A role for orexins in fear learning

焦虑和恐惧障碍涉及恐惧处理的改变，部分原因是大脑中情绪处理回路的持续变化。目前的建议的总体目标是阐明下丘脑食欲素（下丘脑泌素）系统在情绪学习中的作用。有强有力的证据表明，食欲素介导对厌恶刺激的压力和唤醒反应，这可能是形成负面情绪记忆所必需的。杏仁核外侧核（LA）是一个公认的形成、储存和提取这些记忆的大脑区域，也是食欲素活动的第一个逻辑靶点。然而，与该区域的低受体表达一致，在LA中对食欲素受体-1（OrxR 1）的直接药理学操作不影响厌恶学习。初步数据表明，中枢和直接蓝斑（LC）的食欲素受体-1（OrxR 1）拮抗剂SB 334867的管理损害的收购厌恶的记忆。事实上，LC，脑去甲肾上腺素（NE）的主要来源，接收来自食欲素神经元的密集投射，表达高水平的OrxR 1，LC神经元被食欲素兴奋。基于证据表明，蓝斑LC和食欲素神经元的共同激活，在厌恶刺激，食欲素直接激发LC神经元，我假设食欲素可以增强NE释放的LA。事实上，来自我们实验室的数据强烈暗示NE信号通过LA中的β-肾上腺素能受体（β AR）在恐惧关联的学习中。 目前的提议试图证明下丘脑食欲素系统和大脑区域之间的未探索的相互作用，这对情绪学习至关重要。具体而言，我假设食欲素增强厌恶性记忆的形成，通过积极的调制LC在无条件刺激（美国，或刺激，触发先天反应）在线索条件反射。首先，我将在训练前阶段（记忆的获得）和训练后阶段（记忆的巩固）用OrxR 1拮抗剂（SB 334867）测试LC中的食欲素活性。第二，为了证明下丘脑（食欲素）->LC（OrxR 1）->LA（β AR）通路，我将通过在LC中注入SB 334867和在LA中注入普萘洛尔来断开回路。第三，我将使用光激活通道，古视紫红质-3（Arch）在条件刺激（CS，即音调）或US期间抑制食欲素神经元，以检查在训练期间食欲素何时调节LC活性。我假设，在美国，而不是CS，食欲素神经元抑制，将促进厌恶学习。临床证据表明，食欲素缺乏的人表现出厌恶记忆形成的障碍。食欲素系统的失调可以解释恐惧和焦虑症的易感性，并为这些疾病提供诊断措施和治疗目标。

Anxiety and fear disorders involve alterations of fear processing, due in part to persistent changes in emotional processing circuits in the brain. The overall goal of the current proposal is to elucidate the role of the hypothalamic orexin (hypocretin) system in emotional learning. There is strong evidence that orexins mediate stress and arousal responses to aversive stimuli, which may be required for the formation of negative emotional memories. A well established brain area for the formation, storage and retrieval of these memories, and the first logical target for orexin activity, is the lateral nucleus of the amygdala (LA). However, consistent with low receptor expression in this area, direct pharmacological manipulations of orexin receptor-1 (OrxR1) in LA do not affect aversive learning. Preliminary data suggest that both central and direct locus coeruleus (LC) administration of the orexin receptor-1 (OrxR1) antagonist SB 334867 impairs the acquisition of aversive memories. Indeed, the LC, a major source of brain norepinephrine (NE), receives dense projections from orexin neurons, expresses high levels of OrxR1, and LC neurons are excited by orexins. Based on evidence that locus coeruleus LC and orexin neurons are co-activated in response to aversive stimuli, and that orexins directly excite LC neurons, I hypothesize that orexins can enhance NE release in the LA. Indeed, data from our lab strongly implicate NE signaling through beta-adrenergic receptors (betaARs) in the LA in the learning of fear associations. The current proposal seeks to demonstrate an unexplored interaction between the hypothalamic orexin system and brain regions that are critical for emotional learning. Specifically, I hypothesize that orexins enhance aversive memory formation through positive modulation of the LC during the unconditioned stimulus (US, or stimulus that triggers an innate response) in cued conditioning. First, I will test orexin activity in the LC with an OrxR1 antagonist (SB 334867) pre-training period (acquisition of a memory) and post- training period (consolidation of a memory). Second, to demonstrate a hypothalamus (orexin)->LC(OrxR1)->LA(betaAR) pathway, I will pharmacologically ¿disconnect¿ the circuit using contralateral infusions of SB 334867 in the LC and propranolol in LA. Third, I will use a light-activated channel, Archaerhodopsin-3 (Arch) to inhibit orexin neurons during either the conditioned stimulus (CS, i.e. a tone) or the US to examine when during training orexin modulates LC activity. I hypothesize that orexin neuron inhibition during the US, but not the CS, will facilitate aversive learning. Clinical evidence suggests that people deficient in orexins show impairments in aversive memory formation. Dysregulation of the orexin system may explain susceptibility to fear and anxiety disorders and provide both a diagnostic measure and treatment target for these disorders.