Elucidation of Molecular Mechanisms of Pain : Role of PKC and NGF on spinal sensitization in the pathological state following peripheral tissue injury

脊髓的躯体感觉系统直接参与外周伤害性传入的调制，组织损伤后急性和/或慢性外周C纤维激活。然而，在某些条件下，存在一种病理状态，其功能特征在于对伤害性刺激的反应增加（痛觉过敏）和痛阈降低（异常性疼痛）。本研究的目的是检查所观察到的病理性疼痛状态的分子机制，其可能反映了异常的细胞内信号传导，导致细胞内谷氨酸和P物质的过度释放导致细胞内Ca离子增加，以及多种生长因子（NGF）的合成增加，建立大鼠模型，根据本研究，以下是可能的机制：1.外周组织炎症后的疼痛和神经元可塑性增加外周C-福尔马林或芥子油后爪注射引起的纤维活性引起1） ...更多信息 脊髓谷氨酸释放过多（2）NMDA受体拮抗剂阻断痛觉过敏-> NMDA受体激活引起背角神经元活动增加，细胞内Ca^++大量增加;（PKC抑制剂）抑制谷氨酸释放和痛觉过敏->激活PLA 2，PLC，其引起花生四烯酸（PGs）和蛋白激酶C（PKC）的合成，这些物质和酶在脊髓中引发正反馈（持续促进），4）脊髓内突触传递的“上调”，其功能性表示为5）脊髓神经元对外周刺激的反应性增加，“中枢敏感化”：2.神经生长因子（nerve growth factor，NGF）参与易化痛的形成和发展。NGF在周围神经损伤后的发生和恢复过程中的生物学作用已被广泛研究。有证据表明其作为靶源性神经营养因子的作用，调节各种外周组织中的神经支配密度。NGF在成年动物中的作用不太清楚，但越来越多的证据表明，包括目前的结果，NGF是一种外周介质，在促进炎症性疼痛状态。1)高亲和力的NGF受体（trkA）与C-纤维中的sP一起表达; 2）4-甲基乙酰胆碱（4 MC）增加NGF，引起芥子油引起的痛敏以剂量依赖方式增强。-> NGF处理可以促进谷氨酸和sP介导的突触传递，并且可以导致中枢敏化。3)脊髓神经生长因子免疫反应性增强，以代偿神经元树突状损伤（降低的MAP-2免疫反应性）->这可能是由与白细胞介素-1（IL-1）* 激活的巨噬细胞相互作用引起的，其中IL-1是NGF-mRNA水平的关键介质。这些证据有力地表明，NGF是维持上调所必需的，可以导致外周和中枢敏化。在未来的研究中，我们需要进一步阐明外周损伤或伤害性刺激如何导致神经元可塑性改变的理论，以及NGF如何在慢性状态下的易化状态和神经元变性中发挥作用。少

The somatosensory system of spinal cord are directly involved into the modulation of peripheral nociceptive input with acute and/or chronic peripheral C-fibers activation following tissue injury. However, under certain condition, there is a pathological state which is functionally characterized by an increased response to noxious stimuli (hyperalgesia), and the reduction of pain threshold (allodynia). The aim of the present study was to examine the molecullar mechanism of the observed pathological pain state may reflect an abnormal intracellular signaling resulting in increased intracellular Ca ion caused by excessive release of glutamate and substance P and increased syntheses of a variety of growth factors (NGF) using well-established rat model.The followings are possible mechanisms based on the present study.1.Pain and neuronal plasticity following peripheral tissue inflammationIncreased peripheral C-fiber activity resulting from formalin or mustard oil hind paw injection evokes 1) … More excessive release of spinal glutamate (by microdialysis), 2) NMDA antagonist blocked hyperalgesia-> increased neuronal activity of dorsal horn resulting from activation of NMDA receptor and corresponding massive increase in intracellular Ca^<++>,3) Staurosporine (PKC inhivitor) supressed glutamate release and hyperalgesia -> activation of PLA2, PLC which evokes synthesis of arachidonic acid (PGs) and protein kinase C (PKC), these substances and enzyme iniciate positive feed back in spinal cord (sustained facilitation), 4) "up-regulation" of synaptic transmission within the spinal cord functionally expressed as 5) increased responsivity of spinal cord neurons to peripheral stimulus i.c. "central sensitization" : allodynia and/or hyperalgesia.2.Involvement of nerve growth factor (NGF) in facilitated pain state.The biological role of NGF in the developing and restoring processes after peripheral nerve injury has been most intensively studied. There is evidence suggesting its role as a target-derived neurotrophic factor, regulating the density of innervation in a variety of peripheral tissues. The role of NGF in the adult animal is less well characterized, but there is increasing evidence including present results to suggest that NGF is a peripheral mediator in facilitated inflammatory pain states. 1) the high affinity NGF receptor is expressed with sP in C-fiber (trkA),2) 4-methyl cathechol (4MC), which increases NGF,caused enhancement of hyperalgesia in a dosc deppendent manner produced by injecting mustard oil. -> NGF treatment can facilitate glutamate and sP mediated synaptic transmission, and can lead to central sensitization. 3) NGF immunoreactivity of spinal cord was increased to compensate dendritic damage of neuron (decreased MAP-2 immunoreactivity) after formalin injection -> this may be caused by interacting with interleukin-1 (IL-1) * activated macrophage where the IL-1 is the key mediator on NGF-mRNA levels.Taken together, these evidences strongly suggest that NGF is necessary for the maintenance of the up-regulation can lead to a peripheral and central sensitization. In the future study, we need to elucidate further such as the theories proposed to explain how the peripheral injury or noxicious stimulation lead to the alteration in neuronal plasticity and how to play a role of NGF in facilitating state and neuronal degeneration in chronic state. Less