Challet Etienne, Poirel Vincent-Joseph, Malan André, Pévet Paul
Laboratory of Neurobiology of Rhythms (CNRS UMR7518), University Louis Pasteur, Neuroscience Federation (IFR37), Strasbourg, France.
J Neurosci Res. 2003 Jun 1;72(5):629-37. doi: 10.1002/jnr.10616.
The suprachiasmatic nuclei (SCN) of the hypothalamus contain the master circadian clock in mammals. Nocturnal light pulses that reset the circadian clock also lead to rapid increases in levels of Per1 and Per2 mRNA in the SCN, suggesting that these genes are involved in the synchronization to light. During the day, when light has no phase-shifting effects in nocturnal rodents, the consequences of light exposure for Per expression have been less thoroughly studied. Therefore, the effects of light exposure during the day were assessed on Per1 and Per2 mRNA in the SCN of mice. Expression of Per1 and Per2 was generally increased by 30-min light pulses during the subjective day, with more pronounced effects in the morning. One exception was noted for a transient decrease in Per2 expression after a short light pulse applied at midday. Prolonged light exposure (up to 3 hr) starting at midday markedly increased Per2 expression but not that of Per1. Moreover, the amplitude of the daily variations of both Per and the duration of Per1 peak was increased in mice exposed to a light-dark cycle compared with those transferred to constant darkness. Finally, the amplitude of the daily variations of both Per and the basal level of Per1 were increased in mice under a light-dark cycle compared with animals synchronized to a skeleton photoperiod (i.e., with daily dawn and dusk 1-hr exposures to light). Taken together, the results indicate that prolonged light exposure during daytime positively modulates daily levels of Per1 and Per2 mRNA in the SCN of mice.
下丘脑的视交叉上核（SCN）包含哺乳动物的主生物钟。重置生物钟的夜间光脉冲也会导致SCN中Per1和Per2 mRNA水平迅速升高，这表明这些基因参与了与光的同步。在白天，当光对夜行性啮齿动物没有相位转移作用时，光照对Per表达的影响研究得较少。因此，评估了白天光照对小鼠SCN中Per1和Per2 mRNA的影响。在主观白天，30分钟的光脉冲通常会增加Per1和Per2的表达，上午的影响更明显。一个例外是，中午施加短光脉冲后，Per2表达出现短暂下降。从中午开始的长时间光照（长达3小时）显著增加了Per2的表达，但没有增加Per1的表达。此外，与转移到持续黑暗中的小鼠相比，暴露于明暗循环的小鼠中Per的每日变化幅度和Per1峰值持续时间都增加了。最后，与同步到骨架光周期（即每天黎明和黄昏有1小时光照）的动物相比，处于明暗循环的小鼠中Per的每日变化幅度和Per1的基础水平都增加了。综上所述，结果表明白天长时间光照可正向调节小鼠SCN中Per1和Per2 mRNA的每日水平。
