Uni Environment, Uni Research, Bergen, Norway.
J Neuroendocrinol. 2011 Aug;23(8):733-41. doi: 10.1111/j.1365-2826.2011.02164.x.
Salmon parr-smolt transformation (smoltification) is a mid-life transitional stage between life in freshwater and seawater that entails a wide range of neural, endocrine and physiological modifications. In salmon, the neuroendocrine corticotropin-releasing factor (CRF) system regulates pituitary adrenocorticotrophic hormone and thyrotrophin release. Four experimental groups of Atlantic salmon, Salmo salar, were used to investigated CRF neurogenesis and its regulation during smoltification. We compared: (i) developmental stages (parr and early-smolt) in anadromous controls; (ii) a developmentally arrested model: anadromous reared under continuous light (LL) with anadromous controls; (iii) a natural hypoendocrine/incomplete smolt development salmon model (landlocked) with anadromous controls; and (iv) landlocked treated with thyroxine to anadromous control smolt levels. CRF neurogenesis between groups was studied with bromodeoxyuradine (BrdU) incorporation followed by double-labelling CRF and BrdU immunhistochemistry. The rate of CRF neurogenesis in the preoptic area (POA) increased from parr to early-smolts in anadromous salmon. By contrast, neurogenesis was inhibited in the LL group and reduced in the landlocked salmon. The administration of thyroxine in landlocked salmon to match anadromous levels increased the rate of CRF neurogenesis to anadromous levels. In conclusion, newly-formed CRF cells in the POA during smoltification are associated with increased retinal innervation to the POA and endocrine responsiveness to increased photoperiod. Both genetic and environmental factors influence the degree of salmon brain development. Thyroid hormones increase CRF neurogenesis during this critical period of development in salmon. We hypothesise that a positive-feedback of thyroid hormones on CRF neurogenesis may be an important event in reaching the developmental climax during critical periods.
大西洋鲑鱼在洄游和陆封两种不同生活环境下的皮质激素释放因子（CRF）神经元发生及其调控的比较研究
鲑鱼的幼鱼向成鱼变态（即洄游性鱼类的幼鱼在性腺成熟时期入海）是一个在淡水和海水中生活之间的中间过渡阶段，在此期间伴随着广泛的神经、内分泌和生理变化。在鲑鱼中，神经内分泌 CRF 系统调节垂体促肾上腺皮质激素和促甲状腺素的释放。本研究使用了四个实验组的大西洋鲑鱼，分别是：（i）溯河洄游对照组的幼鱼和成鱼；（ii）发育受阻的模型：在连续光照（LL）下饲养的溯河洄游幼鱼，与对照组进行比较；（iii）天然的低内分泌/不完全洄游性幼鱼发育模型（陆封），与对照组进行比较；（iv）陆封组用甲状腺素处理，使其达到对照组的洄游性幼鱼水平。用溴脱氧尿苷（BrdU）掺入法结合 CRF 和 BrdU 免疫组织化学双重标记来研究各组间的 CRF 神经元发生情况。在溯河洄游鲑鱼中，POA 中的 CRF 神经元发生从幼鱼到早期成鱼阶段逐渐增加。相比之下，LL 组的神经元发生受到抑制，陆封组的减少。在陆封鲑鱼中用甲状腺素处理，使其达到对照组的洄游性幼鱼水平，从而增加了 CRF 神经元的发生速率。总之，在鲑鱼变态期间，POA 中新形成的 CRF 细胞与视网膜向 POA 的神经支配增加以及内分泌对光照时间增加的反应性增加有关。遗传和环境因素都影响鲑鱼大脑的发育程度。甲状腺激素在鲑鱼发育的关键时期增加 CRF 神经元的发生。我们假设甲状腺激素对 CRF 神经元发生的正反馈可能是在关键时期达到发育顶点的重要事件。
