting in elevated n-3 FA levels in fish. RV putatively influences ∆6-desaturase, the key enzyme in FA metabolism, and serves as a ligand for PPARα, a transcription factor regulating β-oxidation. Rainbow trout (36.35 ± 0.03 g) were randomly allocated into six groups and fed diets with reduced fish oil levels (F4 = 4%, F2 = 2% and F0 = 0% of dry matter) supplemented with 0.3% (w/w) RV (F4 + RV, F2 + RV and F0 + RV). RV significantly affected FA composition in liver tissue and whole fish homogenates. 20:5n-3 (EPA) and 22:6n-3 (DHA) were significantly increased whereas precursor FA were diminished in fish fed the F2 + RV and F0 + RV diets when compared to F4 + RV and F0. RV significantly elevated ∆6-desaturase protein levels in the livers of F0 + RV fed animals. Hepatic mRNA expression of ∆6-desaturase, PPARα, and its target genes were affected by the dietary fish oil level and not by dietary RV. The results of this study indicated a potential benefit of supplementing RV in fish oil deprived diets elevating n-3 FA levels in rainbow trout.

Biomarker response and hypothalamus-pituitary-interrenal axis functioning in Arctic charr from Bjørnøya (74°30' N), Norway, with high levels of organohalogenated compounds

The populations of Arctic charr (Salvelinus alpinus) residing in Lake Ellasjøen at Bjørnøya Island in the Norwegian Arctic (74° 30'N, 19° 00'E) possess substantially higher levels of organohalogenated compounds (strongly dominated by polychlorinated biphenyls, PCBs) than conspecifics residing in other, proximate lakes on the island. In the present study we sampled large (<400g), immature charr from Lake Ellasjøen (high PCB levels) and Lake Laksvatn (reference lake, low PCB levels) by hook and line for an immediate blood sampling, and blood and tissue sampling after a 1h confinement stressor. This was done in order to investigate possible effects of pollutants on an acute stress performance in a high-latitude fish species by comparing muscle PCB levels, hepatic cytochrome P4501A (CYP1A) biomarker activation and functioning of the hypothalamus-pituitary-interrenal (HPI) axis between these two populations of Arctic charr. As expected sum PCB muscle levels were 8-fold higher on a wet weigh basis, and 19-fold higher on a lipid weight basis, in charr from Ellasjøen than in charr from Laksvatn. This was accompanied by a 3.5-fold higher liver cyp1a mRNA abundance in the Ellasjøen charr compared to Laksvatn charr. Brain transcript levels encoding glucocorticoid receptor 1 and 2 (GR2) and corticotropin-releasing factor, and pituitary transcript levels encoding GR2 and proopiomelanocortin A1 and A2 were higher in Ellasjøen charr than in Laksvatn charr, while interrenal transcript levels encoding melanocortin 2 receptor and steroidogenic acute regulatory protein were lower. There were no differences in plasma cortisol concentration between the two charr populations immediately after capture and one hour after confinement. The strong biomarker response to OHCs and altered mRNA abundances of key genes related to HPI axis functioning in the Ellasjøen charr suggest endocrine disruptive effects of OHCs in this charr population. Possible ecological implications are not known, but it cannot be excluded that a slower growth rate in Ellasjøen charr compared to Laksvatn charr due to an increased metabolic demand associated with the activation of xenobiotic defense and detoxification systems may have contributed to the lower body mass of Ellasjøen charr compared to Laksvatn charr.

Modulation of the stress response in wild fish is associated with variation in dissolved nitrate and nitrite

Disruption of non-reproductive endocrine systems in wildlife by chemicals has received little attention but represents a potentially significant problem. Nitrate is a major anthropogenic contaminant in the freshwater aquatic environment and has been identified as a potential disrupter of endocrine function in aquatic animals. This study was conducted to investigate the relationship between the function of the neuroendocrine stress axis in fish and inorganic N loading along reaches of rivers receiving cumulative point source and diffuse chemical inputs. To accomplish this, the responsiveness of the stress axis, quantified as the rate of release of cortisol to water across the gills during exposure to a standardised stressor, was measured in three-spined sticklebacks (Gasterosteus aculeatus L.) resident at three sites on each of four rivers in north-west England. The magnitude of the stress response in fish captured at the sites furthest downstream on all rivers was more than twice that of fish captured at upstream sites. Site-specific variation in stress axis reactivity was better explained by between-site variation in concentrations of dissolved nitrate, nitrite, and ammonia than by the concentration of wastewater treatment works effluent. An increase in the magnitude of the stress response was seen among sticklebacks at sites where long-term averaged concentrations of NH₃-N, NO₃-N and NO₂-N exceeded 0.6, 4.0 and 0.1 mg/L respectively. These data suggest that either (i) inorganic N is a better surrogate than wastewater effluent concentration for an unknown factor or factors affecting stress axis function in fish, or (ii) dissolved inorganic N directly exerts a disruptive influence on the function of the neuroendocrine stress axis in fish, supporting concerns that nitrate is an endocrine-modulating chemical.

Effects of chronic exposure to dietary selenomethionine on the physiological stress response in juvenile white sturgeon (Acipenser transmontanus)

Selenium (Se) is an essential micronutrient, but at low concentrations can be toxic to aquatic organisms. Selenomethionine (SeMeth) is the primary dietary form of Se aquatic organisms are exposed to and is an environmental concern because it persists and bioaccumulates. White sturgeon (WS) might be particularly susceptible to bioaccumulative toxicants, such as SeMeth, due to their longevity and benthic lifestyle. Se exposure is known to have adverse effects on the physiological stress response in teleosts, but these effects are unknown in WS. Therefore, the goal of this study was to determine effects of dietary SeMeth on the ability of WS to mount a stress response. Juvenile WS were administered food spiked with 1.4, 5.6, 22.4 and 104.4μg Se/g dry mass (dm) for 72days. Lower doses were chosen to represent environmentally relevant concentrations, while the high dose represented a worst case scenario exposure. On day 72, fish were subjected to a 2min handling stressor, and they were sampled at 0, 2 and 24h post-stressor. Cortisol, glucose and lactate concentrations were quantified in blood plasma and glycogen concentrations were quantified in muscle and liver. Transcript abundance of genes involved in corticosteroidogenesis and energy metabolism were determined using qPCR. Under basal conditions, WS fed 104.4μg Se/g dm had significantly greater concentrations of plasma cortisol and lactate, and significantly lower concentrations of plasma glucose and liver glycogen, compared to controls. Corticosteroid 11-beta dehydrogenase 2 (hsd11b2) abundance was lower in WS fed 22.4 and 104.4μg Se/g dm, indicating less conversion of cortisol to cortisone. Abundance of the glucocorticoid receptor (gcr) was significantly lower in high dose WS, suggesting lower tissue sensitivity to glucocorticoids. The increasing trend in phosphoenolpyruvate carboxykinase (pepck) abundance, with increasing SeMeth exposure, was consistent with greater cortisol and glucose concentrations in high dose WS. Exposure to an acute handling stressor elicited a typical cortisol response, but the magnitude of the response appeared to be significantly lower than those typically observed in teleosts. SeMeth also did not appear to modulate the cortisol response to a secondary stressor. However, WS exposed to 22.4μg Se/g dm and sampled 2h post-stressor, had significantly higher concentrations of muscle glycogen compared to controls, indicating effects on their ability to utilize muscle glycogen for energy. Overall, the results indicate that chronic exposure to dietary SeMeth concentrations >22.4μg/g can affect cortisol dynamics and mobilization of energy substrates in juvenile WS.

Maternal programming of offspring hypothalamic-pituitary-interrenal axis in wild sockeye salmon (Oncorhynchus nerka)

In fishes, maternal exposure to a stressor can influence offspring size and behavior. However, less is known about how maternal stress influences physiological processes in offspring, such as function of the hypothalamic-pituitary-interrenal (HPI) axis. We examined the impact of chronic maternal exposure to an acute chase stressor on the stress response/HPI activity of progeny in wild sockeye salmon (Oncorhynchus nerka). Resting plasma cortisol and brain preoptic area (POA) corticotropin-releasing factor (CRF) mRNA levels did not vary between offspring reared from undisturbed, control females and offspring reared from females exposed to the stressor. However, resting levels of POA glucocorticoid receptors (GR1 and GR2), and head kidney melanocortin 2 receptor (MC2R), steroidogenic acute regulatory protein (StAR), and cytochrome P450 side chain cleavage enzyme (P450scc) were elevated in offspring reared from stressor-exposed females. Offspring reared from stressor-exposed females had lower plasma cortisol levels 1-h after an acute chase stressor compared to cortisol levels in offspring reared from control females. In offspring reared from chased females, mRNA levels of genes associated with cortisol biosynthesis were reduced in the head kidney post-chase. In offspring reared from control females, mRNA levels in the head kidney did not vary pre- to post-chase. Together, the results of the present study suggest maternal programming of progeny with respect to baseline and stressor-induced mediators of HPI axis activity.

Long-term water quality data explain interpopulation variation in responsiveness to stress in sticklebacks at both wastewater effluent-contaminated and uncontaminated sites

The magnitude of the corticosteroid response to a standardized stressor varied in proportion to the concentration of effluent in three-spined sticklebacks (Gasterosteus aculeatus L.) captured downstream of 10 wastewater-treatment plants (WWTPs). However, at 9 sites with no upstream WWTP input interpopulation variation in the reactivity of the stress axis occurred across a similar range to that seen for fish at impacted sites, suggesting that the factor(s) responsible for modulating stress responsiveness in sticklebacks is not unique to sites receiving WWTP effluent. Physicochemical data from a long-term monitoring program were employed to investigate whether variation in water quality contributed to between-site variation in stress axis reactivity. Between-site variation in 14 water quality determinands explained between 30% and 60% of the variation in stress reactivity and fish size for sticklebacks at both WWTP-contaminated and uncontaminated sites. At uncontaminated sites the mean mass and length of sticklebacks increased with total oxidized nitrogen (N) concentration (as an indicator of anthropogenic input), whereas at WWTP-contaminated sites fish size decreased with increasing effluent concentration, suggesting that factors adversely affecting growth were present predominantly at WWTP-contaminated sites. In contrast, at both contaminated and uncontaminated sites the magnitude of the corticosteroid response to a standardized stressor increased with anthropogenic input (effluent concentration or total oxidized N, respectively), indicating that a factor or factors modulating the reactivity of the stress axis may be present at both WWTP-contaminated and uncontaminated sites. Environ Toxicol Chem 2016;35:3014-3022. © 2016 SETAC.

ACTH-induced stress in weaned sows impairs LH receptor expression and steroidogenesis capacity in the ovary

BACKGROUND

Stress has been proved to impair the porcine reproduction soundly. Endocrine disruption, which is closely related to the persistent follicles, is possibly one of the results of stress, although the mechanism is unclear. Since the expression of luteinizing hormone receptor (LHR) in ovarian follicular wall and concentrations of steroid hormone in follicular fluid are related to the development of persistent follicles, this study is designed to evaluate the effect of administered adrenocorticotrophic hormone (ACTH) to weaned pigs on their ovarian steroidogenesis capacity and LHR expression.

METHODS

Ten multiparous sows were weaned and randomly divided into two groups (n = 5 each). Sows received 1 IU/kg ACTH (ACTH group) or saline (control group) every 8 h from days 3-9 after jugular vein intubation. Blood samples were collected throughout the experiment, and ovaries were collected after slaughter on day 10. Follicular fluid (FF) was used to determine the steroid hormone concentrations. The ovarian follicle wall was obtained and stored in liquid nitrogen to detect mRNA levels.

RESULTS

The plasma cortisol concentration was significantly (P < 0.01) elevated after ACTH injection. The estradiol (E₂) and androstenedione (ASD) concentrations in FF were significantly lower (P < 0.05) in the ACTH group than in the control group. The LHR, 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 aromatase (P450arom), and cytochrome P450 17a-hydroxylase (P450c17) mRNA levels were significantly (P < 0.05) reduced in the ACTH group. The steroidogenic acute regulatory protein (StAR) level and cytochrome P450 side-chain cleavage (P450scc) was lower in the ACTH group than in the control group, but the difference was not statistically significant (P > 0.05). Immunostaining results revealed 3β-HSD,P450c17, and LHR expression in theca cells, and P450arom expression in granulosa cells. Immunohistochemical staining showed significant differences in the distribution of 3β-HSD, P450c17, LHR, and P450arom between the two groups.

CONCLUSIONS

These findings indicated that ACTH significantly diminished the LHR expression and steroidogenesis capacity of the ovaries of weaned sows.

Microbial modulation of behavior and stress responses in zebrafish larvae

The influence of the microbiota on behavior and stress responses is poorly understood. Zebrafish larvae have unique characteristics that are advantageous for neuroimmune research, however, they are currently underutilized for such studies. Here, we used germ-free zebrafish to determine the effects of the microbiota on behavior and stress testing. The absence of a microbiota dramatically altered locomotor and anxiety-related behavior. Additionally, characteristic responses to an acute stressor were also obliterated in larvae lacking exposure to microbes. Lastly, treatment with the probiotic Lactobacillus plantarum was sufficient to attenuate anxiety-related behavior in conventionally-raised zebrafish larvae. These results underscore the importance of the microbiota in communicating to the CNS via the microbiome-gut-brain axis and set a foundation for using zebrafish larvae for neuroimmune research.

A comparison of two methods for the assessment of stress axis activity in wild fish in relation to wastewater effluent exposure

Riverine fish are particularly vulnerable to chemical exposure - rivers receive chemicals of anthropogenic origin from a variety of sources, one of the most significant being the chemically complex effluents discharged by wastewater treatment works (WWTWs). The extent to which non-reproductive components of the endocrine system in fish may be vulnerable to interference by contaminants associated with WWTW effluent is not well understood, but a significant body of evidence does suggest that contaminants present in the aquatic environment may interfere with the normal function of the neuroendocrine stress axis in fish. Field investigations of stress axis function in free-living populations of fish by measurement of hormone concentrations in blood can be confounded by the remoteness of sampling locations and the size of target species. Two methods for assessing stress axis reactivity in situations where blood samples are unavailable were compared in three-spined sticklebacks in relation to their exposure to WWTWs effluent. Sticklebacks were sampled in two successive years at fifteen sites in north-west England impacted by WWTW effluent and the response of each fish to the combined stressor of capture and a brief period of confinement was evaluated using both whole-body immunoreactive cortisol concentrations (WBIC) and the rate of release of cortisol to water (CRTW). A positive relationship between the magnitude of stress-induced CRTW in sticklebacks of both sexes and WWTW effluent concentration at site of capture was observed in both years. However, the relationship between stress-induced WBIC and WWTW effluent concentration was not consistent. These results suggest that components of WWTW effluent can modulate the magnitude of the neuroendocrine stress response in sticklebacks, and by inference in other fish species, but they raise questions about the measurement and interpretation of stress axis responses in fish via endpoints other than blood hormone concentrations. Possible factors underlying the disparity between the CRTW and WBIC results are discussed.

Disruption of the stress response in wastewater treatment works effluent-exposed three-spined sticklebacks persists after translocation to an unpolluted environment

The hypothalamic-pituitary-adrenal/interrenal (HPA/I) axis plays a key role in responding to biotic and abiotic challenges in all vertebrates. Recent studies have shown that the apical response of the HPI axis to stressors in three-spined sticklebacks varies in proportion to the concentration of wastewater treatment works (WWTW) effluent to which the fish are exposed. This study was conducted to determine whether between-site variation in stress responsiveness among WWTW effluent-exposed sticklebacks is persistent or reversible. Sticklebacks from eight sites in north-west England affected by WWTW effluent and exhibiting between-population variation in HPI axis reactivity, were moved to a clean-water aquarium environment. After five months in the contaminant-free environment the responsiveness of these fish to a standardised stressor was determined, by measuring the rate of stress-induced cortisol release across the gills, and compared with the responses of fish newly sampled from the eight original capture sites. Inter-site differences in the reactivity of the HPI axis, proportional to the effluent concentration at each site, persisted among the translocated female sticklebacks for at least 5 months. In male fish however, the direct relationship between stress responsiveness and site-specific effluent was not evident 5 months post-translocation. These results support previous observations that the HPA/I axis, a non-reproductive endocrine system, is vulnerable to modulation by anthropogenic factors in fish and show for the first time that, in female fish at least, this modulation is not transient. The mechanisms underlying these observations, and the implications for the fitness and resilience of affected populations, requires investigation.

Impaired brain StAR and HSP70 gene expression in zebrafish exposed to Methyl-Parathion based insecticide

Fish production ponds and natural water body areas located in close proximity to agricultural fields receive water with variable amounts of agrochemicals, and consequently, compounds that produce adverse effects may reach nontarget organisms. The aim of this study was to investigate whether waterborne methyl-parathion-based insecticide (MPBI) affected gene expression patterns of brain glucocorticoid receptor (GR), steroidogenic acute regulatory protein (StAR), and heat shock protein 70 (hsp70) in adult zebrafish (Danio rerio) exposed to this chemical for 96 h. Treated fish exposed to MPBI-contaminated water showed an inhibition of brain StAR and hsp70 gene expression. Data demonstrated that MPBI produced a decrease brain StAR and hsp70 gene expression.

A comparative study of the response to repeated chasing stress in Atlantic salmon (Salmo salar L.) parr and post-smolts

When Atlantic salmon parr migrate from fresh water towards the sea, they undergo extensive morphological, neural, physiological and behavioural changes. Such changes have the potential to affect their responsiveness to various environmental factors that impose stress. In this study we compared the stress responses in parr and post-smolt salmon following exposure to repeated chasing stress (RCS) for three weeks. At the end of this period, all fish were challenged with a novel stressor and sampled before (T0) and after 1h (T1). Parr had a higher growth rate than post-smolts. Plasma cortisol declined in the RCS groups within the first week suggesting a rapid habituation/desensitisation of the endocrine stress axis. As a result of the desensitised HPI axis, RCS groups showed a reduced cortisol response when exposed to the novel stressor. In preoptic area (POA) crf mRNA levels were higher in all post-smolt groups compared to parr. 11βhsd2 decreased by RCS and by the novel stressor in post-smolt controls (T1), whereas no effect of either stress was seen in parr. The grs were low in all groups except for parr controls. In pituitary, parr controls had higher levels of crf1r mRNA than the other parr and post-smolt groups, whilst pomcb was higher in post-smolt control groups. Overall, 11βhsd2 transcript abundance in parr was lower than post-smolt groups; after the novel stressor pomcs, grs and mr were up-regulated in parr control (T1). In summary, we highlight differences in the central stress response between parr and post-smolt salmon following RCS.

Steroids in teleost fishes: A functional point of view

Steroid hormones are involved in the regulation of a variety of processes like embryonic development, sex differentiation, metabolism, immune responses, circadian rhythms, stress response, and reproduction in vertebrates. Teleost fishes and humans show a remarkable conservation in many developmental and physiological aspects, including the endocrine system in general and the steroid hormone related processes in particular. This review provides an overview of the current knowledge about steroid hormone biosynthesis and the steroid hormone receptors in teleost fishes and compares the findings to the human system. The impact of the duplicated genome in teleost fishes on steroid hormone biosynthesis and perception is addressed. Additionally, important processes in fish physiology regulated by steroid hormones, which are most dissimilar to humans, are described. We also give a short overview on the influence of anthropogenic endocrine disrupting compounds on steroid hormone signaling and the resulting adverse physiological effects for teleost fishes. By this approach, we show that the steroidogenesis, hormone receptors, and function of the steroid hormones are reasonably well understood when summarizing the available data of all teleost species analyzed to date. However, on the level of a single species or a certain fish-specific aspect of physiology, further research is needed.

Impairment of the cortisol stress response mediated by the hypothalamus-pituitary-interrenal (HPI) axis in zebrafish (Danio rerio) exposed to monocrotophos pesticide

In teleosts, an important component of the stress response is coordinated by the hypothalamic-pituitary-interrenal (HPI) axis. Environmental contaminants might disrupt the stress axis and consequently affect the stress response in fish. To investigate the effect of monocrotophos (MCP) pesticide on the stress response of fish and its potential mechanisms, adult zebrafish (Danio rerio) were exposed to 0, 1, 10, and 100μg/L of a 40% MCP-based pesticide for 21d, after which time fish were subjected to a 3-min air-exposure stressor. Concentrations of the whole-body cortisol were measured by radioimmunoassay and abundances of transcripts of proteins involved in the HPI axis were determined using quantitative real-time PCR. Results showed that 100μg/L of MCP pesticide decreased whole-body cortisol levels of female zebrafish in response to an acute stressor, but without any effect on the cortisol response in males. 100μg/L MCP pesticide reduced POMC and GR expression in the brain, MC2R and P45011β expression in the head kidney, but enhanced 20β-HSD2 expression in the head kidney, suggesting that MCP damaged the HPI axis involving acting at pituitary regulatory levels, inhibiting cortisol synthesis and stimulating cortisol catabolism, or disturbing the negative feedback regulation. Additionally, MCP depressed liver GR transcription but did not affect phosphoenolpyruvate carboxykinase and tyrosine aminotransferase expression in zebrafish, suggesting a role for this pesticide in reducing target tissue responsiveness to cortisol. Considered together, the reduced ability to elevate cortisol levels in response to an acute stress may be an endocrine dysfunction occurring in zebrafish subchronically exposed to MCP pesticide.

Analysis of steroidogenic pathway key transcripts in interrenal cells isolated by laser microdissection (LMD) in stressed rainbow trout

An assessment of the key transcripts expression of the steroidogenesis-related genes in rainbow trout subjected to either acute or chronic stress was performed in both interrenal cells and whole head kidney tissue. The analysis of interrenal cells was possible thanks to the use, for the first time in this specific type of cells, of the technique of laser microdissection (LMD) which allows to isolate specific cells and process them independently of other surrounding cells in the tissue. The results indicated that both acute and chronic stressors induced a significant up-regulation of the steroidogenesis-related genes with a higher but expected degree in the isolated cells. In addition, under acute stress a delay between cortisol levels and transcript expression was found. Under chronic stress a clear relation between plasma cortisol levels, mRNA transcription and interrenal tissue area was observed, since all parameters were concomitantly increased at day 5 after stress. Moreover results indicated that the LMD technique allowed ascertaining with more precision and accuracy whether and when the steroidogenesis-related genes were significantly expressed, disregarding the noise produced by other cells present in the head kidney. Results also showed a typical physiological response in plasma parameters and a positive relationship between plasma cortisol data and transcript abundance in isolated cells. The present results may help to better understand the mechanisms behind the interrenal response to stress challenges in fish.

Modulation of the Expression of Components of the Stress Response by Dietary Arachidonic Acid in European Sea Bass (Dicentrarchus labrax) Larvae

This study reports for the first time on European sea bass, Dicentrarchus labrax (L.), larvae, the effect of different levels of dietary arachidonic acid (ARA; 20:4n-6) on the expression of genes related to the fish stress response. Copies of mRNA from genes related to steroidogenesis [StAR (steroidogenic acute regulatory protein), c-Fos, and CYP11β (11β-hydroxylase gene)], glucocorticoid receptor complex [GR (glucocorticoid receptor) and HSP (heat shock proteins) 70 and 90) and antioxidative stress (catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase] were quantified. Eighteen day-old larvae were fed for 14 days with three experimental diets with increasing levels of ARA (0.3, 0.6 and 1.2% d.w.) and similar levels of docosahexaenoic (22:6n-3) and eicosapentaenoic (20:5n-3) acids (5 and 3%, respectively). The quantification of stress-related genes transcripts was conducted by One-Step TaqMan real time RT-PCR with the standard curve method (absolute quantification). Increase dietary levels of ARA induced a significantly (p < 0.05) down-regulation of genes related to cortisol synthesis, such as StAR and CYP11β and up-regulated genes related to glucocorticoid receptor complex, such as HSP70 and GR. No effects were observed on antioxidant enzymes gene expression. These results revealed the regulatory role of dietary ARA on the expression of stress-related genes in European sea bass larvae.

Stress in Atlantic salmon: response to unpredictable chronic stress

Combinations of stressors occur regularly throughout an animal's life, especially in agriculture and aquaculture settings. If an animal fails to acclimate to these stressors, stress becomes chronic, and a condition of allostatic overload arises with negative results for animal welfare. In the current study, we describe effects of exposing Atlantic salmon parr to an unpredictable chronic stressor (UCS) paradigm for 3 weeks. The paradigm involves exposure of fish to seven unpredictable stressors three times a day. At the end of the trial, experimental and control fish were challenged with yet another novel stressor and sampled before and 1 h after that challenge. Plasma cortisol decreased steadily over time in stressed fish, indicative of exhaustion of the endocrine stress axis. This was confirmed by a lower cortisol response to the novel stressor at the end of the stress period in chronically stressed fish compared with the control group. In the preoptic area (POA) and pituitary gland, chronic stress resulted in decreased gene expression of 11βhsd2, gr1 and gr2 in the POA and increased expression of those genes in the pituitary gland. POA crf expression and pituitary expression of pomcs and mr increased, whereas interrenal gene expression was unaffected. Exposure to the novel stressor had no effect on POA and interrenal gene expression. In the pituitary, crfr1, pomcs, 11βhsd2, grs and mr were down-regulated. In summary, our results provide a novel overview of the dynamic changes that occur at every level of the hypothalamic-pituitary gland-interrenal gland (HPI) axis as a result of chronic stress in Atlantic salmon.

Modulation of adrenocorticotrophin hormone (ACTH)-induced expression of stress-related genes by PUFA in inter-renal cells from European sea bass (Dicentrarchus labrax)

Dietary fatty acids have been shown to exert a clear effect on the stress response, modulating the release of cortisol. The role of fatty acids on the expression of steroidogenic genes has been described in mammals, but little is known in fish. The effect of different fatty acids on the release of cortisol and expression of stress-related genes of European sea bass (Dicentrarchus labrax) head kidney, induced by a pulse of adenocorticotrophin hormone (ACTH), was studied. Tissue was maintained in superfusion with 60 min of incubation with EPA, DHA, arachidonic acid (ARA), linoleic acid or α-linolenic acid (ALA) during 490 min. Cortisol was measured by RIA. The quantification of stress-related genes transcripts was conducted by One-Step TaqMan real-time RT-PCR. There was an effect of the type of fatty acid on the ACTH-induced release of cortisol, values from ALA treatment being elevated within all of the experimental period. The expression of some steroidogenic genes, such as the steroidogenic acute regulatory protein (StAR) and c-fos, were affected by fatty acids, ALA increasing the expression of StAR after 1 h of ACTH stimulation whereas DHA, ARA and ALA increased the expression of c-fos after 20 min. ARA increased expression of the 11β-hydroxylase gene. Expression of heat shock protein 70 (HSP70) was increased in all the experimental treatments except for ARA. Results corroborate previous studies of the effect of different fatty acids on the release of cortisol in marine fish and demonstrate that those effects are mediated by alteration of the expression of steroidogenic genes.

Early exposure of 17α-ethynylestradiol and diethylstilbestrol induces morphological changes and alters ovarian steroidogenic pathway enzyme gene expression in catfish, Clarias gariepinus

Environmental estrogens are major cause of endocrine disruption in vertebrates, including aquatic organisms. Teleosts are valuable and popular models for studying the effects of endocrine disrupting chemicals (EDCs) in the environment. In the present study, we investigated the changes caused by exposure to the synthetic estrogens 17α-ethynylestradiol (EE2 ) and diethylstilbesterol (DES) during early stages of growth and sex differentiation of air-breathing catfish, Clarias gariepinus, at the morphological, histological, and molecular levels. Catfish hatchlings, 0 day post hatch (dph) were exposed continuously to sublethal doses of EE2 (50 ng/L) and DES (10 ng/L) until 50 dph and subsequently monitored for ovarian structural changes and alteration in the gene expression of steroidogenic enzymes till adulthood. Treated fish exhibited morphological deformities such as spinal curvature, stunted growth, and yolk-sac fluid retention. In addition to ovarian atrophy, DES-treated fish showed either rudimentary or malformed ovaries. Detailed histological studies revealed precocious oocyte development as well as follicular atresia. Further, transcript levels of various steroidogenic enzyme and transcription factor genes were altered in response to EE2 and DES. Activity of the rate-limiting enzyme of estrogen biosynthesis, aromatase, in the ovary as well as the brain of treated fish was in accordance with transcript level changes. These developmental and molecular effects imparted by EE2 and DES during early life stages of catfish could demonstrate the deleterious effects of estrogen exposure and provide reliable markers for estrogenic EDCs exposure in the environment.