School of Biomedical Sciences, University of Nottingham, UK.
Mol Cell Endocrinol. 2010 Aug 5;324(1-2):95-101. doi: 10.1016/j.mce.2010.03.018. Epub 2010 Mar 27.
Puberty occurs seasonally in the majority of mammals native to temperate or arctic latitudes, and in species with sufficiently long life spans puberty can be considered to reoccur on an annual basis. The precise timing of puberty and the annual reoccurrence of fertility reflects an interaction of changes in ambient daylength (photoperiod) and endogenous long-term timing processes, which in some species constitute circannual clocks. Recent studies reveal an unexpected common signalling pathway for photoperiodic information in mammals and birds: changes in secretory activity of the pars tuberalis in the pituitary stalk signal to the tanycyte cells in the ependyma lining the third ventricle. The target genes in the tanycytes encode the deiodinase enzymes that regulate the availability of thyroid hormone in the hypothalamus. Central availability of thyroid hormone appears to be the key determinant of seasonal reproductive transitions. Given the necessity of thyroid hormone for the initial development of the central nervous system, it is hypothesized that at puberty and seasonal reoccurrences of fertility it is the changing local levels of thyroid hormone that orchestrate hypothalamic plasticity, ultimately impinging upon the secretion of GnRH.
青春期在大多数温带或北极地区的哺乳动物中呈季节性发生，而在寿命足够长的物种中，青春期可以被认为是每年都会重新出现。青春期的确切时间和生育的年度重现反映了环境日长（光周期）和内源性长期定时过程变化之间的相互作用，在某些物种中，这些过程构成了年周期钟。最近的研究揭示了哺乳动物和鸟类中光周期信息的一个意想不到的共同信号通路：垂体柄结节部的分泌活动的变化向第三脑室衬里的室管膜下的成神经胶质细胞发出信号。成神经胶质细胞中的靶基因编码调节下丘脑甲状腺激素可用性的脱碘酶。中央甲状腺激素的可用性似乎是季节性生殖转变的关键决定因素。鉴于甲状腺激素对中枢神经系统最初发育的必要性，人们假设在青春期和生育的季节性重现中，是变化的局部甲状腺激素水平协调下丘脑的可塑性，最终影响 GnRH 的分泌。
