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，这实质上阻碍了他们恢复功能的尝试。已经确定了许多贡献机制，但没有导致任何新疗法。最初的观察结果表明，大麻素可能对新的治疗方法有希望。人们对内源性大麻素（EC）的参与的认识日益认识，它们是大麻素受体的内源性激动剂（CB1R），尽管尚未确定其作用部位，但通过降低了感觉病（抗伤害感受）的抑制（抗伤害感受）来调节疼痛的中心调节。有证据表明，背侧灰灰色（DPAG）的EC系统是一个关键的疼痛调节中心，可能会导致抗伤害感受。来自我们实验室的有希望的初步数据显示，在神经损伤后未出现神经性疼痛的大鼠子集中，DPAG中大麻素信号传导的上调。因此，我们建议探索DPAG作为疼痛控制的潜在基因座，并测试总体假设，即DPAG中EC系统的激活驱动降低镇痛信号，从而抑制神经性疼痛。自激活和EC调节DPAG神经元以来，DPAG具有与自主控制协调镇痛机制的潜力，可增加交感神经活性和血压。我们以前已经建立了对神经性疼痛发展的敏感性与自主神经激活之间的联系，这表明在受到脊柱神经结扎症（SNL）时，具有升高初始交感神经的大鼠不会产生痛觉过敏。交感神经通常不是EC诱导的镇痛性在慢性疼痛的情况下的所需副作用。因此，我们还将探索DPAG中的EC可以选择性地调节自主神与镇痛的特定机制。该计划分为三个特定目标。在特定的目标1中，我们将表征DPAG电路的解剖和药理特征，特定于抗伤害感受和交感神经兴趣。这些探索将在新的细节级别提供对DPAG电路的关键见解，并确定背角感官神经元（DHN）激活的变化和交感神经流出是否显示出差异控制的模式。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升高的交感神经活性。代理将被微注射到DPAG中，以激发神经元并激活或减弱大麻素系统功能。对将抗伤害感受与交感神经兴趣相结合的DPAG机制的理解将提供机会，使所需的大麻素抗伤害感受与不良心血管效应相结合。在特定的目标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对疼痛的贡献的特定分子后果将在SNL后显示出一系列痛觉过敏的大鼠中表征。 DPAG中大麻素系统成分的基因和蛋白质表达水平将与单个大鼠中痛觉过敏的程度相关。这些实验将检验以下假设：DPAG中上调EC信号传导可防止神经损伤后的痛觉过敏的发展，这表明DPAG大麻素的治疗潜力。最后，在特定目标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。我们的初步发现支持DPAG大麻素信号传导在神经性疼痛产生中的重要且以前无法识别的作用。 DPAG中的大麻素系统功能将通过对CB1R拮抗剂的显微注射或长期通过RNA干扰而急剧地衰减，从而在SNL，神经性疼痛的模型中下调CB1R，并与Hypergeria的水平相关。这些实验将检验以下假设：DPAG中CB1R功能的丧失有助于神经性疼痛的发展。