title: Functions of the temporomandibular system in extracranial chronic pain conditions: modulatory effects on nocifensive behavior in an animal model.
abstract: OBJECTIVE
  Mastication may be able to activate endogenous pain inhibitory mechanisms and therefore lead to modulation of nociceptive processing. The purpose of this study was to examine the possible effect of food consistency on noxious input from the spinal system.
  
  
  METHODS
  Three groups of adult male Sprague-Dawley rats were given an injection of complete Freund adjuvant in a hind paw 10 days after eating soft or hard food (one group received a saline injection-the control group [C]; the other group (D) received no injection). Nocifensive behavior was assessed with the use of the hot plate and tail flick assays at 1, 3, 6, and 12 hours and at 6.5 days after injection for groups A/B, and c-Fos activity was assessed in the brain after testing. Groups C/D had hot plate testing at 1 hour and 6.5 days. The data were analyzed by general linear modeling and 1-way analysis of variance.
  
  
  RESULTS
  There was a small increase in the hot plate percent maximum possible effect (MPE) from -45.7 to -61.1 in group A over the length of the experiment, but a very small decrease for group B over the same period (-33.5 to -28.8). For the saline control group, there was a small increase toward 0 %MPE over the same time frame (-15.0 to 1.7). The %MPE differences were significant between groups A and C (P < .0005), but not significant between the other groups (F = 13.34, df = 2, P = .001, observed power = 99%). Using the pooled results (all time points), the differences between all groups were significant (P < .0005). There were no significant differences in the tail flick test. c-Fos was mainly observed in the raphe pallidus area with significant differences between groups A and B at 3 and 6 hours after injection of CFA (P = .027 and .022, respectively).
  
  
  CONCLUSIONS
  The results of this study indicate that food consistency (hardness) influences nocifensive behavior in this animal model via a descending pathway operating at the supraspinal level.
authors.affiliation: Lecturer/Privatdozent, Department of Rehabilitation Medicine, Hanover Medical School, 30625 Hanover, Germany; Lecturer/Privatdozent, Department of Orthopaedics, Hanover Medical School, Medical University Innsbruck, A-6020 Innsbruck, Austria.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Fischer
authors.affiliation: Department of Psychosomatics and Psychotherapy, Hanover Medical School, 30625 Hanover, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Stephan
authors.affiliation: Professor, Department of Anatomy and Cell Biology, Faculty of Medicine, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Kielstein
authors.affiliation: Department of Rehabilitation Medicine, Hanover Medical School, 30625 Hanover, Germany.
authors.forename: Henning
authors.initials: H
authors.lastname: Rahne
authors.affiliation: Department of Rehabilitation Medicine, Hanover Medical School, 30625 Hanover, Germany.
authors.forename: Boya
authors.initials: B
authors.lastname: Nugraha
authors.affiliation: Professor, Department of Rehabilitation Medicine, Hanover Medical School, 30625 Hanover, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Gutenbrunner
authors.affiliation: Professor, Department of Biomedical Sciences, Program in Neuroscience, School of Dentistry, University of Maryland, Baltimore, MD.
authors.forename: Jin Y
authors.initials: JY
authors.lastname: Ro
authors.affiliation: Professor, Department of Clinical Oral Physiology, School of Dentistry, University of Aarhus, Aarhus, Denmark; Department of Oral and Maxillofacial Surgery, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Svensson
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D059350:Chronic Pain / Q000503:physiopathology*; D004195:Disease Models, Animal; D005502:Food; D008297:Male; D059225:Nociception; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord; D013704:Temporomandibular Joint / Q000503:physiopathology*
keywords: Animal Model; Chronic Pain; Food Consistency; Nociceptive Processing