Neural Basis of Individual Differences in Fear Extinction

摘要 虽然大多数普通民众，特别是战斗退伍军人，经历创伤性事件，只有一个 相对较小的比例继续发展创伤后应激障碍（PTSD），这表明有 个体对创伤性应激的长期后果的易感性差异。PTSD患者也 在恐惧消退、消退回忆和安全学习方面都有障碍， 形成了基于安全性的治疗的基础。我们已经观察到行为（冻结）的个体差异 和心血管反应在灭绝的线索恐惧记忆在远交大鼠，提供了一个模型， 研究PTSD样的恐惧消退抵抗力。我们的首要目标是定义 胆碱能系统，特别是毒蕈碱受体（mACHR），在差异调节皮质- 杏仁核回路诱导个体差异消除恐惧记忆。胆碱能输入来自 基底前脑（BF）为前额叶（PFC）-杏仁核回路提供强有力的输入，这对恐惧很重要 灭绝在我们的大鼠模型中的初步数据表明，个体差异的线索恐惧消退是 与胆碱能神经传递和功能的差异有关，特别是在 基底外侧杏仁核（BLA）。我们的假设是杏仁核中的毒蕈碱受体激活减少 来自PFC的兴奋性输入，以减少抗性（高度冻结）表型中的恐惧消退学习， 因此，在这种具有mACHR的灭绝抗性群体中， 对手。所有实验都比较了具有明显灭绝的雄性和雌性大鼠的个体差异 表型使用多学科的方法，三个目的探索药理学方法的能力 增强灭绝学习或回忆的灭绝抗性表型，并提供一个机械的观点， 这些影响背后的神经生物学效应。目的1测试mACHR的治疗潜力 拮抗剂、激动剂和正变构调节剂在转移性恐惧消退中的作用，重点是M1和M4 选择性化合物我们将研究条件冻结，超声波发声， 在全身和杏仁核内的消退学习和回忆过程中的心血管反应 注射mACHR化合物。目的2检查是否差异释放乙酰胆碱从基底 前脑和/或乙酰胆碱酯酶活性介导恐惧消退的差异。体内微透析将 用于评估乙酰胆碱和谷氨酸流出，转基因大鼠模型将用于 光遗传学刺激或抑制基底前脑胆碱能输入，以检查我们灭绝的影响 表型目的3：研究毒蕈碱对兴奋性反应的调节和突触可塑性， 利用离体光遗传学和电生理学方法在杏仁核中刺激PFC输入 切片mACHR的药理学操作将与光遗传学刺激结合使用。 边缘下输入对恐惧消退至关重要，而记录来自BLA锥体神经元。这些研究将 集中于与PFC输入相关的杏仁核反应，由于强胆碱能神经支配 BLA来自基底前脑，以及位于PFC下游，用于介导行为输出。这些 研究将为基于mACHR的药物干预提供证据，这些药物干预可能会促进灭绝- 基于暴露疗法的方法，加上提供了毒蕈碱剂如何 在雄性和雌性大鼠的恐惧学习和灭绝的神经回路中起作用。

ABSTRACT While most of the general population, and particularly combat veterans, experience traumatic events, only a relatively small proportion go on to develop post-traumatic stress disorder (PTSD), suggesting there are individual differences in susceptibility to the long-term consequences of traumatic stress. PTSD patients also show impairments in fear extinction, extinction recall, and safety learning, so extinction learning processes form the basis of exposure-based therapies. We have observed individual variation in the behavioral (freezing) and cardiovascular responses during the extinction of cued fear memories in outbred rats, providing a model to study PTSD-like resistance to fear extinction. Our overarching goal is to define the mechanistic role of cholinergic system, and specifically muscarinic receptors (mACHRs), in differentially regulating the cortico- amygdalar circuit to induce individual differences in extinguishing fear memories. Cholinergic inputs from the basal forebrain (BF) provide strong inputs to the prefrontal (PFC)-amygdalar circuit which is important for fear extinction. Preliminary data in our rat model suggests that individual differences in cued fear extinction are related to differences in cholinergic neurotransmission and function, but particularly mACHR regulation in the basolateral amygdala (BLA). Our hypothesis is that muscarinic receptor activation in the amygdala decreases excitatory inputs from the PFC to diminish fear extinction learning in the resistant (high freezing) phenotype, and thus extinction learning can be enhanced specifically in this extinction resistant population with mACHR antagonists. All experiments compare individual differences in male and female rats with distinct extinction phenotypes. Using a multidisciplinary approach, three Aims explore the ability of pharmacological approaches to enhance extinction learning or recall in the extinction resistant phenotype, and provide a mechanistic view of the neurobiological effects underlying these effects. Aim 1 tests the therapeutic potential of mACHR antagonists, agonists, and positive allosteric modulators in shifting fear extinction, with a focus on M1 and M4 selective compounds. We will examine extinction of conditioned freezing, ultrasonic vocalizations, and cardiovascular responses during extinction learning and recall with both systemic and intra-amygdalar injections of mACHR compounds. Aim 2 examines if the differential release of acetylcholine from the basal forebrain and/or acetylcholinesterase activity mediates differences in fear extinction. In vivo microdialysis will be used to assess acetylcholine and glutamate efflux, and a transgenic rat model will be used for optogenetically stimulating or inhibiting basal forebrain cholinergic inputs to examine effects in our extinction phenotypes. Aim 3 examines muscarinic modulation of excitatory responses and synaptic plasticity evoked by stimulation of PFC inputs using optogenetic and electrophysiological approaches ex vivo in amygdalar brain slices. Pharmacological manipulations of mACHRs will be used in conjunction with optogenetic stimulation of the infralimbic inputs critical for fear extinction, while recording from BLA pyramidal neurons. These studies will focus on amygdalar responses associated with PFC inputs, due to the strong cholinergic innervation to the BLA from the basal forebrain, as well as being downstream from PFC for mediating behavioral outputs. These studies will provide evidence for mACHR based pharmacological interventions that might enhance extinction- based approaches such as exposure therapy, plus provide a mechanistic profile of how muscarinic agents may be acting within the neural circuitry underlying fear learning and extinction in both male and female rats.