Presynaptic Structural Plasticity in the Amygdala with Fear Conditioning

描述（由申请人提供）：本提案的长期目标是研究恐惧条件反射可能发生的突触前结构的变化以及这些变化背后的分子机制。本研究的具体目标是：目的1)描述听觉恐惧条件反射后丘脑内侧膝状核（MGN）向外侧杏仁核的轴突投射发生的结构变化。我们将通过注射顺行示踪剂和量化结构、轴突长度和外侧杏仁核内突触钮扣数的变化来做到这一点。目的2)确定这些轴突变化是否与分子变化相关，这些分子变化已被证明与听觉恐惧条件反射有关，是由于突触前BDNF的表达。特别是，切除后脑核中的BDNF基因是否会影响恐惧的习得和恐惧学习的结构可塑性？最后，在目标3中，我们将研究突触前TrkB是否与结构变化有机制关联，方法是构建一种病毒，该病毒既表达抑制BDNF受体的显性负TrkB，也表达cre-重组酶，并将其植入具有柔膜结合GFP报告分子基因的小鼠中，该基因可清晰地勾勒轴突膜。利用这种技术，我们可以观察和量化TrkB受体被抑制的神经元轴突突起的结构变化。我们将这种病毒注射到MGN中，然后观察BDNF、trkB和phospho-TrkB的恐惧表达、结构变化和分子表达。总之，我们将首先描述恐惧条件反射后内侧膝状核-杏仁核突触连接发生的结构变化。其次，我们将研究突触前BDNF表达是否对恐惧条件反射和结构可塑性很重要。第三，我们将研究突触前TrkB是否对恐惧条件反射和结构可塑性至关重要。这些拟议的实验将显著地进一步我们对结构可塑性和恐惧条件反射的理解。许多精神疾病，包括创伤后应激障碍、焦虑症和恐惧症，都是当个体变得过度或不适当地恐惧时发生的。更好地了解恐惧学习是如何发生的，将为这些毁灭性疾病的治疗提供进一步的见解。

DESCRIPTION (provided by applicant): The long term objective of this proposal is to examine changes in presynaptic structure that may occur with fear conditioning and the molecular mechanisms that underlie such changes. The specific goals of this study are: Aim 1) To describe the structural changes that take place in the axonal projections from the medial geniculate nucleus (MGN) of the thalamus that project to the lateral amygdala after auditory fear conditioning. We will do this by injecting anterograde tracers and quantifying changes in the structure, axonal length and synaptic bouton number within the lateral amygdala. Aim 2) To determine whether these axonal changes correlate with molecular changes that have already been shown to be involved in auditory fear conditioning are due to presynaptic BDNF expression. In particular, does excising the gene for BDNF n the MGN affect acquisition of fear and the structural plasticity that occurs with fear learning. Finally, in Aim 3) we will examine whether presynaptic TrkB is mechanistically implicated in the structural changes by constructing a virus that expresses both dominant negative TrkB which inhibits the BDNF receptor, and cre- recombinase, into a mouse who has a gene for floxed-membrane bound GFP reporter molecule that clearly outlines axonal membranes. With this technique, we can observe and quantify structural changes in the axonal projections of neurons in which the TrkB receptor is inhibited. We will inject this virus into the MGN, and then observe fear expression, structural changes and molecular expression of BDNF, trkB, and phospho-TrkB. In summary, we will first describe the structural changes that occur in these medial geniculate-amygdala synaptic connections after fear conditioning. Second, we will examine whether or not presynaptic BDNF expression is important for fear conditioning and structural plasticity. Thirdly, we will examine whether or not presynaptic TrkB is essential for fear conditioning and structural plasticity. These proposed experiments will significantly further our understanding of structural plasticity and fear conditioning in general. Many psychiatric disorders including posttraumatic stress disorder, anxiety disorders and phobias occur when an individual becomes excessively or inappropriately fearful. Better understanding of how fear learning occurs will provide further insight into treatment for these devastating disorders.