Cannabinoid Signaling in the dPAG: Specific Analgesic and Autonomic Functions

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。初始 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）的参与，这是大麻素的内源性激动剂 受体（CB1R），通过感觉通路的下行抑制进行疼痛的中枢调节 （抗伤害感受），尽管它们的作用部位尚未确定。有证据表明， 在背侧导水管周围灰质（dPAG），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，在一个特定的细胞中，dPAG中大麻素信号的上调， 在神经损伤后未发生神经性疼痛的大鼠亚组。因此，我们建议探讨 dPAG作为疼痛控制的潜在位点，并测试EC系统激活的总体假设， dPAG驱动抑制神经性疼痛的下行镇痛信号。dPAG具有 协调镇痛机制与自主控制的潜力，因为激活和EC调节 dPAG神经元增加交感神经活动和血压。我们以前建立了一个 神经性疼痛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的患者在脊髓神经结扎时不会出现痛觉过敏 （SNL）.交感神经兴奋通常不是EC诱导镇痛在以下情况下的期望副作用： 慢性疼痛因此，我们还将探讨dPAG中的EC选择性地 调节自主神经激活而不是镇痛。该计划分为三个具体目标。 在具体目标1中，我们将描述dPAG回路的解剖学和药理学特征， 抗伤害感受和交感神经兴奋。这些探索将提供关键的见解dPAG电路在一个 新的细节水平，并确定是否改变背角感觉神经元（DHN）的激活和 交感神经流出显示出不同控制模式。抗伤害感受将通过抑制DHN来定义 交感神经兴奋时的神经元活动将被记录为升高的交感神经活动。剂将 被微注射到dPAG中，兴奋神经元并激活或减弱大麻素系统功能。一个 了解dPAG机制，整合抗伤害感受与交感神经兴奋将提供 将所需的大麻素抗伤害感受与不需要的心血管作用分离的机会。 在具体目标2中，我们将评估损伤诱导的dPAG组分表达的变化 大麻素系统dPAG对疼痛作用的特定分子结果将是 其特征在于大鼠在SNL后表现出一系列痛觉过敏。基因和蛋白质表达水平 dPAG中大麻素系统的组分将与痛觉过敏的程度相关， 在个体大鼠中发展。这些实验将检验在细胞中上调EC信号传导的假设。 dPAG可预防神经损伤后痛觉过敏的发生，提示其治疗潜力。 dPAG大麻素。 最后，在具体目标3中，我们将确定dPAG大麻素系统在发展中的作用。 神经性疼痛我们的初步研究结果支持dPAG的一个重要的和以前未被认识的作用 大麻素信号在神经性疼痛的产生。dPAG中的大麻素系统功能将 通过微量注射CB1R拮抗剂急性减弱或通过RNA干扰慢性下调 CB1R在经历SNL的大鼠中的表达，SNL是一种神经病理性疼痛模型， 痛觉过敏这些实验将检验dPAG中CB1R功能丧失有助于 神经性疼痛的发展。

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.