Analgesic actions of adenosine A1 receptor along axonal tracts in chronic pain

描述（由申请人提供）：超过1.16亿美国人患有持续性疼痛。由于目前的治疗方案不能充分解决广泛的慢性疼痛表现，针灸是一种流行的选择。然而，由于我们对其生物学基础的不完全了解，针灸仍然存在争议。在最近的实验中，我们已经表明，在人类和小鼠中，针灸与穴位局部腺苷浓度的增加有关。此外，小鼠足三里穴局部施用腺苷A1受体激动剂可以模拟针灸的镇痛作用。其他研究人员表明，局部施用PAP（一种能将AMP转化为腺苷的酸性磷酸酶）可以减轻数天的疼痛。由于大多数穴位靠近周围神经，我们推测疼痛纤维中的局部A1受体信号可以减少促痛觉传入输入的传递。基于腺苷在穴位传递，有效降低慢性疼痛小鼠坐骨神经A（delta）和C疼痛纤维的传导，我们建议评估外周疼痛通路中的A1受体信号是否构成一种新的治疗策略，可以提供比针灸本身更持久的镇痛。目的1将评估持续炎性疼痛小鼠模型中A1受体介导的信号传导。在足三里穴位腺苷信号处理前后，记录坐骨神经的复合动作电位。A1受体KO小鼠作为阴性对照。重要的是，这些实验还将评估咖啡因（一种腺苷受体拮抗剂）是否会消除针刺引起的镇痛。这个问题很重要，因为迄今为止还没有临床试验认为咖啡因会直接抵消针灸的临床益处。在慢性炎症性疼痛的实验模型中，沿着轴突束的腺苷A1受体信号的持续增加是否可以触发疼痛的持续抑制。初步数据显示，在足三里穴位注射CD73（一种将内源性AMP转化为腺苷的外核苷酸酶）可以延长疼痛缓解时间。目的3，我们将建立在初步数据的基础上，表明在足三里穴位给予CD73可降低炎症性疼痛小鼠脊髓中P物质的水平。鉴于腺苷的内源性抗炎特征，我们将验证沿传入束的腺苷信号抑制痛觉过敏，导致脊髓炎症介质减少的假设；然后将观察到的抗炎作用与长期针刺进行比较。本实验将促进我们对腺苷信号沿外周疼痛通路参与急性和持久镇痛作用的分子途径的理解。我们希望这些研究能够为治疗慢性疼痛提供新的治疗策略，并进一步了解针灸的生物学基础。

DESCRIPTION (provided by applicant): More than 116 million Americans struggle with persistent pain. As current treatment options do not adequately address the wide spectrum of chronic pain presentations, acupuncture is a popular alternative. Yet, acupuncture remains controversial due to our incomplete understanding of its biological basis. In recent experiments we have shown that acupuncture is linked to an increase in the local concentration of adenosine at the acupoint, in both human subjects and in mice. Moreover, local administration of an adenosine A1 receptor agonist in the Zusanli acupoint in mice mimicked the analgesic actions of acupuncture. Other investigators have shown that local administration of PAP (an acid phosphatase that can convert AMP to adenosine) provides days of pain reduction. As most acupoints are located in close proximity to peripheral nerves, we speculate that local A1 receptor signaling in pain fibers can reduce the transmission of pro-algesic afferent input. Based on the findings that adenosine, delivered in the acupoint, potently reduces the conductance of A(delta) and C pain fibers in the sciatic nerve in mice with chronic pain, we propose to evaluate whether A1 receptor signaling in peripheral pain pathways constitutes a novel therapeutic strategy that could provide longer-lasting analgesia than acupuncture itself. Aim 1 will evaluate A1 receptor mediated signaling in mouse models of persistent inflammatory pain. The compound action potential will be recorded in the sciatic nerve before and after manipulation of adenosine signaling at the Zusanli acupoint. A1 receptor KO mice will serve as a negative control. Importantly, these experiments will also evaluate whether caffeine (an adenosine receptor antagonist) nullifies acupuncture induced analgesia. This issue is important because no clinical trials to date have considered that caffeine may directly counteract the clinical benefits of acupuncture. Aim 2 asks whether prolonged increases in adenosine A1 receptor signaling along axonal tracts can trigger a persistent suppression of pain in experimental models of chronic inflammatory pain. Preliminary data show that administration of CD73 (an ectonucleotidase that converts endogenous AMP to adenosine) in the Zusanli acupoint provides prolonged pain relief. Aim 3, we will build on preliminary data showing that administration of CD73 in the Zusanli acupoint reduced the level of substance P in spinal cord in mice with inflammatory pain. Given adenosine's endogenous anti-inflammatory profile, we will test the hypothesis that the adenosine signaling along afferent tracts suppresses hyperalgesia, leading to a reduction of inflammatory mediators in the spinal cord; then compare the observed anti-inflammatory action with long-term acupuncture. The proposed experiments will advance our understanding of the molecular pathways involved in acute and long-lasting analgesic actions of adenosine signaling along peripheral pain pathways. We hope these studies lead to the development of novel therapeutic strategies for the treatment of chronic pain, with the additional aim of providing insight into the biological basis of acupuncture.