title: Prolonged gum chewing evokes activation of the ventral part of prefrontal cortex and suppression of nociceptive responses: involvement of the serotonergic system.
abstract: 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. To evaluate this hypothesis, oxygenated hemoglobin (oxyHb) and deoxygenated hemoglobin concentrations in the PFC were measured in the PFC during a 20-min time period of gum chewing using 24-channel near-infrared spectroscopy. 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.
authors.affiliation: Anesthesiology and Clinical Physiology, Department of Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan. Kiyanph@tmd.ac.jp
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Kamiya
authors.forename: Masaki
authors.initials: M
authors.lastname: Fumoto
authors.forename: Hiromi
authors.initials: H
authors.lastname: Kikuchi
authors.forename: Tamami
authors.initials: T
authors.lastname: Sekiyama
authors.forename: Yuko
authors.initials: Y
authors.lastname: Mohri-Lkuzawa
authors.forename: Masahiro
authors.initials: M
authors.lastname: Umino
authors.forename: Hideho
authors.initials: H
authors.lastname: Arita
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001931:Brain Mapping; D002638:Chewing Gum; D005260:Female; D006801:Humans; D008297:Male; D008409:Mastication / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology*; D010108:Oxyhemoglobins / Q000378:metabolism; D010146:Pain / Q000503:physiopathology*; D010147:Pain Measurement; D017397:Prefrontal Cortex / Q000098:blood supply / Q000502:physiology*; D011903:Raphe Nuclei / Q000502:physiology; D012701:Serotonin / Q000097:blood / Q000502:physiology*; D019265:Spectroscopy, Near-Infrared
chemical_list: D002638:Chewing Gum; D010108:Oxyhemoglobins; D012701:Serotonin