Obata Koichi, Yamanaka Hiroki, Fukuoka Tetsuo, Yi Dai, Tokunaga Atsushi, Hashimoto Norio, Yoshikawa Hideki, Noguchi Koichi
Department of Anatomy and Neuroscience, Hyogo College of Medicine, 1-1 Mukogawa-cho, Nishinomiya, Hyogo 663-8501, Japan.
Pain. 2003 Jan;101(1-2):65-77. doi: 10.1016/s0304-3959(02)00296-8.
Neuropathic pain models, such as the chronic constriction injury (CCI) model, are partial nerve injury models where there exist both intact and injured peripheral axons. Recent studies suggested that dorsal root ganglion (DRG) neurons with intact axons also show the alteration of excitability and gene expression and might have some role in the pathophysiological mechanisms of neuropathic pain. The incidence of pain-related behavior after the CCI is unstable and variable. In the present study, we used activating transcription factor 3 (ATF3) expression as a neuronal injury marker, and analyzed a relationship between the number of axotomized neurons and the incidence of pain-related behavior. We divided all rats into three groups according to the percentage of ATF3-immunoreactive (IR) neurons, group 1 (<12.5%), group 2 (12.5-25%), and group 3 (>25%). We found that rats in groups 2 and 3 showed thermal hyperalgesia, whereas only the rats in group 2 developed tactile allodynia from the third day to the fourteenth day after surgery. Rats in group 1 did not show thermal hyperalgesia or tactile allodynia. The DRG neurons in group 2 contained ATF3-IR neurons mainly in medium- and large-sized neurons. In order to investigate brain-derived neurotrophic factor (BDNF) and gamma-aminobutyric acid(A)-receptor (GABA(A)-R) regulation in both intact and injured primary afferent neurons after the CCI, we used a double-labeling method with immunohistochemistry and in situ hybridization, as well as double immunofluorescent staining. The CCI induced an increased number of BDNF-labeled neurons in the ipsilateral DRG and the increase in BDNF expression was observed mainly in small- and medium-sized neurons that were mainly ATF3-negative. On the other hand, the number of GABA(A)-Rgamma2 subunit mRNA-positive neurons decreased in the ipsilateral DRG and GABA(A)-R- and ATF3-labeled neurons rarely overlapped. These changes in molecular phenotype in intact and injured primary afferents may be involved in the pathophysiological mechanisms of neuropathic pain produced by partial nerve injury.
神经病理性疼痛模型，如慢性压迫性损伤（CCI）模型，是部分神经损伤模型，其中既有完整的外周轴突，也有受损的外周轴突。最近的研究表明，轴突完整的背根神经节（DRG）神经元也表现出兴奋性和基因表达的改变，并且可能在神经病理性疼痛的病理生理机制中发挥一定作用。CCI后疼痛相关行为的发生率不稳定且存在差异。在本研究中，我们使用活化转录因子3（ATF3）表达作为神经元损伤标记物，并分析了轴突切断神经元数量与疼痛相关行为发生率之间的关系。我们根据ATF3免疫反应性（IR）神经元的百分比将所有大鼠分为三组，第1组（<12.5%），第2组（12.5 - 25%）和第3组（>25%）。我们发现第2组和第3组的大鼠表现出热痛觉过敏，而只有第2组的大鼠在手术后第三天至第十四天出现触觉异常性疼痛。第1组的大鼠未表现出热痛觉过敏或触觉异常性疼痛。第2组的DRG神经元中，ATF3-IR神经元主要存在于中大型神经元中。为了研究CCI后完整和受损的初级传入神经元中脑源性神经营养因子（BDNF）和γ-氨基丁酸A受体（GABA(A)-R）的调节情况，我们使用了免疫组织化学和原位杂交的双重标记方法以及双重免疫荧光染色。CCI导致同侧DRG中BDNF标记的神经元数量增加，并且BDNF表达的增加主要在主要为ATF3阴性的中小型神经元中观察到。另一方面，同侧DRG中GABA(A)-Rγ2亚基mRNA阳性神经元的数量减少，并且GABA(A)-R和ATF3标记的神经元很少重叠。完整和受损初级传入神经元分子表型的这些变化可能参与了部分神经损伤产生的神经病理性疼痛的病理生理机制。
