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.