In mammals, the suprachiasmatic nuclei (SCN) constitute the main circadian clock, receiving input from the retina which allows synchronization of endogenous biological rhythms with the daily light/dark cycle. Over the year, the SCN encodes photoperiodic variations through duration of melatonin secretion, with abundant nocturnal levels in winter and lower levels in summer. Thus, light information is critical to regulate seasonal reproduction in many species and is part of the central photoperiodic integration. Since intrinsically photosensitive retinal ganglion cells (ipRGCs) are vital for circadian photoentrainment and other nonvisual functions, we studied the contribution of ipRGCs in photoperiod integration in C3H retinal degeneration 1 (rd1) mice. We assessed locomotor activity and melatonin secretion in mice exposed to short or long photoperiods. Our results showed that rd1 mice are still responsive to photoperiod variations in term of locomotor activity, melatonin secretion, and regulation of the reproductive axis. In addition, retinas of animals exposed to short photoperiod exhibit higher melanopsin labeling intensity compared with the long photoperiod condition, suggesting seasonal-dependent changes within this photoreceptive system. These results show that ipRGCs in rd1 mice can still measure photoperiod and suggest a key role of melanopsin cells in photoperiod integration and the regulation of seasonal physiology.

中文翻译：

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C3H rd1 小鼠的光周期整合

在哺乳动物中，视交叉上核 (SCN) 构成主要的生物钟，接收来自视网膜的输入，从而使内源性生物节律与每日光/暗周期同步。一年中，SCN 通过褪黑激素分泌的持续时间编码光周期变化，冬季夜间水平丰富，夏季水平较低。因此，光信息对于调节许多物种的季节性繁殖至关重要，并且是中央光周期整合的一部分。由于本质上光敏视网膜神经节细胞 (ipRGCs) 对于昼夜节律光夹带和其他非视觉功能至关重要，我们研究了 ipRGCs 在 C3H视网膜变性 1 ( rd1） 老鼠。我们评估了暴露于短或长光周期的小鼠的运动活动和褪黑激素分泌。我们的研究结果表明，rd1小鼠在运动活动、褪黑激素分泌和生殖轴调节方面仍然对光周期变化有反应。此外，与长光周期条件相比，暴露于短光周期条件下的动物视网膜表现出更高的黑视素标记强度，表明该感光系统内的季节性变化。这些结果表明，rd1小鼠中的 ipRGCs 仍然可以测量光周期，并表明黑视蛋白细胞在光周期整合和季节性生理调节中的关键作用。