Effects of biting on elevation of blood pressure and other physiological responses to stress in rats: Biting may reduce allostatic load

We have investigated how biting modulates some of the physiological changes (blood pressure, core temperature, and chemical mediators in the serum) that are induced by restraint stress. We exposed rats to restraint stress for 60 min. Biting on a wooden stick during restraint significantly suppressed the increase of blood pressure at 30, 45, 60, and 75 min and significantly inhibited the rise in core temperature at 30, 60, 120, and 180 min compared with rats that were restrained but did not bite anything. These differences were visible in infrared thermal images of the restraint-only and restraint-with-biting rats after 60 min. Biochemical analysis revealed that biting significantly suppressed increases of plasma interleukin-1β, interleukin-6, and leptin and that it significantly suppressed a decrease of thyroid-stimulating hormone. These observations suggest that biting produces an anti-stress effect and that para-functional masticatory activity plays an important role in coping with stressful events.