Silent synapses and plasticity of prefrontal-amygdala pathway after emotional distress

 描述(申请人提供)：前额叶皮质和杏仁核功能异常，它们相互作用，控制情绪、记忆和决策，已与主要精神障碍的行为特征有关。然而，关于导致精神疾病的环境因素如何改变这两个结构之间的突触传递，人们知之甚少。心理创伤是其中一个因素。当暴露在另一个创伤事件中时，它会增加未来形成更强恐惧记忆的风险。在这里，我们将测试一个假设，即纯粹的心理创伤使前额叶皮质和杏仁核之间的突触连接在恐惧学习过程中更容易促进，心理创伤后产生的沉默突触负责促进促进作用的增强。我们的初步实验显示，在被动回避范式中，这种暴露增强了未来恐惧记忆的形成。我们还发现在dmPFC-BLA通路中有更多的沉默突触，这些突触有NMDA受体，但没有功能性的AMPA受体。有趣的是，当小鼠在心理创伤后立即接受亚麻药催眠氯胺酮治疗时，沉默突触的出现和增强的回避学习被取消。该提案的目的是了解导致沉默突触形成的过程，它们被氯胺酮移除，以及沉默突触在回避学习过程中dmPFC-BLA连接发生可塑性变化中所起的作用。该方案采用了特定轴突纤维的光遗传刺激，并记录了从暴露于心理创伤和回避学习范例组合中的动物制备的杏仁核片中的突触反应。作为一种平行的方法，我们将使用免疫电子显微镜对dmPFC-BLA突触中的谷氨酸受体进行量化，并通过顺行追踪进行鉴定。将解决以下问题。DmPFC和BLA之间的沉默突触是通过将NMDAR插入细胞膜还是通过去除AMPAR而产生的？它们是否增强了切片中dmPFC-BLA通路的长时程增强？在被动回避学习过程中会使用它们吗？它们被氯胺酮消除的机制是什么？通过对dmPFC-BLA连接和BLA微电路的研究，这项研究将有助于阐明情绪创伤背后的特定细胞和突触元素的作用，并验证它们作为治疗创伤后应激障碍、抑郁和相关情绪障碍的潜在靶点。

 DESCRIPTION (provided by applicant): Abnormal function of the prefrontal cortex and the amygdala, which interact with each other to control emotions, memory, and decision making, have been implicated in behavioral traits of major mental disorders. Yet, very little is known about how synaptic transmission between the two structures is altered by environmental factors that lead to mental disease. Psychological trauma is one of such factors. It increases risk of developing stronger fear memories in the future, upon exposure to another traumatic event. Here, we will test a hypothesis that a purely psychological trauma makes synaptic connections between prefrontal cortex and amygdala more prone to facilitation during fear learning and that silent synapses, which are generated after psychological trauma, are responsible for the enhanced facilitation. Our preliminary experiments, in which mice are exposed to a conspecific under distress, revealed that such exposure enhances future formation of fear memory in the passive avoidance paradigm. We also found increased number of silent synapses in dmPFC-BLA pathway, which have NMDA receptor, but do not have functional AMPA receptor. Interestingly, the emergence of silence synapses and enhanced avoidance learning were abolished when mice were treated with sub-anesthetic doze of ketamine immediately after psychological trauma. The objectives of the proposal are to understand the process leading to formation of silent synapses, their removal by ketamine and the role silent synapses may play in plastic changes that occur in dmPFC-BLA connections during avoidance learning. The proposal employs optogenetic stimulation of specific axonal fibers and recording of synaptic responses in amygdala slices prepared from animals exposed to combinations of psychological trauma and avoidance learning paradigms. As a parallel approach, we will use immuno-electron microscopy quantification of glutamate receptors in dmPFC-BLA synapses, identified using anterograde tracing. The following questions will be addressed. Are silent synapses between dmPFC and BLA generated by insertion of NMDAR into cell membrane, or by removal of AMPAR? Do they enhance long-term potentiation in dmPFC-BLA pathway in slice? Are they used during passive avoidance learning? What is the mechanism of their elimination by ketamine? By focusing on dmPFC-BLA connection and BLA microcircuit, this study will help elucidate role of defined cellular and synaptic elements underlying emotional traumatization and validate them as a potential target for novel therapies PTSD, depression and related emotional disorders.