Role of Medullary Substance P in Acute and Persistent Nociception

描述(申请人提供)：我们对炎症损伤导致延髓吻侧腹内侧区(RVM)痛觉调节神经元功能和特性持续变化的机制的了解仍处于初步阶段。P物质(SubP)有助于损伤后的中枢敏化，但令人惊讶的是，人们对其在RVM调节伤害性感觉中的作用知之甚少，因为在RVM中也存在高浓度的P物质。实验数据表明，在未损伤状态下，SubP对RVM既有抗伤害作用，又有促伤害作用，但在炎性损伤后起调节和维持痛觉过敏的作用。这些数据支持四个相关的假设。1)在非损伤状态下，SubP通过时间依赖性地激活痛觉抑制通路和痛觉易化球脊髓通路，发挥伤害性和抗伤害性两种作用。行为药理学研究将确定未损伤状态下大鼠RVM中SubP作用的剂量依赖关系和持续时间，并确认神经激肽-1(NK1)受体的作用。调节SubP效应的球脊髓通路将通过在注射SubP之前和之后的不同时间用脊髓给药的受体拮抗剂来确定。2)炎性损伤后，RVM释放亚单位P，在痛觉过敏的发生发展过程中起着致痛作用。在完全弗氏佐剂(CFA)诱导的急性和持续性痛觉过敏大鼠的RVM中，将通过NK1受体内化和微量注射NK受体拮抗剂来评估损伤后RVM中内源性SubP的作用。3)亚P效应反映了特定类型的RVM神经元对NK1受体的表达，这种模式在损伤后可能会改变。束追踪和免疫组织化学将通过神经递质含量和对脊髓和DLPT的投射来识别表达NK1受体的RVM神经元。后续的研究将确定这种表达在CFA后是否发生变化，并将确定在损伤后发生NK1受体内化(指示SubP释放)的RVM神经元的类型。4)SubP作用于特定群体的脊髓投射的RVM神经元，并在CFA处理的大鼠中，增强特定类型的RVM神经元的兴奋性输入，以调节痛敏。RVM神经元的全细胞膜片钳记录，结合逆行标记和免疫组织化学染色，将确定哪些类型的RVM神经元表达功能性NK1受体，并确定CFA后SubP的作用如何变化。细胞外记录将确定SubP对ON、OFF和中性细胞的影响，以及它在CFA后这些神经元敏化中的作用。这些研究将提供一个机制框架，其中SubP的抗伤害感受和前伤害感受作用与RVM神经元的特定群体有关。这些数据反过来可能使我们能够识别它们的功能(支持与抗伤害感受)。总而言之，这些结果将促进我们对外周炎症损伤改变关键脑干疼痛调节系统的反应和功能的方法和机制的理解，并为中枢作用止痛药缓解持续性疼痛提供更合理的发展。与公共卫生相关的炎症性持续性疼痛，如与关节炎或软组织损伤有关的疼痛，会给患者带来巨大的经济、情感和身体损失。这些研究的结果将确定持续性疼痛如何改变脑干通路的功能，这些通路在痛觉调节和止痛产生中起关键作用。从这项工作中获得的见解将指导开发新的、更有效的药物疗法或认知方法来缓解持续性疼痛。

DESCRIPTION (provided by applicant): Our understanding of the mechanisms by which inflammatory injury leads to sustained changes in the function and properties of pain modulatory neurons in the rostral ventromedial medulla (RVM) remains rudimentary. Substance P (SubP) contributes to central sensitization after injury, yet surprisingly little is known about its role in the modulation of nociception by the RVM, where it also exists in high concentrations. Pilot data indicate that SubP has both antinociceptive and pronociceptive actions in the RVM in the uninjured state, but acts to mediate and sustain hyperalgesia after inflammatory injury. These data support four related hypotheses. 1) SubP exerts both pronociceptive and antinociceptive effects in the uninjured state by time-dependent activation of pain inhibitory and pain facilitatory bulbospinal pathways. Behavioral pharmacological studies will establish the dose-dependence and duration of SubP effects in the RVM of rats in the uninjured state, and confirm the role of neurokinin-1 (NK1) receptors. The bulbospinal pathways that mediate the effects of SubP will be determined by challenge with spinally-administered receptor antagonists before and at various times after SubP injection. 2) SubP is released in the RVM in response to inflammatory injury, where it plays a pronociceptive role in the development of hyperalgesia. The role of endogenous SubP released in the RVM after injury will be assessed by NK1 receptor internalization and by microinjection of NK receptor antagonists in the RVM of rats with acute and persistent hyperalgesia induced by complete Freund's adjuvant (CFA). 3) SubP effects reflect the expression of the NK1 receptor by specific types of RVM neurons, a pattern that may change after injury. Tract tracing and immunohistochemistry will identify RVM neurons that express NK1 receptors by their neurotransmitter content and projections to the spinal cord and DLPT. Subsequent studies will determine whether this expression changes after CFA, and will identify the types of RVM neurons in which NK1 receptor internalization (indicative of SubP release) occurs after injury. 4) SubP acts at specific populations of spinally-projecting RVM neurons and, in CFA-treated rats, enhances excitatory inputs to specific types of RVM neurons to mediate hyperalgesia. Whole-cell patch clamp recording from RVM neurons, coupled with retrograde labeling and immunohistochemical staining, will identify which types of RVM neurons express functional NK1 receptors and determine how the actions of SubP change after CFA. Extracellular recordings will determine the effect of SubP on ON, OFF and NEUTRAL cells and its role in the sensitization of these neurons after CFA. These studies will provide a mechanistic framework in which the antinociceptive and pronociceptive effects of SubP are related to specific populations of RVM neurons. These data in turn may enable us to identify their function (pro- vs antinociceptive). Collectively, these results will advance our understanding of the means and mechanisms by which peripheral inflammatory injury alters the responses and function of critical brainstem pain modulatory systems, and inform a more rationale development of centrally-acting analgesics for the relief of persistent pain. PUBLIC HEALTH RELEVANCE Persistent pain of an inflammatory nature, such as that associated with arthritis or soft tissue injury, exacts a significant financial, emotional and physical toll on its sufferers. The results of these studies will identify how persistent pain changes the function of brainstem pathways that are critically involved in the regulation of nociception and the production of analgesia. Insights gain from this work will guide the development of new, more effective pharmacotherapies or cognitive approaches for the relief of persistent pain.