Novel Circuits and Mechanisms of Descending Pain Modulation

项目总结/摘要 慢性疼痛困扰着数百万患者，但治疗在很大程度上是无效的，新的，有针对性的药物的开发， 疼痛治疗受到疼痛神经生物学知识缺口的限制。尽管最近取得了进展，但关键问题 仍然是关于令人难以置信的复杂的细胞和功能组织的上升和下降的神经 控制疼痛处理的神经回路解决这些问题对于开发新的、更 有效和更好的针对急性和慢性疼痛的治疗。这项建议的主要目的是 识别我们最近发现的一组新神经元的电路连接和突触机制 在侧脑桥位于A5去甲肾上腺素能细胞群附近，这些神经元（我们称之为LJA 5） 表达强啡肽原和谷氨酸脱羧酶1（GAD 1）。它们不同于A5去甲肾上腺素能 因为它们不表达酪氨酸羟化酶。LJA 5神经元投射到脊髓背角的I层的所有脊髓水平。 背角（DH），以及臂旁核（PB）和导水管周围灰质（PAG）。值得注意的是， 表明这些神经元在疼痛调节中起着重要作用。具体地，化学发生激活 LJA 5神经元抑制辣椒素和炎症诱导的机械性疼痛，但不抑制热敏感性， 而LJA 5的化学发生抑制增强了炎症期间的机械超敏性。我们 初步数据还表明，LJA 5神经元的化学发生激活强烈减弱了神经病理性 疼痛通过全身和鞘内施用设计药物。总的来说，这些发现表明， LJA 5神经元及其投射代表了下行疼痛调制的一种新成分，并且还构成了 关于这个新回路的许多重要问题：1）哪些类型的疼痛由LJA 5神经元调节？（二） LJA 5神经元的关键投射/输出是什么？3)LJA 5利用什么突触机制 神经元？我们的中心假设是LJA 5神经元通过控制突触传递来调节疼痛处理。 在脊髓背角的板层I中的传递。我们将通过以下三个具体目标来检验这一假设： 使用包括化学遗传学操作与行为测试相结合的多学科方法， 膜片钳记录在创新的完整脊髓制备和轴突终扣的双光子Ca 2+成像中的应用 初级传入中枢终末目的1将建立LJA 5神经元在小鼠模型中的作用， 炎性和神经性疼痛。目标2将审查主要LJA 5预测的功能意义。目的 3将确定介导脊髓中LJA 5神经元的抗伤害感受作用的突触机制。 线.这个提议将定义一个新的参与疼痛的下行通路的基本特征 调制，包括其功能连接，突触机制及其在急性和慢性疼痛中的作用 states.这项工作是变革性的，因为它确定了一种新的球脊髓疼痛调节通路， 我们对疼痛基本理解的重大进展，可能为疼痛控制提供替代方法。

Project Summary/Abstract Chronic pain afflicts millions of patients, yet treatments are largely ineffective, and development of new, targeted therapies is limited by knowledge gaps in the neurobiology of pain. Despite recent progress, key questions remain about the incredibly complex cellular and functional organization of ascending and descending neural circuits that control pain processing. Answering these questions is essential for developing new, more efficacious, and better targeted therapeutics for acute and chronic pain. The main objective of this proposal is to identify the circuit connections and synaptic mechanisms of a novel group of neurons that we recently discovered in the lateral pons. Situated juxta the A5 noradrenergic cell group, these neurons (which we termed LJA5) express prodynorphin and glutamic acid decarboxylase 1 (GAD1). They are distinct from the A5 noradrenergic neurons as they do not express tyrosine hydroxylase. LJA5 neurons project to all spinal levels of lamina I of the dorsal horn (DH), as well as to the parabrachial nucleus (PB) and the periaqueductal gray (PAG). Notably, we showed that these neurons play an important role in pain regulation. Specifically, chemogenetic activation of LJA5 neurons suppressed capsaicin- and inflammation-induced mechanical pain, but not thermal sensitivity, whereas chemogenetic inhibition of LJA5 enhanced mechanical hypersensitivity during inflammation. Our preliminary data also showed that chemogenetic activation of LJA5 neurons strongly attenuated neuropathic pain both via systemic and intrathecal administration of a designer drug. Collectively, these findings suggest that LJA5 neurons and their projections represent a novel component of descending pain modulation, and also pose many important questions about this novel circuit: 1) Which types of pain are regulated by LJA5 neurons? 2) What are the key projections/outputs of LJA5 neurons? 3) What synaptic mechanisms are utilized by LJA5 neurons? Our central hypothesis is that LJA5 neurons modulate pain processing by controlling synaptic transmission in lamina I of the dorsal horn of the spinal cord. We will test this hypothesis in 3 specific aims by using a multidisciplinary approach that includes chemogenetic manipulation combined with behavioral testing, patch-clamp recording in innovative intact spinal cord preparation and 2-photon Ca2+ imaging in axonal boutons of primary afferent central terminals. Aim 1 will establish the role of LJA5 neurons in mouse models of inflammatory and neuropathic pain. Aim 2 will examine functional significance of the main LJA5 projections. Aim 3 will determine synaptic mechanisms that mediate the antinociceptive effects of LJA5 neurons in the spinal cord. This proposal will define fundamental characteristics of a novel descending pathway involved in pain modulation, including its functional connectivity, synaptic mechanisms and its role in acute and chronic pain states. This work is transformative because it identifies a novel bulbospinal pain modulatory pathway, a significant advance in our basic understanding of pain that may offer alternative approaches to pain control.