Studies on neural regeneration and reorganization of neural circuits in neuropathic pain

本研究利用nestin启动子介导的绿色荧光蛋白（green fluorescent protein， GFP）转基因小鼠，研究了神经再生和神经回路重组在触觉痛觉（allodynia）诱导中的作用。为了诱导异位性疼痛，我们在先前建立的鞘内注射模型的基础上，通过选择性5^< >腰脊神经横断建立小鼠神经性疼痛模型。我们广泛地检测了GFP在胚胎到成年小鼠的背根神经节（DRG）和脊髓中的表达。在全胚中，GFP在脊髓中央管周围表达强烈，出生后逐渐降低。腰椎片证实了中央椎管周围的这种表达。在DRG神经元中，GFP在周细胞中强烈表达，而不是神经元本身。在神经病变小鼠，术后第2天和第3天，双侧背角gfp阳性细胞增加。炎症消退后，手术的同侧出现神经性疼痛，同侧gfp阳性细胞的数量明显多于对侧。这些细胞未被神经元和星形胶质细胞特异性抗体染色。同时，我们发现在神经性病变小鼠的中枢管周围一氧化氮合酶活性增加。这一发现可能暗示从外周到中央管的有害输入与慢性疼痛或神经可塑性之间的关系。目前，为了弄清神经干细胞在何处增殖、向何处迁移以及如何分化为神经元和胶质细胞，人们正在研究神经干细胞的激活机制和迁移途径。

The present study focused on the role of neural regeneration and reorganization of neural circuit in induction of tactile pain (allodynia) by use of pNestin-GFP transgenic mice, which are introduced by a transgene of green fluorescent protein (GFP) driven by a promotor of nestin, an intermediate filament expressed in neural stem cells. To induce allodynia, we established a neuropathic pain model in mice by selective 5^<th> lumbar spinal nerve transection, in addition to intrathecal injection model previously established.We extensively examined the expression of GFP in dorsal root ganglia (DRG) and spinal cord in embryos to adult mice. In whole embryos, the intense expression of GFP was observed around central canals over the spinal cord, which was gradually decreased after birth. This expression around the central canal was confirmed by the lumbar slice. In DRG neurons, GFP was strongly expressed in pericytes, rather than neurons themselves. In neuropathic mice, GFP-positive cells bilaterally increased in the dorsal horn on days 2 and 3 after operation. Following subsidence of inflammation, neuropathic pain was established in the ipsilateral side to the operation and the number of GFP-positive cells was significantly larger in the ipsilateral side than in the contralateral side. These cells were not stained by antibodies specific for neurons and astrocytes. In parallel, we showed that nitric oxide synthase activity was increased around the central canal in neuropathic mice. This finding may imply that the relationship between noxious inputs from the periphery to the central canal and chronic pain or neural plasticity. At present, in order to clarify where neural stem cells proliferate, to where they migrate, and how they differentiate into neurons and glias, the mechanism of activation and the pathway of migration of neural stem cells are under investigation.