Cannabinoid and opioid modulation of descending pain circuits in chronic pain

项目总结 现在有越来越多的证据表明病理性疼痛状态依赖于 大脑本身的变化。已知下行调节通路介导顶端- 伤害性加工的下调，将皮质和边缘的影响传递到 脊髓的后角。上行疼痛的传递路径也密切相关 与这些调节系统交织在一起，形成正反馈和负反馈循环。 最具特征的痛觉调制系统的输出节点是吻部 延髓腹内侧部(RVM)。在Heinricher实验室的经验基础上定义 RVM神经元的输出，本申请中的研究填补了一个重要的空白， 确定有害输入到达右室的路径。RVM有两个 痛觉调节细胞类型：“on-cell”，它对伤害性感受产生促进作用的网络， 以及“离细胞”，它们具有净抑制作用。当前的首要目标 是为了了解该回路在慢性疼痛状态下的可塑性，以及它是如何 受内源性阿片类药物和大麻素的调节。我们最近展示了 臂旁复合体(PB)是急性伤害性信息传递到RVM的重要中继器。我们 建议测试PB在调节RVM痛觉调制神经元活动中的作用， 阐明阿片和大麻素如何调节PB-RVM突触的活性，以及 确定这种联系在慢性疼痛状态下是如何改变的。这些研究将用于 活体单细胞记录来自已确定的RVM开和离细胞、光遗传学和 药理学操作以检验PB向RVM的投射是 持续炎症后的调节(目标1)。作为对活体工作的补充， AIMS 2和AIMS 3下的平行研究将在成人RVM切片上使用体外电生理学 通过识别的PB-RVM终末的光遗传操作来定义膜 PB-RVM突触的机制，并了解这些突触是如何被 大麻素和阿片类药物。我们还将确定这种联系在慢性疾病中是如何改变的 发炎。通过定义有害信息到达疼痛的途径- 在膜、单个神经元和电路水平上调制神经元，我们可以开始 明确疼痛调节回路是如何在急性和慢性疼痛中被招募的。此信息 如果我们要开发将慢性疼痛作为大脑适应不良的治疗方法，这一点至关重要 疾病。

PROJECT SUMMARY There is now increasing evidence that pathological pain states are dependent on changes in the brain itself. Descending modulatory pathways are known to mediate top- down regulation of nociceptive processing, transmitting cortical and limbic influences to the dorsal horn of the spinal cord. Ascending pain transmission pathways are also intimately intertwined with these modulatory systems, forming positive and negative feedback loops. The output node of the best-characterized pain-modulating system is the rostral ventromedial medulla (RVM). Building on the Heinricher laboratory's experience defining the outputs of RVM neurons, the studies in the present application fill an important gap, identifying a pathway through which noxious input reaches the RVM. The RVM has two pain-modulating cell types: “ON-cells,” which exert a net facilitating influence on nociception, and “OFF-cells,” which have a net inhibitory action. The overarching goals of the present proposal are to understand plasticity of this circuitry in chronic pain states, and how it is modulated by endogenous opioids and cannabinoids. We recently showed that the parabrachial complex (PB) is a critical relay of acute noxious information to the RVM. We propose to test the role of the PB in regulating the activity of RVM pain-modulating neurons, elucidate how opioids and cannabinoids modulate the activity of PB-RVM synapses, and determine how this connection is altered in chronic pain states. These studies will use in vivo single-cell recording from identified RVM ON- and OFF-cells, optogenetics, and pharmacological manipulations to test the hypothesis that the PB projection to the RVM is modulated following persistent inflammation (Aim 1). Complementing this in vivo work, parallel studies under Aims 2 and 3 will use in vitro electrophysiology in an adult RVM slice with optogenetic manipulation of identified PB-RVM terminals to define the membrane mechanisms of PB-RVM synapses and understand how these synapses are modulated by cannabinoids and opioids. We will also determine how this connection is altered in chronic inflammation. By defining pathways through which noxious information reaches pain- modulating neurons at the membrane, individual neuron, and circuit level, we can begin to define how pain-modulating circuits are recruited in acute and chronic pain. This information is critical if we are ever to develop treatments addressing chronic pain as maladaptive brain disease.