University of South Florida, Department of Integrative Biology, 4202 E Fowler Avenue, Tampa, FL 33620, USA.
Gen Comp Endocrinol. 2013 Mar 1;183:32-7. doi: 10.1016/j.ygcen.2012.11.021. Epub 2012 Dec 19.
Glucocorticoids (GCs) help individuals cope with changes throughout life; one such change is the seasonal transition through life-history stages. Previous research shows that many animals exhibit seasonal variation in baseline GCs and GC responses to stressors, but the effects of season on other aspects of GC regulation have been less studied. Moreover, whether elements of GC regulation covary within individuals and whether covariation changes seasonally has been not been investigated. Evolutionarily, strong linkages among GC regulatory elements is predicted to enhance system efficiency and regulation, however may reduce the plasticity necessary to ensure appropriate responses under varying conditions. Here, we measured corticosterone (CORT), the major avian GC, at baseline, after exposure to a restraint stressor, and in response to dexamethasone (to assess negative feedback capacity) in wild house sparrows (Passer domesticus) during the breeding and molting seasons. We also measured hippocampal mRNA expression of the two receptors primarily responsible for CORT regulation: the mineralocorticoid and glucocorticoid receptors (MR and GR, respectively). Consistent with previous studies, restraint-induced CORT was lower during molt than breeding, but negative-feedback was not influenced by season. Receptor gene expression was affected by season, however, as during breeding, the ratio of MR to GR expression was significantly lower than during molt. Furthermore, MR expression was negatively correlated with CORT released in response to a stressor, but only during molt. We found that individuals that most strongly up-regulated CORT in response to restraint were also most effective at reducing CORT via negative feedback; although these relationships were independent of season, they were stronger during molt.
糖皮质激素（GCs）帮助个体应对一生中的变化；其中一种变化是通过生活史阶段的季节性转变。先前的研究表明，许多动物的基础 GCs 和 GC 对压力源的反应表现出季节性变化，但季节对 GC 调节的其他方面的影响研究较少。此外，GC 调节要素在个体内部是否存在相关性，以及这种相关性是否随季节变化，尚未得到调查。从进化的角度来看，GC 调节要素之间的紧密联系预计会增强系统的效率和调节能力，但可能会降低在不同条件下确保适当反应所需的可塑性。在这里，我们在繁殖和换羽季节测量了野生家麻雀（Passer domesticus）在基线、暴露于束缚应激源后和用地塞米松（评估负反馈能力）后的皮质酮（CORT），即主要的鸟类 GC。我们还测量了两个主要负责 CORT 调节的受体的海马 mRNA 表达：盐皮质激素和糖皮质激素受体（MR 和 GR，分别）。与先前的研究一致，换羽期的束缚诱导 CORT 低于繁殖期，但负反馈不受季节影响。受体基因表达受季节影响，然而，在繁殖期，MR 与 GR 表达的比值明显低于换羽期。此外，MR 表达与应激反应中释放的 CORT 呈负相关，但仅在换羽期。我们发现，在应激反应中最强地上调 CORT 的个体，通过负反馈降低 CORT 的效果也最强；尽管这些关系独立于季节，但在换羽期更强。
