AN ENDOCANNABINOID MECHANISM FOR STRESS-INDUCED ANALGESIA

描述(由申请人提供)：环境应激源瞬间激活抑制疼痛反应的神经系统。这种现象称为应激诱导镇痛(SIA)，既涉及阿片类药物机制，也涉及非阿片类药物机制。我们最近报道，非阿片类SIA可能是通过动员中脑导水管周围灰质(PAG)中的内源性大麻化合物，如2-花生四烯基甘油(2-AG)来介导的[Hohmann等，自然，435：1108-1112,2005]。我们的结果表明，非阿片类SIA确实被大麻素受体拮抗剂消除，与2-AG在PAG中的积聚有关，并被阻断2-AG失活的药物增强。然而，SIA过程中PAG中2-AG信号的调控机制仍然很大程度上是未知的。我们的中心假设是，导致非阿片类SIA的应激刺激激活了PAG部分神经元中的磷脂酶C(PLC)和二酰甘油脂肪酶(DGL)，导致2-AG的快速动员。新释放的2-AG与当地的大麻素受体结合，诱导非阿片类SIA，然后通过单酰基甘油脂肪酶(MGL)介导的水解失活。与PLC/DGL正向偶联的I组代谢性受体(MGluR)的谷氨酸能刺激可能是启动这些事件的原因。我们将通过一系列实验来验证这一假说，这些实验有望证明：1)足底电击应激通过激活PLC/DGL引起PAG中2-AG的按需动员；2)选择性抑制PAG中的MGL活性增加了2-AG在该结构中的积累并放大SIA；3)PAG中I组mGluR的激活刺激通过PLC/DGL进行2-AG动员以诱导SIA；以及4)2-AG信号系统的关键成分(即mGluRs、PLC、DGL、大麻素受体，MGL)在PAG的特定神经元中表达。这些研究的结果将首次阐明大脑中控制2-AG信号的生化和生理机制，并确定这种内源性大麻素在痛觉调制中的作用。此外，这些结果将为脑内内源性大麻素失活的机制提供必要的信息，这可能有助于新型止痛和抗应激药物的开发。

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.