Chewing augments stress-induced increase of pERK-immunoreactive cells in the rat cingulate cortex.

The eff ;ects of chewing during restraint stress on the anterior, mid- and posterior cingulate cortices were investigated in rats using immunohistochemistry to detect the expression of phosphorylated extracellular signal-regulated kinase 1 and 2 (pERK1/2), a marker of responding cells. The rats were divided into three groups: control (no immobilization), stress-only (immobilized), and stress-with-chewing (immobilized and allowed to chew a wooden stick). Significant increases in the number of pERK1/2-immunoreactive cells in the anterior, mid- and posterior cingulate cortices were noted in the stress-only group when compared with the control group (p < 0.05). Furthermore, the number of pERK1/2-immunoreactive cells in the anterior, mid- and posterior cingulate cortices in the stress-with-chewing group was also significantly higher than that in the stress-only group (p < 0.05). These findings indicate that the cingulate cortex plays a role in the negative-feedback effect and might be an essential part of the brain where the ameliorating effects of chewing against stress are produced.

Chewing ameliorates the effects of restraint stress on pERK-immunoreactive neurons in the rat insular cortex.

We investigated the effects of chewing on the anterior and posterior insular cortices during restraint stress using phosphorylated extracellular signal-regulated kinase (pERK) levels as a marker of neuronal responses. The stress only group demonstrated increased numbers of pERK-immunoreactive cells in both the anterior and posterior insular cortices compared to the control group (p < 0.01). In the stress with chewing group, the stress-induced increase of pERK-immunoreactive cell numbers was suppressed in both insular cortices and these differences were statistically significant compared to the stress-only group (p < 0.01). The suppressive effects of chewing were more prominent in the anterior insular cortex than in the posterior insular cortex. In general, the anterior insular cortex contributes to emotional processing, whereas the posterior insular cortex is associated with sensorimotor processes. Therefore, these results suggest that chewing ameliorates the emotional and sensorimotor responses to stress in the anterior and posterior insular cortices, respectively, with a greater effect on emotion-forming processes than on sensorimotor processes.