Stress and chewing affect blood flow and oxygen levels in the rat brain

Abstract Objective Mastication, including chewing, would be of great importance not only for food intake, but also for the mental, physical and physiological functioning of the body. Our study showed that mastication, especially chewing, suppresses the stress response and was regarded as a biological response to defend against various stresses. Although mastication altered brain function during stress, the underlying mechanisms have not been elucidated. Methods The effects of chewing during restraint stress on blood flow and oxygen partial pressure (PO2 ) levels in the rat amygdala and hypothalamus were measured using laser Doppler flowmetry and O2 -selective electrodes. Results Amygdaloidal and hypothalamic blood flow were not affected by restraint stress, but PO2 levels were significantly reduced by restraint stress for 180 min compared to unrestrained control rats. The decrease in amygdaloidal and hypothalamic PO2 levels during restraint stress was reduced after chewing for 30 min. Conclusion These results suggested that it is possible to evaluate hypothalamic and amygdaloidal blood flow and PO2 levels in rat brains during restraint stress. Restraint stress reduced cerebral PO2 levels. In addition, chewing would lead to increased blood flow and to recover cerebral PO2 levels.