Journal of medical and dental sciences
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We have proposed a concept that prolonged rhythmic gum chewing causes a suppressed nociceptive flexion reflex via the serotonergic (5-HT) descending inhibitory pathway. However, the mechanism of activation of the 5-HT system by gum chewing remains undetermined. Several human and animal studies have reported that a direct connection exists between the prefrontal cortex (PFC) and 5-HT neurons in the dorsal raphe nucleus; therefore, we hypothesized that activation of the PFC region might be responsible for augmented 5-HT activity. ⋯ A significant increase in oxyHb level was observed in the ventral part of PFC compared with the dorsal part of PFC. We confirmed the previous results in that the nociceptive flexion reflex was significantly suppressed and the 5-HT level in blood was significantly increased following prolonged gum chewing. These results support the hypothesis that activation of the ventral part of PFC during gum chewing evokes augmented activity of 5-HT neurons in the dorsal raphe nucleus, which in turn suppress nociceptive responses.