RVM CCK and Neuropathic Pain

RVM CCK 和神经性疼痛

• 批准号: 6832666
• 负责人: JOSEPHINE LAI
• 金额: $ 35.57万
• 依托单位: UNIVERSITY OF ARIZONA
• 依托单位国家: 美国
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-07-05 至 2008-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6832666
• 关键词: autoradiography; behavior test; brain stem; cholecystokinin; hormone inhibitor; hormone receptor; hormone regulation /control mechanism; in situ hybridization; laboratory rat; microinjections; nerve injury; neural plasticity; neuropathology; neuropharmacology; opioid receptor; pain; receptor expression; spinal nerves; time resolved data

DESCRIPTION (provided by applicant): Recent evidence suggests that processes that initiate neuropathic pain may differ from those that maintain such pain. That persistent neuropathic pain states require descending facilitation arising from the rostral ventromedial medulla (RVM) is suggested by the finding that lidocaine injected into the RVM effectively blocks experimental neuropathic pain at post-in jury day 6 (and later), but not at post-injury day 3. Onset of this descending facilitation may arise from activity of RVM cells that express mu opioid receptors, since either a selective lesion of these cells with a saporin-mu opioid conjugate or surgical lesion of the dorsolateral funiculus (DLF), a descending fiber pathway to the dorsal horn, prevents and reverses the expression of neuropathic pain. These findings implicate a time-dependent activation of descending facilitatory processes in the RVM following injury to maintain, rather than initiate, abnormal pain. The nature of the RVM neuroplasticity that drives such pain is unknown. One clue to this mechanism is our observation that RVM microinjection of a CCK 2 receptor antagonist produces a reversible blockade of established neuropathic pain. In addition, microinjection of CCK-8(S) into the RVM of uninjured rats produces tactile and thermal hypersensitivity reminiscent of states of nerve-injury induced pain. These effects are prevented by lesions of the DLF, or of RVM cells expressing mu opioid receptors, suggesting the possibility that RVM CCK may promote injury- induced pain by activating RVM neurons that are phenotypically defined by the expression of mu opioid receptors. For these reasons, we hypothesize that nerve-injury results in a time-related increase in RVM CCK activity to drive descending facilitation and to maintain nerve-injury induced pain. This hypothesis will be tested by the following specific aims. Aim 1 will characterize (a) the basal CCK activity in the RVM, and changes in CCK activity in response to mechanical and thermal cutaneous inputs in naive rats, and (b) the time-dependent nature of CCK activity in the RVM following nerve injury. Specifically, basal CCK release, and CCK release in response to mechanical and thermal cutaneous inputs in the RVM will be measured at early and late time points after spinal nerve ligation injury. Aim 2 will identify the CCK receptor(s) at which RVM CCK may act to drive descending facilitation. The functional roles of CCK and CCK2 receptor types in the RVM pre- and post-injury will be evaluated pharmacologically by microinjection of selective CCK receptor antagonists. The spatial distribution of the CCK receptors will be analyzed by semi-quantitative in situ hybridization and receptor autoradiography. Aim 2 will also examine the possibility that CCK receptors may co-localize with mu opioid receptors in RVM neurons. The proposed experiments will reveal some features of the RVM plasticity that may be critical in maintaining neuropathic pain. As patients who suffer from neuropathic pain are likely to seek treatment long after the precipitating injury has occurred, understanding the mechanisms that maintain the neuropathic state will be essential for the development of rational therapeutic interventions. In this regard, the proposed experiments may reveal an important role for CCK receptor antagonists as therapy for neuropathic pain.

描述（由申请人提供）：最近的证据表明，引发神经性疼痛的过程可能与维持此类疼痛的过程不同。持续性神经病理性疼痛状态需要由头端腹内侧延髓 (RVM) 产生的下行促进，这一发现表明，注射到 RVM 中的利多卡因在入院后第 6 天（及以后）可有效阻断实验性神经病理性疼痛，但在入院后第 6 天（及以后）则无效。损伤第 3 天。这种下降促进的发生可能是由表达 mu 阿片受体的 RVM 细胞的活性引起的，因为这些受体的选择性损伤具有皂素-mu阿片类药物缀合物的细胞或背外侧索（DLF）的手术损伤（DLF是通往背角的下行纤维通路）可以预防和逆转神经性疼痛的表达。这些发现表明，受伤后 RVM 中的下行促进过程会出现时间依赖性激活，以维持而不是引发异常疼痛。导致这种疼痛的 RVM 神经可塑性的本质尚不清楚。这一机制的一个线索是我们观察到 RVM 显微注射 CCK 2 受体拮抗剂可对已建立的神经性疼痛产生可逆的阻断作用。此外，将CCK-8(S)显微注射到未受伤大鼠的RVM中会产生触觉和热超敏反应，让人想起神经损伤引起的疼痛状态。这些效应被 DLF 或表达 mu 阿片受体的 RVM 细胞损伤所阻止，这表明 RVM CCK 可能通过激活表型由 mu 阿片受体表达定义的 RVM 神经元来促进损伤引起的疼痛。出于这些原因，我们假设神经损伤导致 RVM CCK 活性随时间增加，从而驱动下降促进并维持神经损伤引起的疼痛。这一假设将通过以下具体目标进行检验。目标 1 将表征 (a) RVM 中的基础 CCK 活性，以及​​幼稚大鼠中 CCK 活性响应机械和热皮肤输入的变化，以及 (b) 神经损伤后 RVM 中 CCK 活性的时间依赖性。具体而言，将在脊神经结扎损伤后的早期和晚期时间点测量基础 CCK 释放以及响应 RVM 中机械和热皮肤输入的 CCK 释放。目标 2 将确定 RVM CCK 可能发挥作用驱动下行促进的 CCK 受体。 CCK 和 CCK2 受体类型在 RVM 损伤前后的功能作用将通过显微注射选择性 CCK 受体拮抗剂进行药理学评估。 CCK受体的空间分布将通过半定量原位杂交和受体放射自显影来分析。目标 2 还将研究 CCK 受体可能与 RVM 神经元中的 mu 阿片受体共定位的可能性。拟议的实验将揭示 RVM 可塑性的一些特征，这些特征可能对维持神经性疼痛至关重要。由于患有神经病理性疼痛的患者可能会在诱发性损伤发生后很长时间才寻求治疗，因此了解维持神经病理状态的机制对于制定合理的治疗干预措施至关重要。在这方面，所提出的实验可能揭示CCK受体拮抗剂作为神经性疼痛治疗的重要作用。