Animals make use of changes in photoperiod to adapt their physiology to the forthcoming breeding season. Comparative studies have contributed to our understanding of the mechanisms of seasonal reproduction in vertebrates. Birds are excellent models for studying these phenomena because of their rapid and dramatic responses to changes in photoperiod. Deep brain photoreceptors in birds perceive and transmit light information to the pars tuberalis (PT) in the pituitary gland, where the thyroid-stimulating hormone (TSH) is produced. This PT-TSH locally increases the level of the bioactive thyroid hormone T3 via the induction of type 2 deiodinase production in the mediobasal hypothalamus, and an increased T3 level, in turn, controls seasonal gonadotropin-releasing hormone secretion. In mammals, the eyes are the only photoreceptive structure, and nocturnal melatonin secretion encodes day-length information and regulates the PT-TSH signaling cascade. In Salmonidae, the saccus vasculosus plays a pivotal role as a photoperiodic sensor. Together, these studies have uncovered the universality and diversity of fundamental traits in vertebrates.

中文翻译：

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脊椎动物季节性繁殖的潜在机制。

动物利用光周期的变化使它们的生理适应即将到来的繁殖季节。比较研究有助于我们了解脊椎动物的季节性繁殖机制。鸟类是研究这些现象的优秀模型，因为它们对光周期的变化具有快速而戏剧性的响应。鸟类中的大脑深部感光细胞会感知光信息并将光信息传输至垂体腺中的结缔组织（PT），从而产生甲状腺刺激激素（TSH）。这种PT-TSH通过诱导中下丘脑下丘脑2型脱碘酶的产生，局部增加了生物活性甲状腺激素T3的水平，而升高的T3水平又控制了季节性促性腺激素释放激素的分泌。在哺乳动物中，眼睛是唯一的感光结构，夜间褪黑激素分泌编码日间信息，并调节PT-TSH信号级联。在鲑科中，脉管脉管作为光周期传感器起着关键作用。总之，这些研究揭示了脊椎动物基本特征的普遍性和多样性。