Dai Yi, Iwata Koichi, Fukuoka Tetsuo, Kondo Eiji, Tokunaga Atsushi, Yamanaka Hiroki, Tachibana Toshiya, Liu Yi, Noguchi Koichi
Department of Anatomy and Neuroscience, Hyogo College of Medicine, Hyogo 663-8501, Japan.
J Neurosci. 2002 Sep 1;22(17):7737-45. doi: 10.1523/JNEUROSCI.22-17-07737.2002.
Alteration in the intracellular signal transduction pathway in primary afferent neurons may contribute to pain hypersensitivity. We demonstrated that very rapid phosphorylation of extracellular signal-regulated protein kinases (pERK) occurred in DRG neurons that were taking part in the transmission of various noxious signals. The electrical stimulation of Adelta fibers induced pERK primarily in neurons with myelinated fibers. c-Fiber activation by capsaicin injection induced pERK in small neurons with unmyelinated fibers containing vanilloid receptor-1 (VR-1), suggesting that pERK labeling in DRG neurons is modality specific. Electrical stimulation at the c-fiber level with different intensities and frequencies revealed that phosphorylation of ERK is dependent on the frequency. We examined the pERK in the DRG after application of natural noxious stimuli and found a stimulus intensity-dependent increase in labeled cell size and in the number of activated neurons in the c- and Adelta-fiber population. Immunohistochemical double labeling with phosphorylated ERK/VR-1 and pharmacological study demonstrated that noxious heat stimulation induced pERK in primary afferents in a VR-1-dependent manner. Capsaicin injection into the skin also increased pERK labeling significantly in peripheral fibers and terminals in the skin, which was prevented by a mitogen-activated protein kinase/ERK kinase inhibitor, 1,4-diamino-2,3-dicyano-1,4-bis(2-aminopheylthio)butadiene (U0126). Behavioral experiments showed that U0126 dose-dependently attenuated thermal hyperalgesia after capsaicin injection and suggested that the activation of ERK pathways in primary afferent neurons is involved in the sensitization of primary afferent neurons. Thus, pERK in primary afferents by noxious stimulation in vivo showed distinct characteristics of expression and may be correlated with the functional activity of primary afferent neurons.
初级传入神经元细胞内信号转导通路的改变可能导致疼痛超敏反应。我们证明，参与各种伤害性信号传递的背根神经节（DRG）神经元中，细胞外信号调节蛋白激酶（pERK）会迅速磷酸化。对Aδ纤维的电刺激主要在有髓纤维的神经元中诱导pERK。辣椒素注射激活C纤维会在含有香草酸受体-1（VR-1）的无髓小神经元中诱导pERK，这表明DRG神经元中的pERK标记具有模式特异性。在C纤维水平以不同强度和频率进行电刺激显示，ERK的磷酸化取决于频率。我们在施加自然伤害性刺激后检测了DRG中的pERK，发现标记细胞大小以及C纤维和Aδ纤维群体中激活神经元数量呈刺激强度依赖性增加。用磷酸化ERK/VR-1进行免疫组织化学双重标记和药理学研究表明，伤害性热刺激以VR-1依赖的方式在初级传入神经中诱导pERK。向皮肤注射辣椒素也显著增加了皮肤外周纤维和终末中的pERK标记，这可被丝裂原活化蛋白激酶/ERK激酶抑制剂1,4-二氨基-2,3-二氰基-1,4-双（2-氨基苯硫基）丁二烯（U0126）所阻断。行为学实验表明，U0126能剂量依赖性地减轻辣椒素注射后的热痛觉过敏，提示初级传入神经元中ERK通路的激活参与了初级传入神经元的敏化过程。因此，体内伤害性刺激引起的初级传入神经中的pERK表现出独特的表达特征，可能与初级传入神经元的功能活动相关。
