Hypothalamic-pituitary-interrenal Axis Research Articles

Brain and Pituitary Response to Vaccination in Gilthead Seabream (Sparus aurata L.).

Vaccination is a widely used therapeutical strategy in aquaculture, but whether vaccination elicits stress responses in the central neuroendocrine system and enhances the crosstalk between the immune and endocrine systems in the brain or pituitary after vaccination is unclear. To answer this question two experiments using two different vaccine exposure routes, i.e., bath or intraperitoneal (i.p.) injection, were carried out on gilthead seabream (Sparus aurata L.). In the first one, the stress responses of fish subjected to waterborne Vibrio anguillarum bacterin were compared with responses after air exposure or their combination. In the second experiment, fish were subjected to an intraperitoneal injection of Lactococcus garvieae bacterin and we assessed the central stress response and also whether or not a significant immune response was induced in brain and pituitary. In both experiments, blood, brain and pituitary tissues were collected at 1, 6, and 24 h post stress for plasma hormone determination and gene expression analysis, respectively. Results indicated that bath vaccination induced a decreased central stress response compared to air exposure which stimulated both brain and pituitary stress genes. In the second experiment, injection vaccination kept unchanged plasma stress hormones except cortisol that raised at 6 and 24 h. In agreement, non-significant or slight changes on the transcription of stress-related genes were recorded, including the hormone genes of the hypothalamic pituitary interrenal (HPI) axis and other stress markers such as hsp70, hsp90, and mt genes in either brain or pituitary. Significant changes were observed, however, in crhbp and gr. In this second experiment the immune genes il1β, cox2, and lys, showed a strong expression in both brain and pituitary after vaccination, notably il1β which showed more than 10 fold raise. Overall, vaccination procedures, although showing a cortisol response, did not induce other major stress response in brain or pituitary, regardless the administration route. Other than main changes, the alteration of crhbp and gr suggests that these genes could play a relevant role in the feedback regulation of HPI axis after vaccination. In addition, from the results obtained in this work, it is also demonstrated that the immune system maintains a high activity in both brain and pituitary after vaccine injection.

Environmental Cycles, Melatonin, and Circadian Control of Stress Response in Fish.

Fish have evolved a biological clock to cope with environmental cycles, so they display circadian rhythms in most physiological functions including stress response. Photoperiodic information is transduced by the pineal organ into a rhythmic secretion of melatonin, which is released into the blood circulation with high concentrations at night and low during the day. The melatonin rhythmic profile is under the control of circadian clocks in most fish (except salmonids), and it is considered as an important output of the circadian system, thus modulating most daily behavioral and physiological rhythms. Lighting conditions (intensity and spectrum) change in the underwater environment and affect fish embryo and larvae development: constant light/darkness or red lights can lead to increased malformations and mortality, whereas blue light usually results in best hatching rates and growth performance in marine fish. Many factors display daily rhythms along the hypothalamus-pituitary-interrenal (HPI) axis that controls stress response in fish, including corticotropin-releasing hormone (Crh) and its binding protein (Crhbp), proopiomelanocortin A and B (Pomca and Pomcb), and plasma cortisol, glucose, and lactate. Many of these circadian rhythms are under the control of endogenous molecular clocks, which consist of self-sustained transcriptional-translational feedback loops involving the cyclic expression of circadian clock genes (clock, bmal, per, and cry) which persists under constant light or darkness. Exposing fish to a stressor can result in altered rhythms of most stress indicators, such as cortisol, glucose, and lactate among others, as well as daily rhythms of most behavioral and physiological functions. In addition, crh and pomca expression profiles can be affected by other factors such as light spectrum, which strongly influence the expression profile of growth-related (igf1a, igf2a) genes. Additionally, the daily cycle of water temperature (warmer at day and cooler at night) is another factor that has to be considered. The response to any acute stressor is not only species dependent, but also depends on the time of the day when the stress occurs: nocturnal species show higher responses when stressed during day time, whereas diurnal fish respond stronger at night. Melatonin administration in fish has sedative effects with a reduction in locomotor activity and cortisol levels, as well as reduced liver glycogen and dopaminergic and serotonergic activities within the hypothalamus. In this paper, we are reviewing the role of environmental cycles and biological clocks on the entrainment of daily rhythms in the HPI axis and stress responses in fish.

Transport and Recovery of Gilthead Seabream (Sparus aurata L.) Sedated With Clove Oil and MS-222: Effects on Stress Axis Regulation and Intermediary Metabolism.

Transport processes between aquaculture facilities activate the stress response in fish. To deal with these situations, the hypothalamic-pituitary-interrenal (HPI) axis releases cortisol, leading to an increase in circulating energy resources to restore homeostasis. However, if the allostatic load generated exceeds fish tolerance limits, stress-related responses will compromise health and welfare of the animals. In this context, anesthetics have arisen as potential agents aiming to reduce negative effects of stress response. Here we assessed the effects of a sedative dose of clove oil (CO) and MS-222 on hallmarks involved in HPI axis regulation and energy management after simulated transport, and further recovery, in gilthead seabream (Sparus aurata L.) juveniles. Fish were placed in a mobile setup of water tanks where transport conditions were simulated for 6 h. Sedation doses of either CO (2.5 mg L−1) or MS-222 (5 mg L−1) were added in the water tanks. A control group without anesthetics was also included in the setup. Half of the animals (n = 12 per group) were sampled immediately after transport, while remaining animals were allowed to recover for 18 h in clean water tanks and then sampled. Our results showed that the HPI axis response was modified at peripheral level, with differences depending on the anesthetic employed. Head kidney gene-expressions related to cortisol production (star and cyp11b1) matched concomitantly with increased plasma cortisol levels immediately after transport in CO-sedated fish, but these levels remained constant in MS-222-sedated fish. Differential changes in the energy management of carbohydrates, lipids and amino acids, depending on the anesthetic employed, were also observed. The use of CO stimulated amino acids catabolism, while MS-222-sedated fish tended to consume liver glycogen and mobilize triglycerides. Further studies, including alternative doses of both anestethics, as well as the assessment of time-course HPI activation and longer recovery periods, are necessary to better understand if the use of clove oil and MS-222 is beneficial for S. aurata under these circumstances.

Comparative assessment of cortisol in plasma, skin mucus and scales as a measure of the hypothalamic-pituitary-interrenal axis activity in fish

Cortisol, the end product of the hypothalamus-pituitary-interrenal (HPI) axis, has been traditionally measured in blood as indicator of stress in fish, however, the degree of invasiveness inherent to blood collection is not always possible or desirable. Instead, cortisol measurement in skin mucus is far less invasive, but as blood, this method potentially provides only a brief window of information of the HPI axis activity. The newly described method of cortisol measurement from scales may serve as a long-term, integrated measure of the HPI axis activity in fish. While skin mucus and scales cortisol measurement present practical and conceptual advantages, there are still several unclear issues related to their biological relevance that need deeper study. Accordingly, we aimed to evaluate whether skin mucus and scales cortisol levels can be reliably used as stress indicators by subjecting fish to prolonged, continuous stressful conditions. The present study demonstrates that the measurement of cortisol in skin mucus reflect circulating cortisol concentrations when fish are responding to stress with an intense activation of the HPI axis. Results also revealed that cortisol content in scales strongly correlates to circulating cortisol levels in chronically stressed fish. Besides, we provide further support that scales cortisol assessment offer a retrospective measure of the past stress experience in fish. While this study provides a good basis for future research applying the methods presented, our results open the question of whether these matrices have additional sources of cortisol other than blood, and the route of incorporation or diffusion. Further knowledge about the general robustness and stability of scales cortisol in fish subjected to prolonged stress would largely help strengthen the interpretation of hormone fluctuations in this matrix.

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.

Early-life manipulation of cortisol and its receptor alters stress axis programming and social competence.

In many vertebrate species, early social experience generates long-term effects on later life social behaviour. These effects are accompanied by persistent modifications in the expression of genes implicated in the stress axis. It is unknown, however, whether stress axis programming can affect the development of social competence, and if so, by which mechanism(s). Here, we used pharmacological manipulations to persistently reprogramme the hypothalamic-pituitary-interrenal axis of juvenile cooperatively breeding cichlids, Neolamprologus pulcher. During the first two months of life, juveniles were repeatedly treated with cortisol, mifepristone or control treatments. Three months after the last manipulation, we tested for treatment effects on (i) social competence, (ii) the expression of genes coding for corticotropin-releasing factor ( crf), glucocorticoid receptor ( gr1) and mineralocorticoid receptor ( mr) in the telencephalon and hypothalamus and (iii) cortisol levels. Social competence in a social challenge was reduced in cortisol-treated juveniles, which is in accordance with previous work applying early-life manipulations using different social experiences. During early life, both cortisol and mifepristone treatments induced a persistent downregulation of crf and upregulation of mr in the telencephalon. We suggest that these persistent changes in stress gene expression may represent an effective physiological mechanism for coping with stress. This article is part of the theme issue 'Developing differences: early-life effects and evolutionary medicine'.

Variation in scale cortisol concentrations of a wild freshwater fish: Habitat quality or seasonal influences?

A significant body of literature suggests that aquatic pollutants can interfere with the physiological function of the fish hypothalamic-pituitary-interrenal (HPI) axis, and eventually impair the ability to cope with subsequent stressors. For this reason, development of accurate techniques to assess fish stress responses have become of growing interest. Fish scales have been recently recognized as a biomaterial that accumulates cortisol, hence it can be potentially used to assess chronic stress in laboratory conditions. We, therefore, aimed to evaluate the applicability of this novel method for cortisol assessment in fish within their natural environment. Catalan chub (Squalius laietanus) were sampled from two sites; a highly polluted and a less polluted (reference) site, in order to examine if habitat quality could potentially influence the cortisol deposition in scales. We also evaluated the seasonal variation in scale cortisol levels by sampling fish at three different time points during spring-summer 2014. In each sampling, blood was collected to complement the information provided by the scales. Our results demonstrated that blood and scale cortisol levels from individuals inhabiting the reference site were significantly correlated, therefore increasing the applicability of the method as a sensitive-individual measure of fish HPI axis activity, at least in non-polluted habitats. Since different environmental conditions could potentially alter the usefulness of the technique, results highlight that further validation is required to better interpret hormone fluctuations in fish scales. Scale cortisol concentrations were unaffected by habitat quality although fish from the polluted environment presented lower circulating cortisol levels. We detected a seasonal increase in scale cortisol values concurring with an energetically costly period for the species, supporting the idea that the analysis of cortisol in scales reveals changes in the HPI axis activity. Taken together, the present study suggests that cortisol levels in scales are more likely to be influenced by mid-term, intense energetically demanding periods rather than by long-term stressors. Measurement of cortisol in fish scales can open the possibility to study novel spatio-temporal contexts of interest, yet further research is required to better understand its biological relevance.

Modulation of stress and innate immune response by corticosteroids in pacu (Piaractus mesopotamicus)

Understanding how stress and corticosteroid modulates the innate immune response is one of the keys to improving productivity and reducing losses in intensive aquaculture. Thus, we investigated the effects of dietary corticosteroids (7 days; long-term exposure) and transport (4 h; short-term stress) on stress and innate immune response in pacu. For this end, fish were fed with diets containing dexamethasone (100 mg kg−1) or hydrocortisone (200 mg kg−1), followed by transport, and then were intraperitoneally inoculated with heat-killed Aeromonas hydrophila or PBS (sham-inoculation). Fish were sampled after a 7-day feeding period, immediately post-transport and 24 h post-transport and inoculation. The dietary treatment of corticosteroids decreased resting cortisol levels by inhibiting the production of cortisol on the hypothalamus pituitary interrenal-axis. Further, both corticosteroids reduced hematocrit, red blood cells, haemoglobin and hemolytic activity of the complement, while they increased glucose levels and serum lysozyme concentrations. The transport increased cortisol and glucose levels and reduced the humoral immune defenses such as serum lysozyme concentration and hemolytic activity of the complement system. Interestingly, the hemolytic activity of the complement system increased sharply in fish fed with corticosteroids immediately post-transport, when they had their HPI-axis partially suppressed by the corticosteroids. This finding suggests a stimulatory effect of the catecholamines released during the transport on the activity of the complement system. Our results are highly valuable to understanding the stress and innate immune responses to long-term exposure to corticosteroids and short-term stress in fish and may provide insights into how corticosteroids modulate the innate immune system.

Cortisol does not increase risk of mortality to predation in juvenile bluegill sunfish: A manipulative experimental field study.

The hypothalamic-pituitary-interrenal (HPI) or stress axis in teleost fishes produces their primary glucocorticoid, cortisol. Although generally an adaptive response, prolonged HPI axis stimulation can impair organismal performance. Previous work has shown that stressed teleosts have higher mortality to predation than unstressed conspecifics, suggesting a role for HPI axis in modulating predator-prey interactions. Our current study investigated whether elevated cortisol levels altered the predation rate of a wild teleost fish, the bluegill sunfish (Lepomis macrochirus). Wild juvenile bluegill were given intraperitoneal implants of cocoa butter (i.e., sham), or cocoa butter containing cortisol or cortisol and the glucocorticoid receptor antagonist RU486. After 24 hr, fish were tethered along the bottom of the lake and their survival under natural predation was recorded following 24 hr. A subset of fish was used to validate the efficacy of cortisol implants in this setting. No treatment effect on survival was observed, suggesting that elevated cortisol has minimal involvement in mediating predator-prey interactions in this context. However, experimental fish may have demonstrated resiliency to physiological perturbations owing to the relatively acute duration of our experimental series, and negative effects might be manifested over a more chronic period.

Novel zebrafish behavioral assay to identify modifiers of the rapid, nongenomic stress response.

When vertebrates face acute stressors, their bodies rapidly undergo a repertoire of physiological and behavioral adaptations, which is termed the stress response. Rapid changes in heart rate and blood glucose levels occur via the interaction of glucocorticoids and their cognate receptors following hypothalamic‐pituitary‐adrenal axis activation. These physiological changes are observed within minutes of encountering a stressor and the rapid time domain rules out genomic responses that require gene expression changes. Although behavioral changes corresponding to physiological changes are commonly observed, it is not clearly understood to what extent hypothalamic‐pituitary‐adrenal axis activation dictates adaptive behavior. We hypothesized that rapid locomotor response to acute stressors in zebrafish requires hypothalamic‐pituitary‐interrenal (HPI) axis activation. In teleost fish, interrenal cells are functionally homologous to the adrenocortical layer. We derived eight frameshift mutants in genes involved in HPI axis function: two mutants in exon 2 of mc2r (adrenocorticotropic hormone receptor), five in exon 2 or 5 of nr3c1 (glucocorticoid receptor [GR]) and two in exon 2 of nr3c2 (mineralocorticoid receptor [MR]). Exposing larval zebrafish to mild environmental stressors, acute changes in salinity or light illumination, results in a rapid locomotor response. We show that this locomotor response requires a functioning HPI axis via the action of mc2r and the canonical GR encoded by nr3c1 gene, but not MR (nr3c2). Our rapid behavioral assay paradigm based on HPI axis biology can be used to screen for genetic and environmental modifiers of the hypothalamic‐pituitary‐adrenal axis and to investigate the effects of corticosteroids and their cognate receptor interactions on behavior.

Validating the use of dermal secretion as a matrix for monitoring glucocorticoid concentrations in African amphibian species.

The complex interaction between factors leading to amphibian declines is responsible for the inability to develop robust, standardized conservation action plans. Monitoring physiological stress responses in amphibians may provide an ideal tool to assist conservationists in this regard. This study aimed to validate dermal secretions as a robust matrix for monitoring glucocorticoid alterations in an African amphibian, the edible bullfrog (Pyxicephalus edulis). Both a biological (handling) and physiological (ACTH challenge) validation were conducted to determine which of five available enzyme immunoassays (EIAs) tested is most suited for monitoring alterations in dermal glucocorticoid (dGC) concentrations. Additionally, the most optimal body region for monitoring dGC concentrations in P. edulis was identified. To confirm the activation of the hypothalamic-pituitary-interrenal (HPI) axis following ACTH administration, urinary glucocorticoid metabolites (uGCM) were also quantified. The tested corticosterone EIA was the only assay able to monitor alterations in dGC concentrations following the handling event in P. edulis. Further validation during the ACTH challenge supported the corticosterone EIA in this regard. Dermal secretions collected from both the ventral and dorsal regions were suitable for monitoring dGC concentrations in both sexes. A considerable increase in uGCM concentrations following ACTH administration was found, suggesting that the dGC concentrations observed were derived from the HPI axis. This study offers further support for the use of dermal secretions as an important matrix for monitoring physiological stress, and thus general health, in amphibian species.

Chronic Plasma Cortisol Elevation Does Not Promote Riskier Behavior in a Teleost Fish: A Test of the Behavioral Resiliency Hypothesis.

SynopsisStressed fish have been shown to have higher predator-induced mortality than unstressed conspecifics, suggesting a role for the hypothalamic–pituitary–interrenal axis in modifying risk-taking behaviors. Yet, there is also evidence of behavioral resiliency in the face of chronic stressors. Here, we tested the behavioral resiliency hypothesis, which posits that animals can maintain consistent behavioral phenotypes in the face of significant physiological challenges. We determined whether chronic plasma cortisol elevation promotes risk-taking behaviors in a model teleost fish, the pumpkinseed sunfish (Lepomis gibbosus). Experimental fish were implanted with cocoa butter either as a sham or with cortisol. At 48 h post-implantation, the behavior of individual focal fish was tested in an experimental arena comprising of a simulated physical refuge, an open zone containing a constrained conspecific shoal, and a compartment containing either a model of a northern pike (Esox lucius) paired with corresponding pike olfactory cues in lake water or no pike model (control) paired with sham lake water cues only. The fish were assayed individually for their refuge utilization, shoaling tendency, and general activity. Neither cortisol treatment nor predation-risk treatment influenced any of these behaviors. This suggests that sunfish, in the context of our experiment, were behaviorally resilient to the physiological effects of chronic plasma cortisol elevation and in the face of an apparent threat of predation. Our results thus provide support for the behavioral resiliency hypothesis in fish under both physiological and ecological stressors. We posit that behavioral resiliency is an evolutionary adaptation ensuring appropriate responses to environmental conditions.

Disrupted-in-Schizophrenia-1 is essential for normal hypothalamic-pituitary-interrenal (HPI) axis function

Psychiatric disorders arise due to an interplay of genetic and environmental factors, including stress. Studies in rodents have shown that mutants for Disrupted-In-Schizophrenia-1 (DISC1), a well-accepted genetic risk factor for mental illness, display abnormal behaviours in response to stress, but the mechanisms through which DISC1 affects stress responses remain poorly understood. Using two lines of zebrafish homozygous mutant for disc1, we investigated behaviour and functioning of the hypothalamic-pituitary-interrenal (HPI) axis, the fish equivalent of the hypothalamic-pituitary-adrenal (HPA) axis. Here, we show that the role of DISC1 in stress responses is evolutionarily conserved and that DISC1 is essential for normal functioning of the HPI axis. Adult zebrafish homozygous mutant for disc1 show aberrant behavioural responses to stress. Our studies reveal that in the embryo, disc1 is expressed in neural progenitor cells of the hypothalamus, a conserved region of the vertebrate brain that centrally controls responses to environmental stressors. In disc1 mutant embryos, proliferating rx3+ hypothalamic progenitors are not maintained normally and neuronal differentiation is compromised: rx3-derived ff1b+ neurons, implicated in anxiety-related behaviours, and corticotrophin releasing hormone (crh) neurons, key regulators of the stress axis, develop abnormally, and rx3-derived pomc+ neurons are disorganised. Abnormal hypothalamic development is associated with dysfunctional behavioural and neuroendocrine stress responses. In contrast to wild type siblings, disc1 mutant larvae show altered crh levels, fail to upregulate cortisol levels when under stress and do not modulate shoal cohesion, indicative of abnormal social behaviour. These data indicate that disc1 is essential for normal development of the hypothalamus and for the correct functioning of the HPA/HPI axis.

Involvement of HPI-axis in anesthesia with Lippia alba essential oil citral and linalool chemotypes: gene expression in the secondary responses in silver catfish.

In teleost fish, stress initiates a hormone cascade along the hypothalamus-pituitary-interrenal (HPI) axis to provoke several physiological reactions in order to maintain homeostasis. In aquaculture, a number of factors induce stress in fish, such as handling and transport, and in order to reduce the consequences of this, the use of anesthetics has been an interesting alternative. Essential oil (EO) of Lippia alba is considered to be a good anesthetic; however, its distinct chemotypes have different side effects. Therefore, the present study aimed to investigate, in detail, the expression of genes involved with the HPI axis and the effects of anesthesia with the EOs of two chemotypes of L. alba (citral EO-C and linalool EO-L) on this expression in silver catfish, Rhamdia quelen. Anesthesia with the EO-C is stressful for silver catfish because there was an upregulation of the genes directly related to stress: slc6a2, crh, hsd20b, hspa12a, and hsp90. In this study, it was also possible to observe the importance of the hsd11b2 gene in the response to stress by handling. The use of EO-C as anesthetics for fish is not recommended, but, the use of OE-L is indicated for silver catfish as it does not cause major changes in the HPI axis.

Does experimental cortisol elevation mediate risk-taking and antipredator behaviour in a wild teleost fish?

The hypothalamic-pituitary-interrenal (HPI) axis is centrally implicated in stressor mitigation in teleost fishes. Sustained HPI axis activation can be detrimental to the physiological functioning of an organism and can result in fitness-related trade-offs. Predator-induced mortality is known to be higher in stressed fish than in unstressed conspecifics, suggesting a role for the HPI axis in mediating fish behaviour. However, the underlying specific mechanism(s) for this phenomenon is(are) unknown. The purpose of the current study was to address how the HPI axis influences risk-taking, and antipredator behaviours in a wild teleost, the pumpkinseed sunfish (Lepomis gibbosus). Here, individual juvenile pumpkinseed were implanted either with cocoa butter as a sham control or with a biologically-relevant concentration of cortisol. Forty-eight hours post-implantation, fish were assessed for behavioural metrics associated with boldness and risk taking in three sequential behavioural tests: (i) a predation-risk test, (ii) an exploration tendency test, and (iii) a shoaling tendency test, with test order randomized among different trials. Cortisol treatment had no influence on antipredator, exploratory, or shoaling behaviours. However, post-attack swimming duration (in predation-risk test) and exploratory activity (in Z-maze exploration test) were significantly affected by body mass. Collectively, our results indicate that cortisol may not have a role in mediating sociability, boldness, and risk-taking behaviours in pumpkinseed sunfish, at least under the current laboratory conditions. However, cortisol may nonetheless play a role in mediating predator-prey interactions in fishes in more natural environmental settings that were not considered here.

Characterization and Expression Dynamics of Key Genes Involved in the Gilthead Sea Bream (Sparus aurata) Cortisol Stress Response during Early Ontogeny.

The present study identified and characterized six key genes involved in the hypothalamic-pituitary-interrenal (HPI) axis of gilthead sea bream (Sparus aurata), a commercially important European aquaculture species. The key genes involved in the HPI axis for which gene structure and synteny analysis was carried out, comprised of two functional forms of glucocorticoid receptors (GR), as well as three forms of pro-opiomelanocortin (POMC) genes and one form of mineralocorticoid receptor (MR) gene. To explore their functional roles during development but also in the stress response, the expression profiles of gr1, gr2, mr, pomc_aI, pomc_aII, and pomc_β were examined during early ontogeny and after an acute stress challenge. The acute stress challenge was applied at the stage of full formation of all fins, where whole body cortisol was also measured. Both the cortisol and the molecular data implied that sea bream larvae at the stage of the full formation of all fins at 45dph are capable of a response to stress of a similar profile as observed in adult fish.

Microcystin-LR affects the hypothalamic-pituitary-inter-renal (HPI) axis in early life stages (embryos and larvae) of zebrafish

Frequencies and durations of blooms of cyanobacteria are increasing. Some cyanobacteria can produce cyanotoxins including microcystins (MCs). MCs are the most common toxic products of hazardous algal blooms (HABs), with the greatest potential for exposure and to cause toxicity. Recently, MCs have been shown to disrupt endocrine functions. In this study, for the first time, effects of MC-LR on the hypothalamic-pituitary-inter-renal (HPI) axis during early embryonic development (embryos/larvae) of zebrafish (Danio rerio), were investigated. Embryos/larvae of zebrafish were exposed to 1, 10, 100, or 300 μg MC-LR/L during the period of 4–168 h post-fertilization (hpf). Exposure to 300 μg MC-LR/L resulted in significantly greater concentrations of whole-body cortisol than those in controls. Expressions of genes along the HPI axis and mineralocorticoid receptor (MR-) and glucocorticoid receptor (GR-) centered gene networks were evaluated by use of quantitative real-time PCR. Expression of mRNA for crh was significantly down-regulated by exposure to 300 μg MC-LR/L, while expressions of crhbp, crhr1, and crhr2 were significantly up-regulated, relative to controls. MC-LR caused significantly lesser levels of mRNA for steroidogenic genes including hmgra, star, and cyp17, but expression of mRNA for hsd20b was significantly greater than that of controls. Treatment with MC-LR also altered profiles of transcription of MR- and GR-centered gene networks, which might result in multiple responses. Taken together, these results demonstrated that MC-LR affected the corticosteroid-endocrine system of larvae of zebrafish. This study provided valuable insights into molecular mechanisms behind potential toxicity and endocrine disruption of MCs.

Vibrio lentus as a probiotic candidate lowers glucocorticoid levels in gnotobiotic sea bass larvae

Plasma cortisol is the classical parameter to assess acute stress in vertebrates, while in fish larvae whole body cortisol is used. Immuno assays are commonly adopted for cortisol determination in a pool of fish larvae. At present no method exists for quantification of a full glucocorticoid profile of a single fish larva providing a detailed snap-shot of hypothalamic-pituitary-interrenal (HPI) axis activity. To date, a substantial amount of studies has confirmed the potential of probiotics to positively impact fish welfare by alleviating the general stress response. However, no study investigated how probiotics impact the glucocorticoid profile in an individual fish larva.In this respect, this study assessed the effect of the administration of the probiotic candidate Vibrio lentus, previously shown to protect European sea bass (Dicentrarchus labrax) larvae, on the HPI axis activity. Therefore, V. lentus was administered to germ-free European sea bass larvae and a ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) method for quantifying cortisol, its precursors (17α-hydroxyprogesterone and 11-deoxycortisol) and phase I metabolites (cortisone, 20β-dihydrocortisone, tetrahydrocortisol and tetrahydrocortisone) in the whole body of a single fish larva was developed in an EN ISO/IEC 17025 regulated environment and validated according the requirements of the Commission Decision No. 2002/657/EC and applied, making this the first study in its kind.In the supplemented larvae, the administration of the probiotic candidate V. lentus significantly decreased glucocorticoid baseline levels. This study provides a better insight into the effect of the probiotic candidate V. lentus on the HPI axis activity in European sea bass larvae.

Urbanization is associated with elevated corticosterone in Jollyville Plateau salamanders

Urbanization has the potential to induce major changes in freshwater systems. Expected increases in human populations will likely amplify these changes and lead to the overall degradation of habitat quality within these systems. Such habitat alterations may function as stressors that can affect glucocorticoid stress hormones in freshwater vertebrates. Examining changes in physiological stress may provide early warning indicators of environmental threats and provide insights into the sub-lethal effects of habitat degradation. The threatened, obligate aquatic, Jollyville Plateau salamander (Eurycea tonkawae) is found in urbanized and rural catchments within central Texas and has experienced population declines in heavily urbanized areas. We tested the prediction that salamanders from urbanized sites would have different levels of baseline corticosterone (CORT) and muted or no stress responsiveness (to an external stressor, agitation) compared to salamanders from rural sites. We collected water-borne hormones to measure baseline CORT release rates (n=3years) and stress responsiveness (n=2years) in salamanders inhabiting urbanized and rural sites. We also measured “background” CORT from stream water alone at each visit. For the first two years we found that baseline CORT was higher in urbanized sites but not in the third year. Across years and populations, salamanders showed stress responsiveness, suggesting that, even if physiological stress is higher in urbanized areas, it has not resulted in the impairment of the hypothalamic–pituitary–interrenal axis. Background CORT was higher in urban than in rural streams and was positively correlated with mean baseline CORT of salamanders across populations and years. Our results contribute to the goal of finding early warning indicators of environmental threats by demonstrating a relationship between urbanization and the physiological status of E. tonkawae, using a rapid, non-invasive measure of stress.

The brain-gut axis of fish: Rainbow trout with low and high cortisol response show innate differences in intestinal integrity and brain gene expression

In fish, the stress hormone cortisol is released through the action of the hypothalamic pituitary interrenal axis (HPI-axis). The reactivity of this axis differs between individuals and previous studies have linked this to different behavioural characteristics and stress coping styles. In the current study, low and high responding (LR and HR) rainbow trout in terms of cortisol release during stress were identified, using a repeated confinements stress test. The expression of stress related genes in the forebrain and the integrity of the stress sensitive primary barrier of the intestine was examined. The HR trout displayed higher expression levels of mineralocorticoid and serotonergic receptors and serotonergic re-uptake pumps in the telencephalon during both basal and stressed conditions. This confirms that HPI-axis reactivity is linked also to other neuronal behavioural modulators, as both the serotonergic and the corticoid system in the telencephalon are involved in behavioural reactivity and cognitive processes. Involvement of the HPI-axis in the brain-gut-axis was also found. LR trout displayed a lower integrity in the primary barrier of the intestine during basal conditions compared to the HR trout. However, following stress exposure, LR trout showed an unexpected increase in intestinal integrity whereas the HR trout instead suffered a reduction. This could make the LR individuals more susceptible to pathogens during basal conditions where instead HR individuals would be more vulnerable during stressed conditions. We hypothesize that these barrier differences are caused by regulation/effects on tight junction proteins possibly controlled by secondary effects of cortisol on the intestinal immune barrier or differences in parasympathetic reactivity.