Significant of masticatory exercise in defensive reaction to stress

对压力的反应有可能与疾病的原因有关。颞下颌关节紊乱病(TMD)是一种典型的症状，被认为是由于异常咀嚼运动(如应激导致的磨牙症)或咬合不当导致的肌肉疲劳。然而，骨骼肌中这些事件背后的机制还没有建立起来。在一些早期的小鼠束缚压力实验中，我们注意到了一种有趣的行为类型。当鼠标被放进一个无法转动的狭窄圆柱体(前端用一条无色的薄塑料条部分封闭，后端用胶带封闭)时，鼠标就会咬住塑料条。鼠标可以在圆柱体内来回移动，并自由选择咬住塑料条。然而，如果它的尾巴被胶带固定在圆柱体的后端，鼠标就无法到达条子，因此也就无法咬到它。使用这两种不同的方法，我们可以检验有或没有咬合(分别为RG和RG-)的约束的效果。我们假设，咬人行为的影响会减少对心理压力的反应。我们检查了咬合行为是否降低了束缚引起的血清糖皮质激素或皮质醇的升高。结果显示，RG小鼠的血清皮质醇升高幅度小于RG小鼠。因此，RG-可能比RG产生更多的挫折感，导致小鼠产生更多的糖皮质激素。我们测量了在给定时间点被咬掉的塑料的总重量作为累积咬合活动(CGA)的指标，并测量了每2小时内塑料损失的重量作为咬合率。我们注意到CGA对小鼠的一天中的时间。因此，CGA在夜间明显大于白天。总而言之，我们的研究结果表明，咬人行为可以减少对心理压力的反应。

There is a possibility that the reaction to stress relates to the cause of the illness. Temporomandibular disorders (TMD) are typical symptoms that are thought to be due to muscle fatigue resulting from abnormal masticatory exercise (such as bruxism resulting from stress) or from improper occlusion. However, the mechanisms underlying these events in skeletal muscle have yet to be established. During some earlier experiments on restraint stress in mice, we noticed an interesting type of behavior. When a mouse is put into a narrow cylinder in which it is unable to turn (the front end being partially closed with a thin, colorless plastic strip, and the back end closed with tape), the mouse gnaws away at the plastic strip. The mouse can move back and forth within the cylinder and freely chooses to bite the plastic strip. However, if its tail is fastened to the back end of the cylinder by tape, the mouse cannot reach the strip and therefore cannot bite it. Using these two variations of the method, we could examine the effects of restraint with or without gnawing (R+G+ and R+G-, respectively). We hypothesize that the effects of gnawing behavior reduces reaction to psychological stress. We examined Whether the gnawing behavior reduced the restraint-induced elevation of serum glucocorticoids or cortisol. As a result R+G+ mice showed a smaller elevation of serum cortisol than that shown by R+G- mice. Thus, R+G- may produce more frustration than R+G+, leading the mouse to produce more glucocorticoids. We measured the total weight of plastic gnawed away up to a given time-point as an index of cumulative gnawing activity (CGA), and the weight of plastic lost per 2-h period as the rate of gnawing. We took notice of time of day on CGA in mice. As a result, CGA was significantly greater in the nighttime hours than in the daytime. In conclusion, our results cold suggest that gnawing behavior reduces reaction to psychological stress.