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: 8966633
• 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/8966633
• 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; Health; 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; endocannabinoid signaling; endogenous cannabinoid system; enzyme activity; insight; midbrain central gray substance; nerve injury; neurochemistry; novel; novel therapeutic intervention; novel therapeutics; pain behavior; painful neuropathy; prevent; programs; protein expression; receptor function; research study; therapeutic development

DESCRIPTION (provided by applicant): 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.

描述（由申请人提供）： 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努力。已经确定了许多促成机制，但尚未导致任何新的治疗方法。初步观察表明，大麻素可能有望成为新的治疗方法。越来越多的人认识到内源性大麻素（ECs），这是大麻素受体（CB1R）的内源性激动剂，通过感觉通路的下行抑制（抗伤害性感受）参与疼痛的中枢调节，尽管其作用部位尚未确定。有证据表明，背侧导水管周围灰质（dPAG）的EC系统，一个关键的疼痛调节中心，可能有助于抗伤害感受。来自我们实验室的有希望的初步数据显示，在神经损伤后未发生神经性疼痛的大鼠亚组中，dPAG中大麻素信号传导上调。因此，我们建议探索dPAG作为疼痛控制的潜在位点，并测试整体假设，即激活dPAG中的EC系统驱动抑制神经病理性疼痛的镇痛信号下降。dPAG具有协调镇痛机制与自主控制的潜力，因为dPAG神经元的激活和EC调节增加交感神经活性和血压。我们以前已经建立了一个链接之间的易感性发展的神经性疼痛和自主激活显示，大鼠与初始交感神经张力升高不发展痛觉过敏时，脊髓神经结扎（SNL）。交感神经兴奋通常不是慢性疼痛背景下EC诱导镇痛的预期副作用。因此，我们也将探讨特定的机制，使内皮细胞在dPAG可以选择性地调节自主激活与镇痛。该计划分为三个具体目标。在具体目标1中，我们将描述抗伤害感受和交感神经兴奋特异性dPAG回路的解剖学和药理学特征。这些探索将以新的细节水平提供对dPAG电路的重要见解，并确定背角感觉神经元（DHN）激活和交感神经流出的变化是否显示出差异控制模式。抗伤害感受将通过抑制DHN神经元活性来定义，而交感神经兴奋将被记录为交感神经活性升高。将试剂微注射到dPAG中，兴奋神经元并激活或减弱大麻素系统功能。了解dPAG机制，整合抗伤害性感受与交感神经兴奋将提供机会，解离所需的大麻素抗伤害性感受不必要的心血管效应。在具体目标2中，我们将评估损伤诱导的dPAG大麻素系统组分表达的变化。将在SNL后显示一系列痛觉过敏的大鼠中表征dPAG对疼痛贡献的特定分子后果。dPAG中大麻素系统组分的基因和蛋白质表达水平将与个体大鼠中痛觉过敏发展的程度相关。这些实验将测试dPAG中上调的EC信号传导防止神经损伤后痛觉过敏的发展的假设，表明dPAG大麻素的治疗潜力。最后，在具体目标3中，我们将确定dPAG大麻素系统在神经性疼痛发展中的作用。我们的初步研究结果支持了dPAG大麻素信号在神经性疼痛产生中的重要且先前未被认识的作用。在经历SNL的大鼠中，通过微量注射CB1R拮抗剂或通过RNA干扰以下调CB1R（一种神经性疼痛模型）慢性地减弱dPAG中的大麻素系统功能，以及与痛觉过敏水平相关的作用。这些实验将检验dPAG中CB1R功能丧失有助于神经性疼痛发展的假设。