Amygdala Serotonin Neurotransmission and Neuropathic Pain

描述（由申请人提供）：疼痛的多维特征提出了一个治疗挑战，如果能更好地理解调节其复杂情绪-情感方面的高级大脑功能，将极大地受益。神经性疼痛通常被认为是由神经可塑性不良引起的，但潜在的机制，特别是在大脑高级中枢的机制，还没有得到很好的理解。该项目将重点关注杏仁核的异常功能，杏仁核是一个被认为在疼痛的情绪-情感维度中起关键作用的大脑区域。我们的目标是减轻不适应杏仁核的可塑性和阻止慢性神经性疼痛的发展。我们认为，一个关键的决定因素是5-羟色胺5-HT2C受体（5-HT2CR）控制杏仁核中促肾上腺皮质激素释放因子（CRF）信号的疼痛相关可塑性，因为CRF与5-HT2CR介导的负情感状态和CRF1受体介导炎症性疼痛的杏仁核可塑性有关。本研究提出杏仁核中5-HT2CR功能异常是慢性神经性疼痛及其情绪-情感成分的关键机制，也是选择性5-羟色胺再摄取抑制剂（SSRIs）治疗神经性疼痛疗效有限的可能原因。具体来说，我们提出了一个新的假设，即杏仁核基底外侧（BLA，杏仁核输入区）的5-HT2CR驱动一个涉及CRF1受体的恶性循环，导致中央核（CeA，输出区）的异常活动。5- ht2cr驱动的BLA-CeA回路的适应性不良可塑性在慢性神经性疼痛中起关键作用。三个特定目的（SAs）将确定在神经性疼痛脊髓神经结扎（SNL）大鼠模型中操纵杏仁核5-HT2CR功能的突触和细胞机制以及行为后果。补充药理学和新的病毒载体敲除策略将用于所有目标的局部失活或消除杏仁核中的5-HT2CR。行为实验（SA1）将确定5-HT2CR和CRF1在神经性疼痛的情绪-情感成分中的BLA的作用。体内电生理学（SA2）将检验BLA中的5-HT2CR驱动CRF1激活和CeA输出神经元的中枢敏化的假设。脑切片膜片钳研究（SA3）将确定BLA-CeA网络可塑性的兴奋性和（非）抑制性突触和细胞机制，该机制是由异常的5-HT2CR功能驱动持续CRF1信号传导引起的。在SA1和SA2中系统应用5-HT2CR拮抗剂和SSRI将验证它们的临床实用性和可行性。这些概念新颖的研究将描述杏仁核中5-HT2CR/CRF1相互作用作为慢性神经性疼痛的重要机制。我们还将确定消除或破坏这种信号机制的策略，以阻止不适应的杏仁核可塑性，从而导致神经性疼痛。对疼痛的高级脑功能和药物靶点的机制分析将促进循证医学所需的基础科学知识，并为药物治疗和/或基因治疗提供转化策略。

DESCRIPTION (provided by applicant): The multidimensional character of pain presents a therapeutic challenge that would benefit greatly from a better understanding of higher brain functions that regulate its complex emotional-affective aspects. Neuropathic pain is generally believed to result from maladaptive neuroplasticity but underlying mechanisms, particularly those in higher brain centers, are not well understood. This project will focus on abnormal function of the amygdala, a brain area that is recognized as a key player in the emotional-affective dimension of pain. Our goal is to mitigate maladaptive amygdala plasticity and block the development of chronic neuropathic pain. A critical determinant, we believe, is pain-related plasticity of serotonin 5-HT2C receptor (5-HT2CR) control of corticotropin-releasing factor (CRF) signaling in the amygdala because CRF is associated with 5-HT2CR- mediated negative affective states and CRF1 receptors mediate amygdala plasticity in inflammatory pain. Here we advance the novel concept that abnormal function of 5-HT2CR in the amygdala is a critical mechanism of chronic neuropathic pain and its emotional-affective component, and is also the likely cause of the limited efficacy of selective serotonin reuptake inhibitors (SSRIs) to treat neuropathic pain. Specifically, we propose the novel hypothesis that 5-HT2CR in the basolateral amygdala (BLA, amygdala input region), drives a vicious cycle involving CRF1 receptors that results in abnormal activity in the central nucleus (CeA, output region). 5- HT2CR-driven maladaptive plasticity in the BLA-CeA circuitry plays a critical role in chronic neuropathic pain. Three Specific Aims (SAs) will determine synaptic and cellular mechanisms and behavioral consequences of manipulation of 5-HT2CR function in the amygdala in the spinal nerve ligation (SNL) rat model of neuropathic pain. Complementary pharmacological and novel viral vector knockdown strategies will be utilized in all aims for local inactivation or elimination of 5-HT2CR in the amygdala. Behavioral experiments (SA1) will determine the role of 5-HT2CR and CRF1 in the BLA in the emotional-affective component of neuropathic pain. Electrophysiology in vivo (SA2) will examine the hypothesis that 5-HT2CR in the BLA drives CRF1 activation and central sensitization of CeA output neurons. Patch-clamp studies in brain slices (SA3) will determine excitatory and (dis-)inhibitory synaptic and cellular mechanisms of plasticity in the BLA-CeA network that results from abnormal 5-HT2CR function driving persistent CRF1 signaling. Systemic application of a 5-HT2CR antagonist and SSRI in SA1 and SA2 will validate their clinical utility and viability. These conceptually novel studies will characterize the 5-HT2CR/CRF1 interaction in the amygdala as an important mechanism of chronic neuropathic pain. We will also identify strategies to eliminate or disrupt this signaling mechanism to block maladaptive amygdala plasticity and thus neuropathic pain. The mechanistic analysis of higher brain functions and drug targets in pain will boost basic science knowledge required for evidence-based medicine and provide translational strategies for pharmacotherapeutics and/or gene therapy.