Long-term activation of spinal opioid analgesia after inflammation

描述（由申请人提供）：严重的组织损伤会产生中枢致敏（CNS痛觉神经元对正常或亚阈值传入输入的反应性增加），导致痛觉过敏。潜伏致敏（LS）是一种沉默形式的中枢致敏，在组织愈合和明显的痛觉过敏症状消退后持续存在。LS可以通过阿片受体拮抗剂或逆激动剂“重新点燃”或恢复痛觉过敏来发现。因此，LS期间的疼痛缓解可能是由强直性阿片受体活性维持的，这种活性掩盖了LS的前觉性成分。LS很重要，因为它启动了伤害系统，当抑制系统失效时，疼痛发作就会随之而来。理解LS的关键第一步是证明其翻译意义，我们现在证明阿片受体逆激动剂纳洛酮可以在一级热损伤后继发性痛觉过敏缓解1周后给予实验性疼痛恢复。特异性目标1验证了烧伤或手术触发LS和人类长期阿片类镇痛的假设。为了进一步研究LS的神经生物学机制，我们还将使用持久、强大、范围广、可重复的小鼠模型，并将其转化为人类研究。我们发现mu阿片受体（MOR）逆激动剂恢复痛觉过敏的行为和分子体征，即使在组织损伤几个月后给药，这需要NMDA受体激活腺苷酸环化酶1型（AC1）。我们的研究结果很重要，因为它们表明，任何事件，如压力，在LS期间干扰MOR镇痛都会导致人类慢性疼痛综合征的痛觉过敏复发。特异性目的2验证了一个假设，即DH或前腹内侧延髓内的阿片肽对MOR构成活性（MORCA）和/或MOR、delta （DOR）或kappa （KOR）受体的激活维持了内源性镇痛，从而将LS限制在疼痛缓解状态。特异性目的3确定MORs在LS期间抑制DH空间协调神经活动（使用创新的64通道场记录系统）和初级传入伤害感受器突触前末端或DH神经元（使用膜片钳电生理学）的突触强度的程度。然后特异性Aim 4测试MORs是否特异性抑制脊髓NMDA受体亚基（GluN2A或GluN2B）和/或Epac1（由cAMP直接激活的交换蛋白，最近发现有助于外周疼痛敏感）以阻断LS期间的疼痛。该项目的完成将使我们更接近缓解慢性疼痛的长期目标，b: a)促进内源性阿片类镇痛，从而将LS限制在缓解状态；b)完全消除LS，例如使用选择性AC1或Epac1抑制剂。我们的一般模型和假设与异稳态的概念有相似之处：在对立过程（MOR和LS）之间通过相互反馈促进彼此的病理升高的平衡。我们的长期愿景是慢性疼痛治疗的新概念策略，以恢复体内平衡，既没有中枢致敏也没有more代偿反应。

DESCRIPTION (provided by applicant): Severe tissue injury generates central sensitization (increased responsiveness of CNS nociceptive neurons to normal or sub-threshold afferent input) that contributes to hyperalgesia. Latent sensitization (LS) is a silent form of central sensitization that persists after tissue has healed and overt signs of hyperalgesia have resolved. LS can be revealed with opioid receptor antagonists or inverse agonists that "rekindle" or reinstate hyperalgesia. Thus, pain remission during LS is likely maintained by tonic opioid receptor activity that masks the pronociceptive components of LS. LS is important because it primes nociceptive systems such that, when inhibitory systems fail, a pain episode ensues. A key first step in understanding LS is to demonstrate the translational significance, and we now show that the opioid receptor inverse agonist, naloxone, can reinstate experimental pain when delivered 1 wk after the resolution of secondary hyperalgesia following first degree thermal injury. Specific Aim 1 tests the hypothesis that burn or surgery triggers LS and long-term opioid analgesia in humans. To further study the neurobiological mechanisms of LS, we will also use a mouse model that is long-lasting, powerful, broad range, repeatable, and translates to human studies. We found that mu opioid receptor (MOR) inverse agonists reinstated behavioral and molecular signs of hyperalgesia, even when administered months after tissue injury, and this required NMDA receptor activation of adenylyl cyclase type 1 (AC1). Our results are important because they suggest that any event, such as stress, that interferes with MOR analgesia during LS will lead to relapse of hyperalgesia in chronic pain syndromes in humans. Specific Aim 2 tests the hypothesis that MOR constitutive activity (MORCA) and/or activation of MOR, delta (DOR), or kappa (KOR) receptors by opioid peptides in the DH or rostroventromedial medulla maintains endogenous analgesia and thereby restricts LS to a state of pain remission. Specific Aim 3 determines the extent to which MORs inhibit spatially coordinated neural activity in the DH (using an innovative 64-channel field recording system) and synaptic strength in presynaptic terminals of primary afferent nociceptors or on DH neurons (using patch clamp electrophysiology) during LS. Specific Aim 4 then tests whether MORs specifically inhibit spinal NMDA receptor subunits (GluN2A or GluN2B) and/or Epac1 (exchange protein directly activated by cAMP, recently found to contribute to peripheral pain senstization) to block pain during LS. Completion of this project will bring us closer to our long-term goal of alleviating chronic pain b either: a) facilitating endogenous opioid analgesia, thus restricting LS within a state of remission; or b) extinguishing LS altogether, for example with a selective AC1 or Epac1 inhibitor. Our general model and hypothesis shares similarities with the concept of allostasis: a pathologically-elevated balance between opposing processes (MOR and LS) that facilitate each other by mutual feedback. Our long-term vision is a new conceptual strategy for chronic pain therapy, to restore homeostasis, where there is neither central sensitization nor MOR compensatory responses.