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

项目摘要 视交叉上核（SCN）是大脑生物钟的所在地，在介导 许多重要功能的昼夜节律性。越来越多的研究表明，这些行动 不仅经由SCN的硬连线传出投射介导，而且经由可扩散信号介导。尽管如此， 来自SCN的可扩散信号的作用，以及这种信号传导方式是否以及如何被调节， 有待确定。在发现下丘脑-垂体门脉系统近90年后， 在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 脑室周围器（circumventricular organ），即终板血管器（OVLT）。这本小说 门静脉系统，这里命名为SCN-OVLTP，是一个可能的候选血管途径，通过它可以输送少量的血管。 SCN中产生的生物学上重要的分泌物可以到达OVLT中的特定局部靶点。 由于OVLT为门静脉系统提供了直接进入CSF的途径，因此该系统可以协调节律 在整个身体。然而，为了证明这一点，SCN-OVLTP的基本特性，包括 必须确定血流的方向性和潜在的调节机制。处理这个关键 在我们的知识空白中，我们首先询问SCN-OVLTp通路是否如我们在小鼠中所示的那样在大鼠中发生。 使用iDisco清理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实际上存在于大鼠中。与SCN一样，OVLT是一种异构结构， 这对于评估哪些OVLT隔室是门脉通路中携带的信号的靶是至关重要的。重要的是我们 开发了一种新的手术/成像实验方法，首次实现了体内评估 SCN-OVLTp中的血流及其调节。我们确定血液从SCN单向流动 而在夜晚，它会随着时间的推移而变化。此外，我们表明，系统 血管加压素（VP）可以进入该门脉系统并在其中移动。总的来说，这些数据使我们提出 总体新假设，SCN-OVLTP是一种功能相关的途径，通过该途径， SCN内产生的信号可以以扩散的方式作用，通过de CSF有效地调节远处的靶点 建议的工作将描述（1）在SCN内的门户血管起源，以及达到的目标 通过该CVO及其有窗血管内的SCN-OVLTp，并由此至CSF;以及（2）血液是否 SCN-OVLTP内的流动以活性依赖性方式通过光刺激和/或 系统性稳态挑战。在目标1中使用多学科方法和最先进的技术 我们将描述大鼠SCN-OVLTP的特征，以确定SCN内门静脉血管的起源， 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是否为 OVLTP是受监管的。我们希望这项工作的结果有助于更好地了解 SCN协调整个身体的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