Integration of circadian and homeostatic signals in a peptidergic circuit in Drosophila

越来越多的证据表明，扰乱睡眠、活动和进食的昼夜节律模式会导致有害的健康后果。虽然生物钟机制已经得到了很好的研究，但一天中的时间线索与饥饿等体内平衡驱动之间的关系却知之甚少。昼夜节律信息与营养线索的整合发生在大脑核心时钟细胞的下游，位于多个行为回路的交叉点。本研究利用黑腹果蝇的遗传模型来研究昼夜节律信号与摄食回路的整合机制，从而协调运动节律与摄食行为。脑间部果蝇（PI）是哺乳动物下丘脑的类似物，是一个肽能中枢，接收一天中的时间和营养状态信息。基于已发表的和初步的发现，我提出PI通过神经肽信号接收来自核心时钟神经元的兴奋性输入，以及来自胆碱能分泌hugin的味觉中间神经元的抑制性输入。我假设每个多肽能PI种群（DH44+，胰岛素样肽产生，SIFamide+和饕餮）接收一组独特的输入，然后必须在PI内整合以协调行为输出，并且这种整合通过PI内旁分泌神经肽信号发生。因此，PI种群可能会根据营养状况调节休息：活动节奏和摄食行为，以允许对急性环境线索做出反应。在这个项目的指导阶段，我将描述从中央大脑时钟（目标1）和hugin+味觉中间神经元（目标2）到PI的连接，并研究这些电路如何调节进食和休息：活动行为（目标1和2）。在这个项目的独立阶段，我将使用在指导阶段获得的技能来研究饥饿如何超越PI神经元生理和行为的时钟控制（目标3），以及PI内连接在协调运动节律和摄食行为中的作用（目标4）。为了实现这些目标，我将结合使用遗传工具，包括RNAi和CRISPR，生理分析，包括电生理学和钙成像，以及运动节律和喂养的行为分析。这个项目的成功完成将在神经回路和行为水平上提供重要的进展。首先，它将开始阐明交叉回路如何使用神经调节肽进行通信。在哺乳动物系统中研究神经调节信号已被证明是困难的，这项工作可以为哺乳动物神经肽能区域的研究提供见解，特别是在下丘脑。其次，它将促进对昼夜节律和进食在回路和行为层面的复杂相互作用的理解。不仅要了解神经回路如何塑造行为，还要了解诸如进食模式改变之类的行为如何反馈给大脑，这对于开发改善人类健康的干预措施非常重要。

There is rapidly accumulating evidence that disruptions of circadian patterns of sleep, activity and feeding lead to deleterious health consequences. While circadian clock mechanisms are well-studied, the relationship between time-of-day cues and homeostatic drives such as hunger are poorly understood. The integration of circadian information with nutritional cues occurs downstream of the core clock cells in the brain at the intersection of multiple behavioral circuits. This proposal exploits the Drosophila melanogaster genetic model to examine the mechanism by which circadian signals integrate with feeding circuitry to coordinate locomotor rhythms with feeding behavior. The Drosophila pars intercerebralis (PI), an analog of the mammalian hypothalamus, is a peptidergic center that receives both time-of-day and nutritional state information. Based on published and preliminary findings, I propose that the PI receives excitatory input from core clock neurons via neuropeptide signals, as well as inhibitory inputs from cholinergic Hugin-producing gustatory interneurons. I hypothesize that each of the peptidergic PI populations (DH44+, insulin-like peptide producing, SIFamide+ and Taotie) receives a unique set of inputs, which must then be integrated within the PI to coordinate behavioral outputs, and that this integration occurs via intra-PI paracrine neuropeptide signaling. Thus, PI populations likely modulate both rest:activity rhythms and feeding behavior depending on nutritional state to allow responses to acute environmental cues. In the mentored phase of this project I will characterize the connectivity from the central brain clock (Aim 1) and the hugin+ gustatory interneurons (Aim 2) to the PI and examine how each of these circuits modulates feeding and rest:activity behavior (Aims 1 and 2). In the independent phase of this project I will use skills gained in the mentored phase to investigate how starvation overrides clock control of PI neuron physiology and behavior (Aim 3) and the role of intra-PI connectivity in coordinating locomotor rhythms and feeding behavior (Aim 4). To pursue these aims I will use a combination of genetic tools including RNAi and CRISPR, physiological assays including electrophysiology and calcium imaging, and behavioral assays for locomotor rhythms and feeding. Successful completion of this project will offer important advances at both the level of neural circuitry and behavior. First, it will begin to elucidate how intersecting circuits communicate using neuromodulatory peptides. Neuromodulatory signaling has proven difficult to study in mammalian systems, and this work can offer insights that will be applicable to studies of neuropeptidergic regions in mammals, particularly in the hypothalamus. Second, it will advance understanding of the complex interplay of circadian rhythms and feeding both at the circuit and behavioral levels. Understanding not only how circuitry shapes behavior, but how behavior such as altered feeding patterns feeds back to the brain is important for developing interventions to improve human health.