Regulation of the corticosteroid signalling system in rainbow trout HPI axis during confinement stress

Abstract

This study aims to shed light on corticosteroid regulation of stress in teleost fish with focus on the corticosteroid signalling system. The role of the mineralocorticoid-like hormone 11-deoxycorticosterone (DOC) in fish is still enigmatic, as is the function of the mineralocorticoid receptor, MR. Low plasma DOC levels and ubiquitous tissue distribution of MR question the physiological relevance of the mineralocorticoid-axis. Furthermore, the particular purpose of each of the three corticosteroid receptors in fish, the glucocorticoid receptors, GR1 and GR2, and the MR, is still largely unknown. Therefore we investigate the regulation of cortisol and DOC in plasma and mRNA levels of MR, GR1 and GR2 in the HPI-axis tissues (hypothalamus, pituitary and interrenal gland) during a detailed confinement stress time-course. Here we show a sustained up-regulation of plasma DOC levels during a confinement stress time-course. However, the low DOC levels compared to cortisol measured in the plasma do not favour an activity of DOC through MR receptors. Furthermore, we show differential contribution of the CRs in regulation and control of HPI axis activity following confinement stress. Judged by the variation of mRNA levels negative feedback regulation of cortisol release occurs on the level of the pituitary via MR and on the level of the interrenal gland via GR2. Finally, asa significant effect of confinement stress on CR expressions was observed in the pituitary gland, we completed this experiment by demonstrating that corticosteroid receptors (GR1, GR2 and MR) are co-expressed in the ACTH cells located in the adenohypophysis. Overall, these data suggest the involvement of these receptors in the regulation of the HPI axis activity by cortisol.

Ovarian transcriptomic signatures of zebrafish females resistant to different environmental perturbations

“…Fish subjected to chronic stress showed lower GR levels in the brain (Piato et al, ). Further, changes in rainbow trout GR expression levels in the HPI axis were found after 7 days of confinement (Kiilerich et al, ). As cortisol exerts different effects on various organ systems, it is likely that the functional targets of GR were different in each tissue (Le et al, ).…”

“…As cortisol exerts different effects on various organ systems, it is likely that the functional targets of GR were different in each tissue (Le et al, 2005). The cortisol plasma levels increased after 7 and 14 days of chronic confinement in sea bream (Sparus aurata; Barton, Ribas, Acerete, & Tort, 2005) and rainbow trout (Kiilerich et al, 2018), respectively, but they were recovered in longer confinement experiments (~200 days) in wedge sole (Dicologoglossa cuneate; Herrera, Ruiz-Jarabo, Vargas-Chacoff, de la Roca, & Mancera, 2015). In a similar manner, no difference in cortisol levels was found in juvenile zebrafish subjected to HD during 45 days (Ribas et al, 2017a) but, when sexually mature, GR was downregulated in the gonads at the highest densities, especially in females.…”

The Use of Dietary Additives in Fish Stress Mitigation: Comparative Endocrine and Physiological Responses

“…Eissa and Huang (33) have revised thoroughly all genes involved in the fish stress response depending on stressor type, and stated that the use of genomic tools to study the candidate genes associated with stress responses are often unique signatures or imprints of specific stressors and could determine early signs of stressors. Having this in mind, Kiilerich et al (34) have recently studied the expression of glucocorticoid and mineralocorticoid receptors (i.e., GR1, GR2, and MR) at different levels, concluding that the control and release of cortisol after stress is regulated through a negative cortisol feedback occurring at pituitary level; to the date, it was thought that this feedback occurred at every level of the HPI axis. Other authors have concluded that cortisol regulation is also dependent on circulating glucose concentration under acute stress, reporting a stimulatory effect of increasing glucose levels on the cortisol release (35).…”

Transcriptional Profiles of Genes Related to Stress and Immune Response in Rainbow Trout (Oncorhynchus mykiss) Symptomatically or Asymptomatically Infected With Vibrio anguillarum

“…The brain, kidney, and spleen were collected for RNA-Seq. Previous studies in trout revealed important genes involved in regulating stress responses and immune functions (35)(36)(37)(38)(39)(40); therefore, we targeted these candidate genes (Figure 1). Our studies showed that complement-and TNF-associated immune defenses were specifically activated in AT.…”