MOLECULARBIOLOGICAL STUDY OF NITRIC OXIDE IN THE DEVELOPMENT OF ODONTOBLAST

本研究用免疫组织化学方法检测了大鼠磨牙预备后牙髓中一氧化氮合酶(NOS)，尤其是内皮型一氧化氮合酶(ENOS)和诱导型一氧化氮合酶(INOS)以及参与诱导型一氧化氮合酶基因翻译的核因子-κB的表达。正常牙牙本质/牙髓界面的成牙本质细胞未见eNOS和iNOS免疫反应阳性。NF-κB阳性反应定位于成牙本质细胞。牙髓中未见eNOS、iNOS和NF-κB阳性表达。在预备后2天，牙本质/牙髓界面可见大柱状细胞(成牙本质母细胞)。在界面处，修复性牙本质开始形成，中性粒细胞侵入。11天后，洞下形成丰富的修复性牙本质。术后2天，洞下牙本质/牙髓界面的细胞eNOS和iNOS呈阳性反应。在排列成牙本质细胞的圆形细胞和侵袭的中性粒细胞中，iNOS也呈阳性反应。牙体预备2天后，整个牙髓细胞，尤其是成牙本质细胞和中性粒细胞均有较强的NF-κB免疫反应。这些发现表明，在机械刺激下，成牙本质细胞和中性粒细胞中的NF-κB被激活。由此可见，牙齿预备直接刺激成牙本质细胞产生大量的NO。提示NO可能参与牙齿刺激后成牙本质细胞的分化和修复性牙本质的形成。此外，据推测，在牙髓炎的进展和修复性牙本质的形成过程中，NF-κB控制着几个基因的表达。

In this study, the expression of nitric oxide synthases (NOSs), especially endothelial NOS (eNOS) and inducible NOS (iNOS), and NF-κB, which is considered to takes part in the translation of iNOS gene, was examined in the dental pulp after tooth preparation of rat molars compared to normal dental pulp with immunohistochemistry. Any immunoreactivity for eNOS and iNOS was not found in odontoblast at the dentin/pulp interface of normal tooth. NF-κB positive reaction localized in the odontoblasts. Any other cell in the pulp was not positive for eNOS, iNOS, or NF-κB. On the other hand, 2 days after tooth preparation, the layer of big columnar cells (odontoblasts) was found along the dentin/pulp interface under the prepared cavity. At the interface, reparative dentin formation started and invasion of neutrophils were found. After 11 days abundant reparative dentin was formed under the cavity. After 2 days operation, the cells at the dentin/pulp interface beneath the cavity were positive for eNOS and iNOS. Positive reaction for iNOS was also found in the round-shaped cells arranged to odontoblasts and invaded neutrophils. Strong immunoreactivity for NF-κB was found in whole dental pulp cells, especially odontoblasts and neutrophils after 2 days tooth preparation. These finding suggested that NF-κB is activated in odontoblasts and neutrophils by mechanical stimulation. Therefore, it is indicated that abundant NO production is induced in odontoblasts directly stimulated by tooth preparation. It is suggested that NO may take a part in odontoblast differentiation and reparative dentin formation after tooth irritant. Furthermore, it is speculated that NF-κB controls several gene expression in the progression of pulpitis and formation of reparative dentin.