Cellular and circuit mechanisms that modulate serotonin signaling in C. elegans

 描述（由申请人提供）：血清素是一种重要的神经调质，参与许多生理过程，如情绪、食欲和攻击性。血清素水平的改变与几种神经系统疾病有关，如重度抑郁症、恐慌症和广泛性焦虑症。5-羟色胺信号传导的机制还没有很好地理解，导致对改进的治疗方法的持续需求。现有的治疗方法并不总是有效的，而且经常引起脱靶副作用。了解血清素信号传导的机制是为患者创造更有效治疗方法的第一步。线虫C. elegans是研究血清素信号传导的强大模型。它的世代时间很短，遗传学很好理解，它的生殖行为，产卵，是由血清素驱动的。产卵回路仅由三种细胞类型组成，产卵是一种易于分析的行为。携带影响血清素信号的突变的动物会因未下蛋而变得臃肿，这使得它们很容易被识别。egl-6（gf）就是这样一种突变。egl-6编码一种神经肽受体，该受体由一对促排卵的肾上腺素能运动神经元HSN表达。EGL-6抑制5-羟色胺从HSN释放，具有功能获得性突变（egl-6（gf））的动物不能释放足够的5-羟色胺，导致动物因未产卵而肿胀。为了发现新的5-羟色胺信号调节剂，对egl-6（gf）的抑制剂进行了筛选。筛选结果显示cca-1发生了突变。这意味着egl-6（gf）动物因未产卵而肿胀，但egl-6（gf）cca-1突变体双突变体表现出野生型产卵行为。cca-1编码T型钙通道。T型钙通道调节神经元的兴奋性，或神经元对刺激的反应程度。在人类中，T型钙通道的突变与包括失神癫痫在内的几种病理状态有关。由于cca-1突变有效抑制egl-6（gf），因此假设CCA-1将与EGL-6一起由HSNS表达。然而，事实并非如此。该提议的第一目的是确定CCA-1在哪些小区中起作用。第二个目标是了解cca-1突变如何改变雌激素能产卵回路中细胞的功能连接。发现T细胞中的突变 型钙通道可以深刻地影响胡萝卜素驱动的行为是新颖的和意想不到的。拟议的研究将建立胆碱能回路和T型钙通道之间的联系。通过识别受cca-1突变影响的细胞，确定它们如何在功能上与5-羟色胺神经元耦合，并确定T型通道的突变如何改变这种耦合，这些研究将阐明5-羟色胺对神经回路调节行为的作用所需的机制。这些研究将促进我们对这种神经调节系统的理解，这种神经调节系统是许多治疗方法的目标，可以被调节和操纵。

 DESCRIPTION (provided by applicant): Serotonin is an important neuromodulator involved in many physiological processes, such as mood, appetite, and aggression. Altered serotonin levels have been linked to several neurological disorders, such as major depressive disorder, panic disorder, and generalized anxiety disorder. The mechanism of serotonin signaling is not well understood, resulting in a continued demand for improved therapeutics. The therapeutics that do exist are not always effective and often cause off-target side effects. Understanding the mechanism of serotonin signaling is the first step to creating more effective treatments for patients. The nematode worm C. elegans is a powerful model for studying serotonin signaling. It has a short generation time and well-understood genetics, and its reproductive behavior, egg laying, is driven by serotonin. The egg-laying circuit is comprised of only three cell types, and egg laying is an easy-to-assay behavior. Animals carrying mutations that affect serotonin signaling become bloated with unlaid eggs, making them easily identifiable. One such mutation is egl-6(gf). egl-6 encodes a neuropeptide receptor that is expressed by the pair of serotonergic motor neurons, the HSNs, that drive egg laying. EGL-6 inhibits serotonin release from the HSNs, and animals with a gain-of- function mutation (egl-6(gf)) do not release enough serotonin, causing the animals to become bloated with unlaid eggs. To discover novel regulators of serotonin signaling, a screen for suppressors of egl-6(gf) was performed. The screen yielded a mutation in cca-1. This means that egl-6(gf) animals are bloated with unlaid eggs, but egl-6(gf) cca-1 mutant double mutants exhibit wild-type egg-laying behavior. cca-1 encodes a T-type calcium channel. T-type calcium channels regulate neuronal excitability, or how easily neurons respond to stimuli. In humans, mutations in T-type calcium channels have been linked to several pathological states including absence epilepsy. Because cca-1 mutation potently suppresses egl-6(gf), it was hypothesized that CCA-1 would be expressed by the HSNS alongside EGL-6. However, it is not. The first aim of this proposal is to determine in what cells CCA-1 acts. The second aim is to understand how cca-1 mutation changes the functional connections of the cells in the serotonergic egg-laying circuit. The finding that a mutation in a T type calcium channel can profoundly affect a serotonin-driven behavior was novel and unexpected. The proposed studies will establish a link between serotoninergic circuits and T-type calcium channels. By identifying the cells that are affected by cca-1 mutation, determining how they are functionally coupled to serotonin neurons, and determining how mutation of a T-type channel alters that coupling, these studies will elucidate mechanisms required for the effects of serotonin on a neural circuit to regulate behavior. These studies will advance our understanding of how this neuromodulator system, which is targeted by many therapeutics, can be modulated and manipulated.