Synaptic mechanisms of amygdala-dependent behaviors

恐惧行为有助于保护机体免受危险，但在精神疾病期间，它们可能会变得适应不良。杏仁核是大脑中负责控制恐惧行为的主要区域，我们正试图了解它的突触特性如何与正常和病理状态下的恐惧调节功能相关。这些知识将提供有助于开发与病理性恐惧相关的精神障碍治疗方法的信息。 杏仁核的运作可以归结为两个功能：执行功能和学习功能。执行功能包括两个活动：1）分析传入的感官信息，2）如果传入的信号预测危险，则触发防御反应。学习（联想）功能包括在中性刺激和厌恶刺激之间建立联系;它使防御反应能够预测信号。 我们研究的第一个问题是杏仁核如何在突触水平上区分来自大脑不同区域的不同类型的信息。为了解决这个问题，人们需要通过选择性地刺激来自特定大脑区域的纤维来询问特定的输入。在过去的几年里，这些研究，包括我们实验室的研究，主要局限于比较分析通过外囊进入杏仁核的皮质纤维和通过内囊进入杏仁核的丘脑纤维中的突触传递，因为这两种输入在解剖学上是分开的，并且可以彼此隔离地刺激。然而，大多数其他输入彼此混合，并且不能通过使用电极来孤立地刺激。然而，最近随着用于选择性激活或沉默特定神经元或轴突的基于视蛋白的技术的发展，孤立地分析任何神经元输入成为可能。 在上一个财政年度，我们的目标是在实验室中建立基于视蛋白的技术，并启动对杏仁核输入的比较分析，这些输入将不同类型的信息带入杏仁核。为此，我们将472 nM蓝色激光和LED纳入我们的电生理设置中，用于切片中的全细胞记录，并开始在小鼠大脑中腺相关病毒介导的通道视紫红质表达。 在最初的一系列基于通道视紫红质的实验中，我们比较了两种杏仁核输入的特性，即来自嗅周皮层的输入，它携带多模态感觉信息，以及来自前扣带皮层（ACC）的输入，它携带高度处理的信息，包括关于疼痛的不愉快。这两种输入都针对相同的杏仁核神经元，并在杏仁核内混合。我们发现这两条通路的突触可塑性有显著差异。虽然来自嗅周皮层的突触传递（LTP）的长时程增强需要抑制GABA α受体介导的抑制，但ACC-杏仁核通路中的LTP则不需要。此外，切断外囊和杏仁核之间的联系，即使在GABA α受体介导的抑制的存在下，也能在嗅周皮层的输入中产生LTP。这些发现有两个影响：第一，外囊的抑制性神经元似乎门的可塑性杏仁核输入从嗅周皮质，第二，高度精炼的信息从ACC遇到一个不太严格的门在杏仁核比处理信息从嗅周皮质。 我们未来的目标是利用光遗传学来测试特定的杏仁核输入，在体外研究，调节自由移动的动物的恐惧行为。此外，通过靶向GABA能神经元亚群中视蛋白的表达，我们计划研究杏仁核神经元间群如何有助于分析传入的感觉信息和产生防御反应。

Fear behaviors serve to protect the organism from dangers, but they can become maladaptive during mental illness. Amygdala is the main area of the brain responsible for control of fear behaviors, and we are trying to understand how its synaptic properties relate to its fear-regulating functions in normal and pathological states. This knowledge will provide information that will help in developing treatments for mental disorders associated with pathological fear. Amygdala operations can be reduced to two functions: the executive function and the learning function. The executive function comprises two activities: 1) analysis of incoming sensory information, 2) triggering of defensive responses if the incoming signals predict danger. The learning (associative) function consists of making association between neutral and aversive stimuli; it enables defensive responses to the danger-predicting signals. The first question of our investigation is how amygdala distinguishes, at the synaptic level, between different types of information, which arrives from different areas of the brain. To address this question, one needs to interrogate a specific input by selectively stimulating fibers coming from a specific brain area. In the past several years, such studies, including those in our laboratory, were mainly limited to comparative analysis of synaptic transmission in the cortical fiber that enter amygdala via the external capsule and thalamic fibers that enter amygdala via the internal capsule, because these two inputs are well separated anatomically and can be stimulated in isolation from each other. Yet, most of other inputs are intermingled with one another and cannot be stimulated in isolation by using an electrode. However, analysis of any neuronal input in isolation became possible recently following development of opsin-based techniques for selective activation or silencing of specific neurons or axons. During the last fiscal year, our goals were to establish opsin-based techniques in the laboratory and to initiate comparative analysis of amygdala inputs, which bring different types of information into amygdala. To this end, we incorporated 472 nM blue laser and LED into our electrophysiology setups for whole cell recording in slice, and began adeno-associated virus mediated expression of channelrhodopsin in the mouse brain. In the initial series of channelrhodopsin-based experiments, we compared properties of two amygdala inputs, the input from perirhinal cortex, which carries multimodal sensory information, and the input from anterior cingulate cortex (ACC), which carries highly processed information including that about unpleasantness of pain. Both inputs target same amygdala neurons and are intermingled inside amygdala. We found significant difference in synaptic plasticity between the two pathways. While long-term potentiation of synaptic transmission (LTP) in the input from perirhinal cortex required suppression of GABAa receptor-mediated inhibition, LTP in the ACC-amygdala pathway did not. Moreover, severing connections between external capsule and amygdala enabled LTP in the input from perirhinal cortex even in the presence of GABAa receptor-mediated inhibition. These findings have two implications: first, inhibitory neurons of the external capsule appear to gate plasticity in the amygdala input from perirhinal cortex, and, second, highly refined information from ACC encounters a less stringent gate at amygdala than the less processed information from perirhinal cortex. Our future goal is to use optogenetics for testing how specific amygdala inputs, investigated in vitro, modulate fear behaviors in free-moving animals. In addition, by targeting expression of opsins in subpopulations GABAergic neurons, we plan to investigate how interneuronal populations of amygdala contribute in analysis of incoming sensory information and in generation of defensive response.