Ontogenesis of the HPI axis and molecular regulation of the cortisol stress response during early development in Dicentrarchus labrax.

Abstract

The cortisol stress response and the molecular programming of the corticoid axis were characterized for the first time during early ontogeny in a Mediterranean marine teleost, the European sea bass (Dicentrarchus labrax). Sea bass embryos, pre-larvae and larvae at specific points of development were exposed to acute stressors and the temporal patterns of cortisol whole body concentrations and the expression of genes involved in corticosteroid biosynthesis, degradation and signaling were determined. Expression of genes (gr1, gr2, mr, crf) involved into the corticoid response regulation combined with histological data indicated that, although a cortisol stress response is evident for the first time around first feeding, a pattern becomes established in larvae at flexion until the formation of all fins. Moreover, mRNA transcript levels of 11β-hydroxylase and 11β-hsd2 showed a strong correlation with the whole body cortisol concentrations. Concluding, our data reveal the presence of an adaptive mechanism in European sea bass at early ontogeny enabling to cope with external stressful stimuli and provide a better insight into the onset and regulation of the stress response in this species.

Early life low intensity stress experience modifies acute stress effects on juvenile brain cell proliferation of European sea bass ( D. Labrax )

“…The present study focused on the effects of early life stress within the active neurogenic zones in juvenile European sea bass brain, using UCLIS application, a valid chronic low intensity stress protocol for E. sea bass during early development [32]. This study based on histological, hormonal (cortisol) and molecular data, lasting effects by modulating AS responses later in life, in adolescence and therefore may be considered critical periods for E sea bass brain development.…”

“…A chronic low intensity stress protocol was applied, in duplicate, for a period of 14 days, as described previously [32], starting at the beginning of two different developmental phases; the flexion or the formation of all fins. In parallel, during the same period, two more groups of larvae were kept undisturbed and served as controls.…”

“…To address the hypothesis that early life mild adversity could be beneficiary for the organism resulting in better coping to future environmental challenges, we used a teleost as an alternative model, the European sea bass, a marine species widely used in aquaculture of great economic importance, sensitive to ordinary husbandry stressors and characterized by high blood cortisol levels in response to stress [29][30][31]. European sea bass is known to respond to an early chronic low intensity stress (UCLIS) protocol, with high water cortisol release rates in the rearing tanks of stressed larvae in all developmental phases applied [32]. Evidence provided on the long-term effects of early life stress influences on juvenile sea bass responses to aquaculture stressors, would further advance our knowledge on long-term stress effects on brain plasticity data.…”

Early life stress and effects at subsequent stages of development in European sea bass (D. labrax)

“…Thus, and based on survival and growth data of both larvae and juvenile fish, the most critical period for exposure to noxius stimuli appeared to be that of first feeding and all fins. In a recent study on European sea bass, based on histological, hormonal (cortisol) and molecular data, it was shown that the first appearance of a distinct and functional hypothalamo-hypophysial-interrenal axis is observed at first feeding, but the stress response becomes fully functional and mature around the stage of all fins (Tsalafouta et al, 2014). This may explain the differential effects of the UCLIS depending on the developmental stage applied.…”

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“…Neurons in the hypothalamus in response to an environmental stressor secrete CRF. CRF is a neurotransmitter that regulates the release of ACTH which binds to the interrenal cells of the head kidney and excites the production and release of cortisol 32 . In the course of HPI activation, glucocorticoid and mineralocorticoid receptors are the mediators of transcriptional effects of cortisol on the peripheral tissues.…”