Exploring transcriptional and post-transcriptional epigenetic regulation of crf and 11βhsd2 in rainbow trout brain during chronic social stress.

Using dominance hierarchies in juvenile rainbow trout (Oncorhynchus mykiss) as a model of chronic social stress in fish, we explored whether epigenetic transcriptional and post-transcriptional mechanisms are involved in the gene expression of corticotropin-releasing factor (crf) and 11β-hydroxysteroid dehydrogenase (11βhsd2), key factors involved in the regulation of the endocrine stress axis response. In juvenile rainbow trout pairs, subordinate individuals display sustained elevation of circulating cortisol concentrations. Cortisol production is controlled by the hypothalamic-pituitary-interrenal (HPI) axis in fish and initiated by CRF release from the preoptic area (POA).

Negative feedback regulation in the hypothalamic-pituitary-interrenal axis of rainbow trout subjected to chronic social stress.

The formation of dominance hierarchies in pairs of juvenile rainbow trout (Oncorhynchus mykiss) results in subordinate individuals exhibiting chronically elevated plasma cortisol concentrations. Cortisol levels reflect a balance between cortisol production, which is coordinated by the hypothalamic-pituitary-interrenal (HPI) axis in teleost fish, and negative feedback regulation and hormone clearance, which act to lower cortisol levels. However, the mechanisms contributing to the longer-term elevation of cortisol levels during chronic stress are not well established in fishes.

The relationship between hypoxia exposure and circulating cortisol levels in social and solitary African mole-rats: An initial report.

Hypoxemia from exposure to intermittent and/or acute environmental hypoxia (lower oxygen concentration) is a severe stressor for many animal species. The response to hypoxia of the hypothalamic-pituitary-adrenal axis (HPA-axis), which culminates in the release of glucocorticoids, has been well-studied in hypoxia-intolerant surface-dwelling mammals. Several group-living (social) subterranean species, including most African mole-rats, are hypoxia-tolerant, likely due to regular exposure to intermittent hypoxia in their underground burrows.

Social status-dependent regulation and function of the somatotropic axis in juvenile rainbow trout.

Juvenile rainbow trout (Oncorhynchus mykiss) develop social hierarchies when competing for resources in a constrained environment. Among the physiological consequences of social status are changes in organismal energy metabolism, which generally favour anabolic pathways in dominant fish and catabolic pathways in subordinate fish. The somatotropic axis is an important regulator of metabolism and growth that could be involved in mediating metabolic changes in response to social status in juvenile rainbow trout.

Regulation of cortisol production during chronic social stress in rainbow trout.

Chronic stress resulting from social interactions impacts the endocrine stress response in many vertebrates, including teleost fishes. Juvenile rainbow trout held in pairs form a dominance hierarchy with the subordinate individual exhibiting chronic elevation of plasma cortisol and an attenuated cortisol response to an additional acute stressor. The current study investigated the mechanisms underlying this apparent dichotomy in cortisol production at the level of the head kidney (adrenal homolog).

Chronic social stress alters protein metabolism in juvenile rainbow trout, Oncorhynchus mykiss.

When confined in pairs, juvenile rainbow trout (Oncorhynchus mykiss) form dominance hierarchies in which subordinate fish exhibit characteristic physiological changes including reduced growth rates and chronically elevated plasma cortisol concentrations. We hypothesized that alterations in protein metabolism contribute to the reduced growth rate of socially stressed trout, and predicted that subordinate trout would exhibit reduced rates of protein synthesis coupled with increases in protein degradation. Protein metabolism was assessed in dominant and subordinate fish after 4 days of social interaction, and in fish that were separated after 4 days of interaction for a 4 days recovery period, to determine whether effects on protein metabolism recovered when social stress was alleviated.

Loss of hypoxia-inducible factor 1α affects hypoxia tolerance in larval and adult zebrafish ().

The coordination of the hypoxic response is attributed, in part, to hypoxia-inducible factor 1α (Hif-1α), a regulator of hypoxia-induced transcription. After the teleost-specific genome duplication, most teleost fishes lost the duplicate copy of Hif-1α, except species in the cyprinid lineage that retained both paralogues of Hif-1α (Hif1aa and Hif1ab). Little is known about the contribution of Hif-1α, and specifically of each paralogue, to hypoxia tolerance.

Cortisol modulates metabolism and energy mobilization in wild-caught pumpkinseed (Lepomis gibbosus).

Acute elevation of cortisol via activation of the hypothalamic-pituitary-interrenal (HPI) axis aids the fish in dealing with a stressor. However, chronic elevation of cortisol has detrimental effects and has been studied extensively in lab settings. However, data pertaining to wild teleosts are lacking.

Epigenetics in teleost fish: From molecular mechanisms to physiological phenotypes.

While the field of epigenetics is increasingly recognized to contribute to the emergence of phenotypes in mammalian research models across different developmental and generational timescales, the comparative biology of epigenetics in the large and physiologically diverse vertebrate infraclass of teleost fish remains comparatively understudied. The cypriniform zebrafish and the salmoniform rainbow trout and Atlantic salmon represent two especially important teleost orders, because they offer the unique possibility to comparatively investigate the role of epigenetic regulation in 3R and 4R duplicated genomes. In addition to their sequenced genomes, these teleost species are well-characterized model species for development and physiology, and therefore allow for an investigation of the role of epigenetic modifications in the emergence of physiological phenotypes during an organism's lifespan and in subsequent generations.

Cortisol elevation post-hatch affects behavioural performance in zebrafish larvae.

Maternal cortisol is essential for cortisol stress axis development and de novo production of this steroid commences only after hatch in zebrafish (Danio rerio). However, very little is known about the effect of elevated cortisol levels, during the critical period of stress axis activation, on larval performance. We tested the hypothesis that elevated cortisol levels post-hatch affect behavioural performance and this is mediated by glucocorticoid receptor (GR) activation in zebrafish larvae.

Maternal cortisol stimulates neurogenesis and affects larval behaviour in zebrafish.

Excess glucocorticoid transferred from stressed mother to the embryo affects developing vertebrate offspring, but the underlying programming events are unclear. In this study, we tested the hypothesis that increased zygotic glucocorticoid deposition, mimicking a maternal stress scenario, modifies early brain development and larval behaviour in zebrafish (Danio rerio). Cortisol was microinjected into the yolk at one cell-stage, to mimic maternal transfer, and the larvae [96 hours post-fertilization (hpf)] displayed increased activity in light and a reduction in thigmotaxis, a behavioural model for anxiety, suggesting an increased propensity for boldness.

Maternal stress-associated cortisol stimulation may protect embryos from cortisol excess in zebrafish.

Abnormal embryo cortisol level causes developmental defects and poor survival in zebrafish (Danio rerio). However, no study has demonstrated that maternal stress leads to higher embryo cortisol content in zebrafish. We tested the hypothesis that maternal stress-associated elevation in cortisol levels increases embryo cortisol content in this asynchronous breeder.

The antidepressant venlafaxine disrupts brain monoamine levels and neuroendocrine responses to stress in rainbow trout.

Venlafaxine, a serotonin-norepinephrine reuptake inhibitor, is a widely prescribed antidepressant drug routinely detected in the aquatic environment. However, little is known about its impact on the physiology of nontarget organisms. We tested the hypothesis that venlafaxine perturbs brain monoamine levels and disrupts molecular responses essential for stress coping and feeding activity in fish.

Environmental levels of the antidepressant venlafaxine impact the metabolic capacity of rainbow trout.

The antidepressant venlafaxine is detected at parts per billion levels in tertiary-treated municipal wastewater effluent. However, the impact of this serotonin-norepinephrine reuptake inhibitor (SNRI) on non-target aquatic animals is poorly understood. We tested the hypothesis that environmentally relevant levels of venlafaxine disrupt the highly conserved cortisol and glucose response to stress in rainbow trout (Oncorhynchus mykiss).