Role of Medullary Substance P in Acute and Persistent Nociception

描述（由申请人提供）：我们对炎性损伤导致延髓头端腹内侧（RVM）疼痛调节神经元功能和特性持续变化的机制的理解仍然是初步的。P物质（SubP）有助于损伤后的中枢致敏，但令人惊讶的是，它在RVM的伤害感受调制中的作用知之甚少，它也以高浓度存在。初步数据表明，SubP在未受伤状态下在RVM中具有抗伤害感受和原伤害感受作用，但在炎症损伤后介导和维持痛觉过敏。这些数据支持四个相关假设。1)SubP在未损伤状态下通过时间依赖性激活疼痛抑制和疼痛易化的球脊髓通路发挥疼痛感受和抗伤害感受作用。行为药理学研究将建立剂量依赖性和持续时间的SubP的影响，在RVM的大鼠在未受伤的状态，并确认神经激肽-1（NK 1）受体的作用。将通过在SubP注射之前和之后的不同时间用脊髓施用的受体拮抗剂激发来确定介导SubP作用的球脊髓通路。2)SubP在RVM中响应于炎性损伤而释放，在那里它在痛觉过敏的发展中发挥原伤害感受作用。将通过NK 1受体内化和通过在具有由完全弗氏佐剂（CFA）诱导的急性和持续性痛觉过敏的大鼠的RVM中微量注射NK受体拮抗剂来评估损伤后RVM中释放的内源性SubP的作用。3)SubP效应反映了特定类型RVM神经元的NK 1受体表达，这种模式可能在损伤后发生变化。束追踪和免疫组织化学将通过其神经递质含量和向脊髓和DLPT的投射来识别表达NK 1受体的RVM神经元。随后的研究将确定CFA后这种表达是否发生变化，并将确定损伤后发生NK 1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RVM神经元，并在CFA处理的大鼠中，增强对特定类型的RVM神经元的兴奋性输入以介导痛觉过敏。RVM神经元的全细胞膜片钳记录，加上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NK 1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NEUTRAL细胞的影响及其在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的抗伤害性和原伤害性效应与RVM神经元的特定群体有关。这些数据反过来可以使我们能够确定它们的功能（亲与抗伤害）。总的来说，这些结果将促进我们的理解的手段和机制，外周炎症损伤改变的反应和关键脑干疼痛调节系统的功能，并通知一个更合理的开发中枢作用镇痛剂的缓解持续性疼痛。 与公共卫生的相关性炎症性质的持续性疼痛，例如与关节炎或软组织损伤相关的疼痛，对患者造成重大的经济、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，这些通路与伤害感受的调节和镇痛的产生密切相关。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.