Boswell Timothy, Olson Sarena K, Bentley George E, Perfito Nicole, Ramenofsky Marilyn
School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, UK.
Department of Neurobiology Physiology Behavior, University of California, Davis, Davis, California, USA.
J Neuroendocrinol. 2025 Jun;37(6):e70036. doi: 10.1111/jne.70036. Epub 2025 Apr 28.
Before migration, birds express hyperphagia leading to deposition of fuel in support of long-distance flight. Long days in spring stimulate a photoperiodic neuroendocrine cascade leading to heightened food intake. A major component of the response of the reproductive system to increased daylength in birds is the local conversion of thyroxine (T4) to triiodothyronine (T3) in the medial basal hypothalamus. However, mechanisms of photostimulation regulating hyperphagia in migratory birds have yet to be resolved. We report results from two studies of Gambel's White-crowned Sparrow (Zonotrichia leucophrys gambelii), a long-distance migrant. We used quantitative PCR to measure basal hypothalamic gene expression of several neuropeptides, glucocorticoid receptors, type II and type III iodothyronine deiodinase enzymes (DIO2 and DIO3), and α1 and α2 subunits of the cellular energy sensor AMP-activated protein kinase (AMPKα1 and AMPKα2). The first study involved birds on short days of 9L:15D exposed to 18 h food deprivation. In the second study, birds were photostimulated by one or two long days of 20L:4D. We observed no significant effects of food deprivation on hypothalamic gene expression. However, photostimulation significantly increased food intake on the first and second long days and was associated with significant increases in agouti-related protein (AGRP) and AMPKα2 mRNAs and in the ratio of DIO2/DIO3 expression. The pattern of increased DIO2 and decreased DIO3 gene expression is likely to have increased basal hypothalamic T3 content. This, in turn, may lead to altered local AMPK signaling to increase AGRP biosynthesis and thereby promote photostimulated hyperphagia.
在迁徙之前，鸟类会出现食欲亢进，从而储存能量以支持长途飞行。春季的长日照会刺激光周期神经内分泌级联反应，导致食物摄入量增加。鸟类生殖系统对日照延长的反应的一个主要组成部分是内侧基底下丘脑将甲状腺素（T4）局部转化为三碘甲状腺原氨酸（T3）。然而，调节候鸟食欲亢进的光刺激机制尚未得到解决。我们报告了两项对甘贝尔白冠雀（Zonotrichia leucophrys gambelii）的研究结果，这是一种长途迁徙鸟类。我们使用定量PCR来测量几种神经肽、糖皮质激素受体、II型和III型碘甲状腺原氨酸脱碘酶（DIO2和DIO3）以及细胞能量传感器AMP激活蛋白激酶（AMPKα1和AMPKα2）的α1和α2亚基在基底下丘脑的基因表达。第一项研究涉及处于9小时光照：15小时黑暗短日照条件下且经历18小时食物剥夺的鸟类。在第二项研究中，鸟类通过一或两个20小时光照：4小时黑暗的长日照进行光刺激。我们观察到食物剥夺对下丘脑基因表达没有显著影响。然而，光刺激在第一个和第二个长日照时显著增加了食物摄入量，并且与刺鼠相关蛋白（AGRP）和AMPKα2 mRNA的显著增加以及DIO2/DIO3表达比值的增加有关。DIO2基因表达增加和DIO3基因表达减少的模式可能增加了基底下丘脑的T3含量。反过来，这可能导致局部AMPK信号改变，以增加AGRP的生物合成，从而促进光刺激引起的食欲亢进。
