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尝试。已经确定了许多贡献机制，但尚未产生任何新的疗法。初步观察表明，大麻素可能有望成为新的治疗方法。人们越来越认识到内源性大麻素 (EC) 是大麻素受体 (CB1R) 的内源性激动剂，通过递减感觉通路抑制（镇痛）来参与疼痛的中枢调节，尽管其作用位点尚未确定。有证据表明，导水管周围灰质背侧 (dPAG) 中的 EC 系统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，在神经损伤后未出现神经病理性疼痛的一组大鼠中，dPAG 中的大麻素信号上调，这是有希望的。因此，我们建议探索 dPAG 作为疼痛控制的潜在位点，并测试 dPAG 中 EC 系统的激活驱动下行镇痛信号传导抑制神经性疼痛的总体假设。 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 调节会增加交感神经活动和血压。我们之前通过证明初始交感神经张力升高的大鼠在接受脊神经结扎（SNL）时不会出现痛觉过敏，建立了神经性疼痛发生的易感性与自主神经激活之间的联系。在慢性疼痛的情况下，交感神经兴奋通常不是 EC 诱导镇痛的理想副作用。因此，我们还将探索 dPAG 中的 EC 可以选择性调节自主神经激活与镇痛的具体机制。该计划分为三个具体目标。在具体目标 1 中，我们将描述抗伤害和交感神经兴奋特有的 dPAG 电路的解剖学和药理学特征。这些探索将以新颖的细节水平提供对 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差异控制模式。抗伤害作用将通过 DHN 神经元活动的抑制来定义，而交感神经兴奋将被记录为交感神经活动的升高。药物将被显微注射到 dPAG 中，激发神经元并激活或减弱大麻素系统功能。了解将抗伤害作用与交感神经兴奋相结合的 dPAG 机制将为将所需的大麻素抗伤害作用与不良心血管效应分开提供机会。在具体目标 2 中，我们将评估损伤引起的 dPAG 大麻素系统成分表达的变化。 dPAG 导致疼痛的具体分子后果将在 SNL 后表现出一系列痛觉过敏的大鼠中得到表征。 dPAG 中大麻素系统成分的基因和蛋白质表达水平将与个体大鼠痛觉过敏发生的程度相关。这些实验将检验以下假设：dPAG 中 EC 信号传导的上调可防止神经损伤后痛觉过敏的发生，这表明 dPAG 大麻素具有治疗潜力。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 dPAG 大麻素信号传导在神经性疼痛产生中的重要且先前未被认识的作用。在接受 SNL（一种神经性疼痛模型）的大鼠中，通过显微注射 CB1R 拮抗剂，dPAG 中的大麻素系统功能会急剧减弱，或者通过 RNA 干扰下调 CB1R 会长期减弱，其影响与痛觉过敏水平相关。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生。