Lane Samuel J, Emmerson Michael G, VanDiest Isaac J, Hucul Catherine, Beck Michelle L, Davies Scott, Gilbert Elizabeth R, Sewall Kendra B
Virginia Tech, Department of Biological Sciences, 1405 Perry Street, Blacksburg, VA 24061, United States.
Virginia Tech, Department of Biological Sciences, 1405 Perry Street, Blacksburg, VA 24061, United States.
Gen Comp Endocrinol. 2021 Sep 1;310:113809. doi: 10.1016/j.ygcen.2021.113809. Epub 2021 May 6.
Urban habitats present animals with persistent disturbances and acute stressors not present in rural habitats or present at significantly lower levels. Differences in the glucocorticoid stress response could underlie colonization of these novel habitats. Despite urban habitats characterization as more stressful, previous comparisons of urban and rural birds have failed to find consistent differences in baseline and stress induced glucocorticoid levels. Another aspect of glucocorticoid regulation that could underlie an animal's ability to inhabit novel habitats, but has yet to be well examined, is more efficient termination of the glucocorticoid stress response which would allow birds in urban habitats to recover more quickly after a disturbance. The glucocorticoid stress response is terminated by negative feedback achieved primarily through their binding of receptors in the hippocampus and hypothalamus and subsequent decreased synthesis and release from the adrenals. We investigated if male song sparrows (Melospiza melodia) in urban habitats show more efficient termination of the glucocorticoid stress response than their rural counterparts using two approaches. First, we measured glucocorticoid receptor, mineralocorticoid receptor and 11β-HSD2 (an enzyme that inactivates corticosterone) mRNA expression in negative feedback targets of the brain (the hippocampus and hypothalamus) as a proxy measure of sensitivity to negative feedback. Second, we measured plasma corticosterone levels after standardized restraint and again following a challenge with the synthetic glucocorticoid, dexamethasone, as a means of assessing how quickly birds decreased glucocorticoid synthesis and release. Though there were no differences in the hypothalamus of urban and rural song sparrows, urban birds had lower glucocorticoid receptor and 11β-HSD2 mRNA expression in the hippocampus. Further, urban and rural birds had similar reductions in corticosterone following the dexamethasone challenge, suggesting that they do not differ in how quickly they decrease glucocorticoid synthesis and release. Thus, urban and rural song sparrows display similar termination of the glucocorticoid stress response even though urban birds have decreased hippocampal glucocorticoid receptor and 11β-HSD2 abundance.
城市栖息地给动物带来了持续的干扰和急性应激源，而这些在农村栖息地并不存在或水平显著更低。糖皮质激素应激反应的差异可能是这些新栖息地殖民化的基础。尽管城市栖息地被认为压力更大，但之前对城市和农村鸟类的比较未能在基线和应激诱导的糖皮质激素水平上找到一致的差异。糖皮质激素调节的另一个方面可能是动物适应新栖息地能力的基础，但尚未得到充分研究，即糖皮质激素应激反应的更有效终止，这将使城市栖息地的鸟类在干扰后能更快恢复。糖皮质激素应激反应通过负反馈终止，主要是通过它们与海马体和下丘脑的受体结合，随后肾上腺合成和释放减少来实现。我们采用两种方法研究了城市栖息地的雄性歌带鹀（Melospiza melodia）是否比农村的同类表现出更有效的糖皮质激素应激反应终止。首先，我们测量了大脑负反馈靶点（海马体和下丘脑）中糖皮质激素受体、盐皮质激素受体和11β-HSD2（一种使皮质酮失活的酶）的mRNA表达，作为对负反馈敏感性的替代指标。其次，我们测量了标准化束缚后以及用合成糖皮质激素地塞米松激发后的血浆皮质酮水平，以此评估鸟类降低糖皮质激素合成和释放的速度。尽管城市和农村歌带鹀的下丘脑没有差异，但城市鸟类海马体中的糖皮质激素受体和11β-HSD2 mRNA表达较低。此外，地塞米松激发后，城市和农村鸟类的皮质酮减少情况相似，这表明它们在降低糖皮质激素合成和释放的速度上没有差异。因此，尽管城市鸟类海马体中的糖皮质激素受体和11β-HSD2丰度降低，但城市和农村歌带鹀的糖皮质激素应激反应终止情况相似。
