Differential effects of 17β-estradiol and 11-ketotestosterone on the endocrine stress response in zebrafish (Danio rerio)
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Sexually dimorphic stress responses are present in species across all vertebrate taxa and it has been suggested that these effects are mediated by circulating sex steroids. While a few species of fish have been identified as having a sexually dimorphic stress response, there is conflicting evidence as to the effects of sex steroids on the stress axis. In this study, we tested whether zebrafish exhibit a sexually dimorphic cortisol stress response and whether 17β-estradiol (E2) or 11-ketotestosterone (11KT) modulate the activity of the hypothalamic-pituitary-interrenal (HPI) axis. To accomplish this, we quantified the whole body cortisol response to a physical stressor, cortisol release in vitro, and the expression of key HPI axis regulating genes of control and E2- or 11KT-exposed zebrafish. Under control conditions no dimorphisms in the HPI axis were apparent at rest or in response to a standardized stressor. In contrast, E2-exposure blunted the cortisol response of male fish in vivo and in vitro and as well as corticotropin-releasing factor (crf) expression in the pre-optic area (POA) of the brain. While the expression of some interrenal genes was suppressed by E2-exposure, these changes occurred in both male and female zebrafish. 11KT-exposure increased whole-body cortisol of males at rest and vortex-exposed females, but had no impact on the rate of cortisol synthesis in vitro or on POA crf expression. Therefore, while we found no evidence that zebrafish exhibit a sexually dimorphic cortisol stress response, both E2 and 11KT can modulate the activity of the HPI axis in this species and do so via different mechanisms.
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