Dissecting the relative contributions of injured and intact primary afferents to neuronal plasticity and neuropathic pain

正常(伤害性)疼痛是当特殊的神经(伤害性感受器)检测到有害刺激时产生的，是帮助我们预防或限制伤害的重要警告系统。伤害性感受器将伤害性刺激的信号发送到脊髓。在这里，信号在被传输到大脑之前被大量修改，在那里产生了疼痛的感觉。与伤害性疼痛不同，神经性疼痛是由神经系统损伤或疾病引起的，是一种没有已知目的的疾病。仅在英国就有500多万人受到影响，其中大多数患者因目前的治疗而失败，生活在致残疼痛中。神经性疼痛是一种疼痛传递功能障碍，可包括自发疼痛(刺痛或灼痛)和/或对有害和非有害刺激的痛觉增强(分别称为痛觉过敏和超感痛觉)。伤害性感受器和脊髓回路功能的改变被认为是神经病理性疼痛的原因之一。然而，我们对神经病理性疼痛的不同方面所涉及的确切神经知之甚少，尤其是自发性疼痛的潜在原因研究得特别少。这是一个极其重要的研究领域，原因有两个。首先，因为自发性疼痛是神经病理性疼痛患者的主要主诉，其次，因为知道哪些神经应该针对哪些神经以及在哪里进行，对于合理设计能够缓解疼痛的新药至关重要。对患者的研究清楚地表明，伤害性感受器中过度的电活动会产生疼痛。神经损伤后，受损的神经和完整的邻近神经会产生自发的电活动，这就提出了这两组神经如何导致疼痛的问题。这将是我研究计划的中心问题。为了进行研究，我将使用一只转基因小鼠，在小鼠中，受损和完整的神经分别被定位于一种蛋白质，这种蛋白质能够在给药时关闭电活动。我将使用新的行为学方法来评估神经病理性疼痛的小鼠模型中的自发疼痛。当受伤或完整的神经被切断时，自发疼痛的水平将被比较，以深入了解它们各自的贡献。虽然伤害性感受器中的电活动对自发疼痛至关重要，但脊髓中信号的处理方式可能会增强或延长感受到的疼痛。因此，为了研究脊髓中发生的变化，我将测量和比较受伤和完整的伤害性感受器激活脊髓回路的相对容易程度。为了直观地观察神经损伤后脊髓回路结构是否发生变化，我将使用基因改变的小鼠，用不同颜色的荧光蛋白标记受损和完整的伤害性感受器。通过这种方式，我将能够比较这些神经在脊髓中的位置，以及它们与脊髓神经的连接在受伤后是否发生了变化。这些研究将通过在组织制剂中记录脊神经来支持，同时激活受损或完整的伤害性感受器。通过这样做，我将回答这两条途径在受伤后是否会得到加强。最后，我将研究受损或完整神经的电活动是否会激活脊髓中的免疫细胞，这是已知的导致慢性疼痛的因素。这将为我们提供重要的信息，即不依赖于伤害性感受器的电活动的免疫系统的激活是否应该是药物开发的重要考虑因素。这项工作将提供有关产生疼痛的神经以及它们的活动如何导致持久和增强的疼痛的重要信息。通过这样做，我将定义新的治疗目标，使我们能够更好地设计治疗神经病理性疼痛的新药。

Normal (nociceptive) pain is generated when specialised nerves (nociceptors) detect noxious stimuli and is a vital warning system that helps us to prevent or limit injury. Nociceptors send signals about the noxious stimuli to the spinal cord. Here, the signal is heavily modified before being transmitted to the brain, where the perception of pain is generated. Unlike nociceptive pain, neuropathic pain, which results from injury or disease of the nervous system, is a condition for which there is no known purpose. It affects over five million people in the UK alone and the majority of these patients are failed by current treatments and live in disabling pain.Neuropathic pain represents a dysfunction of pain transmission that can include spontaneous pain (stabbing or burning pain) and/or enhanced pain perception to both noxious and non-noxious stimuli (termed hyperalgesia and allodynia respectively). Changes in the way nociceptors and spinal circuits function are known to contribute to neuropathic pain. However, we know little about the precise nerves involved in different aspects of neuropathic pain, with the underlying causes of spontaneous pain a particularly understudied example. This is an incredibly important research area for two reasons. Firstly, because spontaneous pain is the major complaint from patients with neuropathic pain and, secondly, because knowing which nerves to target and where to do so, will be vital for the rational design of new drugs capable of ameliorating pain. It is clear from studies in patients that excessive electrical activity in nociceptors generates pain. Following injury to a nerve, injured nerves and intact neighbouring nerves develop spontaneous electrical activity; raising the question of how these two groups contribute to pain. This will be the central question of my research programme. To investigate, I will use a genetically altered mouse in which damaged and intact nerves are targeted separately with a protein capable of turning off electrical activity when a drug is given. I will use new behavioural methods to assess spontaneous pain in mouse models of neuropathic pain. The level of spontaneous pain when injured or intact nerves are switched off will be compared to give an insight into their respective contributions.While electrical activity in nociceptors is vital for spontaneous pain, the way the signal is processed in the spinal cord likely enhances or prolongs the pain experienced. Therefore, to study the changes that occur in the spinal cord, I will measure and compare the relative ease with which injured and intact nociceptors can activate spinal circuits. To visualise whether there are changes in spinal cord circuit structure following nerve injury, I will use genetically altered mice to label injured and intact nociceptors with different colours of fluorescent protein. In this way, I will be able to compare where these nerves go in the spinal cord and whether their connections with spinal nerves change after injury. These studies will be supported by recording from spinal nerves in tissue preparations while activating injured or intact nociceptors. By doing so, I will answer whether either pathway is strengthened following injury. Finally, I will study whether electrical activity in injured or intact nerves activates immune cells in the spinal cord, which are known to contribute to chronic pain. This will give us important information on whether activation of the immune system, independent of nociceptor electrical activity, should be an important consideration for drug development.This work will provide important information on the nerves involved in generating pain and how their activity can result in long-lasting and enhanced pain. In doing so, I will define new therapeutic targets that allow us to better design novel drugs for the treatment of neuropathic pain.