脊髓背角VGluT3神经元介导动态触诱发痛的脊髓机制研究

The mechanisms by which simply brushing the skin can evoke pain in pathological conditions still remain unknown. Clinical studies have established that the symptom, called dynamic mechanical allodynia, is mediated by sensory Abeta fibers normally responsible for the detection of innocuous mechanical stimuli only. According to our previous work published by the journal of Cell in the year 2014, peripheral Abeta mechanoreceptors, together with spina SOM+ exciatatory and Dyn+ inhibitory neurons, form a microcircuit that transmit and gate mechanical allodynia. Ablation of SOM lineage neuron leads to loss of both acute mechanical pain, mechanical allodynia (both static and dynamic), as well as chemical induced itch sensation. .This study is designed to dissect the spinal circuit for dynamic mechanical allodynia. Accoridng to our preliminary resulsts, spinal VGLUT3 lineage excitatory neurons ablated mice selectly lost dyanmic mechanical allodynia, while static allodyina is still intact, after CFA or SNI. Recent electrophyiological recordings in the spinal cord slices show that in VGLUT3 neuron-ablated mice, slow Abeta Abeta-evoked APs in the superficial dorsal horn selectively lost, while fast Abeta-evoked APs no significant change. According to our previous work published in Cell, there are at least two pathways from Abeta to laminar I projection neurons: pathway A and B. Pathway A is characterized is by long latency slow Abeta input to laminar I neurons. Since VGLUT3 ablated mice selectively lost slow Abeta input, our hypothesis is that pathway A mediated dynamica mechanical allodynia. If this study is funded, we will perform more experiments to dissect the spinal circuit for dynamic mechanical allodynia.

我们近期在Cell杂志所发表的研究发现,来自外周的Abeta纤维和脊髓背角表达SOM的兴奋性中间神经元以及表达Dyn的抑制性中间神经元，三者一起在脊髓背角组成了一个传递和“门控”机械痛的微环路。动态触诱发痛是慢性机械性疼痛的一种，由Abeta纤维介导，对吗啡镇痛不敏感，目前临床上尚缺乏有效的治疗手段，主要原因是其机制不明。根据我们前期的工作，脊髓背角SOM神经元敲除小鼠，急性机械痛感觉和炎症和神经损伤后所引起的慢性机械痛感觉，包括静态和动态触诱发痛都丧失了，与此同时，痒的感觉也受到了影响。本项目是在前期工作的基础上，研究阐明：1）脊髓背角特异介导动态触诱发痛的神经元类型，2）Abeta纤维介导动态触诱发痛的脊髓背角相关神经通路，3）脊髓背角调控动态触诱发痛的抑制性中间神经元和4）吗啡对动态触诱发痛不敏感的脊髓机制。研究结果有望为吗啡镇痛不敏感的动态触诱发痛的临床治疗找到更特异的靶点。

机械触诱发痛（mechanical alldoynia）是慢性疼痛的突出症状，是临床上一个十分棘手的问题，主要原因是其机制不明。临床上触诱发痛分为两种类型，一种是动态的轻触刺激如风吹/穿衣所触发的动态触诱发痛(dynamic allodynia)，另外一种是对皮肤表面施加稳定的压力引起的点状或静态触诱发痛(punctate/static allodynia)，而长期困扰大部分疼痛病人的是动态触诱发痛。由于临床上静态和动态触诱发痛对吗啡的敏感性不同，后者对吗啡镇痛不敏感，临床治疗更加棘手，因而迫切需要明确其脊髓环路以及对吗啡镇痛不敏感的机制。本项目的研究发现，特异性敲除脊髓背角表达vesicular glutamate transporter 3 (VGLUT3)（发育过程中短暂表达）的神经元后，在神经损伤（SNI）、炎症（CFA/Carrageenan）和去抑制（bicuculline + strychnine）等多种慢性疼痛小鼠模型上其毛刷轻刷触发的动态触诱发痛显著减轻，而由von Frey纤毛压迫诱发的点状触诱发痛并没有发生明显的改变。应用脊髓切片离体电生理技术，我们对动态触诱发痛在脊髓背角的神经传导通路开展了深入研究。研究结果，在脊髓背角存在多条正常情况下被“门控”的触诱发痛通路，当敲除脊髓背角VGLUT3神经元后，小鼠SNI后选择性地丧失了对吗啡镇痛不敏感的多突触Aβ通路，而由SOM+神经元介导的快的Aβ通路并没有发生显著变化。上述研究结果证明，临床上对吗啡镇痛不敏感的动态触诱发痛是由脊髓背角的VGLUT3神经元通过多突触间接的Aβ通路传递的。该研究结果有望为临床上对阿片类药物镇痛不敏感的顽固性的动态触诱发痛的临床干预和新药靶点的发现提供理论依据。