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。 已经确定了许多起作用的机制，但还没有带来任何新的治疗方法。首字母 观察表明，大麻类药物可能为新的治疗方法带来希望。有越来越多的 对内源性大麻素激动剂--内源性大麻素的参与的认识 感觉通路下行抑制在痛觉中枢调节中的受体(CB1R) (抗伤害性)，尽管它们的作用部位尚未确定。有证据表明，欧盟系统 在背侧中脑导水管周围灰质(DPAG)，一个关键的痛觉调节中心，可能参与抗伤害性感觉。 来自我们实验室的有希望的初步数据显示，在DPAG中大麻素信号上调 神经损伤后没有出现神经病理性疼痛的大鼠的亚组。因此，我们建议探讨 DPAG作为一个潜在的疼痛控制基因，并测试EC系统在 DPAG驱动下行止痛信号，从而抑制神经病理性疼痛。DPAG拥有 自激活和EC调节以来，将镇痛机制与自主神经控制相协调的可能性 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 大鼠对神经病理性疼痛的易感性与自主神经激活之间的联系 在脊神经结扎时，初始交感神经张力升高不会出现痛觉过敏 (SNL)。交感神经兴奋通常不是EC诱导止痛的理想副作用 慢性疼痛。因此，我们还将探索DPAG中的ECs有选择地 调节自主神经激活与止痛。该计划被组织成三个具体目标。 在特定的目标1中，我们将描述DPAG回路的解剖学和药理学特征 抗伤害性感受和交感兴奋。这些探索将提供对DPAG电路的关键见解 新的细节水平并建立是否改变背角感觉神经元(DHN)的激活和 交感神经流出呈不同的控制模式。抗伤害性将被定义为对dHn的抑制 交感神经兴奋时的神经元活动将被记录为交感神经活动增加。工程师将 DPAG内微量注射可兴奋神经元，激活或减弱大麻素系统功能。一个 了解DPAG将抗伤害性感觉与交感兴奋相结合的机制将提供 将可取的大麻素抗伤害作用与有害的心血管效应分开的机会。 在特定的目标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对疼痛的特定分子后果将是 以SNL后表现出一系列痛觉过敏的大鼠为特征。基因和蛋白质的表达水平 DPAG中大麻素系统的组成将与痛觉过敏的程度相关 在个别大鼠体内发育。这些实验将检验这样的假设，即上调EC信号在 DPAG可预防神经损伤后痛觉过敏的发展，提示有治疗潜力 DPAG大麻素。 最后，在具体目标3中，我们将确定DPAG大麻素系统在发展 神经性疼痛。我们的初步发现支持DPAG的一个以前未被认识到的重要作用 大麻素信号在神经病理性疼痛产生中的作用。大麻素系统在DPAG中的作用将是 通过微量注射CB1R拮抗剂而急性减弱或通过RNA干扰下调而慢性减弱 神经病理性疼痛模型SNL大鼠的CB1R及其效应与脑血管紧张素水平 痛觉过敏。这些实验将检验这样一个假设，即DPAG中CB1R功能的丧失有助于 神经病理性疼痛的发展。

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.