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关键作用。此外，在患有焦虑症的人类中，它是过度活跃的。因此，人们普遍认为，许多焦虑症至少在一定程度上是由杏仁核过程的失调引起的，杏仁核过程通常是调节恐惧或防御行为的。因此，对杏仁核兴奋性控制机制的研究可能会为焦虑症的治疗开辟新的途径。这项提议旨在通过研究丘脑中线核(MTH)对杏仁核的影响来实现这一点。以往关于丘脑对杏仁核影响的研究主要集中在丘脑后部，尤其是内侧膝状核的内侧部分。然而，许多追踪研究表明，MTH核也向杏仁基底外侧核(BLA)和中央杏仁核(CEA)贡献了大量投射。然而，除了解剖学数据外，人们对这些强大的谷氨酸能输入的作用知之甚少。这里提出的工作旨在阐明MTH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MTH输入的靶点和突触后机制。事实上，BLA和CEA都包含多种细胞类型，它们表达不同的多肽/受体，并与彼此和外部传入形成不同的联系。因此，在目标1中，我们将结合顺行追踪和免疫细胞化学对各种神经元标记物进行识别，以在光镜和电子显微镜水平上识别杏仁核MTH轴突终末的靶点。在这些结果的基础上，AIM#2将结合光遗传和体外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细胞对杏仁核依赖功能的影响。事实上，最近的研究表明，在甲状旁腺素核内注射蝇草酚后，杏仁核依赖的后天和先天恐惧的表达大大减少。然而，目前尚不清楚这些发现是由于附近丘脑细胞(如背内侧核)的抑制，还是由于投射到杏仁核的甲状旁腺素核团的其他靶点(如前额叶皮质)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，我们将同时对后天恐惧和先天恐惧表达过程中的MTH和杏仁核细胞进行细胞外记录。接下来，在目标4中，我们将使用双重病毒策略，允许我们表达卤视紫质或通道视紫红质，但仅在投射到杏仁核的MTH细胞中表达。然后，我们将通过光遗传学抑制或刺激杏仁核投射的MTH细胞，并研究这如何影响杏仁核依赖任务的行为，这些任务探测后天或先天恐惧。总之，这里提出的实验将揭示在后天和先天恐惧表达过程中，MTH神经元如何调节杏仁核的兴奋性。这一知识将为药物干预铺平道路，目的是通过利用丘脑中线细胞不寻常的受体表达特征来调节中线细胞的活动。

 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.