Functional Role for GPR55 in the periaqueductal gray

描述（由申请人提供）：GPR55最近被确定为lysophosphatidylinositol （LPI）敏感受体，也可能介导大麻素的一些脱靶效应。GPR55在中枢神经系统的广泛分布提示其参与中枢生理和病理。GPR55-/-（敲除）小鼠的表征揭示了GPR55受体在炎症性疼痛、神经性疼痛和骨骼发育中的作用，而其他研究表明GPR55激活具有促致癌作用。重要的是，GPR55-/-小鼠显示炎症性和神经性疼痛减轻。此外，抑制lpi诱导的GPR55的激活可能会减轻神经性疼痛。该应用程序的主要目的是揭示这种新受体GPR55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，也是包括大麻素在内的许多镇痛化合物的主要作用部位。我们的初步数据显示，在中脑切片培养中，PAG中GPR55受体的激活会导致初级神经元细胞内钙、细胞质和线粒体活性氧的增加，以及PAG神经元的去极化。此外，PAG中GPR55的激活显著降低了大鼠的痛阈值。换句话说，PAG中GPR55的激活具有前伤害功能。因此，操纵GPR55信号可能成为疼痛管理的新靶点。我们提出验证一个新的假设，即PAG中GPR55的激活具有伤害反应，拮抗该受体可能具有镇痛功能。在特定Aim 1下的实验中，我们将评估PAG神经元中依赖gpr55的Ca2+反应。Aim 2下的研究将使用电生理学来表征PAG神经元对GPR55激活的膜和突触活动反应。在目标3中，我们将在几种疼痛模型中确定GPR55激动剂/拮抗剂对PAG的体内作用。这些研究将证明GPR55在PAG中的功能作用，目的是确定有效治疗干预的新靶点。具体来说，我们将确定拮抗剂对GPR55的抑制是否可以作为疼痛管理的潜在治疗方法。

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.