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Investigating the Regulation of the Hypothalamic-Pituitary-Interrenal Axis in Atlantic Sturgeon (Acipenser Oxyrinchus) Following an Acute Stressor.

This study investigated the response to acute stress in Atlantic sturgeon (Acipenser oxyrinchus) and HPI axis regulation of glucocorticoid production during stress by examining the expression of key genes― corticotropin-releasing hormone (crh), corticotropin-releasing hormone receptor (crhr), proopiomelanocortin (pomca/pomcb), melanocortin 2 receptor (mc2r), and steroidogenic acute regulatory protein (star)―that are associated with hypothalamus/pituitary/interrenal (HPI) axis of bony fishes. Additionally, tyrosine hydrogenase (th1 and th2) and phosphoenolpyruvate carboxykinase (pepck), found in catecholamine-producing cells in the head kidney of the sturgeon, were investigated as alternative pathways of stress regulation outside of the HPI axis. We sought to test the hypothesis that there is an upregulation of one or several components of the HPI axis in A. oxyrinchus to produce a corticosteroidogenic response to acute stress. Atlantic sturgeons were exposed to an acute stressor and were sampled at 1, 6, and 24 h during recovery, whilst maintaining an unstressed control. The fish were examined for plasma cortisol, plasma glucose, and the relative abundance of crh, crhr, pomca, pomcb, mc2r, star, th1, th2, and pepck.

Our investigations demonstrated a significant elevation in plasma glucose and cortisol in response to stress, however, there was no significant transcriptional upregulation of the expected corticosteroidogenic HPI axis components crh, crhr, pomca, pomcb, mc2r, and star. However, the investigation revealed significant upregulation of th2 and pepck in response to stress, which provides a possible explanation for elevated plasma glucose levels that were observed. These findings indicate that there may be alternative pathways for stress-regulation of plasma glucose in A. oxyrinchus and further investigation is necessary for a more comprehensive understanding. Future studies directed at the stress-responsive regulation of cortisol and catecholamines may offer a greater understanding of the neuroendocrine pathways regulating steroidogenesis and gluconeogenesis during stress in A. oxyrinchus as well as basal vertebrates in general.