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。目前这项提案的总体目标是阐明下丘脑增食欲素(下丘脑)系统在情绪学习中的作用。有强有力的证据表明，食欲素调节压力和对厌恶刺激的唤醒反应，这可能是形成负面情绪记忆所必需的。杏仁核(LA)是形成、存储和提取这些记忆的大脑区域，也是食欲素活动的第一个合乎逻辑的目标。然而，与该区域低受体表达一致的是，在LA对增食欲素受体-1(OrxR1)的直接药理操作不会影响厌恶学习。初步数据表明，中央和直接蓝斑(LC)注射食欲素受体-1(OrxR1)拮抗剂SB 334867都会损害厌恶记忆的获得。事实上，LC是大脑去甲肾上腺素(NE)的主要来源，接受食欲素神经元的密集投射，表达高水平的OrxR1，LC神经元由食欲素兴奋。根据蓝斑LC和食欲素神经元对厌恶刺激的反应是共同激活的证据，以及食欲素直接兴奋LC神经元的证据，我推测食欲素可以促进LA内NE的释放。事实上，来自我们实验室的数据强烈地表明，通过LA中的β-肾上腺素能受体(BetaAR)发出的去甲肾上腺素信号与学习恐惧联系有关。 目前的提案试图证明下丘脑食欲素系统和大脑区域之间的一种未知的相互作用，这两个区域对情绪学习至关重要。具体地说，我假设食欲素通过在线索条件作用的非条件性刺激(US，或触发先天反应的刺激)期间对LC进行正向调制来增强厌恶记忆的形成。首先，我将用OrxR1拮抗剂(SB 334867)测试LC中的食欲素活性，训练前阶段(记忆获得)和训练后阶段(记忆巩固)。其次，为了证明下丘脑(增食欲素)-&GT；LC(OrxR1)-&GT；LA(BetaAR)通路，我将使用对侧LC中的SB 334867和LA中的心得安，从药理上断开该回路。第三，我将使用光激活通道Archaerho品sin-3(Arch)在条件刺激(CS，即音调)或US期间抑制增食欲素神经元，以检测在训练期间增食欲素何时调节LC活动。我假设，在美国抑制食欲素神经元，而不是在CS，将促进厌恶学习。临床证据表明，食欲素缺乏的人在厌恶记忆的形成方面存在障碍。食欲素系统的失调可能解释了恐惧和焦虑症的易感性，并为这些疾病提供了诊断措施和治疗靶点。

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.