Department of Neurobiology of Rhythms, Institute for Cellular and Integrative Neuroscience, University of Strasbourg, Strasbourg, France.
Chronobiotron UMS3415-CNRS, University of Strasbourg, Strasbourg, France.
J Biol Rhythms. 2018 Jun;33(3):302-317. doi: 10.1177/0748730418766601. Epub 2018 Apr 4.
Adaptation of biological rhythms to a seasonal environment in circannual mammals is achieved via the synchronization of intrinsic circannual rhythms to the external year by photoperiod. In mammals, the photoperiodic information is integrated to seasonal physiology via the pineal hormone melatonin regulation of pars tuberalis (PT) TSHβ expression and its downstream control of hypothalamic dio2 gene expression. In the circannual European hamster, however, photoperiodic entrainment of the circannual clock is possible in pinealectomized animals. The present study explores whether the TSHβ expression in the PT and the downstream hypothalamic pathways are regulated by photoperiod in European hamsters in the absence of melatonin. All animals were kept on an accelerated photoperiodic regime, which compressed the natural year to a 6-month cycle. Sham-operated European hamsters and half of the pinealectomized European hamsters entrained their annual cycle in reproduction, body weight, and activity pattern to this cycle, whereas the other half of the pinealectomized animals followed only each second cycle. In all animals, PT TSHβ and hypothalamic dio2 expressions were higher in hamsters displaying a summer physiological state than in those in winter state. Moreover, in agreement with their seasonal state, reproductive animals (summer state) showed higher expression of rfrp and lower expression of kiss1-genes encoding central regulators of the reproductive axis-than those animals in reproductive quiescence (winter state), indicating the hypothalamic integration of the photoperiodic signal even in pinealectomized animals. The appropriate occurrence of a well-characterized activity pattern indicative of a so-called sensitive phase to short photoperiod suggested that the SCN constructs the melatonin-independent photoperiodic message. This message is sufficient to entrain the circannual rhythm in TSHβ expression in the PT and the downstream hypothalamic neuroendocrine pathway through a yet unknown pathway. These results reinforce the hypothesis that the PT is the site for the integration of circannual and photoperiodic information.
年周期哺乳动物通过光周期将内在的年周期节律与外部年同步，从而适应季节性环境中的生物节律。在哺乳动物中，通过松果腺激素褪黑素调节垂体柄（PT）TSHβ表达及其对下丘脑 dio2 基因表达的下游控制，将光周期信息整合到季节性生理学中。然而，在年周期欧洲仓鼠中，即使在松果腺切除的动物中，年周期钟也可以通过光周期进行同步。本研究探讨了在没有褪黑素的情况下，光周期是否调节欧洲仓鼠 PT 中的 TSHβ表达及其下游下丘脑途径。所有动物均保持在加速的光周期条件下，该条件将自然年压缩为 6 个月的周期。假手术操作的欧洲仓鼠和一半的松果腺切除的欧洲仓鼠使其年周期在繁殖、体重和活动模式上与该周期同步，而另一半的松果腺切除的动物仅跟随每个第二个周期。在所有动物中，表现出夏季生理状态的仓鼠的 PT TSHβ 和下丘脑 dio2 表达高于表现出冬季生理状态的仓鼠。此外，与它们的季节性状态一致，繁殖动物（夏季状态）表现出更高的 rfrp 表达和更低的 kiss1-基因表达，这些基因编码生殖轴的中枢调节剂-与处于生殖静止（冬季状态）的动物相比，表明即使在松果腺切除的动物中，下丘脑也整合了光周期信号。适当出现表明对短光周期敏感的特征性活动模式表明 SCN 构建了不依赖于褪黑素的光周期信息。该信息足以通过未知途径使 PT 中的 TSHβ 表达和下游下丘脑神经内分泌途径的年周期节律同步。这些结果强化了以下假设，即 PT 是整合年周期和光周期信息的部位。
