AN ENDOCANNABINOID MECHANISM FOR STRESS-INDUCED ANALGESIA

描述（由申请人提供）：环境应激源短暂激活抑制疼痛反应的神经系统。这种现象被称为应激性镇痛（SIA），涉及阿片类和非阿片类机制。我们最近报道了非阿片类物质SIA可能是由内源性大麻素化合物如2-花生四烯酰甘油（2-AG）在中脑导水管周围灰质（PAG）中的动员介导的[Hohmann et al.，Nature 435：1108-1112，2005]。我们的研究结果表明，事实上，非阿片类SIA被大麻素受体拮抗剂废除，与PAG中的2-AG积累相关，并通过阻断2-AG失活的药理学药物增强。然而，2-AG信号在PAG在SIA期间的机制仍然在很大程度上是未知的。我们的中心假设是，应激刺激，导致非阿片类SIA激活磷脂酶C（PLC）和二酰基甘油脂肪酶（DGL）在选择的PAG神经元，导致2-AG的快速动员。新释放的2-AG与局部大麻素受体结合以诱导非阿片类SIA，随后通过单酰基甘油脂肪酶（MGL）介导的水解失活。与PLC/DGL正偶联的I组代谢型受体（mGluR）的谷氨酸能刺激可能是引发这些事件的原因。我们将通过一系列实验来验证这一假设，这些实验有望证明：1）足电击应激通过激活PLC/DGL来增强PAG中2-AG的按需动员; 2）选择性抑制PAG中的MGL活性增加PAG中2-AG在该结构中的积累并放大SIA; 3）PAG中的I组mGluR激活通过PLC/DGL刺激2-AG动员以诱导SIA;和4）2-AG信号系统的关键组分（即mGluRS、PLC、DGL、大麻素受体、MGL）在PAG的选择神经元中表达。这些研究的结果将首次阐明大脑中2-AG信号传导的生化和生理机制，并确定这种内源性大麻素介质在疼痛调节中的作用。此外，这些结果将提供有关大脑中内源性大麻素失活机制的重要信息，这可能有助于开发新型镇痛和抗应激药物。

DESCRIPTION (provided by applicant): Environmental stressors transiently activate neural systems that inhibit pain responsiveness. This phenomenon, called stress-induced analgesia (SIA), engages both opioid and nonopioid mechanisms. We have recently reported that nonopioid SIA may be mediated by the mobilization of endogenous cannabinoid compounds, such as 2-arachidonoylglycerol (2-AG), in the midbrain periaqueductal gray (PAG) [Hohmann et al., Nature 435: 1108-1112, 2005]. Our results show, indeed, that nonopioid SIA is abolished by cannabinoid receptor antagonists, is associated with 2-AG accumulation in the PAG, and is enhanced by pharmacological agents that block 2-AG deactivation. However, the mechanisms governing 2-AG signaling in the PAG during SIA remain largely unknown. Our central hypothesis is that stress stimuli that result in nonopioid SIA activate phospholipase C (PLC) and diacylglycerol lipase (DGL) in select neurons of the PAG, causing the rapid mobilization of 2-AG. Newly released 2-AG engages local cannabinoid receptors to induce nonopioid SIA, and is subsequently deactivated through monoacylglycerol lipase (MGL)-mediated hydrolysis. Glutamatergic stimulation of group I metabotropic receptors (mGluR), which are positively coupled to PLC/DGL, may be responsible for initiating these events. We will test this hypothesis with a series of experiments, which are expected to demonstrate that: 1) foot shock stress elicits on-demand mobilization of 2-AG in the PAG by activating PLC/DGL; 2) selective inhibition of MGL activity in the PAG increases 2-AG accumulation in this structure and amplifies SIA; 3) group I mGluR activation in the PAG stimulates 2-AG mobilization through PLC/DGL to induce SIA; and 4) key components of the 2-AG signaling system (i.e. mGluRS, PLC, DGL, cannabinoid receptors, MGL) are expressed in select neurons of the PAG. The results of these studies will elucidate, for the first time, biochemical and physiological mechanisms governing 2-AG signaling in the brain and determine the role of this endocannabinoid mediator in pain modulation. Furthermore, the results will provide essential information on the mechanisms responsible for endocannabinoid deactivation in the brain, which may facilitate the development of novel analgesic and anti- stress medicines.