Corticotropin-Releasing Factor (CRF) is one of the main mediators of the Hypothalamic-Pituitary–Interrenal (HPI) axis to stress response. In Atlantic salmon, a comparative understanding of the crf1 paralogs role in the stress response is still incomplete. Our database searches have identified four crf1 genes in Atlantic salmon, named crf1a1, crf1a2, crf1b1 and crf1b2. Brain distribution analysis revealed that the four crf1 paralogs were widely distributed, and particularly abundant in the telencephalon, midbrain, and hypothalamus of Atlantic salmon post-smolts. To increase the knowledge on crf1-mediated response to stress, Atlantic salmon post-smolts were exposed to either repeated chasing, hypoxia or a combination of chasing and hypoxia for eight days, followed by a novel-acute stressor, confinement. Cortisol, glucose, lactate, and creatinine levels were used as markers for the stress response.

The crf1 paralogs mRNA abundance showed to be dependent on the stress exposure regime. Both crf1 mRNA levels in the telencephalon and crf1a1 mRNA levels in the hypothalamus showed similar response profiles to the serum cortisol levels, i.e., increasing levels during the first 24 h after stress exposure followed by a decline during the eight-day exposure. The similar trend between crf1 and cortisol disappeared once exposed to the novel-acute stressor. There was a minor response to stress for both crf1b1 and crf1b2 in the hypothalamus, while no changes at mRNA level were observed in the hypothalamic crf1a2 under the different stress conditions. No or weak relationship was found between the crf1 paralogs mRNA expression and the other serum stress-indicators analysed. In summary, our data provide novel insights on the dynamic of the HPI axis activation in Atlantic salmon, and thus underline the involvement of the crf1 paralogs as additional factors in the regulation of the stress response in this species. Likewise, the data highlight the importance of analysing all crf1 paralogues response to a stress-condition, in particular in this premature knowledge stage of their functionality. Further analysis and a more detailed time-point series will help to elucidate the response of the HPI axis and the link of crf1 paralogs in the stress response mechanism.

促肾上腺皮质激素释放因子 (CRF) 是下丘脑-垂体-肾间 (HPI) 轴对应激反应的主要介质之一。在大西洋鲑鱼中，对crf1旁系同源物在应激反应中作用的比较了解仍然不完整。我们的数据库搜索已经确定了大西洋鲑鱼中的四个crf1基因，分别命名为crf1a1、crf1a2、crf1b1和crf1b2。脑分布分析显示，四个crf1旁系同源物分布广泛，在大西洋鲑鱼的端脑、中脑和下丘脑中尤其丰富。增加对crf1的了解介导的对压力的反应，大西洋鲑鱼在八天的时间里反复追逐、缺氧或追逐和缺氧的组合，然后是一种新的急性压力源，禁闭。皮质醇、葡萄糖、乳酸和肌酐水平被用作应激反应的标志物。

crf1旁系同源物 mRNA 丰度显示取决于压力暴露状态。端脑中的 crf1 mRNA 水平和下丘脑中的 crf1a1 mRNA水平对血清皮质醇水平显示出相似的反应曲线，即在压力暴露后的前 24 小时内水平升高，然后在八天的暴露期间下降。一旦暴露于新的急性压力源， crf1和皮质醇之间的相似趋势就会消失。下丘脑crf1b1和crf1b2对压力的反应很小，而下丘脑crf1a2的 mRNA 水平没有变化在不同的应力条件下。在crf1 paralogs mRNA 表达与分析的其他血清应激指标之间没有发现或发现关系较弱。总之，我们的数据为大西洋鲑鱼中 HPI 轴激活的动态提供了新的见解，从而强调了crf1旁系同源物作为调节该物种应激反应的额外因素的参与。同样，数据强调了分析所有crf1旁系同源物对压力条件的反应的重要性，特别是在其功能的这个不成熟的知识阶段。进一步的分析和更详细的时间点序列将有助于阐明 HPI 轴的响应和crf1的链接应激反应机制中的旁系同源物。