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。本研究的总体目标是阐明下丘脑食欲素（下丘脑分泌素）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）是大脑中形成、储存和提取这些记忆的区域，也是食欲素活动的第一个逻辑目标。然而，与该区域受体低表达一致，直接药理操作食欲素受体-1 （OrxR1）在LA不影响厌恶学习。初步数据表明，中枢和直接蓝斑（LC）给药食欲素受体-1 （OrxR1）拮抗剂SB 334867都会损害厌恶记忆的获得。事实上，作为脑去甲肾上腺素（NE）的主要来源，LC接受来自食欲素神经元的密集投射，表达高水平的OrxR1，并且LC神经元被食欲素兴奋。基于蓝斑LC和食欲素神经元在厌恶刺激下共同激活的证据，以及食欲素直接激活LC神经元的证据，我假设食欲素可以促进LA中NE的释放。事实上，我们实验室的数据强烈暗示，通过LA中的β -肾上腺素能受体（β -肾上腺素能受体）的NE信号在恐惧关联的学习中起作用。

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.