Corticosteroids affect the testicular androgen production in male common carp (Cyprinus carpio L.)

Effects of different hormonal treatments on spermatogenesis advancement in hatchery-produced greater amberjack Seriola dumerili (Risso 1810)

In earlier studies, wild-caught greater amberjack Seriola dumerili (Risso, 1810) males reared in sea cages showed gametogenesis impairment and low sperm production and quality. Here, we (a) examined if F1 hatchery-produced males reared in sea cages also exhibit reproductive dysfunctions and (b) evaluated the effects of gonadotropin releasing hormone agonist (GnRHa) administration through injections (GnRHainj) or sustained-release implants (GnRHaimpl), and human chorionic gonadotropin (hGC) injections on spermatogenesis/spermiation enhancement. Fish were given a hormone treatment just prior to the spawning season, and were transferred to land-based tanks, according to an established spawning induction protocol. Blood samples (n = 6) were obtained on Days 0, 7 and 13 after treatment. Testis samples were obtained on Days 0 (n = 4) and 13 (n = 2 per treatment). The fish prior to their transfer from the sea cages to the land-based tanks, exhibited a low gonadosomatic index, altered sex steroid hormone profile and high density of testicular apoptotic cells. After transfer to tanks, there was a general depression of sex steroid plasma levels parallel to an increase in cortisol concentrations. Despite the negative effect on steroidogenesis by the transfer from the sea, the hormonal treatments increased the number of fish from where sperm could be obtained, as well as testis growth, and reduced testicular apoptosis. Treatment with hCG resulted in the most significant changes in spermatogenesis, while GnRHaimpl appeared to induce less intense, but likely longer-lasting effects. The study indicated that F1 hatchery-produced males also exhibited reproductive dysfunctions as wild-caught captive-reared greater amberjack, and that the observed positive effects of the hormone treatments on spermiation/spermatogenesis were likely mediated by factors other than sex steroid hormones.

Reproductive endocrine disruption and gonadal intersex induction in male Japanese medaka chronically exposed to betamethasone at environmentally relevant levels

The broad utilization of betamethasone in medical treatments may pose a significant ecotoxicological risk to aquatic organisms, yet its potential reproductive toxicity remains unclear. The present study examined the impacts of environmental exposure on male reproduction using Japanese medaka (Oryzias latipes). After 110 days of betamethasone exposure at environmentally relevant concentrations (0, 20 and 200 ng/L), LH/FSH synthesis and release in the pituitary was inhibited, and the production of sex hormones and their signaling pathways in the gonads of male medaka were greatly influenced. This synthetic glucocorticoid restrained testosterone (T) synthesis and gave rise to a significant increase in E₂/T and E₂/11-KT ratios. Furthermore, chronic betamethasone exposure (20 and 200 ng/L) led to the suppression of androgen receptor (AR) signaling and enhancement of estrogen receptors (ERs) signaling. An increase in hepatic vitellogenin contents was also detected, and testicular oocytes were observed in both 20 and 200 ng/L betamethasone-treated groups. It showed that 20 and 200 ng/L betamethasone could induce male feminization and even intersex, triggering abnormal spermatogenesis in medaka males. With its adverse effects on male fertility, betamethasone could potentially influence the fishery productivity and population dynamics in aquatic ecosystems.

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.

Are synthetic glucocorticoids in the aquatic environment a risk to fish?

The glucocorticosteroid, or glucocorticoid (GC), system is largely conserved across vertebrates and plays a central role in numerous vital physiological processes including bone development, immunomodulation, and modification of glucose metabolism and the induction of stress-related behaviours. As a result of their wide-ranging actions, synthetic GCs are widely prescribed for numerous human and veterinary therapeutic purposes and consequently have been detected extensively within the aquatic environment. Synthetic GCs designed for humans are pharmacologically active in non-mammalian vertebrates, including fish, however they are generally detected in surface waters at low (ng/L) concentrations. In this review, we assess the potential environmental risk of synthetic GCs to fish by comparing available experimental data and effect levels in fish with those in mammals. We found the majority of compounds were predicted to have insignificant risk to fish, however some compounds were predicted to be of moderate and high risk to fish, although the dataset of compounds used for this analysis was small. Given the common mode of action and high level of inter-species target conservation exhibited amongst the GCs, we also give due consideration to the potential for mixture effects, which may be particularly significant when considering the potential for environmental impact from this class of pharmaceuticals. Finally, we also provide recommendations for further research to more fully understand the potential environmental impact of this relatively understudied group of commonly prescribed human and veterinary drugs.

Special features of neuroendocrine interactions between stress and reproduction in teleosts

Stress and reproduction are both essential functions for vertebrate survival, ensuring on one side adaptative responses to environmental changes and potential life threats, and on the other side production of progeny. With more than 25,000 species, teleosts constitute the largest group of extant vertebrates, and exhibit a large diversity of life cycles, environmental conditions and regulatory processes. Interactions between stress and reproduction are a growing concern both for conservation of fish biodiversity in the frame of global changes and for the development of sustainability of aquaculture including fish welfare. In teleosts, as in other vertebrates, adverse effects of stress on reproduction have been largely documented and will be shortly overviewed. Unexpectedly, stress notably via cortisol, may also facilitate reproductive function in some teleost species in relation to their peculiar life cyles and this review will provide some examples. Our review will then mainly address the neuroendocrine axes involved in the control of stress and reproduction, namely the corticotropic and gonadotropic axes, as well as their interactions. After reporting some anatomo-functional specificities of the neuroendocrine systems in teleosts, we will describe the major actors of the corticotropic and gonadotropic axes at the brain-pituitary-peripheral glands (interrenals and gonads) levels, with a special focus on the impact of teleost-specific whole genome duplication (3R) on the number of paralogs and their potential differential functions. We will finally review the current knowledge on the neuroendocrine mechanisms of the various interactions between stress and reproduction at different levels of the two axes in teleosts in a comparative and evolutionary perspective.

Habituation and individual variation in the endocrine stress response in the Trinidadian guppy (Poecilia reticulata)

The vertebrate stress response enables individuals to react to and cope with environmental challenges. A crucial aspect of the stress response is the elevation of circulating glucocorticoids. However, continued activation of the stress response under repeated exposure to stressors can be damaging to fitness. Under certain circumstances it may therefore be adaptive to habituate to repeated exposures to a particular stressor by reducing the magnitude of any associated release of glucocorticoids. Here, we investigate whether Trinidadian guppies (Poecilia reticulata) habituate to repeated exposure to a mild stressor, using a waterborne hormone sampling approach that has previously been shown to elicit a stress response in small fish. We also test for individual variation in the extent of habituation to this stressor. Concentrating on freely circulating cortisol, we found that the first exposure to the assay induced high cortisol release rates but that guppies tended to habituate quickly to subsequent exposures. There were consistent differences among individuals in their average cortisol release rate (after accounting for effects of variables such as body size) over repeated exposures. Our analyses did not find evidence of individual differences in habituation rate, although limitations in statistical power could account for this finding. We repeated the analysis for free 11-ketotestosterone, which can also respond to stressors, but found no obvious habituation pattern and no among-individual variation. We also present data on conjugated forms of both hormones, which were repeatable but did not show the expected time-lagged habituation effect. We discuss consistent individual differences around the general pattern of habituation in the flexible stress response, and highlight the potential for individual variation in habituation to facilitate selection against the deleterious effects of chronic stress.

Stress and sex: does cortisol mediate sex change in fish?

Cortisol is the main glucocorticoid (GC) in fish and the hormone most directly associated with stress. Recent research suggests that this hormone may act as a key factor linking social environmental stimuli and the onset of sex change by initiating a shift in steroidogenesis from estrogens to androgens. For many teleost fish, sex change occurs as a usual part of the life cycle. Changing sex is known to enhance the lifetime reproductive success of these fish and the modifications involved (behavioral, gonadal and morphological) are well studied. However, the exact mechanism behind the transduction of the environmental signals into the molecular cascade that underlies this singular process remains largely unknown. We here synthesize current knowledge regarding the role of cortisol in teleost sex change with a focus on two well-described transformations: temperature-induced masculinization and socially regulated sex change. Three non-mutually exclusive pathways are considered when describing the potential role of cortisol in mediating teleost sex change: cross-talk between GC and androgen pathways, inhibition of aromatase expression and upregulation of amh (the gene encoding anti-Müllerian hormone). We anticipate that understanding the role of cortisol in the initial stages of sex change will further improve our understanding of sex determination and differentiation across vertebrates, and may lead to new tools to control fish sex ratios in aquaculture.

Cortisol stimulates arginine vasotocin and isotocin release from the hypothalamo-pituitary complex of round goby (Neogobius melanostomus): Probable mechanisms of action

There were two aims of this in vitro perfusion study. Firstly, to determine which class of receptors, glucocorticoid (GRs) or mineralocorticoid (MRs), are involved in cortisol regulation of arginine vasotocin (AVT) and isotocin (IT) release from the hypothalamo-pituitary (H-P) complex of round goby (Neogobius melanostomus). Secondly, to determine which pathways, genomic or non-genomic, are involved in the aformentioned process.The H-P explants were perfused with cortisol (1.4 × 10(-) (7)  M, 2.8 × 10(-7) M, 0.4 × 10(-6) M); only the highest dose significantly increased a release of both nonapeptides. In the perfusion of H-P explants, we used cortisol (0.4 × 10(-6) M) in combination with GRs antagonist RU486 (0.3 × 10(-6)  M) or MRs antagonist C03DA01 (0.36 × 10(-6)  M) or transcription inhibitor Actinomycin D (1 × 10(-7)  M). All inhibitors were also tested seperately. The contents of AVT and IT in the perfusion media was determined by high-performance liquid chromatography (HPLC) with UV detection. This study suggested that different mechanisms were involved in the regulation of AVT and IT release from H-P complex in round goby. Apparently it was GRs but not MRs that were involved in cortisol regulation of AVT and IT release. In the case of AVT, our data points to both genomic and non-genomic pathways mediating the effect of cortisol; in the case of IT, it is only the non-genomic pathway. This study presents the first feasible mechanisms of cortisol action on AVT and IT release from the H-P complex in round goby.

Induced reproduction in a migratory teleost species by water level drawdown

Captive reproduction is one of the problems faced in aquaculture requiring the manipulation of environmental factors and/or hormonal treatment. Thus, we seek to verify experimentally which gonadal changes were present in mature individuals of Astyanax altiparanae arising from decreased water level. Collections were made every four hours, initiated four hours before and finished 28 hours after stimulation, at the Fish Farming Station of Companhia Energética de São Paulo, São Paulo, Brazil. The gonads were analyzed by light microscopy. The females had ovaries in the spawning capable phase until 12h; in 16h, in a more advanced stage of spawning capable phase; and, from 20h, in the regressing phase. Males had testes in the spawning capable phase until 8h; in 12h, in a more advanced stage of spawning capable phase; and, from 16h, the return to the spawning capable phase. The morphological description was corroborated by the proportion of cell classes. Females presented variation on the gonadosomatic index, but it was not found an emptying of the gonad for neither sex. The process of inducing reproduction with water level drawdown was considered satisfactory, since both sexes presented a reduction in the number of mature gametes at the end of the sample period.

Cortisol administration induces sex change from ovary to testis in the protogynous Wrasse, Halichoeres trimaculatus

Steroid hormones have been shown to play important roles in triggering sex change. However, the upstream mechanism that regulates the secretion of sex steroid hormones controlling sex change is not yet known. Cortisol, the primary glucocorticoid in teleost fish, is known to exhibit anti-stress action and is involved in many physiological functions, including regulation of steroidogenesis. Therefore, cortisol could be one of the candidate factors involved in the onset of sex change. In this study, we investigated the role of cortisol in sex change in the three-spot wrasse, Halichoeres trimaculatus, by prolonged administration of cortisol. Our results showed that gonads of all individuals treated with cortisol (1,000 µg/g diet) for 6 weeks contained spermatogenic germ cells. One of them exhibited matured testes with an ovarian cavity, indicating sex change. Additionally, the plasma estradiol-17β level in the cortisol treatment group was significantly lower than in the control group suggesting that cortisol plays a direct and/or indirect role in the regulation of estrogen production. These data imply that cortisol might be involved in the regulation of steroidogenesis by causing a decrease in the estrogen level, leading to the onset of sex change.

Behavioral and physiological indicators of stress coping styles in larval zebrafish

Different individuals cope with stressors in different ways. Stress coping styles are defined as a coherent set of individual behavioral and physiological differences in the response to a stressor which remain consistent across time and context. In the present study, we have investigated coping styles in larval zebrafish (Danio rerio) at 8 days post-fertilization. Larvae were separated into two groups, according to the emergence sequence from a darkened into a novel well-lit environment, early (EE) and late (LE) emergers. We used brief periods of netting as a stressor. Swimming behavior and kinematics before and after netting stress were analyzed, as were whole-body cortisol levels before and at 10, 30 and 60 min after the stress event. The results show that general swimming activity was different between EE and LE larvae, with lower baseline cumulative distance and more erratic swimming movements in EE than in LE larvae. EE larvae showed a faster recovery to baseline levels after stress than LE larvae. Cortisol baseline levels were not different between EE and LE larvae, but peak levels after stress were higher and the recovery towards basal levels was faster in EE than in LE larvae. This study shows that coping styles are manifest in zebrafish larvae, and that behavior and swimming kinematics are associated with different cortisol responses to stress. A better understanding of the expression of coping styles may be of great value for medical applications, animal welfare issues and conservation.

Small-scale transcriptomics reveals differences among gonadal stages in Asian seabass (Lates calcarifer)

BACKGROUND

The Asian seabass (Lates calcarifer) is a protandrous hermaphrodite that typically matures as a male at approximately 2-4 years of age and then changes sex in subsequent years. Although several sexual maturation stages have been described histologically for both testis and ovary, the underlying gene expression profiles remain lacking. The development of a gene expression platform is therefore necessary to improve our understanding of the gonad development of this cultured teleost species.

METHODS

Thirty Asian seabass gonads were collected from farms in Singapore, examined histologically and staged according to their sex and gonadal maturation status. Partial coding sequences of 24 sex-related genes were cloned using degenerate primers and were sequenced. Additional 13 cDNA sequences were obtained through next-generation sequencing. A real-time qPCR was then performed using the microfluidic-based Fluidigm 48.48 Dynamic arrays.

RESULTS

We obtained 17 ovaries and 13 testes at various stages of sexual maturation. Of the 37 genes that were tested, 32 (86%) showed sexually dimorphic expression. These genes included sex-related genes, sox9, wt1, amh, nr5a2, dmrt1 and nr0b1, which showed testis-enhanced expression similar to other vertebrate species. Known male- and female-enhanced germ cells markers, which were established from studies in other species, similarly showed testis- and ovary-enhanced expression, respectively, in the Asian seabass. Three pro-Wnt signaling genes were also upregulated in the ovary, consistent with existing studies that suggested the role of Wnt signaling in ovarian differentiation in teleosts and mammals. The expression patterns of genes involved in steroidogenesis, retinoic acid metabolism, apoptosis and NF-κB signaling were also described. We were able to classify gonads according to sex and gonadal maturation stages, based on their small-scale transcriptomic profiles, and to uncover a wide variation in expression profiles among individuals of the same sex.

CONCLUSIONS

The analysis of a selected set of genes related to reproduction and in sufficient number of individuals using a qPCR array can elucidate new insights into the molecular mechanisms involved in Asian seabass gonad development. Given the conservation of gene expression patterns found in this study, these insights may also help us draw parallels with other teleosts.

The interrenal gland in males of the cichlid fish Cichlasoma dimerus: relationship with stress and the establishment of social hierarchies

In teleosts, cortisol is the primary glucocorticoid secreted by the steroidogenic cells of the interrenal gland and an increase in its plasma concentration is a frequent indicator of stress. Cortisol has been postulated as an endogenous mediator involved in the regulation of reproduction and aggression related to social dynamics. The cichlid fish Cichlasoma dimerus, is a monogamous species that exhibits complex social hierarchies; males appear in one of two basic alternative phenotypes: non-territorial and territorial males. In this work, we postulated as a general hypothesis that the morphometry of the interrenal gland cells and the plasma levels of cortisol and 11-ketotestosterone (11-KT) are related to the social rank in adult males of C. dimerus. First, the location and distribution of the interrenal gland with respect to its context - the kidney - was studied. Plasma levels of cortisol and 11-KT in territorial and non-territorial males were established by ELISA. Finally, a morphometric analysis of steroidogenic and chromaffin cells of the interrenal gland was performed. Results showed that the interrenal gland was exclusively located in the posterior portion of the cephalic kidney. Non-territorial males presented a greater nuclear area of their steroidogenic cells. Additionally, plasma cortisol and 11-KT levels were lower and higher, respectively, in territorial males. Finally, plasma cortisol levels positively correlated with the nuclear area of interrenal steroidogenic cells. Thus, the interrenal gland, by means of one of its products, cortisol, may be fulfilling an important role in the establishment of social hierarchies and their stability.

Chronic stress alters concentrations of corticosterone receptors in a tissue-specific manner in wild house sparrows (Passer domesticus)

The physiological stress response results in release of glucocorticoid hormones such as corticosterone (CORT). Whereas short-term activation of this response helps animals cope with environmental stressors, chronic activation can result in negative effects including metabolic dysregulation and reproductive failure. However, there is no consensus hormonal profile of a chronically-stressed animal, suggesting researchers may need to look beyond hormone titers to interpret the impacts of chronic stress. In this study, we brought wild house sparrows (Passer domesticus) into captivity. We then compared glucocorticoid and mineralocorticoid receptor concentrations in sparrows exposed either to a standardized chronic stress protocol (n=26) or to standard husbandry conditions (controls; n=20). We used radioligand binding assays to quantify receptors in whole brain, liver, kidneys, spleen, gonads, gastrocnemius and pectoralis muscle, omental and subcutaneous fat, and bib and back skin. In most tissues, CORT receptors did not differ between controls and stressed animals, although we found marginal increases in receptor density in kidney and testis in stressed birds at some time points. Only in pectoralis muscle was there a robust effect of chronic stress, with both receptor types higher in stressed animals. Increased pectoralis sensitivity to CORT with chronic stress may be part of the underlying mechanism for muscle wasting in animals administered exogenous CORT. Furthermore, the change in pectoralis was not paralleled by gastrocnemius receptors. This difference may help explain previous reports of a greater effect of CORT on pectoralis than on other muscle types, and indicate that birds use this muscle as a protein reserve.

Intra- and interspecific challenges modulate cortisol but not androgen levels in a year-round territorial damselfish

Interactions between individuals of different species are commonplace in animal communities. Some behaviors displayed during these interspecific social interactions may be very similar to those displayed during intraspecific social interactions. However, whether functional analogies between intra- and interspecific behaviors translate at the proximate level into an overlap in their underlying endocrine mechanisms remain largely unknown. Because steroids both mediate social behaviors and respond to them, we approached this question by comparing the behavioral and steroid response of free living dusky gregories (Stegastes nigricans [Lacepède, 1802]) to standardized territorial intrusions (sTI) of either conspecific or heterospecific food competitors. S. nigricans is a year-round territorial fish that “cultivates” the algae on which it feeds and is highly aggressive to both intra- and interspecific intruders. Behavioral differences between intra- and interspecific aggressive responses to sTI were marginal, and sTI tests caused an increase in cortisol levels that was positively related with the levels of aggression. In contrast, androgen levels did not increase in response to sTI, yet they showed a positive relationship with agonistic behavior. These results parallel a pattern that was first described for year-round territorial bird species. Furthermore they suggest that changes in endocrine-hormone levels during territoriality might be independent of the species that induces the territorial response.

Covariation between behaviour and physiology indicators of coping style in zebrafish (Danio rerio)

All vertebrates exhibit physiological responses to a wide variety of stressors. The amplitude and profile of the response depend on the intensity, duration, controllability and predictability of the stressor, but there is also individual variation in the response, termed coping style. A better understanding of the expression of coping styles is of great value for medical applications, animal welfare issues and conservation. Here, we investigated the effect of repeated netting stress on proactive and reactive zebrafish (Danio rerio) as an upcoming model system for stress research. Fish were separated by coping styles according to the order of entering a novel environment. Subsequently, repeated netting stress was applied as stressor, over a period of 21 days. Full-body cortisol levels were determined at 0, 15, 30, 60 and 120 min after the last repeated stress event. Our results show that reactive fish display i) increased basal cortisol concentrations after being repeatedly stressed, ii) higher cortisol secretion over time and iii) slow recovery of cortisol concentration towards basal levels after the last repeated stress event. This study shows for the first time in zebrafish that different coping styles are associated with different cortisol responses during the recovery from stress over time and that coping styles can explain otherwise unaccounted variation in physiological stress responses.

Effects of pipothiazine palmitate on handling stress and on the characteristics of semen collected by electroejaculation in bison (Bison bison) bulls

Handling North American bison can pose risk to the handler and evoke stress in the animal. Moreover, this induced stress might affect qualities of semen collected by electroejaculation. The objective of this study was to investigate if a long acting neuroleptic tranquilizer (LAN) would reduce the stress of bison and thereby improve the quality of electroejaculated semen. Eight experimental replicates were conducted between May and November. In each replicate, the same six bison bulls were randomly assigned into LAN-treated (n=3) and non-treated control (n=3) groups. Pipothiazine palmitate (Piportil L4) was administered intramuscularly as a single dose of 100 mg in replicates 1-4 or 200 mg in replicates 5-8. Within each replicate, semen was collected by electroejaculation at 4, 6, 11 and 13 days post treatment. Behavioral parameters, sperm morphology and motility parameters were analyzed. A blood sample was collected before each electroejaculation and serum concentrations of testosterone, cortisol and corticosterone were determined. Treatment bulls with 100 mg of Piportil L4 reduced the restraint time and the struggling of bison bulls during handling compared to the control group (P<0.05). Semen motility parameters and serum concentrations of testosterone, cortisol and corticosterone were not significantly affected when 100mg of the LAN was administered (P>0.05). However, giving 200 mg of Piportil L4 reduced the restraint time of bison bulls and the duration of semen collection (P<0.05). Also, this treatment improved total and progressive sperm motilities when compared to the respective controls (P<0.05). Interestingly, serum concentration of corticosterone, as an endocrine stress indicator, was decreased after administration of 200mg of Pipothiazine palmitate, while testosterone concentrations were increased compared to those values in untreated control bulls (corticosterone: 0.10±0.01 compared with 0.15±0.02 ng/mL; testosterone: 9.11±1.68 compared with 5.33±0.74 ng/mL; P<0.05). In conclusion, this study demonstrated that a treatment dose of 200mg of Piportil L4 can decrease the behavioral and endocrine stress responses in bison bulls, which indirectly increasing testosterone concentrations and improving semen quality.

Functionally similar acoustic signals in the corncrake (Crex crex) transmit information about different states of the sender during aggressive interactions

We combined playback experiments with hormonal manipulations to study the information content of acoustic signals during aggressive interactions between male corncrakes. During territorial conflicts, fights are uncommon, but the intensity of signaling usually increases. Such signals can be temporally and contextually associated with many aggressive behaviors and most likely function as threats or as indicators of the sender's quality or motivation. However, such correlational data are unsatisfactory for the proper interpretation of the function and information content of signals. Experimental tests are required to determine whether signals and aggressive behaviors are controlled by common or independent mechanisms. In our experiment, we assigned subjects to four groups: testosterone-implanted birds, flutamide-implanted birds, birds with empty implants, and non-captured control birds. Males produced two types of calls (quiet soft calls and loud broadcast calls), both of which are known to be reliable predictors of aggressive escalation. When testosterone action was blocked with flutamide, males significantly limited the amount of time spent close to the playback speaker and stopped responding to playback with soft calls. Broadcast calling was unaffected by the blockage of testosterone. Conversely, increased levels of testosterone neither affected calling nor the time spent near the speaker, indicating a permissive, rather than a graded effect of androgens. We concluded that, despite the seemingly similar function, both signals may transmit information about different states of the sender; soft calls seem to imply a threat of force, while broadcast calls appear to be more similar to an announcement, which is only indirectly associated with a male's aggressive behavior.

Stress and the timing of breeding: glucocorticoid-luteinizing hormones relationships in an arctic seabird

In birds, stressful environmental conditions delay the timing of breeding but the underlying mechanisms are poorly understood. The stress hormone corticosterone appears to be a good candidate for mediating the decision to breed and when to start egg-laying, via a possible inhibition of luteinizing hormone (LH) and sex-steroids production. We used luteinizing hormone releasing hormone (LHRH) challenge in pre-laying male and female Black-legged kittiwakes (Rissa tridactyla) to test whether LH and testosterone secretion were depressed by elevated corticosterone levels. Females bearing high baseline corticosterone levels showed reduced baseline LH levels and a low ability to release LH, following LHRH challenge. Further, females bearing low baseline LH levels and elevated baseline corticosterone levels were more likely to skip breeding. However, non-breeding females were physiologically primed for breeding, since they mounted high LHRH-induced LH release. Egg-laying date was advanced in good body condition females but was unaffected by hormones secretion. In males, corticosterone levels had no effect on LH and/or testosterone secretion and did not affect their decision to breed. Interestingly, males with high LHRH-induced testosterone release bred early. Our study highlights clear sex-differences in the HPG sensitivity to stress hormones in pre-laying kittiwakes. Because females have to store body reserves and to build up the clutch, they would be more sensitive to stress than males. Moreover, intrasexual competition could force male kittiwakes to acquire reproductive readiness earlier in the season than females and to better resist environmental perturbations. We suggest that high testosterone releasing ability would mediate behavioural adjustments such as courtship feeding, which would stimulate early egg-laying in females.

Stress transcriptomics in fish: a role for genomic cortisol signaling

The physiological responses to stressors, including hormonal profiles and associated tissue responsiveness have been extensively studied in teleosts, but the molecular mechanisms associated with this adaptive response are not well understood. The advent of cDNA microarray technology has transformed the field of functional genomics by revealing global gene expression changes in response to stressor exposures even in non-mammalian vertebrates, including fish. A unifying response in studies related to stressor exposure is activation of the hypothalamus-pituitary-interrenal (HPI) axis in fish, leading to cortisol release into the circulation. Here we will discuss the implications of some of the gene expression changes observed in response to acute stress in fish, while highlighting a role for cortisol in this adaptive stress response. As liver is a key organ for metabolic adjustments to stressors and also is a major target for cortisol action, the genomic studies pertaining to stress and glucocorticoid regulation have focused mainly on this tissue. The studies have identified several genes that are altered transiently after an acute stressor exposure in fish. A number of these stress-responsive genes were also modulated by glucocorticoid receptor activation, suggesting that elevation in cortisol levels during stressor exposure may be a key signal for target tissue molecular programming, essential for stress adaptation. The identification of regulatory gene networks that are stress activated, and modulated by cortisol, both in hepatic and extra-hepatic tissues, including gonads, brain, immune cells and gills, will provide a mechanistic framework to characterize the multifaceted role of cortisol during stress adaptation.

Adrenocorticotropic hormone suppresses gonadotropin-stimulated estradiol release from zebrafish ovarian follicles

While stress is known to impact reproductive performance, the pathways involved are not entirely understood. Corticosteroid effects on the functioning of the hypothalamus-pituitary-gonadal axis are thought to be a key aspect of stress-mediated reproductive dysfunction. A vital component of the stress response is the pituitary secretion of adrenocorticotropic hormone (ACTH), which binds to the melanocortin 2 receptor (MC2R) in the adrenal glands and activates cortisol biosynthesis. We recently reported MC2R mRNA abundance in fish gonads leading to the hypothesis that ACTH may be directly involved in gonadal steroid modulation. Using zebrafish (Danio rerio) ovarian follicles, we tested the hypothesis that acute ACTH stimulation modulates cortisol and estradiol (E₂) secretion. ACTH neither affected cortisol nor unstimulated E₂ release from ovarian follicles. However, ACTH suppressed human chorionic gonadotropin (hCG)-stimulated E₂ secretion in a dose-related manner, with a maximum decrease of 62% observed at 1 I.U. ACTH mL⁻¹. This effect of ACTH on E₂ release was not observed in the presence of either 8-bromo-cAMP or forskolin, suggesting that the mechanism(s) involved in steroid attenuation was upstream of adenylyl cyclase activation. Overall, our results suggest that a stress-induced rise in plasma ACTH levels may initiate a rapid down-regulation of acute stimulated E₂ biosynthesis in the zebrafish ovary, underscoring a novel physiological role for this pituitary peptide in modulating reproductive activity.

Functional characterization and expression analysis of the androgen receptor in zebrafish (Danio rerio) testis

The biological activity of androgens, important for male sexual differentiation and development, is mediated by the androgen receptor (AR) that binds to specific DNA recognition sites regulating the transcription of androgen target genes. We investigated androgen production by adult zebrafish testis tissue, and identified 11β-hydroxyandrostenedione, 11-ketoandrostenedione (OA), and 11-ketotestosterone (11-KT) as main products, and hence potential ligands, for the zebrafish Ar. These androgens were then included in the pharmacological characterization of the zebrafish Ar. The zebrafish Ar responded well in terms of binding and transactivation to synthetic androgens as well as to testosterone and 11-KT, and reasonably well to OA and androstenedione. In situ hybridization analysis of zebrafish testis revealed that ar mRNA expression was detected in the subpopulation of Sertoli cells contacting early spermatogonia.

Plasma 11-deoxycorticosterone (DOC) and mineralocorticoid receptor testicular expression during rainbow trout Oncorhynchus mykiss spermiation: implication with 17alpha, 20beta-dihydroxyprogesterone on the milt fluidity?

BACKGROUND

In rainbow trout (Oncorhynchus mykiss), the endocrine control of spermiation is not fully understood. Besides 11ketotestosterone (11KT) and 17alpha, 20beta-dihydroxyprogesterone (MIS), the potential physiological ligand of the mineralocorticoid receptor (MR) 11-deoxycorticosterone (DOC), is a credible candidate in O. mykiss spermiation regulation as spermiation is accompanied with changes in aqueous and ionic flows.

METHODS

In this study, we investigated potential roles of DOC during spermiation 1) by describing changes in blood plasma DOC level, MR mRNA abundance during the reproductive cycle and MR localization in the reproductive tract 2) by investigating and comparing the effects of DOC (10 mg/kg) and MIS (5 mg/kg) supplementations on sperm parameters 3) by measuring the in vitro effect of DOC on testis MIS production.

RESULTS

The plasma concentration of DOC increased rapidly at the end of the reproductive cycle to reach levels that were 10-50 fold higher in mature males than in immature fish. MR mRNA relative abundance was lower in maturing testes when compared to immature testes, but increased rapidly during the spermiation period, immediately after the plasma rise in DOC. At this stage, immunohistochemistry localized MR protein to cells situated at the periphery of the seminiferous tubules and in the efferent ducts. Neither DOC nor MIS had significant effects on the mean sperm volume, although MIS treatment significantly increased the percentage of males producing milt. However, a significant reduction in the spermatocrit was observed when DOC and MIS were administrated together. Finally, we detected an inhibitory effect of DOC on testis MIS production in vitro.

CONCLUSION

These results are in agreement with potential roles of DOC and MR during spermiation and support the hypothesis that DOC and MIS mechanisms of action are linked during this reproductive stage, maybe controlling milt fluidity. They also confirm that in O. mykiss MIS is involved in spermiation induction.

Stress adaptation, cortisol and pubertal development in the male common carp, Cyprinus carpio

This paper reviews a series of recent studies on the effect of adaptation to chronic stress on pubertal development in the common carp. In pre-pubertal male common carp adaptation to temperature stress caused a retardation of testicular development. Stress-induced delay of the first wave of spermatogenesis could be prevented by treatment with a cortisol antagonist, indicating that the stress effect is mediated by cortisol. Chronically elevated cortisol levels affected all parts of the brain-pituitary-gonad (BPG)-axis. In the hypothalamus lower levels of sGnRH were observed, in the pituitary the steady state levels of FSHbeta-m RNA were decreased, while the testicular production of especially the 11-oxygenated androgens 11-ketoandrostenedione (OA) and 11keto-testosterone (11KT) was strongly diminished. OA and 11KT have been shown to promote testicular development in fish. The LH-induced androgen synthesis in vitro was strongly inhibited by cortisol and its agonist dexamethasone. Although cortisol was shown also to interfere with the synthesis of the 11-oxygenated androgens in vivo, the lower androgen levels induced by cortisol were mainly due to the reduced testicular mass. Restoration of the plasma concentrations of these androgens by implantation could not prevent the cortisol-induced retardation of testicular growth and the first wave of spermatogenesis. Therefore, it is suggested that cortisol acts directly on Sertoli cells and/or on germ cells, which is supported by the demonstration of GRs on germ cells. We have little indication that the cortisol-induced retardation of testicular development is mediated by a decreased secretion of LH, but a crucial role for FSH can not be excluded.