Neural Basis of Individual Differences in Fear Extinction

摘要 虽然大多数普通民众，特别是退伍军人，都会经历创伤事件，但只有 相对较小的比例继续发展为创伤后应激障碍(PTSD)，这表明有 对创伤应激的长期后果的敏感度存在个体差异。创伤后应激障碍患者也 在恐惧消退、消亡回忆和安全学习中表现出损伤，因此消亡学习过程 形成了基于暴露的疗法的基础。我们观察到了行为(冻结)的个体差异 以及在提示恐惧记忆消失期间的心血管反应，提供了一种模型 研究创伤后应激障碍对恐惧消退的抵抗力。我们的首要目标是定义 胆碱能系统，特别是毒扁豆碱受体(MACHR)，在差异调节皮质醇-肾上腺皮质激素中起重要作用。 杏仁核回路在消除恐惧记忆中诱导个体差异。胆碱能传入 基底前脑(BF)为前额叶(PFC)-杏仁核回路提供强大的输入，该回路对恐惧很重要 灭绝。我们的大鼠模型的初步数据表明，线索恐惧消退的个体差异是 与胆碱能神经传递和功能的差异有关，尤其是mACHR在 杏仁基底外侧核(BLA)。我们的假设是杏仁核中M受体的激活减少 来自PFC的兴奋性输入以减少抵抗(高冰冻)表型中的恐惧消退学习， 因此，在这种具有mACHR的抗灭绝种群中，灭绝学习可以得到特别的增强 对抗者。所有实验都比较了灭绝程度不同的雄性和雌性大鼠的个体差异。 表型。使用多学科方法，三个目的是探索药理学方法的能力 在抗灭绝表型中增强灭绝学习或回忆，并提供机制观点 这些效应背后的神经生物学效应。目的1测试mAchr的治疗潜力 转换恐惧消退中的拮抗剂、激动剂和正变构调节剂，重点是M1和M4 选择性化合物。我们将研究条件性冷冻、超声波发声和 全身性和杏仁体内消退学习和回忆时的心血管反应 注射MACHR化合物。目的2检查乙酰胆碱从基底膜的不同释放 前脑和/或乙酰胆碱酯酶活性调节恐惧消退的差异。体内微透析会 用于评估乙酰胆碱和谷氨酸外流，转基因大鼠模型将用于 光遗传刺激或抑制基底前脑胆碱能输入以检测我们灭绝的影响 表型。目的3研究毒扁豆碱对兴奋性反应和突触可塑性的调节。 利用光遗传学和电生理学方法体外刺激杏仁核的PFC传入 切片。MACHR的药理操作将与光遗传刺激一起使用 当记录来自BLA锥体神经元时，下缘输入对恐惧消退至关重要。这些研究将 重点关注与PFC传入相关的杏仁核反应，这是由于对 BLA来自基底前脑，也位于PFC下游，用于调节行为输出。这些 研究将为基于MACHR的药理干预提供证据，这种干预可能会增强物种灭绝- 以暴露疗法为基础的方法，加上提供了毒鼠碱类药物如何 在雄性和雌性大鼠的恐惧学习和消亡的神经回路中发挥作用。

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.