Modulation of Pruritus by Spinal Cannabinoids

脊髓大麻素调节瘙痒

• 批准号: 7741061
• 负责人: GREGORY W TERMAN
• 金额: $ 22.84万
• 依托单位: UNIVERSITY OF WASHINGTON
• 依托单位国家: 美国
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-06-01 至 2011-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7741061
• 关键词: 2-arachidonylglycerol; AM 251; Adult; Analgesics; Animals; Back; Behavior; Binding; Bombesin Receptor; Breeding; CNR1 gene; Cannabinoids; Cell model; Chronic; Data; Development; Endocannabinoids; Enzymes; Esthesia; Feedback; Feeds; Gastrin releasing peptide; In Vitro; Injection of therapeutic agent; Intrathecal Injections; Investigation; Knock-out; Knockout Mice; Laboratories; Lipid Binding; MK801; Masks; Mediating; Modeling; Morphine; Motor Activity; Mus; N-Methyl-D-Aspartate Receptors; NMDA receptor antagonist; Neonatal; Neurobiology; Nociception; Nociceptors; Opiates; Pain; Peptides; Proteins; Pruritus; Rattus; Reporting; Rodent; SR141716; Spinal; Spinal Cord; Stimulus; Synaptic Transmission; System; Testing; The Sun; Therapeutic; Therapeutic Uses; Work; behavior change; cannabinoid receptor; central sensitization; clinically significant; dorsal horn; immunocytochemistry; in vivo; inhibitor/antagonist; interest; lipoprotein lipase; man; neurochemistry; neurotransmission; novel; presynaptic; public health relevance; pup; relating to nervous system; response

Description (provided by applicant): For several years my laboratory has studied the neurochemical changes that take place in the neonatal rat spinal cord following repeated opiate administration as a cellular model of opiate analgesic tolerance. We have reported NMDA receptor-mediated increases in nociceptive primary afferent synaptic transmission associated with opiate tolerance. We have also discovered that the endocannabinoid 2-arachidonoylglycerol (2-AG), released in response to increased nociceptor activity, feeds back to inhibit such activity by acting at presynaptic CB1 receptors. Recently, we have found that, like nociception, itch sensation, also appears to be increased in animals previously exposed to repeated morphine injections - although this effect is largely masked by concurrent spinal endocannabinoid inhibition. After intrathecal administration of the CB1 receptor antagonist SR141716 (SR) significant increases in scratching behaviors are observed - particularly in rats previously treated with repeated morphine injections. We hypothesize that repeated opiate administration induces central sensitization of primary afferent neurotransmission of pruritus, thereby increasing the synthesis and release of 2-AG, which in turn feeds back to inhibit itch by binding to presynaptic CB1 receptors. The current application proposes to begin testing this hypothesis with three specific aims: 1) To verify that spinal endocannabinoids act at spinal CB1 receptors to inhibit itch. To test this hypothesis, we will first use immunocytochemistry to ascertain that, as in adults, both CB1 receptors and DAG lipase are present in the dorsal horn of neonatal rats. We will also intrathecally inject a different CB1 antagonist (AM251) or a 2-AG synthesizing enzyme (DAG lipase) inhibitor to study whether these means of inhibiting spinal 2-AG effects can also increase scratching behaviors in neonatal rats. Finally, we will attempt to replicate and extend our intrathecal SR studies to adult mice and compare these effects with those in littermate CB1 receptor knockout mice. 2) To study the mechanism by which anti-pruritic endocannabinoids are released in the spinal cord. Our data suggest that following repeated morphine injections not only are nociceptive primary afferents more active but primary afferents related to itch are also more excitable. We have previously found that morphine- induced primary afferent nociceptor sensitization is mediated predominately via NMDA receptors. In these studies we will test whether opiate-induced sensitization to itch is also mediated by NMDA receptors and whether it can be inhibited by the NMDA receptor antagonist MK801. Further, we will use Gastrin Releasing Peptide (GRP) to study whether application of this peptide, recently observed to produce spinally-mediated pruritus, can cause endocannabinoid release as evidenced by SR-induced increases in scratching. 3) To begin investigations of exogenous cannabinoid modulation of scratching behavior. Finally, we will use intrathecal injections of the cannabinoid WIN 55,212-2 in animals with GRP-induced scratching in hopes of demonstrating possible applications of cannabinoids for the treatment of itch. Thus, these studies may suggest novel anti-pruritic therapies for cannabinoids as well as providing new models and concepts to investigate the neural underpinnings of spinal interactions between pain and itch. PUBLIC HEALTH RELEVANCE: Like pain, the sensation of itch has important clinical significance in that chronic itch leads to considerable suffering. We have recently found evidence that endogenous substrates exist within the spinal cord which can inhibit itch and that these systems rely on endogenous cannabinoids. In these proposed preliminary studies, we seek to demonstrate what stimuli activate these endogenous itch-inhibiting systems, which endocannabinoid is primarily involved in inhibiting itch in vivo and what cannabinoid receptor these bioactive lipids bind to in producing their effect. Such studies may suggest novel anti-pruritic therapies for exogenous cannabinoids as well as providing new models and concepts to better understand the neurobiology of itch and, in particular, the spinal interactions between pain and itch.

描述（由申请人提供）：多年来，我的实验室一直在研究重复给予阿片类药物后新生大鼠脊髓中发生的神经化学变化，作为阿片类药物镇痛耐受性的细胞模型。我们已经报道了NMDA受体介导的与阿片耐受相关的伤害性初级传入突触传递的增加。我们还发现，内源性大麻素2-花生四烯酰甘油（2-AG），响应于增加的伤害感受器活性而释放，通过作用于突触前CB 1受体而反馈抑制这种活性。最近，我们发现，与伤害感受一样，在先前暴露于重复吗啡注射的动物中，瘙痒感觉似乎也会增加-尽管这种作用在很大程度上被同时发生的脊髓内源性大麻素抑制所掩盖。鞘内注射CB 1受体拮抗剂SR 141716（SR）后，观察到抓挠行为显著增加-特别是在先前重复注射吗啡的大鼠中。我们假设，反复阿片类药物给药诱导瘙痒的初级传入神经传递的中枢敏化，从而增加2-AG的合成和释放，这反过来又反馈抑制瘙痒结合突触前CB 1受体。本申请提出开始以三个具体目的来测试该假设：1）验证脊髓内源性大麻素作用于脊髓CB 1受体以抑制瘙痒。为了验证这一假设，我们将首先使用免疫细胞化学来确定，在成年人中，CB 1受体和DAG脂肪酶都存在于新生大鼠的背角。我们还将鞘内注射不同的CB 1拮抗剂（AM 251）或2-AG合成酶（DAG脂肪酶）抑制剂，以研究这些抑制脊髓2-AG效应的方法是否也可以增加新生大鼠的抓挠行为。最后，我们将尝试复制和扩展我们的鞘内SR研究，以成年小鼠和比较这些影响与同窝CB 1受体敲除小鼠。2)研究抗癫痫内源性大麻素在脊髓中释放的机制。我们的数据表明，重复注射吗啡后，不仅伤害性初级传入更活跃，而且与瘙痒相关的初级传入也更兴奋。我们以前发现吗啡诱导的初级传入伤害感受器敏化主要是通过NMDA受体介导的。在这些研究中，我们将测试阿片类药物诱导的瘙痒敏感性是否也是由NMDA受体介导的，以及它是否可以被NMDA受体拮抗剂MK 801抑制。此外，我们将使用胃泌素释放肽（GRP），以研究是否应用这种肽，最近观察到产生脊髓介导的瘙痒症，可以引起内源性大麻素的释放，如SR诱导的抓挠增加所证明。3)开始研究外源性大麻素对抓挠行为的调节作用。最后，我们将在GRP诱导的抓挠动物中使用大麻素WIN 55，212 -2的鞘内注射，希望展示大麻素治疗瘙痒的可能应用。因此，这些研究可能提出大麻素的新型抗癫痫疗法，并提供新的模型和概念来研究疼痛和瘙痒之间脊髓相互作用的神经基础。公共卫生相关性：与疼痛一样，瘙痒感具有重要的临床意义，因为慢性瘙痒会导致相当大的痛苦。我们最近发现的证据表明，内源性底物存在于脊髓内，可以抑制瘙痒，这些系统依赖于内源性大麻素。在这些拟议的初步研究中，我们试图证明什么刺激激活这些内源性瘙痒抑制系统，内源性大麻素主要参与抑制体内瘙痒，以及这些生物活性脂质与大麻素受体结合产生其作用。这些研究可能为外源性大麻素提供新的抗瘙痒疗法，并提供新的模型和概念，以更好地了解瘙痒的神经生物学，特别是疼痛和瘙痒之间的脊髓相互作用。