Supraspinal mechanism of 5-HT-dependent descending facilitation in chronic pain

 描述（由申请人提供）：慢性疼痛是一个主要的公共卫生问题，并提供了一个最困难的治疗挑战。虽然慢性疼痛已越来越多地被认为是一种神经系统疾病，但其潜在机制仍不清楚。近年来的研究表明，延髓头端腹内侧区（RVM）下行易化增强或下行抑制减弱可能参与了慢性疼痛的脊髓上机制。新的证据表明，5-HT依赖性下行易化从RVM负责神经损伤后的急性疼痛的慢性化的过渡。然而，解释5-HT依赖性下行易化的突触和细胞信号机制知之甚少。瞬时受体电位香草酸1型（TRPV 1）通道是具有高Ca++渗透性的配体门控非选择性阳离子通道，在初级伤害性感觉神经元中作为有害热和炎症介质的分子传感器而显著表达。最近，TRPV 1通道也被发现在大脑中表达，与其他突触蛋白质相互作用，并作为下游信号传导的整合剂，介导持久的突触可塑性。虽然TRPV 1通道分布在RVM中，但其在下行疼痛调制中的潜在生理和病理意义仍然未知。我们探讨了RVM中神经胶质细胞-细胞因子-神经元的相互作用，这些相互作用是神经损伤后下行痛易化和痛觉过敏维持的基础。因此，我们将进一步研究TRPV 1通道在RVM中的功能特征，扩展我们对含5-HT的RVM神经元的过度兴奋和行为超敏性所涉及的不同信号传导机制的研究。我们的假设是，钙渗透TRPV 1通道的功能表达在RVM 5-HT-含有神经元和调节兴奋性突触传递和神经元活动的RVM。我们进一步假设，RVM TRPV 1的长期上调和敏化是在神经损伤后诱导的，并促进胶质细胞过度活跃和神经元过度兴奋之间的细胞内信号转导。通过整合与细胞因子受体激活相关的下游信号和随后的NMDA受体活性增加，TRPV 1敏化含5-HT的神经元维持神经超兴奋性，并有助于5-HT依赖性下行疼痛促进神经病理性疼痛的维持。以下具体目标将使用多学科方法来检验这些假设。第一名：为了验证以下假设：中央TRPV 1通道存在于RVM中，并在投射到背角的含5-HT的RVM神经元中功能性表达。第二：为了验证以下假设：RVM中TRPV 1的长期上调和致敏发生在神经损伤后，并介导神经病理性疼痛发展的下行易化。第三名：为了检验RVM中胶质细胞过度活跃时释放的促炎细胞因子敏化神经损伤后局部TRPV 1功能的假设，这依赖于细胞内非典型蛋白激酶C/Mzeta信号的长期上调。第四名：为了验证TRPV 1激活通过增强RVM神经元的突触能传递和含5-HT神经元的过度兴奋参与下行疼痛调制的假设。这项研究结果将扩大我们对中央TRPV 1通道在脊髓上5-HT依赖性下行易化机制中的新作用的认识，并为神经病理性疼痛的治疗提供新的治疗靶点。

 DESCRIPTION (provided by applicant): Chronic pain is a major public health problem and offers a most difficult challenge to therapy. Although chronic pain has been increasingly recognized as a disease of the nervous system, the underlying mechanisms remain largely unclear. Recently studies suggest that enhanced descending facilitation or reduced descending inhibition from the rostral ventromedial medulla (RVM), a pivotal structure of descending modulation of trigeminal and spinal nociceptive transmission, contribute to supraspinal mechanisms of chronic pain. New evidence shows that 5-HT-dependent descending facilitation from the RVM is responsible for the transition of acute pain to chronicity after nerve injury. However, the synaptic and cellular signaling mechanisms accounting for 5-HT-dependent descending facilitation are poorly understood. Transient receptor potential vanilloid type 1 (TRPV1) channels are ligand-gated nonselective cation channels with high Ca++ permeability and are prominently expressed in primary nociceptive sensory neurons as molecular sensors for noxious heat and inflammatory mediators. More recently, TRPV1 channels are also found to express in the brain, cross-talk with other synaptic proteins and act as an integrator for downstream signaling to mediate long-lasting synaptic plasticity. Although TRPV1 channels are distributed in the RVM, their potential physiological and pathological significance in descending pain modulation remains unknown. We have explored glia-cytokine-neuronal interaction in the RVM underlying descending pain facilitation and the maintenance of hyperalgesia after nerve injury. Thus, we will further study the functional signature of TRPV1 channels in the RVM, expanding our study of distinct signaling mechanisms involved in hyperexcitability of 5-HT-containing RVM neurons and behavioral hypersensitivity. Our hypothesis is that calcium-permeable TRPV1 channels are functionally expressed in RVM 5-HT-containing neurons and modulate excitatory synaptic transmission and neuronal activity in the RVM. We further hypothesize that the long-lasting upregulation and sensitization of RVM TRPV1 is induced after nerve injury and facilitate intracellular signal transduction between glial hyperactivity and neuronal hyperexcitability. Through integrating downstream signaling relevant to cytokine receptor activation and subsequent increase of NMDA receptor activity, TRPV1 sensitization in 5-HT-containing neurons maintains neural hyperexcitability and contributes to 5-HT-dependent descending pain facilitation underlying the maintenance of neuropathic pain. The following Specific Aims will test these hypotheses using multidisciplinary approaches. #1: To test the hypothesis that central TRPV1 channels are present in the RVM and functionally expressed in 5-HT-containing RVM neurons projecting to the dorsal horn. #2: To test the hypothesis that long-term upregulation and sensitization of TRPV1 in the RVM occur after nerve injury and mediate descending facilitation underlying the development of neuropathic pain. #3: To test the hypothesis that proinflammatory cytokines released upon glial hyperactivity in the RVM sensitize local TRPV1 function after nerve injury, which is dependent on long-lasting upregulation of intracellular atypical protein kinase C/Mzeta signaling. #4: To test the hypothesis that TRPV1 activation is involved in descending pain modulation through potentiation of glutamatergic synaptic transmission in RVM neurons and hyperexcitability of 5-HT-containing neurons. The findings from this proposal will expand our appreciation of a novel role of central TRPV1 channels in supraspinal mechanisms of 5-HT-dependent descending facilitation and provide new therapeutic targets for the treatment of neuropathic pain.