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

Gradation of the stress response in rainbow trout exposed to stressors of different severity: the role of brain serotonergic and dopaminergic systems

After an intense acute stressor, fish develop a metabolic and behavioural response that usually lasts for several hours. Brain monoaminergic systems, particularly the serotonergic system, appear to play a key role in the central regulation of the stress response. However, the influence of stressor severity on brain monoaminergic systems and on the induced stress responses is yet poorly understood. We hypothesise that serotonergic system could have a direct role in the integration of sensory information during stressor exposure and in the organisation of the subsequent integrated stress response. According to our hypothesis, a low stressor intensity would induce a low response of brain serotonergic system and therefore stress responses of low magnitude and duration. To test this hypothesis, we exposed fish to handling disturbance for 5 s, 15 s or 3 min. We sampled fish at 0 (controls), 3, 15, 45 and 240 min after the start of the stress protocol. Brain levels of serotonin, dopamine and their respective main oxidative metabolites were quantified, along with plasma levels of stress markers (catecholamines, cortisol, glucose and lactate). Regarding stress markers, the 5-s and 15-s stress protocols induced similar and relatively low elevations in all parameters assessed. As expected, the 3-min protocol induced responses of a higher intensity and duration in all plasma parameters. Interestingly, the alterations of brain monoaminergic systems did not follow the same trend. The three stress protocols induced increases in the serotonergic activity in all brain regions analysed (hypothalamus, telencephalon and medulla oblongata), independently of the duration of the handling disturbance, whereas the effects on the dopaminergic system were minor and brain region-dependent. These data suggest that the brain serotonergic system, although likely involved in the recognition of the stressor stimuli, is not the only actor determining the magnitude and duration of the acute stress response in trout.

Counter-regulatory response to a fall in circulating fatty acid levels in rainbow trout. Possible involvement of the hypothalamus-pituitary-interrenal axis

We hypothesize that a decrease in circulating levels of fatty acid (FA) in rainbow trout Oncorhynchus mykiss would result in the inhibition of putative hypothalamic FA sensing systems with concomitant changes in the expression of orexigenic and anorexigenic factors ultimately leading to a stimulation of food intake. To assess this hypothesis, we lowered circulating FA levels treating fish with SDZ WAG 994 (SDZ), a selective A1 adenosine receptor agonist that inhibits lipolysis. In additional groups, we also evaluated if the presence of intralipid was able to counteract changes induced by SDZ treatment, and the possible involvement of the hypothalamus-pituitary-interrenal (HPI) axis by treating fish with SDZ in the presence of metyrapone, which decreases cortisol synthesis in fish. The decrease in circulating levels of FA in rainbow trout induced a clear increase in food intake that was associated with the decrease of the anorexigenic potential in hypothalamus (decreased POMC-A1 and CART mRNA abundance), and with changes in several parameters related to putative FA-sensing mechanisms in hypothalamus. Intralipid treatment counteracted these changes. SDZ treatment also induced increased cortisol levels and the activation of different components of the HPI axis whereas these changes disappeared in the presence of intralipid or metyrapone. These results suggest that the HPI axis is involved in a counter-regulatory response in rainbow trout to restore FA levels in plasma.

Is plasma cortisol response to stress in rainbow trout regulated by catecholamine-induced hyperglycemia?

Based on previous studies we hypothesize that under stress conditions catecholamine-induced hyperglycemia contributes to enhance cortisol production in head kidney of rainbow trout. Therefore, treatment with propranolol (β-adrenoceptor blocker) should reduce the hyperglycemia elicited by stress and, therefore, we expected reduced glucosensing response and cortisol production in head kidney. Propranolol treatment was effective in blocking most of the effects of catecholamines in liver energy metabolism resulting in a lower glycemia in stressed fish. The decreased glycemia of stressed fish treated with propranolol was observed along with reduced transcription of genes involved in the cortisol synthetic pathway, which supports our hypothesis. However, changes in putative glucosensing parameters assessed in head kidney were scarce and in general did not follow changes noted in glucose levels in plasma. Furthermore, circulating cortisol levels did not change in parallel with changes in glycemia. As a whole, the present results suggest that glycemia could participate in the regulation of cortisol synthetic pathways but other factors are also likely involved. Propranolol effects on trout stress response were different depending on time passed after stress onset; the direct or indirect involvement of catecholaminergic response in the regulation of cortisol production and release deserves further investigation.

Regulation of hypothalamic-pituitary-interrenal axis function in male smallmouth bass (Micropterus dolomieu) during parental care

Male smallmouth bass (Micropterus dolomieu) provide sole parental care until offspring reach independence, a period of several weeks. During the early parental care period when males are guarding fresh eggs (MG-FE), cortisol responsiveness is attenuated; the response is re-established when males reach the end of the parental care period and are guarding free-swimming fry (MG-FSF). It was hypothesized that attenuation of the cortisol response in male smallmouth bass during early parental care reflected modulation of hypothalamic-pituitary-interrenal (HPI) axis function. Male smallmouth bass were sampled at the beginning (MG-FE) and end of the parental care period (MG-FSF), before and/or 25 min after exposure to a standardized stressor consisting of 3 min of air exposure. Repeated sampling of stressed fish for analysis of plasma cortisol and adrenocorticotropic hormone (ACTH) levels was carried out. Males significantly elevated both plasma cortisol and ACTH levels when guarding free-swimming fry but not during early parental care. Control and stressed fish were terminally sampled for tissue mRNA abundance of preoptic area (POA) and hypothalamic corticotropin-releasing factor (CRF) as well as head kidney melanocortin 2 receptor (MC2R), steroidogenic acute regulatory protein (StAR) and cytochrome P450 side chain cleavage enzyme (P450scc). No significant differences in either hypothalamus CRF or head kidney P450scc mRNA abundance were found across parental care stages or in response to stress. However, POA CRF mRNA abundance and interrenal cell MC2R and StAR mRNA abundances failed to increase in response to stress in MG-FE. Thus, the attenuated cortisol response in males guarding fresh eggs may be explained by hypoactive HPI axis function in response to stress. The present is one of few studies, and the first teleost study, to address the mechanisms underlying resistance to stress during the reproductive/parental care period.

Ontogenesis of the HPI axis and molecular regulation of the cortisol stress response during early development in Dicentrarchus labrax

The cortisol stress response and the molecular programming of the corticoid axis were characterized for the first time during early ontogeny in a Mediterranean marine teleost, the European sea bass (Dicentrarchus labrax). Sea bass embryos, pre-larvae and larvae at specific points of development were exposed to acute stressors and the temporal patterns of cortisol whole body concentrations and the expression of genes involved in corticosteroid biosynthesis, degradation and signaling were determined. Expression of genes (gr1, gr2, mr, crf) involved into the corticoid response regulation combined with histological data indicated that, although a cortisol stress response is evident for the first time around first feeding, a pattern becomes established in larvae at flexion until the formation of all fins. Moreover, mRNA transcript levels of 11β-hydroxylase and 11β-hsd2 showed a strong correlation with the whole body cortisol concentrations. Concluding, our data reveal the presence of an adaptive mechanism in European sea bass at early ontogeny enabling to cope with external stressful stimuli and provide a better insight into the onset and regulation of the stress response in this species.

Social stress modulates the cortisol response to an acute stressor in rainbow trout (Oncorhynchus mykiss)

In rainbow trout (Oncorhynchus mykiss) of subordinate social status, circulating cortisol concentrations were elevated under resting conditions but the plasma cortisol and glucose responses to an acute stressor (confinement in a net) were attenuated relative to those of dominant trout. An in vitro head kidney preparation, and analysis of the expression of key genes in the stress axis prior to and following confinement in a net were then used to examine the mechanisms underlying suppression of the acute cortisol stress response in trout experiencing chronic social stress. With porcine adrenocorticotropic hormone (ACTH) as the secretagogue, ACTH-stimulated cortisol production was significantly lower for head kidney preparations from subordinate trout than for those from dominant trout. Dominant and subordinate fish did not, however, differ in the relative mRNA abundance of melanocortin-2 receptor (MC2R), steroidogenic acute regulatory protein (StAR) or cytochrome P450 side chain cleavage enzyme (P450scc) within the head kidney, although the relative mRNA abundance of these genes was significantly higher in both dominant and subordinate fish than in sham trout (trout that did not experience social interactions but were otherwise treated identically to the dominant and subordinate fish). The relative mRNA abundance of all three genes was significantly higher in trout exposed to an acute net stressor than under control conditions. Upstream of cortisol production in the stress axis, plasma ACTH concentrations were not affected by social stress, nor was the relative mRNA abundance of the binding protein for corticotropin releasing factor (CRF-BP). The relative mRNA abundance of CRF in the pre-optic area of subordinate fish was significantly higher than that of dominant or sham fish 1h after exposure to the stressor. Collectively, the results indicate that chronic social stress modulates cortisol production at the level of the interrenal cells, resulting in an attenuated cortisol response to an acute stressor.

Exposure to environmental levels of waterborne cadmium impacts corticosteroidogenic and metabolic capacities, and compromises secondary stressor performance in rainbow trout

The physiological responses to waterborne cadmium exposure have been well documented; however, few studies have examined animal performances at low exposure concentrations of this metal. We tested the hypothesis that longer-term exposure to low levels of cadmium will compromise the steroidogenic and metabolic capacities, and reduce the cortisol response to a secondary stressor in fish. To test this, juvenile rainbow trout (Oncorhynchus mykiss) were exposed to 0 (control), 0.75 or 2.0 μg/L waterborne cadmium in a flow-through system and were sampled at 1, 7 and 28 d of exposure. There were only very slight disturbances in basal plasma cortisol, lactate or glucose levels in response to cadmium exposure over the 28 d period. Chronic cadmium exposure significantly affected key genes involved in corticosteroidogenesis, including melanocortin 2 receptor, steroidogenic acute regulatory protein and cytochrome P450 side chain cleavage enzyme. At 28 d, the high cadmium exposure group showed a significant drop in the glucocorticoid receptor and mineralocorticoid receptor protein expressions in the liver and brain, respectively. There were also perturbations in the metabolic capacities in the liver and gill of cadmium-exposed trout. Subjecting these fish to a secondary handling disturbance led to a significant attenuation of the stressor-induced plasma cortisol, glucose and lactate levels in the cadmium groups. Collectively, although trout appears to adjust to subchronic exposure to low levels of cadmium, it may be at the cost of impaired interrenal steroidogenic and tissue-specific metabolic capacities, leading to a compromised secondary stress performance in rainbow trout.

Physiological effects of gasoline on the freshwater fish Prochilodus lineatus(Characiformes: Prochilodontidae)

The purpose of this work was to evaluate the effects of the water-soluble fraction of gasoline (WSFG) on the Neotropical freshwater fish Prochilodus lineatus. The WSFG was prepared by mixing gasoline in water (1:4) and animals were exposed for 6, 24 and 96h to 5% diluted WSFG or only to water. After exposure, blood was collected from the caudal vein and the gills were removed. The following parameters were analyzed: hematological (hemoglobin, hematocrit, number of red blood cells), osmo-ionic (plasma Na+, Cl- and K+ and plasma osmolarity), metabolic (total plasma proteins and glucose), endocrine (cortisol), density and distribution of chloride cells [CC] in the gills (immunohistochemistry), and branchial Na+/K+-ATPase (NKA) activity. Hemolysis was found to occur after 96h exposure to WSFG, as indicated by the decrease in the hematological parameters analyzed, followed by an increase in plasma K+. Secondary stress response was revealed by the occurrence of hyperglycemia in the three periods of exposure, despite the absence of significant increases in the plasma cortisol. The exposure to WSFG also caused an increase in the quantity of CC and in plasma Na+, after 24h, as well as in the enzymatic activity of NKA and plasma osmolarity, after 24h and 96h. These results indicate that fish exposed to the WSFG showed physiological adjusts to maintain their osmotic balance. However, the increase in the quantity of CC in the lamellae may interfere in the gas exchange impairing respiration.

The response of brain serotonergic and dopaminergic systems to an acute stressor in rainbow trout: a time-course study

The brain monoaminergic neurotransmitter systems are known to be involved in the integrated response to stress in vertebrates. However, the present knowledge about the timing of their actions as well as their specific roles in the regulation of the endocrine axes that drive the stress response is incomplete. This is partially because of the complexity of the reciprocal interactions among the monoaminergic systems and other biochemical actors of the stress response such as CRF, AVT, ACTH or corticosteroids. In this study, we show for the first time in teleost fish, the short- and mid-term time-course of the response of the forebrain serotonergic and dopaminergic activities after the exposure to an acute stressor in rainbow trout. Other stress markers like the plasma levels of cortisol, glucose and lactate were also monitored, providing a context to precisely locate the monoaminergic activation within the fish acute stress response. Our results show that the acute stress induced a rapid increase in the forebrain serotonergic activity, which became elevated after only 15 seconds of chasing. Several hours after stress, the serotonergic activity recovered its basal levels, in parallel to the recovery of other stress markers such as plasma catecholamines and cortisol. The dopaminergic activity was also increased after stress, but only in the telencephalon and only after 20 minutes post-stress. The increase in serotonergic activity happened before the elevation of plasma catecholamines, suggesting that this monoamine system could have a key role in triggering the initial steps of the activation of not only the hypothalamus-pituitary-interrenal axis, but also the brain-sympathetic-chromaffin axis in fish.

Effects of dietary nucleotides on acute stress response and cannabinoid receptor 1 mRNAs in sole, Solea solea

The objective of the present study was to evaluate the modulation of acute stress response by dietary nucleotides (NT) in sole, Solea solea. A basal diet was supplemented with levels of 0 (normal diet), or 0.4 g NT/kg dry diet for 8 weeks. At the end of feeding trial, fish fed the normal and NT-supplemented diet were subjected to a standardized protocol of disturbance and sampled over a 24h recovery after the stressor exposure. Modulatory effects of NT on acute stress response (cortisol and glucose), proopiomelanocortin (POMC) and cannabinoid receptor 1 splice variants (CB1A and CB1B) mRNA levels were studied. Both plasma cortisol and glucose levels of fish fed NT-supplemented diet were significantly lower than fish fed the control diet at 1 and 4h post-stress time-points. There are no significant effects of dietary NT on POMC and HSP70 mRNA levels. In our study, both CB1A and CB1B trascript levels were induced in fish fed the normal diet at 1 and 4h post-stress intervals. Collectively, the results obtained suggest that dietary NT modulates the CB1-like receptor mRNA expressions leading to attenuation in stressor-induced plasma cortisol level in sole.

ACTH-stimulated cortisol release from head kidney of rainbow trout is modulated by glucose concentration

To assess the hypothesis that cortisol release in rainbow trout is modulated by glucose levels, we first evaluated cortisol release [basal and adrenocorticotropic hormone (ACTH)-regulated] by head kidney tissue superfused with medium reflecting hypoglycaemic, normoglycaemic or hyperglycaemic conditions. Next, cortisol release from head kidney fragments in static incubations was assessed in parallel with changes in parameters related to cortisol synthesis (mRNA abundance of StAR, P450scc, 3βHSD and 11βH) and the GK-mediated glucosensing mechanism (levels of glycogen and glucose, activities of GK, GSase and PK, and mRNA levels of GK, GLUT-2, Kir6.x-like and SUR-like). We then evaluated the effects of two inhibitors of glucose transport, cytochalasin B and phlorizin, on cortisol production and glucosensing mechanisms. The ACTH-induced release of cortisol proved to be modulated by glucose concentration such that increased release occurs under high glucose levels, and decreased ACTH-stimulated cortisol release occurs when glucose transport is inhibited by cytochalasin B. The release of cortisol can be associated with increased synthesis as enhanced mRNA abundance of genes related to cortisol synthesis was also noted in high glucose medium. Specific GK immunoreactivity in the cortisol-producing cells (not in chromaffin cells) further substantiates GK-mediated glucosensing in cortisol production. In contrast, no changes compatible with those of glucose levels and cortisol release/synthesis in the presence of ACTH were noted for any other putative glucosensor mechanisms based on LXR, SGLT-1 or Gnat3. These combined results are the first evidence for a mechanism in fish linking the synthesis and release of a non-pancreatic hormone like cortisol with circulating glucose levels. The relationship was evident for the regulated (ACTH-dependent) pathway and this suggests that under acute stress conditions glucose is important for the regulation of cortisol synthesis and release.

20β-hydroxysteroid dehydrogenase gene promoter: potential role for cyclic AMP and xenobiotic responsive elements

Teleostean 20β-hydroxysteroid dehydrogenase (20β-HSD) is involved in final oocyte maturation and steroid hormone metabolism. It has structural and functional similarities to mammalian carbonyl reductases that are involved in the metabolism of endogenous carbonyl and xenobiotic compounds. To understand the transcriptional regulation of 20β-HSD, here we report the cloning of 20β-HSD promoter from two fish species, rainbow trout and air-breathing catfish. Analysis of the promoter motifs, in silico identified the presence of several sites for transcription factor binding including cAMP, xenobiotic and steroid hormone responsive elements. Luciferase reporter assays with progressive deletion constructs demonstrated that 20β-HSD type B of trout has no promoter activity while 20β-HSD type A of trout and catfish 20β-HSD promoters showed basal promoter activity. A TATA box flanked by a CAAT box is important for basal transcription. Deletion of cAMP responsive element in the promoter decreased basal promoter activity significantly. Reporter assays with forskolin and IBMX, drugs that increase intracellular cAMP induced the promoter activity over the basal level. Intriguingly, β-nafthoflavone, an arylhydrocarbon receptor ligand, induced the 20β-HSD promoter activity and is further evidenced by the induction of 20β-HSD expression in the livers of catfish, in vivo. These results demonstrate for the first time that 20β-HSD expression is not only modulated by cAMP but also by xenobiotics and further studies may provide significance to the ubiquitous distribution and broad substrate specificity of this enzyme.

Modulation of hypothalamic-pituitary-interrenal axis function by social status in rainbow trout

Juvenile rainbow trout (Oncorhynchus mykiss) form stable dominance hierarchies when confined in pairs. These hierarchies are driven by aggressive competition over limited resources and result in one fish becoming dominant over the other. An important indicator of low social status is sustained elevation of circulating cortisol levels as a result of chronic activation of the hypothalamic-pituitary-interrenal (HPI) axis. In the present study it was hypothesized that social status modulates the expression of key proteins involved in the functioning of the HPI axis. Cortisol treatment and fasting were used to assess whether these characteristics seen in subordinate fish also affected HPI axis function. Social status modulated plasma adrenocorticotropic hormone (ACTH) levels, cortisol synthesis, and liver glucocorticoid receptor (GR) expression. Plasma ACTH levels were lower by approximately 2-fold in subordinate and cortisol-treated fish, consistent with a negative feedback role for cortisol in modulating HPI axis function. Although cortisol-treated fish exhibited differences in corticotropin-releasing factor (CRF) and CRF-binding protein (CRF-BP) mRNA relative abundances in the preoptic area and telencephalon, respectively, no effect of social status on CRF or CRF-BP was detected. Head kidney melanocortin 2 receptor (MC2R) mRNA relative levels were unaffected by social status, while mRNA relative abundances of steroidogenic acute regulatory protein (StAR) and cytochrome P450 side chain cleavage (P450scc) enzyme were elevated in dominant fish. Liver GR2 mRNA and total GR protein levels in subordinate fish were lower than control values by approximately 2-fold. In conclusion, social status modulated the functioning of the HPI axis in rainbow trout. Our results suggest altered cortisol dynamics and reduced target tissue response to this steroid in subordinate fish, while the higher transcript levels for steroid biosynthesis in dominant fish leads us to propose an adaptive role for responding to subsequent stressors.

Central and peripheral glucocorticoid receptors are involved in the plasma cortisol response to an acute stressor in rainbow trout

Cortisol, the primary circulating corticosteroid in teleosts, is elevated during stress following activation of the hypothalamus-pituitary-interrenal (HPI) axis. Cortisol exerts genomic effects on target tissues in part by activating glucocorticoid receptors (GR). Despite a well-established negative feedback loop involved in plasma cortisol regulation, the role of GR in the functioning of the HPI axis during stress in fish is still unclear. We used mifepristone (a GR antagonist) to suppress GR signaling in rainbow trout (Oncorhynchus mykiss) and assessed the resultant changes to HPI axis activity. We show for the first time that mifepristone caused a functional knockdown of GR by depleting protein expression 40-75%. The lower GR protein expression corresponded with a compensatory up-regulation of GR mRNA levels across tissues. Mifepristone treatment completely abolished the stressor-induced elevation in plasma cortisol and glucose levels seen in the control fish. A reduction in corticotropin-releasing factor (CRF) mRNA abundance in the hypothalamic preoptic area was also observed, suggesting that GR signaling is involved in maintaining basal CRF levels. We further characterized the effect of mifepristone treatment on the steroidogenic capacity of interrenal tissue in vitro. A marked reduction in cortisol production following adrenocorticotropic hormone stimulation of head kidney pieces was observed from mifepristone treated fish. This coincided with the suppression of steroidogenic acute regulatory protein, but not P450 side chain cleavage mRNA abundances. Overall, our results underscore a critical role for central and peripheral GR signaling in the regulation of plasma cortisol levels during stress in fish.

Tissue-specific metabolic changes in response to an acute handling disturbance in juvenile rainbow trout exposed to municipal wastewater effluent

The objective of this study was to evaluate the effects of municipal wastewater effluent (MWWE) exposure on aspects of both organismal and cellular stress response in rainbow trout (Oncorhynchus mykiss). Juvenile rainbow trout were exposed for 14 d (2-d static renewal) to tertiary-treated MWWE at concentrations of 0%, 20% and 90%. Following the MWWE exposure, fish were subjected to an acute handling stress and sampled at 1, 4 and 24 h post-stressor, to evaluate the fish performance to additional stressors. Organismal stress response evaluation included measuring plasma cortisol, glucose and lactate concentrations, and tissue metabolic capacity, including gluconeogenic (liver) and glycolytic enzyme activities in the liver, brain, heart and gill. No significant differences between treatments were seen in plasma cortisol, glucose or lactate concentrations after 14 d exposure to MWWE. However, MWWE exposure significantly affected plasma cortisol and glucose response to the acute secondary stressor. Acute handling disturbance enhanced liver gluconeogenic capacity in the control group, but this response was altered in the MWWE exposed groups. MWWE exposure did not affect the acute stressor-mediated enhancement of brain or gill glycolytic capacity, but significantly reduced the glycolytic capacity of liver and heart in response to a secondary stressor compared to the control group. Altogether, chronic exposure to MWWE impacts the metabolic performances to a secondary stressor challenge and this includes disruptions in tissue-specific gluconeogenic and glycolytic capacities in rainbow trout.

Flavonoids exhibit diverse effects on CYP11B1 expression and cortisol synthesis

CYP11B1 catalyzes the final step of cortisol biosynthesis. The effects of flavonoids on transcriptional expression and enzyme activity of CYP11B1 were investigated using the human adrenocortical H295R cell model. All tested nonhydroxylated flavones including 3',4'-dimethoxyflavone, α-naphthoflavone, and β-naphthoflavone upregulated CYP11B1 expression and cortisol production, whereas apigenin and quercetin exhibited potent cytotoxicity and CYP11B1 repression at high concentrations. Nonhydroxylated flavones stimulated CYP11B1-catalyzed cortisol formation at transcriptional level. Resveratrol increased endogenous and substrate-supported cortisol production like nonhydroxylated flavones tested, but it had no effect on CYP11B1 gene expression and enzyme activity. Resveratrol appeared to alter cortisol biosynthesis at an earlier step. The Ad5 element situated in the -121/-106 region was required for basal and flavone-induced CYP11B1 expression. Overexpression of COUP-TFI did not improve the responsiveness of Ad5 to nonhydroxylated flavones. Although COUP-TFI overexpression increased CYP11B1 and CYP11B2 promoter activation, its effect was not mediated through the common Ad5 element. Treating cells with PD98059 (a flavone-type MEK1 inhibitor) increased CYP11B1 promoter activity, but not involving ERK signaling because phosphorylation of ERK1/2 remained unvarying throughout the course of treatment. Likewise, AhR was not responsible for the CYP11B1-modulating effects of flavonoids because inconsistency with their effects on AhR activation. 3',4'-dimethoxyflavone and 8-Br-cAMP additively activated CYP11B1 promoter activity. H-89 reduced 3',4'-dimethoxyflavone-induced CYP11B1 promoter activation but to a lesser extent as compared to its inhibition on cAMP-induced transactivation. Our data suggest that constant exposure to nonhydroxylated flavones raises a potential risk of high basal and cAMP-induced cortisol synthesis in consequence of increased CYP11B1 expression.

The interruption of thyroid and interrenal and the inter-hormonal interference in fish: does it promote physiologic adaptation or maladaptation?

Endocrines, the chief components of chemical centers which produce hormones in tune with intrinsic and extrinsic clues, create a chemical bridge between the organism and the environment. In fishes also hormones integrate and modulate many physiologic functions and its synthesis, release, biological actions and metabolic clearance are well regulated. Consequently, thyroid hormones (THs) and cortisol, the products of thyroid and interrenal axes, have been identified for their common integrative actions on metabolic and osmotic functions in fish. On the other hand, many anthropogenic chemical substances, popularly known as endocrine disrupting chemicals, have been shown to disrupt the hormone-receptor signaling pathways in a number fish species. These chemicals which are known for their ability to induce endocrine disruption particularly on thyroid and interrenals can cause malfunction or maladaptation of many vital processes which are involved in the development, growth and reproduction in fish. On the contrary, evidence is presented that the endocrine interrupting agents (EIAs) can cause interruption of thyroid and interrenals, resulting in physiologic compensatory mechanisms which can be adaptive, though such hormonal interactions are less recognized in fishes. The EIAs of physical, chemical and biological origins can specifically interrupt and modify the hormonal interactions between THs and cortisol, resulting in specific patterns of inter-hormonal interference. The physiologic analysis of these inter-hormonal interruptions during acclimation and post-acclimation to intrinsic or extrinsic EIAs reveals that combinations of anti-hormonal, pro-hormonal or stati-hormonal interference may help the fish to fine-tune their metabolic and osmotic performances as part of physiologic adaptation. This novel hypothesis on the phenomenon of inter-hormonal interference and its consequent physiologic interference during thyroid and interrenal interruption thus forms the basis of physiologic acclimation. This interfering action of TH and cortisol during hormonal interruption may subsequently promote ecological adaptation in fish as these physiologic processes ultimately favor them to survive in their hostile environment.

Aroclor 1254 disrupts liver glycogen metabolism and enhances acute stressor-mediated glycogenolysis in rainbow trout

The objective of this study was to investigate the impact of short-term exposure to polychlorinated biphenyls on the acute stress response in rainbow trout. Fish were exposed to dietary Aroclor1254 (10mg kg(-1) body mass/day) for 3 days and then subjected to a 3-min handling disturbance and sampled over a 24h recovery after the stressor exposure. In the pre-stress fish, PCB exposure significantly elevated aryl hydrocarbon receptor (AhR) and cytochrome P4501A1 (Cyp1A1) mRNA abundance and Cyp1A protein expression confirming AhR activation. There was no significant effect of PCB on plasma cortisol and glucose levels, while plasma lactate levels were significantly elevated compared to the sham group. PCB exposure significantly elevated liver glycogen content and hexokinase activity, whereas lactate dehydrogenase activity was depressed. Short-term PCB exposure did not modify the acute stressor-induced plasma cortisol, glucose and lactate responses. Liver glycogen content dropped significantly after stressor exposure in the PCB group but not in the sham group. This was matched by a significantly higher liver LDH activity and a lower HK activity during recovery in the PCB group suggesting enhanced glycolytic capacity to fuel hepatic metabolism. Liver AhR, but not Cyp1A1, transcript levels were significantly reduced during recovery from handling stressor in the Aroclor fed fish. Collectively, this study demonstrates that short-term PCB exposure may impair the liver metabolic performance that is critical to cope with the enhanced energy demand associated with additional stressor exposure in rainbow trout.

Exposure to municipal wastewater effluent impacts stress performance in rainbow trout

The objective of the study was to examine the impact of municipal wastewater effluents on the functioning of the cortisol stress axis in rainbow trout (Oncorhynchus mykiss). Juvenile rainbow trout were caged upstream (reference) and downstream (100% and 10% effluent) of a tertiary-treated municipal wastewater treatment plant outfall and sampled at 14d later (0 time samples). A second set of fish were then subjected to a 5 min handling disturbance and sampled at 1 and 24h post-stressor exposure. Plasma cortisol, glucose and lactate concentrations, liver and brain glucocorticoid receptor (GR) protein levels, head kidney mRNA abundances of corticosteroidogenesis genes, including steroidogenic acute regulatory protein (StAR), cytochrome P450 side chain cleavage (P450scc), 11β-hydroxylase and melanocortin 2 receptor (MC2R), and key liver metabolic enzyme activities, were measured. Exposure to effluent for 14d significantly elevated plasma cortisol and lactate levels in 100% effluent group compared to the reference and 10% effluent sites. There was a significantly higher StAR mRNA abundance in the effluent groups compared to the upstream control. GR protein levels in the liver, but not the brain, were significantly higher in the 100% effluent group compared to the upstream control group. Chronic exposure to 100% effluent for 14d significantly lowered liver hexokinase and glucokinase activities, but did not affect glycogen content or the activities of phosphoenolpyruvate carboxykinase, pyruvate kinase, lactate dehydrogenase, aspartate aminotransferase and alanine aminotransferase compared to the other two groups. Subjecting these fish to a secondary acute stressor elicited a physiological stress response, including significant transient elevation in plasma cortisol, glucose and lactate levels at 1h which dropped to pre-stress levels at 24h after stressor exposure, in the control and 10% effluent groups, but this conserved stress response was impaired in the 100% effluent group. The 100% effluent group fish also had significantly higher StAR and P450scc mRNA abundances at 1h post-stress, while transcript abundances of all the major corticosteroidogenesis genes were suppressed at 24h post-stressor compared to the control and 10% effluent groups. Considered together, exposure to full-strength MWWE for 14d elicits a chronic stress response in rainbow trout, and perturbs the conserved adaptive response to an acute stressor. Our results reveal that the impact of tertiary-treated MWWE on stress performance in rainbow trout is abolished by 90% effluent dilution.

Cadmium-mediated disruption of cortisol biosynthesis involves suppression of corticosteroidogenic genes in rainbow trout

Cadmium is widely distributed in the aquatic environment and is toxic to fish even at sublethal concentrations. This metal is an endocrine disruptor, and one well established role in teleosts is the suppression of adrenocorticotrophic hormone (ACTH)-stimulated cortisol biosynthesis by the interrenal tissue. However the mechanism(s) leading to this steroid suppression is poorly understood. We tested the hypothesis that cadmium targets genes encoding proteins critical for corticosteroid biosynthesis, including melanocortin 2 receptor (MC2R), steroidogenic acute regulatory protein (StAR) and cytochrome P450 side chain cleavage enzyme (P450scc), in rainbow trout (Oncorhynchus mykiss). To test this, head kidney slices (containing the interrenal tissues) were incubated in vitro with cadmium chloride (0, 10, 100 and 1000nM) for 4h either in the presence or absence of ACTH (0.5IU/mL). In the unstimulated head kidney slices, cadmium exposure did not affect basal cortisol secretion and the mRNA levels of MC2R and P450scc, while StAR gene expression was significantly reduced. Cadmium exposure significantly suppressed ACTH-stimulated cortisol production in a dose-related fashion. This cadmium-mediated suppression in corticosteroidogenesis corresponded with a significant reduction in MC2R, StAR and P450scc mRNA levels in trout head kidney slices. The inhibition of ACTH-stimulated cortisol production and suppression of genes involved in corticosteroidogenesis by cadmium were completely abolished in the presence of 8-Bromo-cAMP (a cAMP analog). Overall, cadmium disrupts the expression of genes critical for corticosteroid biosynthesis in rainbow trout head kidney slices. However, the rescue of cortisol production as well as StAR and P450scc gene expressions by cAMP analog suggests that cadmium impact occurs upstream of cAMP production. We propose that MC2R signaling, the primary step in ACTH-induced cortocosteroidogenesis, is a key target for cadmium-mediated disruption of cortisol production in trout.

Acute handling disturbance modulates plasma insulin-like growth factor binding proteins in rainbow trout (Oncorhynchus mykiss)

The effects of acute stressor exposure on proximal (growth hormone [GH]) and distal (insulin-like growth factor-I [IFG-I] and insulin-like growth factor-binding proteins [IFGBPs]) components of the somatotropic axis are poorly understood in finfish. Rainbow trout (Oncorhynchus mykiss) were exposed to a 5-min handling disturbance to mimic an acute stressor episode, and levels of plasma GH, IGF-I, and IGFBPs at 0, 1, 4, and 24 h post-stressor exposure were measured. An unstressed group was also sampled at the same clock times (09:00, 10:00, 13:00, and 08:00 [the following day]) as acute stress sampling to determine temporal changes in the above somatotropic axis components. The acute stressor transiently elevated plasma cortisol and glucose levels at 1 and 4 h post-stressor exposure, whereas no changes were seen in the unstressed group. Plasma GH levels were not affected by handling stress or sampling time in the unstressed animals. Plasma IGF-I levels were significantly depressed at 1 and 4 h post-stressor exposure, but no discernible temporal pattern was seen in the unstressed animals. Using a western ligand blotting technique, we detected plasma IGFBPs of 21, 32, 42, and 50 kDa in size. The plasma levels of the lower-molecular-weight IGFBPs (21 and 32 kDa) were unaffected by handling stressor, nor were there any discernible temporal patterns in the unstressed animals. By contrast, the higher-molecular-weight IGFBPs (42 and 50 kDa) were affected by stress or time of sampling. Levels of the 42-kDa IGFBP levels significantly decreased over the sampling period in unstressed control animals, but this temporal drop was eliminated in stressed animals. Levels of the 50-kDa IGFBPs also decreased significantly over the sampling time in unstressed trout, whereas handling disturbance transiently increased levels of this IGFBP at 1 h but not at 4 and 24 h post-stressor exposure compared with the control group. Overall, our results suggest that acute stress adaptation involves modulation of plasma IGF-1 and high-molecular-mass IGFBP levels (42 and 50 kDa) in rainbow trout.

Stirring up new ideas about the regulation of the hypothalamic-pituitary-interrenal axis in zebrafish (Danio rerio)

The dynamic relationships between the changes in cortisol synthesis during and after a stressor and the expression pattern of the key genes that regulate the different levels of the hypothalamic-pituitary-interrenal (HPI) stress axis are poorly understood. This study established a novel vortex stressor and characterized its impact at all levels of the HPI axis in adult zebrafish. Exposure to a moderate vortex speed for 60 min was associated with a marked 18-fold increase in whole-body cortisol after 10 min followed by a gradual return to basal values 30 min poststress. The changes in whole-body cortisol were paralleled by increases in the expression of preoptic area corticotropin-releasing factor, pituitary prohormone convertase 1, and interrenal melanocortin 2 receptor, steroid acute regulatory protein, 11β-hydroxylase and 11β-hydroxysteroid dehydrogenase 2. The response to the vortex stressor also included delayed increases in preoptic area urotensin I and pituitary pro-opiomelanocortin mRNA levels but no change in the expression of other putative HPI axis regulators. Notably, the expression of several genes was depressed below control values 30 min poststress. These findings suggest that multiple genes at all levels of the HPI axis play an active role in the stimulation and termination of the cortisol stress response in zebrafish.

Cortisol promotes and integrates the osmotic competence of the organs in North African catfish (Clarias gariepinus Burchell): Evidence from in vivo and in situ approaches

The short-term in situ and long-term in vivo effects of cortisol were examined in North African catfish (Clarias gariepinus) to identify how this major corticosteroid integrates the osmotic competence of fish organs. In the in situ approach, the hydromineral effects of cortisol perfusion (75-300 ng ml(-1)) for 20 min were tested and the indices of hydromineral and metabolic regulations were measured in our in vivo experimental fish after three alternate intraperitoneal cortisol injections (40 and 200 ng g(-1) body mass) for 5 days. Na(+), K(+)-ATPase activity, a measure of cellular osmotic competence, responded to in situ and in vivo cortisol treatments. In situ cortisol delivery increased the Na(+), K(+)-ATPase activity in the gill (P<0.001) and kidney (P<0.001) but decreased (P<0.01) in the liver and showed no effect on intestine. In vivo cortisol treatment, on the contrary, increased Na(+), K(+)-ATPase activity in the gills (P<0.01), intestine (P<0.05) and liver (P<0.01) but decreased (P<0.05) in the kidney. As expected, plasma cortisol increased (P<0.001) with increasing doses of cortisol injections which produced direct effects on the metabolites and the mineral contents including the elevations of glucose (P<0.05), lactate (P<0.05) and Mg(2+) (P<0.05) and reductions of urea (P<0.05), Na(+) (P<0.05) and K(+) (P<0.05) in the plasma. A decline of triiodothyronine (P<0.01) occurred in the catfish after in vivo cortisol treatment and that implies a direct cortisol action on the homeostatic integration in this fish. Evidence is thus presented that in catfish cortisol regulates the whole body hydromineral and metabolite homeostasis by promoting and integrating the osmotic and metabolic functions of the multiple organ systems including liver.

Bisphenol A in oocytes leads to growth suppression and altered stress performance in juvenile rainbow trout

Background

Bisphenol A (BPA), used in the manufacture of plastics, is ubiquitously distributed in the aquatic environment. However, the effect of maternal transfer of these xenobiotics on embryonic development and growth is poorly understood in fish. We tested the hypothesis that BPA in eggs, mimicking maternal transfer, impact development, growth and stress performance in juveniles of rainbow trout (Oncorhynchus mykiss).

Methodology/Principal Findings

Trout oocytes were exposed to 0, 30 and 100 µg.mL⁻¹ BPA for 3 h in ovarian fluid, followed by fertilization. The embryos were maintained in clean water and sampled temporally over 156-days post-fertilization (dpf), and juveniles were sampled at 400-dpf. The egg BPA levels declined steadily after exposure and were undetectable after 21- dpf. Oocyte exposure to BPA led to a delay in hatching and yolk absorption and a consistently lower body mass over 152-dpf. The growth impairment, especially in the high BPA group, correlated with higher growth hormone (GH) content and lower GH receptors gene expression. Also, mRNA abundances of insulin-like growth factors (IGF-1 and IGF-2) and their receptors were suppressed in the BPA treated groups. The juvenile fish grown from the BPA-enriched eggs had lower body mass and showed perturbations in plasma cortisol and glucose response to an acute stressor.

Conclusion

BPA accumulation in eggs, prior to fertilization, leads to hatching delays, growth suppression and altered stress response in juvenile trout. The somatotropic axis appears to be a key target for BPA impact during early embryogenesis, leading to long term growth and stress performance defects in fish.

Effects of fish cytochromes P450 inducers and inhibitors on difloxacin N-demethylation in kidney of Chinese idle (Ctenopharyngodon idellus)

Cytochromes P450 (CYPs) play key roles in drug metabolism which are widely distributed in kidney in aquatic organisms. CYP(s) mainly catalyzed the N-demethylation reaction of difloxacin (DIF) biotransformation to sarafloxacin (SAR). However, limited information is available about CYP investigation in fish. In order to supply useful information on CYP(s) characterization for DIF N-demethylation, the present study assessed the effects of fish potent CYP inducers and inhibitors on DIF N-demethylation and the inductive and inhibitive enzyme kinetics in kidney of Chinese idle (Ctenopharyngodon idellus) by reversed-phase high-performance liquid chromatography (RP-HPLC). Results demonstrated that the amounts of SAR formation pretreated by β-naphthoflavone (BNF) increased by 1.1-fold and α-naphthoflavone (ANF) inhibited SAR formation level by 0.6-fold at the third day. Enzymatic parameters V(max) and Cl(int) of DIF N-demethylase were increased by 0.56- and 0.38-fold due to β-naphthoflavone (BNF) pretreatment. DIF N-demethylation inhibition by varying ANF concentrations represented a mixed-type inhibition with the value of the inhibition constants (K(i)) 12.9mg/kg. BNF and ANF are the separate typical inducer and inhibitor for CYP1A in fish. Thus, we suggest that CYP1A may be responsible for DIF N-demethylation in kidney. This study provides instructive information to ensure treatment success in fisheries medication with two or more drugs.

Regulation of steroidogenic acute regulatory protein transcription in largemouth bass by orphan nuclear receptor signaling pathways

The steroidogenic acute regulatory (StAR) protein mediates the rate-limiting step of mitochondrial transport of cholesterol for steroid biosynthesis. To investigate the regulation of this protein in lower vertebrates, we cloned the StAR coding region from large-mouth bass for analysis. Induction of the mRNA corresponded with increasing levels of plasma sex steroids in vivo. Cultures of largemouth bass ovarian follicles were exposed to dibutyryl cAMP (dbcAMP), a potent signaling molecule for steroidogenesis. StAR mRNA expression was significantly up-regulated by dbcAMP signaling, suggesting that the 5' regulatory region of the gene is functionally conserved. To further analyze its transcriptional regulation, a 2.9-kb portion of the promoter was cloned and transfected into Y-1 cells, a steroidogenic mouse adrenocortical cell line. The promoter activity was induced in a dose-responsive manner upon stimulation with dbcAMP; however, deletion of 1 kb from the 5' end of the promoter segment significantly diminished the transcriptional activation. A putative retinoic acid-related receptor-alpha/rev-erb alpha element was identified between the -1.86- and -2.9-kb region and mutated to assess its potential role in dbcAMP regulation of the promoter. Mutation of the rev-erb alpha element significantly impeded dbcAMP-induced activation. Chromatin immunoprecipitation and EMSA results revealed rev-erb alpha and retinoic acid-related receptor-alpha enrichment at the site under basal and dbcAMP-induced conditions, respectively. These results implicate important roles for these proteins previously uncharacterized for the StAR promoter. Altogether these data suggest novel regulatory mechanisms for dbcAMP up-regulation of StAR transcription in the distal part of the largemouth bass promoter.

Beta-naphthoflavone causes an AhR-independent inhibition of invasion and intracellular multiplication of Listeria monocytogenes in murine hepatocytes

We recently reported a heretofore unknown role for the aryl hydrocarbon receptor in host resistance to listeriosis in mice. Hepatocytes are an important site for Listeria monocytogenes multiplication in vivo. In this study, we investigated whether activation of AhR in TIB73 murine embryonic hepatocytes affects the ingestion and intracellular multiplication of L. monocytogenes. Treatment of TIB73 cells with the AhR agonist beta-naphthoflavone (BNF) significantly inhibited the ingestion and intracellular growth of L. monocytogenes. The inhibitory effects of BNF were dose-dependent and correlated with up-regulation of CYP1A1. Surprisingly, pretreatment with AhR antagonists (3'-MNF or alpha-naphthoflavone) or knocking-down of AhR with siRNA did not abolish the inhibitory effects of BNF. Moreover, the inhibitory effects of BNF on invasion and intracellular growth of L. monocytogenes by BNF were observed in AhR-deficient (CRL-2710), or ARNT-dysfunctional (CRL-2717) Hepa cells. We also observed similar inhibitory effects of BNF treatment using primary hepatocytes recovered from AhR(+/-) or AhR(-/-) mice. Moreover, the prototypic AhR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) did not inhibit the invasion and intracellular growth of L. monocytogenes in TIB73 cells. Mechanistic studies demonstrated that ROS, but not TNF-alpha or iNOS, plays an important role in mediating BNF-induced inhibition. In conclusion, BNF caused an AhR-independent inhibition of ingestion and intracellular multiplication of L. monocytogenes in murine hepatocytes, mediated in part by production of ROS.

Non-steroidal anti-inflammatory drugs disturb the osmoregulatory, metabolic and cortisol responses associated with seawater exposure in rainbow trout

While detectable levels of non-steroidal anti-inflammatory drugs (NSAIDs) have been reported in various aquatic habitats, little is known about the mechanism of action of these pharmaceutical drugs on organisms. Recently we demonstrated that NSAIDs disrupt corticosteroidogenesis in rainbow trout (Oncorhynchus mykiss). As cortisol is a seawater adapting hormone, we hypothesized that exposure to NSAIDs will impair the hyposmoregulatory capacity of this species in seawater. Trout were exposed to either waterborne salicylate or ibuprofen in fresh water for four days and the salinity switched to 50% seawater for two days, followed by 100% seawater and sampled two days later. NSAIDs disturbed the seawater-induced elevation in plasma osmolality and concentrations of Cl(-) and K(+), but not Na(+) in rainbow trout. This was accompanied by enhanced gill glycolytic capacity and reduced liver glycogen content in seawater with NSAIDs, suggesting enhanced metabolic demand to fuel ion pumps. While salicylate did not affect gill Na(+)/K(+)-ATPase activity, ibuprofen inhibited the seawater-induced elevation in gill Na(+)/K(+)-ATPase activity. The drugs also further enhanced the seawater-induced elevation in plasma cortisol concentration; this response was greater with salicylate compared to ibuprofen. There were no changes in the transcript levels of key proteins involved in steroidogenesis with NSAIDs, whereas gill and brain GR protein expression expression was reduced with salicylate. Altogether, salicylate and ibuprofen exposures impaired the hyposmoregulatory capacity of rainbow trout in seawater, but the mode of action of the two drugs in bringing about these changes appears distinct in trout.

Molecular biomarkers of endocrine disruption in small model fish

A wide range of environmental contaminants can interfere with hormonal regulation in vertebrates. These endocrine disrupting chemicals (EDCs) are of high relevance for human and wildlife health, since endocrine signalling controls many essential physiological processes which impact on the individual's health, such as growth and development, stress response, and ultimately reproduction and population development. Small fish represent a cost-effective model for testing potential EDCs allowing the possibility to integrate from molecular to phenotypic and functional effects. We have comprehensively reviewed exposure-effect data from four different small model fish: zebrafish, medaka, fathead minnow, and the three-spined stickleback. The majority of available data refer to EDCs interfering with reproductive hormones. However, we have also included interactions with other hormone systems, particularly the thyroid hormones. We demonstrate that the available data clearly indicates the predictive potential of molecular biomarkers, supporting the development and regulatory application of simple molecular-based screening assays using small model fish for EDC testing.

Molecular characterization, tissue-specific expression, and regulation of melanocortin 2 receptor in rainbow trout

ACTH, the primary secretagogue for corticosteroid biosynthesis, binds to melanocortin 2 receptor (MC2R) and activates the signaling cascade leading to steroid biosynthesis in the adrenal cortex. Whereas MC2R regulation has been studied using mammalian models, little is known about the molecular mechanisms involved in ACTH signaling in nonmammalian vertebrates. A full-length cDNA encoding MC2R was sequenced from rainbow trout (Oncorhynchus mykiss) interrenal tissue (analogous to the adrenal cortex in mammals) and showed about 60 and about 44% amino acid sequence similarity to teleosts and humans, respectively. Phylogenetic analysis confirmed that MC2R from all species clustered together and was distant from other MCRs. Quantitative real-time PCR revealed a marked tissue-specific difference in MC2R mRNA abundance, with the highest levels observed in the interrenal tissue, ovary, and testis. Acute ACTH, but not alpha-MSH or [Nle4, d-Phe7]-MSH, stimulation resulted in a time- and dose-related elevation in MC2R mRNA abundance in the interrenal tissue. This corresponded with higher steroidogenic acute regulatory protein and cytochrome P450 side-chain cleavage enzyme gene expression as well as elevated cortisol production. An acute stressor transiently elevated plasma ACTH and cortisol levels at 1 h, and this was followed by a significant increase in MC2R mRNA abundance at 4 h after stressor exposure. Taken together, our results demonstrate that ACTH regulation of MC2R is highly conserved in vertebrates, whereas the tissue-specific distribution of this receptor transcript level leads us to propose a role for ACTH signaling in the stressor-mediated suppression of sex steroid levels in fish.

Modulation of steroidogenesis and xenobiotic biotransformation responses in zebrafish (Danio rerio) exposed to water-soluble fraction of crude oil

The induction of CYP enzyme activities, particularly CYP1A1, through the aryl hydrocarbon receptor (AhR) in most vertebrate species is among the most studied biochemical response to planar and aromatic organic contaminant exposure. Since P450 families play central roles in the oxidative metabolism of a wide range of exogenous and endogenous compounds, interactions between the biotransformation processes and reproductive physiological responses are inevitable. Steroidogenesis is the process by which specialized cells in specific tissues, such as the gonad, brain (neurosteroids) and kidney, synthesize steroid hormones. In the present study, we evaluated the effects of water-soluble fraction (WSF) of crude oil on the xenobiotic biotransformation and steroidogenic processes in the head (brain) and whole-body tissue of a model species by transcript analysis using quantitative (real-time) polymerase chain reaction (qPCR), enzyme activities and steroid hormone (testosterone: T and 17beta-estradiol: E2) levels using enzyme immune assay (EIA). Our data showed that exposure of fish to WSF produced an apparent concentration-specific increase of AhR1, CYP1A1 and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) mRNA levels, and decrease of AhR2. On the activity level, WSF produced concentration-specific increase of ethoxyresorufin O-deethylase (EROD), benzyloxyresorufin (BROD) methoxyresorufin (MROD) and pentoxyresorufin (PROD) activities in whole-body tissue. In the steroidogenic pathway, WSF exposure produced apparent concentration-specific decrease of ER* and ERbeta, steroidogenic acute regulatory (StAR) protein, cytochrome P450 side-chain cleavage (P450scc), P450aromA and P450aromB mRNA expression. For steroid hormones, while T levels decreased, E2 levels increased in an apparent WSF concentration-specific manner. In general, the xenobiotic biotransformation and estrogenic responses showed negative relationship after exposure of zebrafish to WSF, suggesting an interaction between these physiological pathways. The relationship between WSF mediated changes in brain StAR, P450scc, 3beta-HSD, ER*alpha, ERbeta, P450aromA, P450aromB and whole-body steroid hormone levels suggests that the experimental animals might be experiencing altered neurosteroidogenesis probably through increased activity level of the biotransformation system. Thus, these responses might represent sensitive diagnostic tools for short-term and acute exposure of fish or other aquatic organisms to WSF.

Brain transcriptomics in response to beta-naphthoflavone treatment in rainbow trout: the role of aryl hydrocarbon receptor signaling

Polychlorinated biphenyls (PCBs) exposure disrupts steroid production in teleostean fishes. While this suppression of plasma steroid levels is thought to involve aryl hydrocarbon receptor (AhR) signaling, the target tissues impacted and the molecular mechanisms involved have rarely been addressed. We tested the hypothesis that AhR activation downregulates genes involved in neuroendocrine function, including the control of brain-pituitary-interrenal (BPI) and -gonadal (BPG) axes in rainbow trout. To elucidate receptor-specific signaling, we utilized a pharmacological approach using beta-naphthoflavone (BNF) and resveratrol (RVT) as AhR agonist and antagonist, respectively. The gene expression pattern in the brain was analysed using a low-density targeted trout cDNA array enriched with genes encoding proteins involved in endocrine signaling, stress response and metabolic adjustments. Upregulation of AhR and CYP1A1 gene expression with BNF and the inhibition of this response by RVT confirmed AhR-dependent signaling. RVT by itself impacted only a few genes, while BNF treatment significantly modulated the transcript level of 49 genes, many of which are involved in the neuroendocrine control of stress and reproduction. Of these, only 27% of the BNF-mediated transcriptional response was blocked by RVT, suggesting molecular regulation of neuroendocrine pathways that are also AhR-independent. Gene expression pattern for select genes seen with the microarray analysis was also confirmed using quantitative real-time PCR. Overall, our results reveal for the first time that BNF disrupts several key genes involved in the neuroendocrine control of stress and sex steroid biosynthesis, while the mode of action involves both AhR-dependent and -independent pathways in trout.

Acute and prolonged stress responses of brain monoaminergic activity and plasma cortisol levels in rainbow trout are modified by PAHs (naphthalene, beta-naphthoflavone and benzo(a)pyrene) treatment

We have investigated if treatment with two different PAHs such as naphthalene (NAP) and benzo(a)pyrene (BaP), and the PAH-like compound beta-naphthoflavone (BNF), may modify the stress responses elicited in rainbow trout by acute or prolonged stress stimuli, and the possible involvement of brain monoamines in those responses. Two experiments (acute and prolonged stress) were performed. In the acute stress experiment, fish were i.p. injected with vegetable oil alone (control) or oil containing NAP, BNF or BaP (10 mg kg(-1)), and 72 h after injection fish were acutely stressed by chasing for 15 min. In the prolonged stress experiment, a similar group-design and injection protocol were followed, but fish were submitted to severe confinement stress by maintaining fish under high stock density (70 kg fish mass m(-3)) for 72 h. The levels of cortisol, glucose and lactate were assayed in plasma. In addition, the contents of dopamine (DA), noradrenaline (NA) and serotonin (5HT), as well as their oxidized amine metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxy-3-indoleacetic acid (5HIAA) were assayed in telencephalon, hypothalamus, preoptic region, optic tectum and brain stem, as well as the pituitary. Both acute and prolonged stress stimuli increased plasma levels of cortisol, which further increase with NAP and BNF treatments after acute stress. In contrast, cortisol levels of fish exposed to prolonged stress showed a clear tendency to decrease after the treatment with BNF and BaP. Stress stimuli also increased plasma glucose levels, which were not affected by PAHs in acute stressed fish but decreased in fish exposed to prolonged stress. Increased plasma levels of lactate in fish exposed to stress decreased after PAHs treatment in acute stress but not in prolonged stress. With respect to monoaminergic systems, major changes induced by both acute and prolonged stress were increases of the metabolites DOPAC and 5HIAA and DOPAC/DA or 5HIAA/5HT ratios in several brain regions. PAHs induced alterations in the normal responses of monoaminergic systems to stress, with dopaminergic system being the most affected after acute stress, and serotonergic system after prolonged stress. Those alterations, especially after prolonged stress, showed certain parallelism with alterations of plasma cortisol levels. Thus, results suggest that in stressed fish PAH effects on plasma cortisol levels (and its derived metabolic actions) could be in part mediated by alterations on the monoaminergic systems at the CNS of rainbow trout.

beta-Naphthoflavone and benzo(a)pyrene treatment affect liver intermediary metabolism and plasma cortisol levels in rainbow trout Oncorhynchus mykiss

To assess the effects of the polycyclic aromatic hydrocarbons (PAHs) beta-naphthoflavone (beta-NF) and benzo(a)pyrene (BaP) on liver intermediary metabolism and plasma steroid hormones, immature female rainbow trout (Oncorhynchus mykiss) were intraperitoneally injected (2 microl g(-1)) with vegetable oil alone (control) or containing beta-NF or BaP (10 mg kg(-1)) and returned to their tanks; 3, 24, and 72 h after injection, 11 fish were sampled from each group. On each sampling time, plasma hormone levels (cortisol and 17beta-estradiol) and metabolic parameters in plasma (glucose, lactate, and alpha-amino acid levels) and liver (glycogen, glucose, lactate, and alpha-amino acid levels, and HK, GK, PK, LDH, G6Pase, G6PDH, FBPase, GDH, Asp-AT, and HOAD activities) were assessed. Changes described for hormonal systems resulted in an increase in plasma levels of cortisol after 24 and 72 h of treatment with both PAHs whereas no changes were noticed for 17beta-estradiol levels. Changes in intermediary metabolism described effects in several pathways due to treatment with both PAHs. These changes can be summarized as increased glucose and lactate levels in plasma, and increased glycogenolysis and gluconeogenesis in liver after 24 and 72 h of treatment with both PAHs. Furthermore, beta-NF treatment stimulated amino acid catabolism in liver. These metabolic changes can be associated with increased levels of plasma cortisol, and suggest a different metabolic behavior depending on PAHs.

Chronic oral exposure to bunker C fuel oil causes adrenal insufficiency in ranch mink (Mustela vison)

Animals living in the near-shore marine environment are predisposed to contact with chemical contaminants through land- and ocean-based activities. The release of petroleum hydrocarbons into the marine environment is a stressor to this environment and its resident wildlife. The stress response to chemical threats is dependent on an intact hypothalamic-pituitary-adrenal axis, which also may be a target to the effects of these chemicals. Ranch mink (Mustela vison) were used as surrogates for sea otters (Enhydra lutris) to examine the development of adrenal hypertrophy after chronic, oral exposure to low concentrations of bunker C fuel oil. Animals were fed three different concentrations of fuel oil (48, 520, and 908 ppm) or mineral oil (control) for 60-62 days. At the end of the exposure, blood and fecal samples were collected and organs were weighed and examined microscopically. In all fuel oil groups, exposure resulted in adrenal hypertrophy, an adaptation suggestive of adrenal activation. However, concentrations of serum and fecal glucocorticoids and serum progesterone were not elevated over control values. Hematologic parameters and serum chemistries showed no changes consistent with increased adrenal activity. In addition, adrenal glands from animals fed the higher concentrations of fuel oil contained large numbers of heavily vacuolated cells. We conclude that petroleum hydrocarbons are inducing an adrenal insufficiency that leads to the adaptive enlargement of the gland. This would increase the susceptibility of fuel oil-exposed animals to the deleterious effects of other environmental stressors.

Molecular targets of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) within the zebrafish ovary: insights into TCDD-induced endocrine disruption and reproductive toxicity

TCDD is a reproductive toxicant and endocrine disruptor, yet the mechanisms by which it causes these reproductive alterations are not fully understood. In order to provide additional insight into the molecular mechanisms that underlie TCDD's reproductive toxicity, we assessed TCDD-induced transcriptional changes in the ovary as they relate to previously described impacts on serum estradiol concentrations and altered follicular development in zebrafish. In silico computational approaches were used to correlate candidate regulatory motifs with observed changes in gene expression. Our data suggest that TCDD inhibits follicle maturation via attenuated gonadotropin responsiveness and/or depressed estradiol biosynthesis, and that interference of estrogen-regulated signal transduction may also contribute to TCDD's impacts on follicular development. TCDD may also alter ovarian function by disrupting various signaling pathways such as glucose and lipid metabolism, and regulation of transcription. Furthermore, events downstream from initial TCDD molecular-targets likely contribute to ovarian toxicity following chronic exposure to TCDD. Data presented here provide further insight into the mechanisms by which TCDD disrupts follicular development and reproduction in fish, and can be used to formulate new hypotheses regarding previously documented ovarian toxicity.

Occurrence and biological effect of exogenous steroids in the Elkhorn River, Nebraska, USA

Recent studies of surface waters in North America, Japan and Europe have reported the presence of steroidogenic agents as contaminants. The current study has three objectives: 1) to determine if steroidogenic compounds are present in the Elkhorn River, 2) to determine if sediments collected from the Elkhorn River can act as a source of steroidogenic compounds to aquatic organisms, and 3) to determine if site-specific biological effects are apparent in the hepatic gene expression of fathead minnows. Evidence was obtained using three approaches: 1) deployment of polar organic chemical integrative samplers (POCIS), 2) deployment of caged fathead minnows, and 3) a laboratory experiment in which POCIS and fish were exposed to sediments from the deployment sites. Deployment sites included: the Elkhorn River immediately downstream from a Nebraska wastewater treatment plant, two waterways (Fisher Creek and Sand Creek) likely to be impacted by runoff from cattle feeding operations, and a reference site unlikely to be impacted by waste water inputs. The POCIS extracts were analyzed for a number of natural steroids and metabolites, as well as four different synthetic steroids: ethinylestradiol, zearalonol, 17beta-trenbolone and melengestrol acetate. Estrogenic and androgenic metabolites, as well as progesterone and trace levels of melengestrol acetate were detected in POCIS deployed at each site. POCIS deployed in tanks containing field sediments from the four sites did not accumulate the synthetic steroids except for ethinylestradiol, which was detected in the aquarium containing sediments collected near the wastewater treatment plant. Fish deployed in Sand Creek and at the wastewater treatment plant experienced significantly elevated levels of gene expression for two genes (StAR and P450scc) relative to those deployed in Fisher Creek. Fish exposed to the sediments collected from Sand Creek had significantly higher levels of hepatic StAR and P450scc gene expression than did fish exposed to sediments from the two other field sites, as well as the no-sediment control tank.

IN CONCLUSION

1) detectable levels of steroidogenic compounds were detected in passive samplers deployed in the Elkhorn River, 2) sediments do not appear to be a significant source for steroidogenic compounds, and 3) site-specific differences were found in mRNA expression among the different treatment groups of fish; however, a functional explanation for these differences is not readily forthcoming.

Salicylate impacts the physiological responses to an acute handling disturbance in rainbow trout

While salicylates (non-steroidal anti-inflammatory drugs) have been detected in the aquatic environment, few studies have focused on the mechanism of action of these pharmaceuticals on aquatic organisms. We reported previously that salicylate disrupted the acute trophic hormone-stimulated corticosteroidogenesis in rainbow trout (Oncorhynchus mykiss) interrenal tissue in vitro. Here, we tested the hypothesis that this drug will inhibit the adaptive plasma cortisol response and the associated metabolic response to an acute stressor in trout. Fish were fed salicylate-laced feed (100 mg/kg body weight) for 3 days, subjected to an acute (5 min) handling disturbance and sampled 1, 4 and 24 h after the stressor exposure. Salicylate treatment attenuated the stressor-induced plasma cortisol but not glucose or lactate elevations. The disruption of cortisol response corresponded with a significant reduction in transcript levels of the steroidogenic acute regulatory protein (StAR), but not peripheral-type benzodiazepine receptor, cytochrome P450 side-chain cleavage or 11beta-hydroxylase. Salicylate did not modify the stressor-induced elevation of brain glucocorticoid receptor (GR) protein expression, while liver GR protein content was reduced. Salicylate impact on liver metabolic capacity involved depressed liver glycogen content, whereas no significant changes in liver hexokinase, glucokinase, lactate dehydrogenase, pyruvate kinase, phosphoenolpyruvate carboxykinase, aspartate aminotransferase and alanine aminotransferase activities were observed. Taken together, salicylate impairs the stressor-mediated plasma cortisol response and the associated liver metabolic capacity in trout. The mode of action of salicylate involves disruption of StAR and liver GR, two key proteins critical for cortisol production and target tissue responsiveness to this steroid, respectively.

Health of herring gulls (Larus argentatus) in relation to breeding location in the early 1990s. II. Cellular and histopathological measures

Organosomatic indices, hematological indicators of stress, and histopathological lesions were quantified for over 150 incubating herring gulls (Larus argentatus) sampled in 11 colonies throughout the Great Lakes and reference colonies in Lake Winnipeg and the Bay of Fundy. Of 21 parameters assessed, significantly more differed between Great Lakes colonies and reference colonies than between the two reference colonies. Relative adrenal, kidney, and liver masses of gulls from some Great Lakes colonies were reduced and thyroid masses increased relative to gulls from reference colonies. Foci of cellular atypia were observed in the hepatocytes of two Great Lakes gulls. Chronic periportal hepatitis, lipogranulomas and vacuolation of hepatocytes, and chronic granulomatous interstitial nephritis were more prevalent or severe in gulls from Great Lakes colonies and were associated with contaminants. The kidneys of gulls from the three most contaminated locations were damaged and functionally compromised. Interstitial nephritis was likely the most functionally significant histopathological lesion. Portal-tract fibrosis, granulomatous hepatitis, and kidney tubule dilation/obstruction and splenic enlargement were more prevalent or severe at reference sites and were associated with blood-borne parasites. Amyloid deposits were observed in the spleen, kidneys, or liver of nearly half of the gulls. Associations between the prevalence or severity of lesions and contaminant levels in gull tissues or the trophic level of their diet suggest some lesions are toxicopathic. Associations were most frequently found with planar halogenated aromatic hydrocarbons and lead. The stress response, as measured by the heterophil/lymphocyte ratio, was attenuated in gulls from Areas of Concern and associated with decreased adrenal mass. Our findings suggest that adult Great Lakes gulls suffered from chronic exposure to chemical stressors in the early 1990s sufficient to modulate endocrine function and physiological processes and induce structural changes in tissues.

The effects of prenatal PCBs on adult female paced mating reproductive behaviors in rats

Polychlorinated biphenyls (PCBs) are a family of toxicants that persist in measurable quantities in human and wildlife tissues, despite their ban in production in 1977. Some PCB mixtures can act as endocrine disrupting chemicals (EDCs) by mimicking or antagonizing the actions of hormones in the brain and periphery. When exposure to hormonally active substances such as PCBs occurs during vulnerable developmental periods, particularly prenatally or in early postnatal life, they can disrupt sex-specific patterning of the brain, inducing permanent changes that can later be manifested as improper sexual behaviors. Here, we investigated the effects of prenatal exposure to the PCB mixture Aroclor (A) 1221 on adult female reproductive behaviors in a dose-response model in the Sprague-Dawley rat. Using a paced mating paradigm that permits the female to set the timing of mating and control contact with the male during copulation, we were able to uncover significant differences in female-typical sexual activities in A1221-exposed females. Specifically, A1221 causes significant effects on mating trial pacing, vocalizations, ambulation and the female's likelihood to mate. The results further demonstrate that the intermediate treatment group has the greatest number of disrupted endpoints, suggestive of non-linear dose responses to A1221. These data demonstrate that the behavioral phenotype in adulthood is disrupted by low, ecologically relevant exposures to PCBs, and the results have implications for reproductive success and health in wildlife and women.

Disruption of glucocorticoid action by environmental chemicals: potential mechanisms and relevance

Glucocorticoids play an essential role in the regulation of key physiological processes, including immunomodulation, brain function, energy metabolism, electrolyte balance and blood pressure. Exposure to naturally occurring compounds or industrial chemicals that impair glucocorticoid action may contribute to the increasing incidence of cognitive deficits, immune disorders and metabolic diseases. Potentially, "glucocorticoid disruptors" can interfere with various steps of hormone action, e.g. hormone synthesis, binding to plasma proteins, delivery to target cells, pre-receptor regulation of the ratio of active versus inactive hormones, glucocorticoid receptor (GR) function, or export and degradation of glucocorticoids. Several recent studies indicate that such chemicals exist and that some of them can cause multiple toxic effects by interfering with different steps of hormone action. For example, increasing evidence suggests that organotins disturb glucocorticoid action by altering the function of factors that regulate the expression of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) pre-receptor enzymes, by direct inhibition of 11beta-HSD2-dependent inactivation of glucocorticoids, and by blocking GR activation. These observations emphasize on the complexity of the toxic effects caused by such compounds and on the need of suitable test systems to assess their effects on each relevant step.

Salicylate disrupts interrenal steroidogenesis and brain glucocorticoid receptor expression in rainbow trout

Varying levels of pharmaceuticals, including salicylate, ibuprofen, and acetaminophen, have been reported in the aquatic environment, but few studies have actually addressed the impact of these drugs on aquatic organisms. We tested the hypothesis that these pharmaceuticals are endocrine disruptors in fish by examining their impact on interrenal corticosteroidogenesis in rainbow trout. Indeed, acute adrenocorticotrophic hormone (ACTH)-mediated cortisol production in trout interrenal cells in vitro was significantly depressed (20-40%) by these pharmaceutical drugs. Furthermore, we investigated whether this interrenal dysfunction involved inhibition of the steroidogenic capacity in rainbow trout. To this end, we fed trout salicylate-laced feed (100 mg/kg body weight) for 3 days and assessed the transcript levels of key proteins involved in corticosteroidogenesis, including steroidogenic acute regulatory protein (StAR), peripheral-type benzodiazepine receptor (PBR), cytochrome P450 cholesterol side chain cleavage (P450scc), and 11beta-hydroxylase. Salicylate treatment did not affect the resting plasma cortisol or glucose levels, whereas the acute ACTH-stimulated cortisol production was significantly depressed in the interrenal tissue. This disruption of steroidogenesis by salicylate corresponded to a significant drop in the gene expression of StAR and PBR, but not P450scc or 11beta-hydroxylase, compared to the sham-treated fish. Also, brain glucocorticoid receptor (GR) protein content and not GR mRNA level was significantly reduced by salicylate. Taken together, salicylate is a corticosteroid disruptor in trout and the targets include the key rate-limiting step in interrenal steroidogenesis and brain glucocorticoid signaling.