CNRS, IFCE, INRAE, Université de Tours, PRC, Nouzilly, France.
Institute for Cellular and Integrative Neuroscience, University of Strasbourg, Strasbourg, France.
J Neuroendocrinol. 2022 May;34(5):e13124. doi: 10.1111/jne.13124. Epub 2022 Apr 5.
Synchronization of mammalian breeding activity to the annual change of photoperiod and environmental conditions is of the utmost importance for individual survival and species perpetuation. Subsequent to the early 1960s, when the central role of melatonin in this adaptive process was demonstrated, our comprehension of the mechanisms through which light regulates gonadal activity has increased considerably. The current model for the photoperiodic neuroendocrine system points to pivotal roles for the melatonin-sensitive pars tuberalis (PT) and its seasonally-regulated production of thyroid-stimulating hormone (TSH), as well as for TSH-sensitive hypothalamic tanycytes, radial glia-like cells located in the basal part of the third ventricle. Tanycytes respond to TSH through increased expression of thyroid hormone (TH) deiodinase 2 (Dio2), which leads to heightened production of intrahypothalamic triiodothyronine (T3) during longer days of spring and summer. There is strong evidence that this local, long-day driven, increase in T3 links melatonin input at the PT to gonadotropin-releasing hormone (GnRH) output, to align breeding with the seasons. The mechanism(s) through which T3 impinges upon GnRH remain(s) unclear. However, two distinct neuronal populations of the medio-basal hypothalamus, which express the (Arg)(Phe)-amide peptides kisspeptin and RFamide-related peptide-3, appear to be well-positioned to relay this seasonal T3 message towards GnRH neurons. Here, we summarize our current understanding of the cellular, molecular and neuroendocrine players, which keep track of photoperiod and ultimately govern GnRH output and seasonal breeding.
哺乳动物繁殖活动与光周期和环境条件的年度变化同步对于个体生存和物种延续至关重要。自 20 世纪 60 年代早期证明褪黑素在这一适应过程中的核心作用以来，我们对光调节性腺活动的机制的理解有了很大的提高。目前的光周期神经内分泌系统模型指出，褪黑素敏感的垂体中间叶（PT）及其季节性调节的促甲状腺激素（TSH）的产生，以及 TSH 敏感的下丘脑门脉细胞（tanycytes），在调节季节性繁殖中起着关键作用。门脉细胞通过增加甲状腺激素（TH）脱碘酶 2（Dio2）的表达来对 TSH 做出反应，这导致在春季和夏季较长的日子里，下丘脑内三碘甲状腺原氨酸（T3）的产生增加。有强有力的证据表明，这种局部的、长日照驱动的 T3 增加将 PT 处的褪黑素输入与促性腺激素释放激素（GnRH）输出联系起来，使繁殖与季节同步。T3 影响 GnRH 的机制尚不清楚。然而，中基底下丘脑的两种不同的神经元群体，表达（Arg）（Phe）-酰胺肽 kisspeptin 和 RFamide 相关肽-3，似乎很适合将这种季节性 T3 信息传递给 GnRH 神经元。在这里，我们总结了我们对细胞、分子和神经内分泌参与者的当前理解，这些参与者跟踪光周期并最终控制 GnRH 输出和季节性繁殖。
