title: Psychological stress may contribute to temporomandibular joint disorder in rats.
abstract: BACKGROUND
  Psychological stress is considered a possible pathogenic factor for temporomandibular joint disorders (TMJD), but few reports have supplied direct evidence. This study was designed to observe the effects of psychological stress on the masticatory muscles and condylar processes in rats to directly investigate the role of psychological stress in TMJD morbidity.
  
  
  METHODS
  A well-established rat communication box model was used to compare the myoelectric profiles of temporal and masseter muscles and condylar microstructure among rats in a control group, a psychological stress group (PS group), and a diazepam (anxiolytic agent) injection group (PS + DI group). Reverse-transcription polymerase chain reaction was also used to analyze the substance P mRNA and calcitonin gene-related peptide mRNA levels expressed in condylar cartilages during different phases of psychological stress.
  
  
  RESULTS
  At 1, 3, and 5 wk, both temporal and masseter muscles in the PS group exhibited a significantly higher electrical potential in relaxation than those in the control group (P < 0.01). The electrical potential during contraction of the temporal and masseter muscles was higher than in the relaxation or control group at 1, 3, and 5 wk (P < 0.01). Scanning electron microscopy demonstrated pathologic changes in condylar processes in the PS group that were not observed in the PS + DI group. Reverse-transcription polymerase chain reaction also showed that the expression of substance P and calcitonin gene-related peptide in rat temporomandibular joint was upregulated during each phase of the psychological stress (P < 0.05).
  
  
  CONCLUSIONS
  Psychological stress may play an important role in the formation of TMJD.
authors: Department of Stomatology, Jinan General Military Hospital, Jinan, China.
authors: Gaoyi
authors: G
authors: Wu
authors: Lei
authors: L
authors: Chen
authors: Huang
authors: H
authors: Fei
authors: Yucheng
authors: Y
authors: Su
authors: Guoxiong
authors: G
authors: Zhu
authors: Yongjin
authors: Y
authors: Chen
mesh_terms: D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D004576:Electromyography; D008297:Male; D008410:Masticatory Muscles / Q000502:physiology; D008855:Microscopy, Electron, Scanning; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013315:Stress, Psychological / Q000150:complications*; D013373:Substance P / Q000378:metabolism; D013705:Temporomandibular Joint Disorders / Q000209:etiology* / Q000378:metabolism / Q000523:psychology
chemical_list: D013373:Substance P; D015740:Calcitonin Gene-Related Peptide