Functional analysis of the Mrg receptor family in pain sensation

描述（由申请人提供）：我们研究的长期目标是了解在正常条件下和慢性疼痛状态下疼痛感受神经元在分子水平上的功能。在哺乳动物中，疼痛刺激的最初检测是由一组感觉神经元进行的，称为伤害感受神经元或疼痛感受神经元。在慢性疼痛状态下，伤害感受神经元对疼痛刺激变得超敏感。最近，我们已经确定了一个大家族的G蛋白偶联受体，称为Mrgs，表达特异性的疼痛感觉神经元。我们还发现了几种RFamide肽，包括FMRFamide，γ 2-MSH和NPFF，在异源系统中作为Mrgs的配体。我们的电生理学研究表明，FMRFamide可以显著增加伤害性神经元的兴奋性，在Mrg依赖的方式。我们的行为分析表明，Mrg基因簇敲除小鼠表现出较长的炎症疼痛反应相比，野生型小鼠。这些数据表明，Mrgs在疼痛中起着调节作用。在这里，我们建议进一步研究Mrg基因敲除小鼠在疼痛感觉中的功能。目的分析Mrg基因缺陷小鼠的疼痛行为表型，以确定Mrg基因在体内是否具有促进或降低疼痛敏感性的作用，以及是否在慢性疼痛中发挥作用。在目的II中，我们将表征Mrg配体肽注射到野生型小鼠中是否会引起伤害性效应。如果是这样，我们将确定这种效应是否依赖于Mrg。我们最近的数据表明，肥大细胞可能表达Mrgs的内源性配体。一个有希望的候选者是哺乳动物肽NPFF。我们将测试肥大细胞是否表达这种肽。如果是这样，我们将检查肥大细胞的脱粒是否可以释放肽。我们还将使用放射性标记的NPFF和γ 2-MSH通过放射自显影研究Mrg受体结合位点。目的III研究Mrg配体肽诱导神经元超兴奋的分子机制。许多离子通道参与了伤害感受神经元兴奋性的调节。我们将采用电生理记录技术，以确定是否Mrgs可以调节培养的DRG神经元的离子通道的活动。拟议的研究将增强我们对Mrg在疼痛中的功能的理解，这可能允许开发特定的新型治疗药物用于慢性疼痛，副作用有限。

DESCRIPTION (provided by applicant): The long-term objective of our research is to understand how pain-sensing neurons function at the molecular level under both normal conditions and chronic pain states. In mammals, the initial detection of pain stimuli is carried out by a group of sensory neurons, known as nociceptive neurons or pain-sensing neurons. Under chronic pain states, nociceptive neurons become hypersensitive to pain stimuli. Recently, we have identified a large family of G protein coupled receptors, called Mrgs, expressed specifically in pain-sensing neurons. We also found several RFamide peptides, including FMRFamide, gamma2-MSH and NPFF, acting as ligands for Mrgs in heterologous systems. Our electrophysiological studies indicate that FMRFamide can significantly increase excitability of nociceptive neurons in an Mrg-dependent manner. Our behavioral analysis showed that Mrg gene cluster knockout mice exhibit a prolonged inflammatory pain response as compared to wild-type mice. These data suggest that Mrgs play a modulatory role in pain. Here we propose to study the function of Mrgs in pain sensation further using Mrg knockout mice. Aim I is to analyze pain behavioral phenotypes in Mrg-deficient mice, from which we would like to determine whether Mrgs act to promote or reduce pain sensitivity in vivo and whether they play roles in chronic pain. In Aim II, we will characterize whether the injection of Mrg ligand peptides into wild-type mice can cause nociceptive effects. If they do, we will determine whether such effects are Mrg-dependent. Our recent data suggest that mast cells are likely to express the endogenous ligands for Mrgs. One promising candidate is the mammalian peptide NPFF. We will test whether mast cells express the peptide. If they do, we will check whether the degranulation of mast cells can release the peptide. We will also investigate Mrg receptor binding sites by autoradiography using radiolabeled NPFF and gamma2-MSH. Aim III is to study the molecular mechanisms of neuronal hyperexcitability induced by Mrg ligand peptides. Many ion channels have been implicated in regulating neuronal excitability of nociceptive neurons. We will employ electrophysiological recording techniques to determine whether Mrgs can modulate the activities of the ion channels in cultured DRG neurons. The proposed research will enhance our understanding of Mrg function in pain, which may allow the development of specific novel therapeutic agents for chronic pain with limited side effects.