Functional Role for GPR55 in the periaqueductal gray

描述（由申请人提供）：GPR 55最近被鉴定为溶血磷脂酰肌醇（LPI）敏感性受体，其也可能介导大麻素的一些脱靶效应。GPR 55广泛的中枢神经系统（CNS）分布表明其参与中枢生理学和病理学。GPR 55-/-（敲除）小鼠的表征揭示了GPR 55受体在炎性疼痛、神经性疼痛和骨发育中的作用，而其他研究表明GPR 55活化是促癌的。重要的是，GPR 55-/-小鼠表现出减少的炎症和神经性疼痛。此外，抑制LPS诱导的GPR 55活化可减少神经性疼痛。该应用的主要目标是揭示这种新受体GPR 55在导水管周围灰质（PAG）中的功能作用，PAG是参与疼痛调节的最重要区域之一，也是许多镇痛化合物（包括大麻素）的主要作用部位。我们的初步数据显示，在PAG中的GPR 55受体的激活产生在原代神经元中的细胞内钙和细胞质和线粒体活性氧种类的增加，以及在中脑切片培养物中PAG神经元的去极化。此外，PAG中GPR 55的激活显著降低大鼠的痛阈。换句话说，PAG中GPR 55的激活具有促伤害感受功能。因此，操纵GPR 55信号可能是疼痛管理的新目标。我们提出了一个新的假设，即PAG中GPR 55的激活具有伤害性反应，拮抗该受体可能具有镇痛功能。在特定目标1下的实验中，我们将评估PAG神经元中的GPR 55依赖性Ca 2+反应。目标2下的研究将使用电生理学来表征PAG神经元对GPR 55激活的膜和突触活性反应。在目的3中，我们将确定GPR 55激动剂/拮抗剂在几种疼痛模型中对PAG的体内作用。 这些研究将证明GPR 55在PAG中的功能作用，目的是确定有效治疗干预的新靶点。具体而言，我们将确定拮抗剂对GPR 55的抑制是否可用作疼痛管理的潜在治疗剂。

DESCRIPTION (provided by applicant): GPR55 has recently been identified as a lysophosphatidylinositol (LPI)-sensitive receptor that may also mediate some off-target effects of cannabinoids. The broad central nervous system (CNS) distribution of GPR55 suggests its involvement in central physiology and pathology. Characterization of GPR55-/- (knock-out) mice reveals roles for the GPR55 receptor in inflammatory pain, neuropathic pain, and bone development while other studies indicate that GPR55 activation is pro-carcinogenic. Importantly, GPR55-/- mice show decreased inflammatory and neuropathic pain. Further, inhibition of LPI-induced activation of GPR55 may reduce neuropathic pain. The main goal of this application is to uncover the functional role of this new receptor, GPR55, in the periaqueductal gray (PAG), one of the most important regions involved in pain modulation and also a primary site of action of many analgesic compounds including cannabinoids. Our preliminary data revealed activation of GPR55 receptors in the PAG produces increases in intracellular calcium and cytoplasmic and mitochondrial reactive oxygen species in primary neurons and depolarization of PAG neurons in midbrain slice cultures. Furthermore, activation of GPR55 in PAG significantly reduced the pain threshold in rats. In other words, the activation of GPR55 in the PAG has a pro-nociceptive function. Thus, manipulating GPR55 signaling could be a new target for pain management. We propose to test a new hypothesis that the activation of GPR55 in the PAG has nociceptive response and antagonizing this receptor could have analgesic function. In the experiments under specific Aim 1, we will evaluate the GPR55-dependent Ca2+ response in PAG neurons. Studies under Aim 2 will use electrophysiology to characterize the membrane and synaptic activity responses of PAG neurons to GPR55 activation. In aim 3, we will determine the in vivo effect of GPR55 agonist(s)/antagonist(s) on PAG in several pain models. These studies will demonstrate the functional role of GPR55 in PAG, with the objective of identifying novel targets for effective therapeutic interventions. Specifically, we will determine whether the inhibition of GPR55 by antagonist(s) can be used as potential therapeutics for pain management.