前扣带回神经元在神经病理性疼痛中的突触传递机制

Peripheral nerve injury and center sensitization is one of the main pathogenesis of neuropathic pain. After peripheral nerve injury, synaptic transmission can be enhanced in the spinal cord dorsal horn neurons, this long-term potentiation (LTP) is the basis of central sensitization and neuropathic pain caused by nerve damage . Recent studies have shown the anterior cingulate cortex (ACC) plays an important role in encoding pain information ; The in vitro brain slice study found that , under the conditions of neuropathic pain , the excitability of anterior cingulate cortical neurons may occur a long-term change; While new evidence found that the noxious mechanical stimulation alone can change some electrophysiological properties of ACC neurons. Therefore, we intend to use the neuropathic pain model, to study the change of membrane potential, induced discharge and neurons'morphology by patch clamp recording and laser confocal imaging in vivo. then induced the formation of local field potential in ACC by electrical stimulation of the medial thalamic nuclei, and compare the presynaptic release and postsynaptic response in peripheral nerve injury in order to clarify the role of synaptic transmission in the central sensitization .We test the change of protein level of NR2B subunit in ACC neurons of rats with neuropathic pain by Western blot,which will further reveal the molecular mechanism of synaptic transmission.

外周神经损伤并导致中枢敏化是神经病理性疼痛的主要发病机制之一。外周神经损伤后在脊髓水平可导致脊髓背角神经元的突触传递效能增强，这种长时程增强（LTP）是神经损伤引起的中枢敏化及神经病理性疼痛的基础。最近研究表明，脊髓以上的更高级中枢前扣带回皮层（ACC）在编码疼痛信息方面起重要的作用。离体脑片研究发现，神经病理性疼痛条件下，前扣带回皮层神经元的兴奋性可发生长时程改变。最近整体研究显示，单纯伤害性机械刺激可改变ACC神经元的部分电生理特性。因此，我们拟在神经病理疼痛条件下，采用膜片钳记录与共聚焦成像在整体水平研究ACC神经元的膜电位、诱发放电及其形态的变化；并通过电刺激内侧丘脑核团，诱导ACC局部场电位的形成，比较突触前释放及突触后反应在外周神经损伤后的改变。采用Western blot方法检测ACC区NR2B亚基表达的变化，进一步揭示ACC神经元在神经病理性疼痛中突触传递的分子机制。

前扣带回皮层在处理痛觉及情绪信息过程中发挥重要作用，外周神经损伤后至ACC神经元兴奋性增高可能参与了神经病理性疼痛的发生与发展。本研究通过在体及离体膜片钳实验观察了大鼠ACC神经元在外周神经慢性卡压疼痛及外周瘙痒时的动作电位频率、膜电位振荡频率、兴奋性突触后反应及诱发放电的变化。结果发现：（1）与假手术组比较，慢性疼痛组ACC神经元膜电位振荡频率明显增高，且动作电位的自发发放频率亦增高，这种改变在外周疼痛阻断后可持续存在。(2)与生理盐水组比较，急性瘙痒组胺组mEPSC的频率和幅度明显升高(P<0.05)，两组mIPSC频率和幅度差异无统计学意义。（3）与对照组比较，慢性瘙痒组大鼠ACC神经元兴奋性突触后微电流的频率与幅度均增加，AMPA/NMDA电流的比率亦增加，ACC锥体神经元AMPAR受体介导内向整流电流增加。这些研究结果提示，在慢性疼痛及瘙痒条件下，ACC神经元膜电位及兴奋性突触后反应增加，ACC神经元兴奋性的改变参与了慢性疼痛及瘙痒的发生发展。