Significant of masticatory exercise in defensive reaction to stress

对压力的反应有可能与疾病的起因有关。颞下颌紊乱（TMD）是典型的症状，被认为是由于不正常的咀嚼运动（如由压力引起的磨牙）或不适当的咬合引起的肌肉疲劳。然而，骨骼肌中这些事件的机制尚未确定。在一些早期的老鼠约束压力实验中，我们注意到一种有趣的行为。当把老鼠放进一个不能转动的窄圆柱体（前端用一条无色的细塑料条部分封闭，后端用胶带封闭），老鼠就会啃噬塑料条。鼠标可以在圆筒内来回移动，自由选择咬塑料条。然而，如果它的尾巴被胶带固定在圆筒的后端，老鼠就够不到胶带，因此咬不到它。使用该方法的这两种变体，我们可以检查有或没有啃咬的约束效果（分别为R+G+和R+G-）。我们假设啃食行为的影响会减少对心理压力的反应。我们研究了啃咬行为是否会降低抑制诱导的血清糖皮质激素或皮质醇的升高。结果显示，R+G+小鼠的血清皮质醇升高幅度小于R+G-小鼠。因此，R+G-可能比R+G+产生更多的挫折感，导致小鼠产生更多的糖皮质激素。我们测量了到给定时间点被啃掉的塑料的总重量，作为累积啃咬活动（CGA）的指标，并以每2小时的塑料损失重量作为啃咬率。我们注意到了小鼠体内CGA的时间变化。因此，CGA在夜间明显大于白天。总之，我们的研究结果表明，啃食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.