Metabotropic Glutamate Receptor-Mediated Neuromodulation in Sound Localization Circuits

项目摘要 中枢听觉回路的正常发育依赖于起源于 耳蜗(一种外周机构)。这种活动的中断会导致听觉回路的异常发育 以及受损的听觉处理和行为。我们的试点工作揭示了新陈代谢的激活 谷氨酸受体5(MGluR5)是I组mGluRs的成员之一，它在脑内触发模式自发活动。 听觉脑干神经元，暗示了自发活动潜在的中枢机制 听觉回路发育和成熟所必需的。为了充分了解这一机制，我们将 深入研究mGluR5在发育过程中的解剖学、生理学和功能丧失后果 在小鼠的脑干声音定位(BSL)电路。我们的中心假设是mGluR5是 对于电路的正常形成和功能是必需的，并且功能失调的mGluR5会导致损害 双耳处理的神经特性。具体来说，我们试图确定：1)时空 MGluR5的表达模式；2)mGluR5的生理功能；3)哪些发育方面 如果mGluR5被消除，电路的许多部分被中断。我们假设：1)mGluR5的表达为 发育调节；2)mGluR5调节回路中的神经元特性；以及3)消除mGluR5 中断了BSL电路的发展。为了验证这些假说，我们将使用先进的解剖学分析， 体外生理学、光学成像、免疫组织化学、行为评估和遗传操作 追求两个具体目标。在目标1中，我们将研究mGluR5在 发育和成熟。我们将确定mGluR5的细胞和亚细胞定位，然后 通过检验我们关于mGluR5增强内在兴奋性的预测来检验mGluR5的调制功能 并在电路中产生图案化的自发活动。在目标2中，我们将研究这些机制 在基因操作的小鼠中潜在的电路畸形和故障。通过使用强大的 Cre-loxP系统(通过将神经元或星形胶质细胞特异的Cre小鼠与mGluR5小鼠杂交)，我们是 能够消除谷氨酸能通路或星形胶质细胞中的mGluR5。我们预测， MGluR5的消除损害了电路功能背后的核心神经元属性。在此之前 这个项目的成功完成，我们希望对mGluR5神经调节有一个深入的了解 在BSL电路的发展中，提供了支持图案化自发的中央机制 对听觉回路的发展至关重要的活动。MGluR5一直是药物开发的目标 治疗多种脑部疾病。我们的研究将为药物干预提供基础， 预防或挽救听觉回路的畸形和功能障碍。

Project Summary Proper development of central auditory circuits depends on the patterned spontaneous activity originating in the cochlea (a peripheral mechanism). Disruption of this activity results in abnormal development of auditory circuits and compromised auditory processing and behavior. Our pilot work revealed that activation of metabotropic glutamate receptor 5 (mGluR5), one member of group I mGluRs, triggered patterned spontaneous activity in auditory brainstem neurons, implying a potential central mechanism underlying the spontaneous activity necessary for the development and maturation of auditory circuits. To fully understand the mechanism, we will examine in-depth the anatomy, physiology, and loss-of-function consequences of mGluR5 in the development of the brainstem sound localization (BSL) circuit in the mouse. Our central hypothesis is that mGluR5 is necessary for proper formation and function of the circuit, and dysfunctional mGluR5 leads to compromised neural properties underlying binaural processing. Specifically, we seek to determine: 1) the spatiotemporal pattern of mGluR5 expression; 2) the physiological functions of mGluR5; and 3) which developmental aspects of the circuit are disrupted if mGluR5 is eliminated. We hypothesize that: 1) mGluR5 expression is developmentally regulated; 2) mGluR5 modulates neuronal properties in the circuit; and 3) elimination of mGluR5 disrupts development of the BSL circuit. To test these hypotheses, we will use advanced anatomical analyses, in vitro physiology, optical imaging, immunohistochemistry, behavioral assessments, and genetic manipulations to pursue two specific aims. In Aim 1, we will investigate the anatomy and physiology of mGluR5 during development and into maturation. We will determine the cellular and subcellular localization of mGluR5, and then examine the modulatory functions of mGluR5 by testing our prediction that mGluR5 enhances intrinsic excitability and produces patterned spontaneous activity in the circuit. In Aim 2, we will investigate the mechanisms underlying malformation and malfunction of the circuit in genetically manipulated mice. By using the powerful Cre-loxP system (by crossing a neuron or astrocyte specific Cre mouse with a floxed mGluR5 mouse), we are able to eliminate mGluR5 exclusively on the glutamatergic pathways or in astrocytes. We predict that the elimination of mGluR5 compromises the core neuronal properties underlying the function of the circuit. Upon the successful completion of this project, we expect to obtain an in-depth understanding of mGluR5 neuromodulation in the development of the BSL circuit, providing a central mechanism underlying the patterned spontaneous activity critical for the development of auditory circuits. mGluR5 has been the target for drug development for treating numerous brain disorders. Our study will provide a foundation for pharmaceutical interventions that may prevent or rescue malformation and dysfunction of auditory circuits.