Fundamental study on humoral factors regulating postnatal development, aging and maintenance of masticatory system

咀嚼系统的发育、老化和维持涉及多种因素。在本研究中，我们研究了各种体液因素，以及牙周韧带感觉末梢的感觉输入缺失对下颌运动调节系统的影响。我们得到了以下结果和结论：早期牙列部分缺失导致来自牙周感觉末梢的Me5和Su5对Mo5运动神经元的感觉输入不可避免地减少，从而可能导致支配咬肌的Mo5咀嚼运动神经元的过早减少，而在动物出生后发育的早期有限时间内，仅部分缺牙就很容易对其数量的减少产生显著影响。此外，目前的结果合理地表明，由于肌外纤维的萎缩，咬肌功能下降，其次导致支配咬肌肌梭的Me5神经元数量减少。本研究还表明，即使在健康小鼠中，牙周事件的退化也可能在出生后较早的时期开始。在这些小鼠中，我们发现包括性激素和FGFs在内的各种体液因子参与了咀嚼系统的衰老和维护。

The various factors are involved in the development, aging and maintenance of the masticatory system. In the present study, we investigated effects of various humoral factors, and those of the lack of the sensory input from the sensory endings in the periodontal ligaments, resulted from tooth-loss on the regulatory system of the jaw movement. We obtained following results and conclusions : early partial loss of dentition induce the inevitable decrease in the sensory input to the Mo5 motoneurons, via Me5 and Su5 from periodontal sensory endings, then might result in the precocious reduction in masticatory motoneurons in the Mo5 that innervate the masseter muscle, and significant effects on the decrease in the number may be easily caused only by the partial tooth-loss during an early limited period in the postnatal development of animals. Moreover, it is reasonably suggested by the present results that a functional decrease in the masseter muscle, due to the atrophy of the extrafusal muscle fibers, secondarily cause the reduction in the number of Me5 neurons innervating muscle spindles in the masseter muscle. The present study also suggests that the degeneration of periodontal afferents may start at a comparatively early period during the postnatal life even in healthy mice. In these mice, we found that various humoral factors including sex hormones and FGFs are involved in aging and the maintenance of the masticatory system.