Institute of Cellular and Integrative Neurosciences, CNRS and University of Strasbourg, Strasbourg, France.
Multidisciplinary faculty, LPRD, Sultan Moulay Slimane University, Beni-Mellal, Morocco.
Eur J Neurosci. 2021 Jun;53(11):3612-3620. doi: 10.1111/ejn.15228. Epub 2021 Apr 27.
The duration of daytime light phase (photoperiod) controls reproduction in seasonal mammals. Syrian hamsters are sexually active when exposed to long photoperiod, while gonadal atrophy is observed after exposure to short photoperiod. The photorefractory period, or photorefractoriness, is a particular state of spontaneous recrudescence of sexual activity that occurs after a long-term exposure to short photoperiod. Expression of core clock genes in the master circadian clock contained in the suprachiasmatic nuclei depends on photoperiodic conditions. Interestingly, the expression of the Clock gene is also modified in photorefractory Syrian hamsters. Since melatonin and testosterone levels in seasonal species are dependent on photoperiod, photoperiodic variations of Clock mRNA levels in the suprachiasmatic clock could be a consequence of these hormonal changes. To test this hypothesis, we analysed the effects of pinealectomy on Clock mRNA changes due to long to short photoperiod transition and of gonadectomy on Clock mRNA levels in photorefractory period. Our data show that the suprachiasmatic integration of the short photoperiod (assessed by a rhythmic expression profile of Clock) is independent of the presence of melatonin. Furthermore, constitutively low expression of Clock observed during the photorefractory period does not require the presence of either melatonin or testosterone. However, we show that both hormones provide positive feedback on average levels of Clock expression. Thus, our data support the hypothesis that daily variations of Clock levels in the suprachiasmatic nuclei are influenced by photoperiodic changes and the time spent in short photoperiod, independently of seasonal modifications of melatonin or testosterone levels.
光周期（白天时间长度）控制季节性哺乳动物的繁殖。叙利亚仓鼠在暴露于长光周期时具有性活动能力，而在暴露于短光周期后则观察到性腺萎缩。光感受性不应期或光感受性迟钝是一种特殊的自发恢复性活动状态，发生在长期暴露于短光周期之后。主生物钟中包含的视交叉上核中的核心时钟基因的表达取决于光周期条件。有趣的是，Clock 基因的表达在光感受性迟钝的叙利亚仓鼠中也被修饰。由于季节性物种中的褪黑素和睾酮水平取决于光周期，因此视交叉上核时钟中 Clock mRNA 水平的光周期变化可能是这些激素变化的结果。为了验证这一假设，我们分析了松果腺切除术对长光周期到短光周期转变过程中 Clock mRNA 变化的影响，以及性腺切除术对光感受性迟钝期间 Clock mRNA 水平的影响。我们的数据表明，短光周期对视交叉上核的整合（通过 Clock 的节律表达模式来评估）独立于褪黑素的存在。此外，在光感受性迟钝期间观察到的 Clock 持续低表达不需要褪黑素或睾酮的存在。然而，我们表明，这两种激素都对 Clock 表达的平均水平提供正反馈。因此，我们的数据支持这样一种假设，即视交叉上核中 Clock 水平的日变化受光周期变化和短光周期持续时间的影响，而不受褪黑素或睾酮水平的季节性变化的影响。
