Psychological stress may contribute to temporomandibular joint disorder in rats

• Published in: The Journal of surgical research Vol. 183; no. 1; pp. 223 - 229
• Main Authors: Wu, Gaoyi, PhD, Chen, Lei, PhD, Fei, Huang, PhD, Su, Yucheng, PhD, Zhu, Guoxiong, PhD, Chen, Yongjin, PhD
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.07.2013
• Subjects: Animals; Calcitonin Gene-Related Peptide - metabolism; Calcitonin gene–related peptide; Electromyography; Foot shock; Male; Masticatory Muscles - physiology; Microscopy, Electron, Scanning; Psychological stress; Random Allocation; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; Sprague-Dawley rats; Stress, Psychological - complications; Substance P; Substance P - metabolism; Surgery; Temporomandibular joint disorders; Temporomandibular Joint Disorders - etiology; Temporomandibular Joint Disorders - metabolism; Temporomandibular Joint Disorders - psychology; Psychological stress; Calcitonin gene–related peptide; Sprague-Dawley rats; Temporomandibular joint disorders; Substance P; Foot shock
• ISSN: 0022-4804; 1095-8673
• DOI: 10.1016/j.jss.2012.12.014

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. Materials and 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.