Effects of mastication on hippocampal neurons as well as learning and memory ability

老年斑（SPs）淀粉样蛋白β(a β)蛋白是阿尔茨海默病（AD）的一种神经病理改变，其沉积和神经元丢失是阿尔茨海默病病理级联的必要条件。尽管a β沉积的机制尚不清楚，但提示AD患者大脑中a β蛋白的清除活性可能受损。先前的研究表明，小胶质细胞可以通过释放金属蛋白酶或吞噬来清除a β，提示小胶质细胞可能在阻止a β沉积在中枢神经系统（CNS）中发挥重要作用。另一方面，据报道，由于缺乏功能性巨噬细胞集落刺激因子（M-CSF），骨增生（op/op）无牙小鼠的小胶质细胞数量减少。咀嚼功能损伤可引起海马神经元的变性。因此，本研究旨在检测Aβ在op/op小鼠大脑中的沉积和海马神经元的数量。在op/op小鼠的大脑皮层、海马、杏仁核和下丘脑中检测到大量成熟的Sps，而在正常小鼠中未观察到Aβ沉积的定量证据。此外，与对照组相比，op/op小鼠CA1和CA3区域的锥体细胞数量明显减少。结果表明，a β沉积和咀嚼减少影响神经元的丧失，SPs的表达可能在一定的生理条件下受到小胶质细胞的调控。

Amyloid β(Aβ) protein of senile plaques (SPs) is a neuropathological change which characterize Alzheimer's disease (AD), and its deposition and neuron loss are essential for the pathological cascade of the disease. Although the mechanism of Aβ deposition still remains unclear, it is suggested that a clearance activity for the Aβ protein may be impaired in AD's brain. Previous studies demonstrated that microglia could remove Aβ by releasing a metalloprotease or by phagocytosis, suggesting that microglia may play an important role in preventing Aβ deposition in the central nervous system (CNS). On the other hand, it was reported that the number of microglia was reduced in osteopetrotic (op/op) toothless mice resulting from the lack of functional macrophage colony-stimulating factor (M-CSF). It was also exhibited that impairment of masticatory function caused degeneration of hippocampal neurons. The present study was thus designed to examine the Aβ deposition and the number of hippocampal neurons in the brain of op/op mice. A number of mature Sps were detected in the cerebral cortex, hippocampus, amygdala and hypothalamus in op/op mice, however, no quantitative evidence of Aβ deposition was observed in normal mice. Moreover, the number of pyramidal cells in the CA1, and CA3 regions was significantly reduced in op/op mice than in the controls. It is shown that Aβ deposition and reduced mastication influence the neuron loss and expression of SPs may be in part regulated by microglia under a physiological conditions.