Novel SCN-OVLT portal system: Dissecting Anatomical and Functional Properties

项目总结 视交叉上核(SCN)是大脑昼夜节律的中枢，在中枢神经系统中起着重要的调节作用 许多重要功能的昼夜节律性。越来越多的工作支持这些行动是 不仅通过SCN的硬连接传出投射进行调节，还通过可扩散的信号进行调节。尽管如此，路线 来自SCN的可扩散信号的作用，以及这种信号方式是否以及如何受到调节，仍然存在 待定。在发现下丘脑-垂体门脉系统近90年后，人们认为 大脑中唯一的大脑门户系统，我们确定了一个新的门户系统，连接SCN和 室周细胞器，小鼠终板的血管器(OVLT)。这部小说 门脉系统，在这里被称为SCN-OVLTP，是一种可能的候选血管通路，少量的 在SCN中产生的具有生物学意义的分泌物可以到达OVLT中的特定局部靶点。 由于OVLT为门户系统提供了对CSF的直接访问，因此该系统可以编排节奏 遍及全身。然而，为了证明这一点，SCN-OVLTP的基本属性包括 必须确定血流的方向性和潜在的调节机制。要解决这一关键问题 在我们的知识差距中，我们首先询问SCN-OVLTp途径是否像我们在小鼠中所显示的那样在大鼠中发生。 使用IDISCO清晰度和高分辨率光片显微镜，我们令人兴奋的初步数据表明 SCN-OVLTP实际上存在于大鼠体内。与SCN一样，OVLT是一个异质结构，它将是 对于评估哪些OVLT间隔是门脉通路中携带的信号的目标至关重要。重要的是，我们 开发了一种新的外科/成像实验方法，首次能够进行活体评估 SCN-OVLTp的血流及其调节。我们确定血液从SCN单向流动 对于OVLT，值得注意的是，它随着昼夜周期的不同而变化。此外，我们还展示了系统性的 加压素(VP)可以进入这个门脉系统，并在其中穿行。总而言之，这些数据使我们提出 最新的假设认为，SCN-OVLTP是一条功能相关的途径，通过它，低剂量的 在SCN内产生的信号可以以可扩散的方式起作用，以通过De-CSF有效地调节远处的目标 拟议的工作将描绘(1)门静脉在SCN内的起始点，以及所达到的目标 通过SCN-OVLTp在这个CVO和它的开窗血血管内，然后从那里到脑脊液；以及(2)血液 SCN-OVLTP内的流量以依赖于活动的方式调节，通过光刺激和/或通过 系统性动态平衡挑战。在目标1中使用多学科方法和最先进的技术 我们将确定大鼠SCN-OVLTP的特征，以确定SCN和OVLTP内门静脉的起源 他们在OVLT的目标。在目标2中，我们将定义SCN内的血流方向性和速度- OVLTP是受监管的。我们期待这项工作的结果有助于更好地理解 SCN协调全身昼夜节律的基本机制。 1

PROJECT SUMMARY The suprachiasmatic nucleus (SCN), the locus of the brain’s circadian clock, plays a critical role in mediating circadian rhythmicity of numerous important functions. A growing body of work supports that these actions are not only mediated via hard-wired efferent projections from the SCN, but also via diffusible signals. Still, the routes by which diffusible signals from the SCN act, and whether and how this signaling modality is regulated, remains to be determined. Almost 90 years after the discovery of thehypothalamic-pituitary portal system, considered the sole brain portal system in the brain, we identified a new portal system connecting the SCN and a cirumventricular organum, the organum vascullosum of the lamina terminalis (OVLT) in mouse. This novel portal system, named hereSCN-OVLTP, stands as a likely candidate vascular route by which small amounts of biologically significant secretions generated in the SCN could reach specialized local targets in the OVLT. Because the OVLT provides the portal system with direct access to the CSF, this system can orchestrate rhythms throughout the body. For this to be proven however, fundamental properties of the SCN-OVLTP, including directionality of blood flow and underlying regulatory mechanisms must be determined. To address this critical gap in our knowledge, we first asked whether the SCN-OVLTp pathway occurs in rats as we showed for mice. Using iDisco clearing and high resolution light sheet microcopy our exciting preliminary data indicates that the SCN-OVLTP is in fact present in the rat. The OVLT, like the SCN is a heterogeneous structure, and it will be critical to assess which OVLT compartments are target of signals carried in the portal pathway. Importantly, we developed a novel surgical/imaging experimental approach that enables, for the first time, the in vivo assessment of blood flow and its regulation in the SCN-OVLTp. We determined that blood flows unidirectionally from the SCN towards the OVLT and notably, it varies according to the day-night cycle. In addition, we show that systemic vasopressin (VP) can access and travel within this portal system. Collectively, these data lead us to propose the overarching novel hypothesis that the SCN-OVLTP is a functionally relevant route by which low amounts of signals generated within the SCN can act in a diffusible manner to efficiently regulate distant targets via de CSF The proposed work will delineate (1) where the portal vessels originate within the SCN, and the targets reached by SCN-OVLTp within this CVO and its fenestrated blood veesels, and thence to the CSF; and (2) whether blood flow within the SCN-OVLTP is regulated in an activity-dependent manner, by photic stimulation and/or by systemic homeostatic challenges. Using a multidisciplinary approach and state-of-the-art techniques in Aim 1 we will characterize the SCN-OVLTP in the rat to determine the origin of the portal vessels within the SCN and their targets in the OVLT. In Aim 2, we will define whether blood flow directionality and velocity within SCN- OVLTP is amenable to regulation. We expect results from this work to contribute to a better understanding of fundamental mechanisms by which the SCN orchestrates circadian rhythmicity throughout the body. 1