Photorefractoriness in mammals: Dissociating a seasonal timer from the circadian-based photoperiod response
Photorefractoriness in mammals: Dissociating a seasonal timer from the circadian-based photoperiod response
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DOI：
10.1210/en.2005-0132
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发表时间：
2005-09-01
期刊：
影响因子：
4.8
通讯作者：
Hazlerigg, DG
中科院分区：
文献类型：
--
作者：
Lincoln, GA;Johnston, JD;Hazlerigg, DG
在季节性动物中，长时间暴露在恒定的光周期下会引起光不应性，导致生理机能自发恢复到之前的光周期状态。这项研究测试了这样的假设：光不反应的发生与视交叉上核（昼夜节律起搏器）和结节部（PT，褪黑激素靶组织）中时钟基因的昼夜节律表达变化相关。将索伊羊暴露在夏季光周期（16 小时光照）下 6 周或 30 周，以产生光刺激和光不应性生理机能，并通过测量长期催乳素周期来跟踪季节变化。在整个 24 小时内，每隔 4 小时处死动物。与假设相反，视交叉上核和 PT 中时钟基因（Rev-erb α、Per1、Per2、Bmal1、Cry1）的 24 小时节律表达反映了环境光周期/褪黑激素信号，而不是变化的生理学。相比之下，在光难治动物中，α-糖蛋白激素亚基（α GSU）和β TSH 的 PT 表达下降，趋于短日照样内分泌。我们得出的结论是，长期内分泌周期的产生取决于驱动初始光周期响应的基于昼夜节律的褪黑激素依赖性计时器和驱动长寿物种的昼夜节律的非昼夜节律计时器之间的相互作用。在恒定的光周期下，两个定时器可以分离，导致明显的不应状态。
In seasonal animals, prolonged exposure to constant photoperiod induces photorefractoriness, causing spontaneous reversion in physiology to that of the previous photoperiodic state. This study tested the hypothesis that the onset of photorefractoriness is correlated with a change in circadian expression of clock genes in the suprachiasmatic nucleus (circadian pacemaker) and the pars tuberalis (PT, a melatonin target tissue). Soay sheep were exposed to summer photoperiod (16-h light) for either 6 or 30 wk to produce a photostimulated and photorefractory physiology, and seasonal changes were tracked by measuring the long-term prolactin cycles. Animals were killed at 4-h intervals throughout 24 h. Contrary to the hypothesis, the 24-h rhythmic expression of clock genes (Rev-erb alpha, Per1, Per2, Bmal1, Cry1) in the suprachiasmatic nucleus and PT reflected the ambient photoperiod/melatonin signal and not the changing physiology. Contrastingly, the PT expression of alpha-glycoprotein hormone subunit (alpha GSU) and beta TSH declined in photorefractory animals toward a short day-like endocrinology. We conclude that the generation of long-term endocrine cycles depends on the interaction between a circadian-based, melatonin-dependent timer that drives the initial photoperiodic response and a non-circadian-based timer that drives circannual rhythmicity in long-lived species. Under constant photoperiod the two timers can dissociate, leading to the apparent refractory state.