Cannabinoid Signaling in the dPAG: Specific Analgesic and Autonomic Functions

dPAG 中的大麻素信号传导：特定的镇痛和自主功能

• 批准号: 8762234
• 负责人: Quinn H Hogan
• 金额: --
• 依托单位: CLEMENT J. ZABLOCKI VA MEDICAL CENTER
• 依托单位国家: 美国
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-10-01 至 2017-09-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8762234
• 关键词: Absence of pain sensation; Acute; Adverse effects; Afferent Neurons; Agonist; Amputation; Analgesics; Anatomy; Animal Model; Animals; Attenuated; Automobile Driving; Behavioral; Blood Pressure; Brain; CNR1 gene; Cannabinoids; Cardiovascular system; Clinical; Cutaneous; Data; Development; Diabetes Mellitus; Disease; Distress; Dorsal; Endocannabinoids; Esthesia; Gene Expression; Generations; Heart Rate; Hyperalgesia; Hypersensitivity; Individual; Infection; Injury; Kidney; Ligation; Limb structure; Link; Measures; Microinjections; Midbrain structure; Modeling; Molecular; Monitor; Nature; Nerve; Neurons; Neuropathy; Operative Surgical Procedures; Opioid; Pain; Pain management; Pathway interactions; Pattern; Peripheral Nerves; Peripheral nerve injury; Pharmaceutical Preparations; Predisposition; RNA Interference; Rattus; Regulation; Rehabilitation therapy; Reverse Transcriptase Polymerase Chain Reaction; Role; Sensory; Signal Transduction; Site; Slipped Disk; Specificity; Spinal nerve structure; Stimulus; System; Testing; Therapeutic; Thoracotomy; Trauma; Up-Regulation; Veterans; Western Blotting; base; behavioral response; cannabinoid receptor; chronic neuropathic pain; chronic pain; dorsal horn; effective therapy; endogenous cannabinoid system; enzyme activity; insight; midbrain central gray substance; nerve injury; neurochemistry; novel; novel therapeutic intervention; pain behavior; painful neuropathy; prevent; programs; protein expression; public health relevance; receptor function; research study; therapeutic development

Neuropathic pain is common among Veterans, substantially impeding their attempts to rehabilitate function. Numerous contributing mechanisms have been identified, but have not led to any new therapies. Initial observations show that cannabinoids may hold promise for new therapeutic approaches. There is growing recognition of the participation of endocannabinoids (ECs), which are endogenous agonists of cannabinoid receptors (CB1R), in the central regulation of pain by descending inhibition of sensory pathways (antinociception), although their site of action has not been determined. There is evidence that the EC system in the dorsal periaqueductal gray (dPAG), a key pain regulatory center, may contribute to antinociception. Promising preliminary data from our lab shows an upregulation of cannabinoid signaling in the dPAG in a subset of rats that did not develop neuropathic pain after nerve injury. Therefore, we propose to explore the dPAG as a potential locus for pain control, and test the overall hypothesis that activation of the EC system in the dPAG drives descending analgesic signaling that suppresses neuropathic pain. The dPAG has the potential to coordinate analgesic mechanisms with autonomic control since activation and EC-modulation of dPAG neurons increases sympathetic nerve activity and blood pressure. We have previously established a link between susceptibility to development of neuropathic pain and autonomic activation by showing that rats with elevated initial sympathetic tone do not develop hyperalgesia when subjected to spinal nerve ligation (SNL). Sympathoexcitation is typically not a desired side effect of EC-induced analgesia in the setting of chronic pain. We will therefore also explore specific mechanisms whereby ECs in the dPAG could selectively regulate autonomic activation versus analgesia. The program is organized into three Specific Aims. In Specific Aim 1, we will characterize anatomic and pharmacologic features of dPAG circuitry specific to antinociception and sympathoexcitation. These explorations will provide critical insights into dPAG circuitry at a novel level of detail and establish whether changes in dorsal horn sensory neuron (DHN) activation and sympathetic outflow show patterns of differential control. Antinociception will be defined by inhibition of DHN neuron activity while sympathoexcitation will be recorded as elevated sympathetic nerve activity. Agents will be microinjected into the dPAG that excite neurons and activate or attenuate cannabinoid system function. An understanding of the dPAG mechanisms that integrate antinociception with sympathoexcitation will provide opportunities to dissociate the desirable cannabinoid antinociception from unwanted cardiovascular effects. In Specific Aim 2, we will evaluate injury-induced changes in the expression of components of the dPAG cannabinoid system. Specific molecular consequences underlying dPAG contributions to pain will be characterized in rats showing a range of hyperalgesia after SNL. Gene and protein expression levels of components of the cannabinoid system in the dPAG will be correlated with the degree to which hyperalgesia develops in individual rats. These experiments will test the hypothesis that upregulated EC signaling in the dPAG prevents the development of hyperalgesia following nerve injury, suggesting a therapeutic potential of dPAG cannabinoids. Finally, in Specific Aim 3, we will identify the role of the dPAG cannabinoid system in the development of neuropathic pain. Our preliminary findings support an important and previously unrecognized role of dPAG cannabinoid signaling in the generation of neuropathic pain. Cannabinoid system function in the dPAG will be attenuated acutely by microinjection of a CB1R antagonist or chronically by RNA interference to downregulate CB1R in rats undergoing SNL, a model of neuropathic pain, and the effects correlated with levels of hyperalgesia. These experiments will test the hypothesis that loss of CB1R function in the dPAG contributes to the development of neuropathic pain.

神经性疼痛在退伍军人中很常见，严重阻碍了他们恢复功能的尝试。 已经确定了许多贡献机制，但尚未产生任何新的疗法。最初的 观察表明，大麻素可能有望成为新的治疗方法。有不断增长的 认识到内源性大麻素（EC）的参与，它是大麻素的内源性激动剂 受体 (CB1R)，通过感觉通路的递减抑制来调节疼痛的中枢 （抗伤害作用），尽管其作用部位尚未确定。有证据表明 EC 系统 导水管周围灰质背侧（dPAG）是一个关键的疼痛调节中心，可能有助于镇痛。 我们实验室的初步数据显示，dPAG 中大麻素信号的上调是有希望的。 神经损伤后未出现神经性疼痛的大鼠子集。因此，我们建议探索 dPAG 作为疼痛控制的潜在位点，并测试了 EC 系统激活的总体假设 dPAG 驱动下行镇痛信号，抑制神经性疼痛。 dPAG 具有 由于激活和 EC 调节，具有协调镇痛机制与自主控制的潜力 dPAG 神经元增加交感神经活动和血压。我们之前已经建立了一个 通过显示大鼠对神经性疼痛发展的易感性与自主神经激活之间的联系 初始交感神经张力升高，进行脊神经结扎时不会出现痛觉过敏 （周六夜现场）。在以下情况下，交感神经兴奋通常不是 EC 诱导镇痛的理想副作用： 慢性疼痛。因此，我们还将探索 dPAG 中的 EC 可以选择性地 调节自主神经激活与镇痛。该计划分为三个具体目标。 在具体目标 1 中，我们将描述 dPAG 电路的解剖学和药理学特征 抗伤害和交感兴奋。这些探索将为 dPAG 电路提供重要的见解 新的细节水平，并确定背角感觉神经元（DHN）激活和 交感神经流出显示差异控制模式。抗伤害作用将通过抑制 DHN 来定义 交感神经兴奋时的神经元活动将被记录为交感神经活动升高。代理商将 显微注射到 dPAG 中，兴奋神经元并激活或减弱大麻素系统功能。一个 了解将抗伤害作用与交感神经兴奋相结合的 dPAG 机制将提供 有机会将所需的大麻素抗伤害作用与不良心血管作用分开。 在具体目标 2 中，我们将评估损伤引起的 dPAG 成分表达变化 大麻素系统。 dPAG 导致疼痛的具体分子后果将是 大鼠在 SNL 后表现出一系列痛觉过敏。基因和蛋白表达水平 dPAG 中大麻素系统的成分将与痛觉过敏的程度相关 在个体大鼠中发育。这些实验将检验上调 EC 信号传导的假设 dPAG 可预防神经损伤后痛觉过敏的发生，这表明其具有治疗潜力 dPAG 大麻素。 最后，在具体目标 3 中，我们将确定 dPAG 大麻素系统在开发中的作用 神经性疼痛。我们的初步研究结果支持 dPAG 的重要且之前未被认识到的作用 大麻素信号传导在神经性疼痛的产生中。 dPAG 中的大麻素系统功能将是 通过显微注射 CB1R 拮抗剂急剧减弱或通过 RNA 干扰下调 接受 SNL（一种神经性疼痛模型）的大鼠中的 CB1R 及其与 CB1R 水平相关的影响 痛觉过敏。这些实验将检验以下假设：dPAG 中 CB1R 功能的丧失会导致 神经性疼痛的发展。