Significant of masticatory exercise in defensive reaction to stress

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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.