Morphological approach to the light entrainment mechanism of the circadian clock

夜间光照诱导Perl和Per2基因，从而导致哺乳动物昼夜节律中心视交叉上核（SCN）生物钟的重置。我们研究了它们生物钟的光重置机制。通过原位杂交技术，我们发现Perl用于时钟的提前，而Per2用于时钟的延迟。其次，在哺乳动物中，光是使内源性节律与环境同步的主要环境信号。昼长或光周期也影响许多生理事件，如运动活动、睡眠-觉醒节律、温度和激素分泌。我们研究了光周期对SCN中Perl基因日表达的影响。我们认为光周期的变化不仅影响视网膜投射丰富的VLSCN，也影响没有视网膜直接投射的DMSCN。此外，我们还观察到，在临界光脉冲的诱导下，大鼠视交叉上核的多细胞水平振幅下降是不同步的基础。采用原位杂交方法，研究了促动素（PK2）和促动素受体2 （PKR2）在大鼠SCN中的定位。PK2 mrna阳性神经元分布于背内侧和腹外侧SCN。相比之下，含有PKR2 mrna的神经元聚集在SCN的背外侧。然后，为了检查PKR2在SCN中的作用，我们创建了PKR2基因破坏的小鼠（PKR2(-/-)）。表型分析表明，Pkr2（-/-）小鼠OB发育不全，Pkr2（-/-）小鼠生殖系统严重萎缩。在Pkr2（-/-）小鼠中，免疫组织化学分析显示Pkr2（-/-）小鼠下丘脑中没有促性腺激素释放激素神经元。Pkr2（-/-）小鼠的表型与Kallmann综合征的临床特征相似。

Nocturnal light induces Perl and Per2 genes, which leads to resetting of the circadian clock in the suprachiasmatic nucleus (SCN), the mammalian circadian center. We investigated the light resetting mechanism of their circadian clocks. By using in situ hybridization technique, we found that Perl is used for the advance of the clock and Per2 is used for the delay. Next, in mammals, light is the primary environmental signal used to synchronize endogenous rhythms to the environment. Daylength, or photoperiod also affects many physiological events such as locomotor activity, sleep-wake rhythms, temperature and hormonal secretion. We examined the effects of photoperiod on the daily expression of Perl gene in the SCN. We suggested that the change of photoperiod affected not only in the VLSCN that has rich projection from the retina but also in the DMSCN that is absent from the direct retinal projection. Also, we observed that desynchronization underlies the multicell-level amplitude decrease in the rat suprachiasmatic nucleus induced by critical light pulses.Using in situ hybridization methods, we investigated the localization of Prokineticin (PK2) and prokineticin receptor 2 (PKR2) in the rat SCN. PK2 mRNA-positive neurons were scattered in both the dorsomedial and ventrolateral SCN. In contrast, PKR2 mRNA-containing neurons were clustered in the dorsolateral part of the SCN. Then, to examine the role of PKR2 in the SCN, we created PKR2-gene-disrupted mice (Pkr2(-/-)). Phenotypic analysis indicated that Pkr2(-/-) mice exhibited hypoplasia of the OB. In addition, the Pkr2(-/-) mice showed severe atrophy of the reproductive system. In the Pkr2(-/-) mice, Immunohistochemical analysis revealed that gonadotropin-releasing hormone neurons were absent in the hypothalamus in the Pkr2(-/-) mice. The phenotype of the Pkr2(-/-) mice showed similarity to the clinical features of Kallmann syndrome.