Astrocyte-neuron interactions in the developing auditory system

项目摘要 在听力开始之前在听觉通路中发生的自发神经元活动的特征在于： 高度刻板的，周期性的动作电位爆发，起源于耳蜗，并通过 大脑的听觉中枢发育中的下丘（IC）的神经元活动发生在离散的 频带，对应于听力开始后明显的音调分布频率图。初步 研究中，我发现IC中的星形胶质细胞显示出周期性的，有组织的细胞内 钙，这与IC神经元在听觉发作前表现出的活动模式惊人地相似。 年龄本研究旨在确定星形胶质细胞中这种信号转导的分子机制，并评估 星形胶质细胞和神经元之间的这种动态相互作用是否促进神经元回路成熟。 这些研究将检验星形胶质细胞细胞内钙离子周期性升高依赖于 星形胶质细胞代谢型谷氨酸受体（mGluR 5）的激活由谷氨酸释放上升 在发展中的IC中。在第一个目标中，我将成像神经元和星形胶质细胞的钙活性， 同时在表达遗传编码的钙指示剂的转基因小鼠中， 神经元和星形胶质细胞在IC发育中的时间相互作用。我会有选择地操纵 神经元活动并测量对星形胶质细胞钙信号传导的影响。 在第二个目标中，我将确定星形胶质细胞的相关活性是否由mGluR 5介导。 受体。首先，我将使用qRT-PCR确定mGluR 5的mRNA表达水平和空间定位 以及不同发育时间点的原位杂交。接下来，我将使用药理学 操作和星形胶质细胞特异性条件性敲除小鼠体内抑制mGluR 5受体， 对星形胶质细胞中的钙活性进行成像。 在第三个目标中，我将研究对星形胶质细胞活动的早期模式的操纵是否会影响星形胶质细胞的功能。 听觉启动前下丘神经元的放电行为和听觉中声音的音调定位表征 动物我将使用损害星形胶质细胞钙活性的转基因小鼠品系， 对IC中神经元活动的空间模式的影响，自发诱导或响应于 刻板的声音刺激为了明确星形胶质细胞在IC中的作用，我将操纵星形胶质细胞 钙局部使用病毒和测量对神经元回路的功能完善的影响。 这种对听觉系统发育中神经元和星形胶质细胞之间相互作用的分析， 将提供新的洞察机制，诱导神经元回路完善，使听力。这些 研究可能揭示新的途径，以促进电路成熟，并确定新的目标，为治疗 通过扩大我们对星形胶质细胞在这一关键过程中如何改变的理解， 发育期影响听觉回路处理感觉信息的能力。

Project Summary Spontaneous neuronal activity that occurs in the auditory pathway prior to hearing onset is characterized by highly stereotyped, periodic bursts of action potentials that originate in the cochlea and propagate through auditory centers of the brain. Neuronal activity in the developing inferior colliculus (IC) occurs in discrete bands, corresponding to tonotopic frequency maps that are apparent after hearing onset. In preliminary studies, I found that astrocytes in the IC show periodic, tonotopically organized elevations of intracellular calcium before hearing onset that are strikingly similar to the activity patterns exhibited by IC neurons at this age. This study aims to define the molecular mechanisms underlying this signaling in astrocytes and assess whether this dynamic interaction between astrocytes and neurons promotes neuronal circuit maturation. The studies will test the hypothesis that periodic elevation of intracellular calcium in astrocytes is dependent on activation of astrocyte metabotropic glutamate receptors (mGluR5) by glutamate released from ascending projections into the developing IC. In the first aim I will image neuronal and astrocyte calcium activity simultaneously in transgenic mice that express genetically encoded calcium indicators to define the spatial and temporal interactions between neurons and astrocytes in the developing IC. I will selectively manipulate neuronal activity and measure the effect on astrocytic calcium signaling. In the second aim I will determine whether the correlated activity of astrocytes is mediated by mGluR5 receptors. First I will define the mRNA expression levels and spatial localization of mGluR5 using qRT-PCR and in situ hybridization during different developmental time points. Next, I will use pharmacological manipulations and astrocyte specific conditional knockout mice to inhibit mGluR5 receptors in vivo while imaging calcium activity in astrocytes. In the third aim, I will investigate whether manipulation of this early pattern of astrocyte activity affects the firing behavior of IC neurons prior to hearing onset and the tonotopic representation of sound in hearing animals. I will use transgenic mouse lines that impair astrocyte calcium activity and measure the consequences on the spatial pattern of neuronal activity in the IC, induced spontaneously or in response to stereotyped sound stimuli. To define specifically the role of astrocytes in the IC, I will manipulate astrocyte calcium locally using viruses and measure the effect on the functional refinement of neuronal circuits. This analysis of reciprocal interactions between neurons and astrocytes in the developing auditory system will provide new insight into the mechanisms that induce neuronal circuit refinement to enable hearing. These studies may reveal new pathways to promote circuit maturation and identify new targets for treatment of developmental disorders by expanding our understanding of how alterations in astrocytes during this critical period of development impact the ability of auditory circuits to process sensory information.