Involvement of neurotrophins in development/regeneration of the periodontal Ruffini endings-An analysis using NT-4/5 KO mice

我们以前的研究表明，脑源性神经营养因子(BDNF)参与了牙周Ruffini终末的发育和再生。由于神经营养因子的配体TrkB也与NT-4/5结合，本研究旨在通过免疫细胞化学和定量分析研究NT-4/5纯合子小鼠和野生型小鼠牙周Ruffini的发育和再生。主要结果如下：1.神经末梢形态发育及神经密度的时序性变化定量分析显示，出生后8周，两型小鼠牙周神经纤维的神经密度逐渐增加，并达到平台期。与野生型小鼠相比，纯合子小鼠在出生后8周(PO8周)表现出较低的神经密度，差异有统计学意义。野生型和纯合子鼠三叉神经节和牙周膜中TrkB和p75-NGFR的蛋白和mRNA表达水平无显著差异。3.野生型和纯合子鼠的终末雪旺细胞形态和密度无明显差异。4.在下牙槽神经损伤的实验研究中，纯合子鼠的牙周Ruffini末梢再生延迟。特别是，纯合子小鼠在PO3和10天时表现出明显的较低的神经细胞密度，这些发现有力地表明NT-4/5在早期发育和再生中起着关键作用。结合我们以前对BDNF-KO小鼠的研究，牙周Ruffini末端的发育和再生是由多种神经营养因子以时间依赖的方式控制的。

Our previous studies have shown the involvement of brain derived neurotrophic factor (BDNF) in the development and regeneration of the periodontal Ruffini endings. Since TrkB, a ligand for BDNF, also binds NT-4/5, the present research project was undertaken to investigate the development and regeneration of the periodontal Ruffini ending in the NT-4/5 homozygous mice, compared to wild-type mice by immunocytochemistry and quantitative analysis. The obtained main results are as follows.1.Developmental aspects of terminal morphology and chronological changes in neural densityThe quantitative analysis showed that the neural density of the periodontal nerve fibers increased day by day to reach a plateau at postnatal 8 weeks both typed mice. Compared to wild type mice, the homozygous mice exhibited lower neural density with significant differences by postnatal weeks 8 (PO 8w). In addition, there were significant differences between PO2 and 3w, and PO3 and 8w in the homozygous mice2.Protein and mRNA levels for TrkB and p75-NGFR did not differ in the trigeminal ganglion and periodontal ligament between wild type and homozygous mice.3.No significant difference in morphology and density of the terminal Schwann cells was found between wild type and homozygous mice.4.In an experimental study to injury inferior alveolar nerve, the regeneration of the periodontal Ruffini endings delayed in the homozygous mice during the observation period. In particular, the homozygous mice showed apparent lower neural density through PO3 and 10 days.These findings strongly suggest that NT-4/5 plays in crucial roles in development and regeneration at early stage. Combined with our previous studies on BDNF-KO mice, the development and regeneration of the periodontal Ruffini endings are controlled by multiple neurotrophins in a time dependent manner.