Evidence for ultra-short-loop feedback in ACTH-induced interrenal steroidogenesis in coho salmon: acute self-suppression of cortisol secretion in vitro

Long-term stress induced cortisol downregulation, growth reduction and cardiac remodeling in Atlantic salmon

Stress and elevated plasma cortisol in salmonids have been linked with pathological remodeling of the heart and deterioration of fitness and welfare. However, these associations were based on biomarkers that fail to provide a retrospective view of stress. This study is the first whereby the association of long-term stress, using scale cortisol as a chronic stress biomarker, with cardiac morphology and growth performance of wild Atlantic salmon (Salmo salar) is made. Growth, heart morphology, plasma and scale cortisol levels, and expression of genes involved in cortisol regulation of the hypothalamic-pituitary-interrenal axis of undisturbed fish (control) were compared with those of fish exposed daily to stress for 8 weeks. Though scale cortisol levels showed a time-dependent accumulation in both groups, plasma and scale cortisol levels of stress group fish were 29.1% and 25.0% lower than those of control fish, respectively. These results correlated with the overall upregulation of stress-axis genes involved in the systemic negative feedback of cortisol, and local feedback via 11β-hydroxysteroid dehydrogenases, glucocorticoid and mineralocorticoid receptors in the stress treatment at the hypothalamus and pituitary level. These lower cortisol levels were, however, counterintuitive in terms of the growth performance as stress group fish grew 33.7% slower than control fish, which probably influenced the 8.4% increase in relative ventricle mass in the stress group. Though compact myocardium area between the treatments was comparable, these parameters showed significant linear correlations with scale cortisol levels, indicating the involvement of chronic stress in cardiac remodeling. These findings underscore the importance of scale cortisol as biomarker when associating chronic stress with long-term processes including cardiac remodeling.

Effects of CBD (Cannabidiol) on the physiology of Nile tilapia (Oreochromisn niloticus) as a chronic stress mitigating agent In-vivo

This study evaluates the effects of Cannabidiol (CBD) on the physiology of stressed and non-stressed Nile tilapia, reared in a recirculating aquaculture system. Tilapia were fed with and without CBD (0.001% of feed weight) and with and without hydrocortisone stress hormone (0.01% of body weight) every day for four weeks. This experiment compared the plasma cortisol, blood glucose and protein levels, liver and spleen somatic indices (HSI and SSI, respectively), and lysozyme activity of the fish. Stress group (S) had a significantly higher value than the control group (C) in two of the parameters, glucose and lysozyme activity, this is an indication of stress. CBD had a stress reducing effect under stressed conditions in lysozyme activity. Although not significant, the stress reducing effect of CBD on stress biomarkers such as glucose and HSI also seemed promising. Further investigation into the matter may not just be useful in stress mediation in aquatic organisms but may also have implications in human medicine as well.

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

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

Controlled experiments to explore the use of a multi-tissue approach to characterizing stress in wild-caught Pacific halibut (Hippoglossus stenolepis)

The integration of multiple tissues in physiological and ecological analyses can enhance methodological approaches, increase applications for data and extend interpretation of results. Previous investigations of the stress response in fish have focused primarily on cortisol levels in a single matrix-blood plasma-which confines interpretations of cortisol levels to a short temporal frame. Epidermal mucus has been proposed as an alternative or complement to plasma that may provide a view to cortisol levels over a different temporal window allowing comparative assessment. Here, we explore the potential for multi-tissue cortisol analysis using both plasma and epidermal mucus in Pacific halibut (Hippoglossus stenolepis). The relative timing at which cortisol increased and decreased in the two matrices as well as cortisol concentrations at estimated peak levels were compared in two trials after (i) inducing cortisol synthesis by adrenocorticotropic hormone (ACTH_1-24) administration and (ii) inducing cortisol elimination using cortisol (hydrocortisone, 98%) injection. The ACTH treatment elicited a peak plasma cortisol response approximately 12 hours post-injection, while mucus cortisol concentrations peaked later at approximately 62 hours post-injection. Exogenous cortisol treatments suggested relatively little transfer of cortisol from plasma to mucus, potentially reflecting differential effects of endogenous and exogenous cortisol. Our results suggest the potential utility of mucus as a sampling matrix that provides an extended window for detection of the stress response as compared to plasma. Results also suggest the utility of a multi-tissue approach to cortisol analysis with potential applications to applied fisheries research. Increased understanding of the relative scale of the cortisol response to stress (e.g. capture) will allow researchers and managers to better interpret the physiological condition and survival outcome of fish subjected to regulatory discard.

Arginine Vasotocin and Cortisol Co-regulate Vasotocinergic, Isotocinergic, Stress, and Thyroid Pathways in the Gilthead Sea Bream (Sparus aurata)

In teleosts, a complex interaction between several endocrine axes modulates physiological functions related to metabolism, stress, and osmoregulation. Although many studies in fish underline the interconnection between the hypothalamic–pituitary–interrenal (HPI) and hypothalamic–pituitary–thyroid (HPT) endocrine axes, their relationship with the vasotocinergic and isotocinergic systems remains unknown. The aim of the present study is therefore to shed light on the potential cross-regulations between HPT, HPI, and the vasotocinergic and isotocinergic axes in gilthead sea bream (Sparus aurata) at hypothalamic, hypophyseal, and plasma levels. Sea breams were administered with intraperitoneal slow-release implants containing different doses of vasotocin (the active peptide in vasotocinergic system) or cortisol (the last component of HPI axis). Plasma osmolality was higher in active neuropeptides vasotocin (Avt)-treated fish, indicating an osmoregulatory function of this hormone. Low concentrations of Avt increased hypothalamic arginine vasotocin precursor (avt) mRNA levels and increased Avt storage in the pituitary. Avt treatment down-regulated hypothalamic arginine vasotocin receptor v1a-type (avtrv1a), suggesting a negative paracrine co-regulation of the HPI axis due to the close location of avtrv1a and adrenocorticotropin hormone (Acth) cells in the anterior pituitary. Furthermore, the up-regulation observed in arginine vasotocin receptor v2-type (avtrv2) suggests their involvement in metabolic and cortisol-related pathways in the hypothalamus. The decrease in isotocin (It) pituitary storage and the up-regulation of it receptor, observed in the Avt-treated group, reinforce the idea of an interconnection between the vasotocinergic and isotocinergic systems. Cortisol and Avt administration each inhibited the HPI axis, down-regulating crh gene expression in the absence of variations in corticotropin releasing hormone binding protein (crhbp). Finally, both hormonal treatments activated the HPT axis via up-regulation of trh and down-regulation of thrb. Our results provide evidence for strong interactions among the Avt/It, HPI, and HPT axes of marine teleosts, particularly at the hypothalamic level.

Regulation of the corticosteroid signalling system in rainbow trout HPI axis during confinement stress

This study aims to shed light on corticosteroid regulation of stress in teleost fish with focus on the corticosteroid signalling system. The role of the mineralocorticoid-like hormone 11-deoxycorticosterone (DOC) in fish is still enigmatic, as is the function of the mineralocorticoid receptor, MR. Low plasma DOC levels and ubiquitous tissue distribution of MR question the physiological relevance of the mineralocorticoid-axis. Furthermore, the particular purpose of each of the three corticosteroid receptors in fish, the glucocorticoid receptors, GR1 and GR2, and the MR, is still largely unknown. Therefore we investigate the regulation of cortisol and DOC in plasma and mRNA levels of MR, GR1 and GR2 in the HPI-axis tissues (hypothalamus, pituitary and interrenal gland) during a detailed confinement stress time-course. Here we show a sustained up-regulation of plasma DOC levels during a confinement stress time-course. However, the low DOC levels compared to cortisol measured in the plasma do not favour an activity of DOC through MR receptors. Furthermore, we show differential contribution of the CRs in regulation and control of HPI axis activity following confinement stress. Judged by the variation of mRNA levels negative feedback regulation of cortisol release occurs on the level of the pituitary via MR and on the level of the interrenal gland via GR2. Finally, asa significant effect of confinement stress on CR expressions was observed in the pituitary gland, we completed this experiment by demonstrating that corticosteroid receptors (GR1, GR2 and MR) are co-expressed in the ACTH cells located in the adenohypophysis. Overall, these data suggest the involvement of these receptors in the regulation of the HPI axis activity by cortisol.

Russian sturgeon cultured in a subtropical climate shows weaken innate defences and a chronic stress response

Russian sturgeon (Acipenser gueldenstaedtii) has been successfully farmed in Uruguay for the past ten years. However, during the Uruguayan summer fish endure high water temperatures and increased bacterial infections that threaten aquaculture. Our understanding of sturgeon's immune system and its interplay with environmental factors like temperature is almost unknown. This study analysed the way in which seasonal variations affect enzymatic blood components of Russian sturgeon's innate defences, including the serum alternative complement pathway (ACP), ceruloplasmin (Cp) and lysozyme activities. Results showed that summertime conditions in the farm altered these defences in different ways, inducing a significant decrease in ACP and Cp, and an increase in lysozyme. In addition, serum levels of total protein and cortisol decreased in summer, suggesting a chronic stress response was induced in parallel. Subsequently, we analysed whether the increase in water river temperature during summer could account for the observed results. To that end, we acclimated juvenile sturgeons to mild (18 °C) or warm (24 °C) temperatures for 37 days. Like in summer, sturgeons exposed to 24 °C showed lower levels of serum ACP, Cp and total proteins, together with a progressive decrease in body weight and increased fish mortality. Administration of an immunostimulant containing Se and Zn slightly reverted the temperature-induced effects on sturgeon's defences. Altogether, our study provides novel data on various physiological parameters of the Russian sturgeon and highlights the impact warm temperature has on stress and innate immunity in this chondrostean fish.

The relationship between handling time and cortisol release rates changes as a function of brain parasite densities in California killifish Fundulus parvipinnis

This study validated a technique for non-invasive hormone measurements in California killifish Fundulus parvipinnis, and looked for associations between cortisol (a stress hormone) and 11-ketotestosterone (KT, an androgen) release rates and the density or intensity of the trematode parasites Euhaplorchis californiensis (EUHA) and Renicola buchanani (RENB) in wild-caught, naturally infected F. parvipinnis. In experiment 1, F. parvipinnis were exposed to an acute stressor by lowering water levels to dorsal-fin height and repeatedly handling the fish over the course of an hour. Neither parasite was found to influence cortisol release rates in response to this acute stressor. In experiment 2, different F. parvipinnis were exposed on four consecutive days to the procedure for collecting water-borne hormone levels and release rates of 11-KT and cortisol were quantified. This design examined whether F. parvipinnis perceived the water-borne collection procedure to be a stressor, while also exploring how parasites influenced hormone release rates under conditions less stressful than those in experiment 1. No association was found between RENB and hormone release rates, or between EUHA and 11-KT release rates. The interaction between EUHA density and handling time, however, was an important predictor of cortisol release rates. The relationship between handling time and cortisol release rates was negative for F. parvipinnis harbouring low or intermediate density infections, and became positive for fish harbouring high densities of EUHA.

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.

Crowding stress inhibits serotonin 1A receptor-mediated increases in corticotropin-releasing factor mRNA expression and adrenocorticotropin hormone secretion in the Gulf toadfish

Stimulation of the serotonin 1A (5-HT1A) receptor subtype by 5-HT has been shown to result in an elevation in plasma corticosteroid levels in both mammals and several species of teleost fish, including the Gulf toadfish (Opsanus beta); however, in the case of teleost fish, it is not clearly known at which level of the hypothalamic-pituitary-interrenal axis the 5-HT1A receptor is stimulated. Additionally, previous investigations have revealed that chronic elevations of plasma cortisol mediate changes in brain 5-HT1A receptor mRNA and protein levels via the glucocorticoid receptor (GR); thus, we hypothesized that the function of centrally activated 5-HT1A receptors is reduced or abolished as a result of chronically elevated plasma cortisol levels and that this response is GR mediated. Our results are the first to demonstrate that intravenous injection of the 5-HT1A receptor agonist, 8-OH-DPAT, stimulates a significant increase in corticotropin-releasing factor (CRF) precursor mRNA expression in the hypothalamic region and the release of adrenocorticotropic hormone (ACTH) from the pituitary of teleost fish compared to saline-injected controls. We also provide evidence that cortisol, acting via GRs, attenuates the 5-HT1A receptor-mediated secretion of both CRF and ACTH.

Elevated cortisol inhibits adrenocorticotropic hormone- and serotonin-stimulated cortisol secretion from the interrenal cells of the Gulf toadfish (Opsanus beta)

Stimulation of the toadfish 5-HT(1A) receptor by serotonin (5-hydroxytryptamine; 5-HT) or 8-OH-DPAT, a 5-HT(1A) receptor agonist, results in a significant elevation in plasma cortisol. Conversely, chronic elevation of plasma cortisol has been shown to decrease brain 5-HT(1A) receptor mRNA and protein levels via the glucocorticoid receptor (GR); however, there appears to be a disconnect between brain levels of the receptor and cortisol release. We hypothesized that elevated plasma cortisol would inhibit both adrenocorticotropic hormone (ACTH)- and 5-HT-stimulated cortisol release from the interrenal cells of Gulf toadfish, that ACTH sensitivity would not be GR-mediated and 5-HT-stimulated cortisol release would not be via the 5-HT(1A) receptor. To test these hypotheses, interrenal cells from uncrowded, crowded, vehicle-, and cortisol-implanted toadfish were incubated with either ACTH, 5-HT or 5-HT receptor agonists, and cortisol secretion was measured. Incubation with ACTH or 5-HT resulted in a stimulation of cortisol secretion in uncrowded toadfish. Cortisol secretion in response to ACTH was not affected in crowded fish; however, interrenal cells from cortisol-implanted toadfish secreted significantly less cortisol than controls, a response that was not reversed upon treatment with the GR antagonist RU486. 5-HT-stimulated cortisol release was significantly lower from both crowded and cortisol-implanted toadfish interrenal cells compared to controls. Incubation with either a 5-HT(4) or a 5-HT(2) receptor agonist significantly stimulated cortisol secretion; however, incubation with 8-OH-DPAT did not, suggesting that the 5-HT(1A) receptor is not a mediator of cortisol release at the level of the interrenal cells. Combined, these results explain in part the disconnect between brain 5-HT(1A) levels and cortisol secretion.

High levels of corticosterone, and gene expression of star, cyp17a2, hsd3b, cyp21, hsd11b2 during acute stress in common carp with interrenal hyperplasia

We investigated the acute stress response in a common carp strain (E5) with interrenal hyperplasia due to 17α-hydroxylase deficiency, and in an isogenic standard (STD) carp strain. Cortisol, corticosterone and the head kidney-somatic index were measured during and after a 3 h net confinement stress. Star, cyp17a2, hsd3b, cyp21, hsd11b2 mRNA levels were measured in head kidneys using real-time qPCR. The results show very high corticosterone levels and enlargement of the head kidney in E5 fish. This is the first report in a teleost fish showing a significant increase of corticosterone levels in response to stress due to interrenal hyperplasia. The high levels of corticosterone in E5 suggest that corticosterone is not converted to aldosterone in common carp. star and hsd3b mRNA levels were significantly higher in E5 compared to STD fish, while cyp17a2 levels were significantly lower in E5. In contrast to E5, star levels did not change during stress and recovery in STD, suggesting that the enzyme is regulated in a different manner in E5 and STD fish. In E5, the levels of cyp17a2 dropped below control values after 20 min stress. These findings strongly suggest that cyp17a2 is impaired at (post)-transcriptional level. As a consequence the accumulated precursor (pregnenolone) is not converted to cortisol, but to corticosterone. In contrast to STD, significant levels of cortisol could not be detected in E5. Finally, hsd11b2 mRNA levels were significantly lower in E5 compared to STD, and did not change during stress and recovery. These results support the idea that hsd11b2 is involved in the conversion of physiologically active cortisol to inactive cortisone, as reported earlier for STD carp. In conclusion our results show high levels of corticosterone in E5 and differences in star and mRNA levels of steroidogenic genes between E5 and STD carp during net confinement stress.

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.

Effects of chronic manipulation of adrenocorticotropic hormone levels in Chinook salmon on expression of interrenal steroidogenic acute regulatory protein and steroidogenic enzymes

The effects of chronic exposure to adrenocorticotropic hormone (ACTH) or the synthetic glucocorticoid dexamethasone (DEX) on the expression of genes involved in cortisol synthesis were examined using quantitative RT-PCR and immunohistochemistry. Juvenile Chinook salmon were treated with either ACTH via micro-osmotic pumps or with DEX via a lipid-based sustained release vehicle. Plasma cortisol levels were significantly elevated in ACTH-treated fish after 1 day, with a significant reduction in this effect with increasing treatment duration. ACTH also appeared to cause progressive hyperplasia of interrenal cells. Steroidogenic acute regulatory protein (StAR) and cytochrome P450 side chain cleavage enzyme (P450scc) transcripts but not 3β-hydroxysteroid dehydrogenase-isomerase (3β-HSD) or cytochrome P450 11β-hydroxylase (P45011β) transcripts in head kidneys significantly increased after 5 days of ACTH treatment. Significant linear relationships between plasma cortisol levels and transcript levels were identified at day 1 and day 5 for StAR, and day 5 for P450scc. Increased immunoreactivity for P450scc was observed in interrenal cells of ACTH-treated fish after 5 and 10 days. No effect of ACTH on 3β-HSD immunoreactivity was apparent at any time point. P45011β immunoreactivity was more intense after 5 days treatment with ACTH. DEX significantly reduced resting plasma cortisol levels and induced interrenal cell atrophy. Although no significant effect of treatment with DEX was found for any transcript, immunoreactivity for P450scc and P45011β appeared to be reduced. These results indicate that StAR and P450scc are subject to transcriptional regulation by chronic changes in ACTH levels.

Cortisol receptor expression differs in the brains of rainbow trout selected for divergent cortisol responses

In rainbow trout (Oncorhynchus mykiss), selection for divergent post-stress plasma cortisol levels has yielded low (LR)- and high (HR) responsive lines, differing in behavioural and physiological aspects of stress coping. For instance, LR fish display prolonged retention of a fear response and of previously learnt routines, compared to HR fish. This study aims at investigating putative central nervous system mechanisms controlling behaviour and memory retention. The stress hormone cortisol is known to affect several aspects of cognition, including memory retention. Cortisol acts through glucocorticoid receptors 1 and 2 (GR1 and 2) and a mineralcorticoid receptor (MR), all of which are abundantly expressed in the salmonid brain. We hypothesized that different expressions of MR and GRs in LR and HR trout brains could be involved in the observed differences in cognition. We quantified the mRNA expression of GR1, GR2 and MR in different brain regions of stressed and non-stressed LR and HR trout. The expression of MR was higher in LR than in HR fish in all brain parts investigated. This could be associated with reduced anxiety and enhanced memory retention in LR fish. MR and GR1 expression was also subject to negative regulation by stress in a site-specific manner.

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.

Whole-body cortisol response of zebrafish to acute net handling stress

Zebrafish, Danio rerio, are frequently handled during husbandry and experimental procedures in the laboratory, yet little is known about the physiological responses to such stressors. We measured the whole-body cortisol levels of adult zebrafish subjected to net stress and air exposure at intervals over a 24 h period; cortisol recovered to near control levels by about 1 h post-net-stress (PNS). We then measured cortisol at frequent intervals over a 1 h period. Cortisol levels were more than 2-fold higher in net stressed fish at 3 min PNS and continued to increase peaking at 15 min PNS, when cortisol levels were 6-fold greater than the control cortisol. Mean cortisol declined from 15 to 60 min PNS, and at 60 min, net-stressed cortisol was similar to control cortisol. Because the age of fish differed between studies, we examined resting cortisol levels of fish of different ages (3, 7, 13, and 19 months). The resting cortisol values among tanks with the same age fish differed significantly but there was no clear effect of age. Our study is the first to report the response and recovery of cortisol after net handling for laboratory-reared zebrafish.

Evidence for the onset of feedback regulation of cortisol in larval summer flounder

We investigated the functional development of feedback regulation of cortisol levels during early development in a marine teleost, summer flounder, using a novel pharmaceutical approach. Larvae were immersed for 4h in the glucocorticoid agonist dexamethasone (20 microM) and/or the glucocorticoid-receptor antagonist RU486 (0.12 microM) at 1, 7, or 21 days after hatching. The hypothesis was that, if feedback regulation were operational, tissue cortisol concentrations would be suppressed by dexamethasone and stimulated by RU486. Whole-body cortisol content of 1-day-old larvae was significantly decreased from 0.32 ng/g body weight (mean) to 0.08-0.12 ng/g by immersion in dexamethasone, RU486, or both, perhaps due to displacement of cortisol from the yolk sac. There were no changes in cortisol content among treatment groups in 7-day-old larvae. The expectations of our hypothesis were met in 21-day-old larvae. Immersion in RU486 increased cortisol content from 0.29 ng/g (control) to 2.00 ng/g, whereas immersion in dexamethasone (with or without RU486) suppressed cortisol to 0.03-0.04 ng/g. The results indicate that a fully functional hypothalamic-pituitary-interrenal axis is established by 3 weeks after yolk-sac resorption, but before the onset of metamorphosis in summer flounder. This is the earliest detection of feedback regulation in a teleost fish.

Stress-induced facilitation of the cortisol response in 17alpha-hydroxylase deficient XX mas-1/mas-1 carp (Cyprinus carpio)

Facilitation of the stress response results from a reduction of the inhibitory effects of circulating corticosteroids, allowing an animal to respond to a novel stressor. In this study, the existence of a facilitated cortisol stress response in normal (STD) and 17alpha-hydroxylase deficient XX mas-1/mas-1 (E5) carp was investigated. E5 carp had previously been characterized as having a low cortisol response to stress. Fish were subjected to either cortisol feeding or daily-acute stress, from 45 until 140 days post-hatch (dph) and were then subjected to a novel net-confinement stressor at 141 dph. Growth of E5 fish was reduced in both the daily-acute stress and cortisol-fed groups, but STD fish were only affected by daily-acute stress. Cortisol feeding had no effect on the stress response of STD fish but daily-acute stress significantly inhibited the response to a subsequent novel stressor. In contrast, daily-acute stress facilitated the cortisol stress response of E5 fish to a novel stressor, while cortisol feeding inhibited the cortisol response. Facilitation was accompanied by significant enlargement of the head-kidney tissue (which contains the steroidogenic interrenal tissue) in E5 fish. To our knowledge this is the first report of stress-induced facilitation in a lower vertebrate.

Hypocorticism and interrenal hyperplasia are not directly related to masculinization in XX mas(-1)/mas(-1) carp, Cyprinus carpio

This study reports on a homozygous XX male strain of common carp (E5), which fail to mount a normal cortisol stress response. Earlier classical genetic analysis had indicated that masculinization of E5 fish was caused by a putative recessive mutation (mas(-1)/mas(-1)). Hypocorticism in E5 fish was studied to investigate if it was related to masculinization. Head-kidney tissues isolated from E5 fish showed a low cortisol-producing capacity in vitro, and also demonstrated a reduced sensitivity to stimulation with ACTH, when compared with an isogenic XY male carp strain (STD). There was no strain difference in androgen production by head-kidney tissues in vitro. E5 fish exhibited significant hyperplasia of the interrenal tissue (adrenal homologue of teleost fish) located in the head-kidney. Conversion of pregnenolone was significantly lower in E5 head-kidney homogenates, compared to STD homogenates, however, no strain difference was found in the conversion of 17alpha-hydroxyprogesterone into cortisol. Gonad homogenates incubated with pregnenolone showed no strain difference in conversion to corticosteroids and androgens. Results indicate that the interrenal hyperplasia and hypocorticism in this strain of carp may be due to a dysfunction of the 17alpha-hydroxylase activity of the enzyme P450c17 in the interrenal, but that this defect may not be the primary factor resulting in masculinization of these XX genotypes.

11beta-hydroxysteroid dehydrogenase complementary deoxyribonucleic acid in rainbow trout: cloning, sites of expression, and seasonal changes in gonads

11beta-Hydroxysteroid dehydrogenases (11beta-HSDs) are important steroidogenic enzymes for catalyzing the interconversion of active glucocorticoid (cortisol and corticosterone) and inert 11-keto forms (cortisone and 11-dehydrocorticosterone) in mammals. In teleosts, 11beta-HSD also plays a role in the production of the predominant androgen, 11-ketotestosterone, in male fish. In this study we cloned cDNAs encoding rainbow trout 11beta-HSD (rt11beta-HSD) from testes and head kidney. The predicted amino acid sequence, hydrophobicity analysis, and transient transfection assays with rt11beta-HSD in HEK293 cells showed that rt11beta-HSD is a homolog of mammalian 11beta-HSD type 2. rt11beta-HSD transcripts are present in steroidogenic tissues and in a number of other tissues. Strong in situ hybridization signals for rt11beta-HSD transcripts were found in Leydig cells of testes, in thecal cells of the early vitellogenic ovarian follicles, and in thecal and granulosa cells of the midvitellogenic and postovulatory follicles. Weaker signals were also found in head kidney interrenal cells from juvenile rainbow trout. Seasonal changes in rt11beta-HSD transcripts in testes showed a pattern similar to that of stress-induced serum cortisol levels, but not to serum androgen levels. High levels of rt11beta-HSD transcripts were found in ovarian follicles from late vitellogenesis through ovulation. These results raise the possibility of a role for rt11beta-HSD in the protection of developing gonads from the inhibitory effects of stress-induced cortisol.

Survey of the Adrenal Homolog in Teleosts

The adrenal homolog of teleosts is not a compact organ as the adrenal glands of most vertebrates but is composed by aminergic chromaffin and interrenal steroidogenic cells located mostly inside the head kidney that, in this taxon, generally has a hematopoietic function. The two tissues can be mixed, adjacent, or completely separated and line the endothelium of the venous vessels or are located in close proximity. The chromaffin cells in some species are also present in the posterior kidney. Histological and ultrastructural work revealed cytological peculiarities of both types of cells as compared to those of other vertebrate species. In particular, the interrenal ones can show some variations in ultrastructure depending on sex, time of the year, and relation to stress events. A periodic renewal of the whole gland tissue is also sustained by some studies. Research regarding development is scanty as compared to mammals and most studies go back to the early years of the past century. The adrenal homolog of teleosts is under hormonal and neuronal control. Moreover, local paracrine interactions may play an important role in modulating a system involved in stress response and osmoregulation. Most previous studies involved a few species with the object of intensive rearing for commercial purposes; in fact cortisol, the main hormone secreted by the interrenal cells, can also influence reproduction and growth. This review summarizes data from morphocytological work and refers to other excellent reviews regarding physiology. Some of the results are compared to data available from other fishes and vertebrate classes with the aim of including them in an evolutionary and environmental framework.

Modulation of catecholamine release and cortisol secretion by social interactions in the rainbow trout, Oncorhynchus mykiss

The objective of the present study was to investigate the effect of social status on the ability of rainbow trout to secrete the stress hormones, cortisol, and catecholamines. Rainbow trout were confined in pairs for six days to permit the formation of dominance hierarchies. An in situ saline-perfused posterior cardinal vein (PCV) preparation was then used to assess cortisol secretion or release of the catecholamine hormones, adrenaline and noradrenaline, in response to the inclusion of appropriate secretagogues in the perfusate. Fish identified as subordinate on the basis of their behaviour showed a characteristic elevation of circulating plasma cortisol concentrations when compared with dominant fish. When the interrenal cells were stimulated in situ with adrenocorticotropic hormone, subordinate fish displayed a significantly lower rate of cortisol secretion than dominant fish. However, social status had no significant effect on either adrenaline or noradrenaline secretion rates upon stimulation of the chromaffin cells in situ with acetylcholine. These results suggest that the chronic elevation of plasma cortisol associated with subordinate social status in rainbow trout reduces the sensitivity of the cortisol-secreting interrenal cells, presumably through negative feedback mechanisms.

Hematological effects of high dose of cortisol on the carp (Cyprinus carpio L.): cortisol effect on the carp blood

The level of circulating cortisol and peripheral blood parameters were determined in carp age 2 years (K(2)) 24, 72, and 216 h after a single intraperitoneal injection of a high dose (200 mg x kg(-1) body wt) of hydrocortisone. The most striking effect of cortisol was manifest as a significant change in the percentage composition of leukocytes, whose number per unit volume of blood remained relatively constant. A profound lymphopenia and eosinopenia were compensated for in the general balance by an increased number of circulating promyelocytes and myelocytes as well as metamyelocytes and mature polymorphonuclear neutrophilic granulocytes. The results and their possible reasons are discussed on the background of literature data.

Pituitary proopiomelanocortin-derived peptides and hypothalamus-pituitary-interrenal axis activity in gilthead sea bream (Sparus aurata) during prolonged crowding stress: differential regulation of adrenocorticotropin hormone and alpha-melanocyte-stimulating hormone release by corticotropin-releasing hormone and thyrotropin-releasing hormone

Plasma levels of cortisol, growth hormone (GH), adrenocorticotropin hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), N-acetyl-beta-endorphin, in vitro ACTH-stimulated cortisol secretion, and in vitro corticotropin-releasing hormone (CRH)- and thyrotropin-releasing hormone (TRH)-stimulated ACTH and alpha-MSH secretion were investigated in gilthead sea bream exposed to high stocking density (30 kg m(-3)) for 23 days. Within 3 days after the onset of crowding, plasma levels of cortisol, ACTH, alpha-MSH, and N-acetyl-beta-endorphin were above control values. After 7 days, plasma parameters had returned to control levels, but at 23 days, cortisol, alpha-MSH, and N-acetyl-beta-endorphin levels were again elevated over controls, indicating a long-term activation of the melanotrope cells. In contrast, crowding stress elicited a prolonged reduction in plasma GH levels concomitant with the increased hypothalamus-pituitary-interrenal axis (HPI) activation. Crowding stress enhanced cortisol secretory activity of the unstimulated interrenal cells. However, interrenal tissue from crowded fish in vitro displayed an attenuated response to ACTH stimulation compared with tissue from control fish, indicating a desensitization of these cells to ACTH during crowding. The involvement of pituitary proopiomelanocortin-derived peptides in the HPI axis of sea bream is indicated by the observed modulation of the CRH and TRH responsiveness of the corticotropes and melanotropes in crowded fish. At day 1, when there were crowding-induced plasma increases in ACTH and alpha-MSH, there was an attenuated CRH-stimulated but not TRH-stimulated, ACTH release. However, at that time, CRH- and TRH-induced responses of alpha-MSH secretion, and the unstimulated secretory activity of the MSH cells, were enhanced in crowded sea bream. These data provide evidence for stimulatory roles of multiple hypothalamic (CRH and TRH) and pituitary (ACTH and alpha-MSH) peptides in the activation of the hypothalamus-pituitary-interrenal axis under crowding conditions in sea bream.

Native urotensins influence cortisol secretion and plasma cortisol concentration in the euryhaline flounder, platichthys flesus

Adrenocorticotrophic hormone (ACTH) and flounder urotensins I and II (UI and UII) stimulate cortisol secretion of isolated interrenal/head kidney preparations of seawater (SW)-adapted flounder. UI and UII at concentrations of 10(-6) and 10(-7) M, respectively, increased cortisol secretion when acting on SW-derived interrenal but did not affect cortisol secretion in tissue derived from freshwater (FW) fish. Combined UI and UII had no synergistic or additive steroidogenic action, but either 10(-7) M UI or 10(-7) M UII in combination with ACTH produced a very marked, additive, or synergistic steroidogenic response, most apparent on interrenal derived from FW fish. These results suggest that urotensins enhance the steroidogenic action of ACTH in flounder. In all cases, significant steroidogenesis was apparent within 1 h postperifusion of ligands. In SW-adapted flounder intraarterial infusion of UII in vivo caused a concentration-dependent increase in plasma cortisol concentration within 1 h after infusion, while after 5 x 10(-6) M UI infusion a similar trend was evident but this did not achieve statistical significance. The data suggest that the caudal neurosecretory system may control interrenal cortisol secretion, to modulate cortisol secretion independently of the hypophysial axis, perhaps in response to specific stress-induced or osmoregulatory challenge.

Cloning and expression of two proopiomelanocortin mRNAs in the common carp (Cyprinus carpio L.)

Proopiomelanocortin (POMC) is the precursor for a number of biologically active peptides such as adrenocorticotropic hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH) and beta-endorphin. It is well known that these peptides are involved in the stress response in fish as well as in mammals. We have cloned two different carp POMC cDNAs called, POMC-I and POMC-II. The nucleotide sequences of 955 bp for POMC-I and 959 bp for POMC-II share 93.5% identity in their cDNAs, and the deduced amino acid sequences (both 222 amino acids) are 91.4% identical. In the ACTH and beta-MSH domain, two amino acid substitutions are found, whereas alpha-MSH and beta-endorphin are identical. For beta-MSH, the serine replacement (in POMC-I) by a glycine (in POMC-II) results in a putative amidation site Pro-X-Gly for POMC-II. We used RT-PCR to show that both POMC mRNAs are expressed in the hypophysis, hypothalamus and other parts of the brain of a single fish. Furthermore, in a phylogenetic tree based on POMC sequences the divergence of carp POMC-I and -II from tetraploid animals (salmon, trout and xenopus) is demonstrated.

Characterisation of glucocorticoid receptors in peripheral blood leukocytes of Carp, Cyprinus carpio L

Binding studies with [3H]cortisol revealed the presence of a single class of cortisol-binding sites on carp peripheral blood leukocytes (PBL). These binding sites showed high affinity (Kd of 3.8 nM) and low capacity (490 binding sites per cell), indicative of receptor binding. Affinity for cortisone was 254-fold lower than for cortisol. Affinity for the two synthetic glucocorticoids dexamethasone and triamcinolone acetonide (TA) was 4- and 10-fold higher than for cortisol, respectively. Further evidence for the GR character of the receptor came from results showing that cortisol induced apoptosis, which could be blocked by the glucocorticoid analogue RU486. A single meal of cortisol-containing food elevated plasma cortisol concentrations and decreased GR density in PBL, as measured 3 h later. The percentage of circulating B lymphocytes also decreased. Cortisol-induced redistribution of B lymphocytes from the blood, due to cortisol treatment, may explain the decrease of GR numbers in PBL, although downregulation of available GR remains possible.