Midline thalamic control of the amygdala

 描述（由申请人提供）：杏仁核在防御行为的发生中起着至关重要的作用。此外，它在患有焦虑症的人中过度活跃。因此，人们普遍认为，许多焦虑症至少部分是由通常介导恐惧或防御行为的杏仁核过程失调引起的。因此，对控制杏仁核兴奋性的机制的研究可能会为治疗焦虑症开辟新的方法。该提案旨在通过研究中线丘脑 (MTh) 核对杏仁核的影响来实现这一目标。先前关于丘脑对杏仁核影响的研究主要集中在来自丘脑后部的输入，特别是来自内侧膝状体核的内侧部分的输入。然而，许多追踪研究表明，MTh 核也对基底外侧 (BLA) 和中央 (CeA) 杏仁核做出了巨大的投射。然而，除了解剖数据之外，人们对这些强谷氨酸输入的作用知之甚少。这里提出的工作旨在阐明 MTh 输入对杏仁核的影响。为此，我们将首先使用解剖学（目标#1）和生理学（目标#2）方法确定杏仁核中 MTh 输入的目标和突触后机制。事实上，BLA 和 CeA 都包含多种细胞类型，这些细胞类型表达不同的肽/受体，并相互形成对比的连接以及外部传入。因此，在目标#1中，我们将顺行示踪与各种神经元标记物的免疫细胞化学相结合，以在光和电子显微镜水平上识别杏仁核中MTh轴突末端的靶标。基于这些结果，目标#2 将在体外结合光遗传学和膜片钳记录技术来研究 MTh 输入对杏仁核细胞的影响。有了这些信息，最后两个目标将检查 MTh 细胞对杏仁核依赖性功能的影响。事实上，最近的研究表明，在 MTh 核中注入蝇蕈醇后，依赖于杏仁核的后天恐惧和先天恐惧的表达会大大减少。然而，尚不清楚这些蝇蕈醇的发现是否是由于附近丘脑细胞（例如背内侧核）的抑制，或投射到杏仁核的 MTh 核的其他目标（例如前额皮质）的障碍所致。将使用两种不同的方法来解决这个问题。首先，在目标#3中，我们将在习得性恐惧和先天性恐惧的表达过程中同时进行 MTh 和杏仁核细胞的细胞外记录。接下来，在目标#4中，我们将使用双重病毒策略，使我们能够表达盐视紫红质或通道视紫红质，但仅限于投射到杏仁核的 MTh 细胞。然后，我们将通过光遗传学抑制或激发杏仁核投射的 MTh 细胞，并研究这如何影响杏仁核依赖性任务的行为，这些任务探究习得或先天的恐惧。总之，这里提出的实验将揭示 MTh 神经元在表达后天恐惧和先天恐惧期间如何调节杏仁核的兴奋性。这些知识将为药物干预铺平道路，旨在通过利用中线丘脑细胞不寻常的受体表达谱来调节其活性。

 DESCRIPTION (provided by applicant): The amygdala plays a critical role in the genesis of defensive behaviors. Moreover, it is hyperactive in humans afflicted with anxiety disorders. Thus, it is commonly believed that many anxiety disorders result, at least in part, from a dysregulation of amygdala processes normally mediating fear or defensive behaviors. Accordingly, research on the mechanisms controlling amygdala excitability might open new approaches for the treatment of anxiety disorders. This proposal aims to do just that, by studying the influence of midline thalamic (MTh) nuclei on the amygdala. Prior studies on thalamic influences over the amygdala have focused on inputs arising from the posterior thalamus, particularly from the medial portion of the medial geniculate nucleus. Yet, a number of tracing studies have revealed that MTh nuclei also contribute massive projections to the basolateral (BLA) and central (CeA) amygdala. However, other than anatomical data, little is known about the role of these strong glutamatergic inputs. The work proposed here aims to shed light on the influence of MTh inputs to the amygdala. To this end, we will first identify the targets and postsynaptic mechanisms of MTh inputs in the amygdala using anatomical (Aim #1) and physiological (Aim #2) methods. Indeed, BLA and CeA both contain multiple cell types that express different peptides/receptors and form contrasting connections with each other and extrinsic afferents. Therefore, in Aim #1, we will combine anterograde tracing with immunocytochemistry for various neuronal markers to identify the targets of MTh axon terminals in the amygdala at the light and electron microscopic levels. Building on these results, Aim #2 will combine optogenetic and patch clamp recording techniques in vitro to study the impact of MTh inputs on amygdala cells. Armed with this information, the last two aims will examine the influence of MTh cells on amygdala-dependent functions. Indeed, recent studies have revealed that following muscimol infusions in MTh nuclei, the expression of amygdala-dependent learned and innate fear is drastically reduced. However, it is unclear whether these muscimol findings result from the inhibition of nearby thalamic cells (e.g. mediodorsal nucleus), or the disfacilitaton of other targets of MTh nuclei (e.g. prefrontal cortex), that project to the amygdala. Two differen approaches will be used to address this question. First, in Aim #3, we will perform simultaneous extracellular recordings of MTh and amygdala cells during the expression of learned and innate fear. Next, In Aim #4, we will use a dual viral strategy allowing us to express halorhodopsin or channelrhodopsin, but only in MTh cells that project to the amygdala. We will then optogenetically inhibit or excite amygdala-projecting MTh cells and examine how this affects behavior on amygdala-dependent tasks that probe learned or innate fear. Together, the experiments proposed here will reveal how MTh neurons regulate the excitability of the amygdala during the expression of learned and innate fear. This knowledge will pave the way for pharmacological interventions aiming to regulate the activity of midline thalamic cells by taking advantage of their unusual profile of receptor expression.