Prolonged cortisol elevation alters whole body and tissue metabolism in rainbow trout (Oncorhynchus mykiss)

Status-dependent metabolic effects of social interactions in a group-living fish

Social interactions can sometimes be a source of stress, but social companions can also ameliorate and buffer against stress. Stress and metabolism are closely linked, but the degree to which social companions modulate metabolic responses during stressful situations-and whether such effects differ depending on social rank-is poorly understood. To investigate this question, we studied Neolamprologus pulcher, a group-living cichlid fish endemic to Lake Tanganyika and measured the metabolic responses of dominant and subordinate individuals when they were either visible or concealed from one another. When individuals could see each other, subordinates had lower maximum metabolic rates and tended to take longer to recover following an exhaustive chase compared with dominants. In contrast, metabolic responses of dominants and subordinates did not differ when individuals could not see one another. These findings suggest that the presence of a dominant individual has negative metabolic consequences for subordinates, even in stable social groups with strong prosocial relationships.

Hormonal effects on glucose and ketone metabolism in a perfused liver of an elasmobranch, the North Pacific spiny dogfish, Squalus suckleyi

Hormonal influence on hepatic function is a critical aspect of whole-body energy balance in vertebrates. Catecholamines and corticosteroids both influence hepatic energy balance via metabolite mobilization through glycogenolysis and gluconeogenesis. Elasmobranchs have a metabolic organization that appears to prioritize the mobilization of hepatic lipid as ketone bodies (e.g. 3-hydroxybutyrate [3-HB]), which adds complexity in determining the hormonal impact on hepatic energy balance in this taxon. Here, a liver perfusion was used to investigate catecholamine (epinephrine [E]) and corticosteroid (corticosterone [B] and 11-deoxycorticosterone [DOC]) effects on the regulation of hepatic glucose and 3-HB balance in the North Pacific Spiny dogfish, Squalus suckleyi. Further, hepatic enzyme activity involved in ketogenesis (3-hydroxybutyrate dehydrogenase), glycogenolysis (glycogen phosphorylase), and gluconeogenesis (phosphoenolpyruvate carboxykinase) were assessed in perfused liver tissue following hormonal application to discern effects on hepatic energy flux. mRNA transcript abundance key transporters of glucose (glut1 and glut4) and ketones (mct1 and mct2) and glucocorticoid function (gr, pepck, fkbp5, and 11βhsd2) were also measured to investigate putative cellular components involved in hepatic responses. There were no changes in the arterial-venous difference of either metabolite in all hormone perfusions. However, perfusion with DOC increased gr transcript abundance and decreased flow rate of perfusions, suggesting a regulatory role for this corticosteroid. Phosphoenolpyruvate carboxykinase activity increased following all hormone treatments, which may suggest gluconeogenic function; E also increased 3-hydroxybutyrate dehydrogenase activity, suggesting a function in ketogenesis, and decreased pepck and fkbp5 transcript abundance, potentially showing some metabolic regulation. Overall, we demonstrate hormonal control of hepatic energy balance using liver perfusions at various levels of biological organization in an elasmobranch.

Cortisol enhances aerobic metabolism and locomotor performance during the transition to land in an amphibious fish

Amphibious fishes on land encounter higher oxygen (O2) availability and novel energetic demands, which impacts metabolism. Previous work on the amphibious mangrove killifish (Kryptolebias marmoratus) has shown that cortisol becomes elevated in response to air exposure, suggesting a possible role in regulating metabolism as fish move into terrestrial environments. We tested the hypothesis that cortisol is the mechanism by which oxidative processes are upregulated during the transition to land in amphibious fishes. We used two groups of fish, treated fish (+metyrapone, a cortisol synthesis inhibitor) and control (-metyrapone), to determine the impact of cortisol during air exposure (0 and 1 h, 7 days) on O2 consumption, terrestrial locomotion, the phenotype of red skeletal muscle, and muscle lipid concentration. Metyrapone-treated fish had an attenuated elevation in O2 consumption rate during the water to air transition and an immediate reduction in terrestrial exercise performance relative to control fish. In contrast, we found no short- (0 h) or long-term (7 days) differences between treatments in the oxidative phenotype of red muscles, nor in muscle lipid concentrations. Our results suggest that cortisol stimulates the necessary increase in aerobic metabolism needed to fuel the physiological changes that amphibious fishes undergo during the acclimation to air, although further studies are required to determine specific mechanisms of cortisol regulation.

Oral cortisol and dexamethasone intake: Differential physiology and transcriptional responses in the marine juvenile Sparus aurata

This study approached the long-term oral administration of cortisol (F) and dexamethasone (DEX), two synthetic glucocorticoids, compared to a control group (CT) in the juveniles of a marine teleost, the gilthead seabream (Sparus aurata). Physiologically, DEX treatment impaired growth, which appears to be linked to carbohydrate allocation in muscle and liver, hepatic triglycerides depletion, and reduced hematocrit. Hypophyseal gh mRNA expression was 2-fold higher in DEX than in CT or F groups. Similarly, hypothalamic trh and hypophyseal pomcb followed this pattern. Plasma cortisol levels were significantly lower in DEX than in CT, while F presented intermediate levels. In the posterior intestine, measured short circuit-current (Isc) was more anion absorptive in CT and F compared to the DEX group, whereas Isc remained unaffected in the anterior intestine. The derived transepithelial electric resistance (TEER) significantly differed between intestinal regions in the DEX group. These results provide new insights to understand better potential targeted biomarkers indicative of the differential glucocorticoid or mineralocorticoid-receptors activation in fish.

Impact of stress phenotype, elevated temperature, and bacterin exposure on male Atlantic salmon (Salmo salar) growth, stress, and immune biomarker gene expression

In this study, postsmolt male Atlantic salmon, previously identified as low responders (LRs) or high responders (HRs) based on poststress cortisol levels, had their head kidney and liver sampled at 12°C and 20°C before injection (time 0) and after injection (i.e., at 12- and 24-h postinjection, respectively) with either Forte Micro (a multivalent vaccine containing bacterin, to capture peak antibacterial responses) or an equal volume of PBS. Quantitative real-time PCR (qPCR) was then used to measure the expression of 15 biomarker genes in the head kidney and 12 genes in the liver at each temperature/sampling point. Target transcripts were chosen that were related to growth, stress, and innate antibacterial immune responses. Many temperature, phenotype, and injection effects were found for individual genes within these three broad categories, and multivariate statistical analyses (i.e., principal component analysis and permutational multivariate analysis of variance) were used to look for overall patterns in transcript expression. These analyses revealed that HR salmon at 20°C mounted a more robust response (P < 0.05) for the 10 head kidney immune-related transcripts when injected with Forte Micro than LR salmon. In contrast, the seven liver stress-related transcripts displayed a greater response (P = 0.057) in LR versus HR fish with Forte Micro at 12°C. Overall, although this research did find some differences between LR and HR fish, it does not provide strong (conclusive) evidence that the selection of a particular phenotype would have major implications for the health of salmon over the temperature range examined.NEW & NOTEWORTHY This is the first paper to describe the impact of both temperature and bacterial stimulation on head kidney and liver transcript expression in Atlantic salmon characterized as LRs versus HRs. Notably, we found that HR salmon at 20°C mounted a more robust innate antibacterial immune response than LR salmon. In addition, LR fish at 12°C may (P = 0.057) exhibit higher expression of stress-related transcripts in response to vaccine injection relative to HR fish.

Social status influences relationships between hormones and oxidative stress in a cichlid fish

An individual's social environment can have widespread effects on their physiology, including effects on oxidative stress and hormone levels. Many studies have suggested that variation in oxidative stress experienced by individuals of different social statuses might be due to endocrine differences, however, few studies have evaluated this hypothesis. Here, we assessed whether a suite of markers associated with oxidative stress in different tissues (blood/plasma, liver, and gonads) had social status-specific relationships with circulating testosterone or cortisol levels in males of a cichlid fish, Astatotilapia burtoni. Across all fish, blood DNA damage (a global marker of oxidative stress) and gonadal synthesis of reactive oxygen species [as indicated by NADPH-oxidase (NOX) activity] were lower when testosterone was high. However, high DNA damage in both the blood and gonads was associated with high cortisol in subordinates, but low cortisol in dominants. Additionally, high cortisol was associated with greater production of reactive oxygen species (greater NOX activity) in both the gonads (dominants only) and liver (dominants and subordinates). In general, high testosterone was associated with lower oxidative stress across both social statuses, whereas high cortisol was associated with lower oxidative stress in dominants and higher oxidative stress in subordinates. Taken together, our results show that differences in the social environment can lead to contrasting relationships between hormones and oxidative stress.

Sex-Specific and Long-Term Impacts of Early-Life Venlafaxine Exposure in Zebrafish

Venlafaxine, a selective serotonin and norepinephrine reuptake inhibitor, is a widely prescribed antidepressant that is detected in municipal wastewater effluents at µg/L concentrations. It has been shown to impact the early life stages of fish, including neurodevelopment and behaviour in larvae, but whether such early exposures have longer-term consequences are far from clear. Here, we sought to determine whether zygotic deposition of venlafaxine, mimicking a maternal transfer scenario, disturbs the metabolic rate and behavioural performance using zebrafish (Danio rerio). This was tested using freshly fertilized embryos (1-4 cell stage) microinjected with either 0, 1 or 10 ng of venlafaxine and raised to either juvenile (60 days post-fertilization) or adult (10-12 months post-fertilization). Zygotic venlafaxine exposure led to a reduction in the active metabolic rate and aerobic scope, but this was only observed in female fish. On the other hand, the total distance travelled in an open field assessment was greater at the highest concentration of venlafaxine only in the adult males. At the juvenile stage, behavioural assessments demonstrated that venlafaxine exposure may increase boldness-including hyperactivity, lower thigmotaxis, and a reduction in the distance to a novel object. Taken together, these results demonstrate that zygotic venlafaxine exposure may impact developmental programming in a sex-specific manner in fish.