title: The protective role of testosterone in the development of temporomandibular joint pain.
abstract: The lower prevalence of many pain conditions, including temporomandibular dysfunctions, in men than in women has not as yet been clarified. The aim of this study was to investigate the effect of testosterone on the risk of development of temporomandibular joint (TMJ) pain and on acute persistent TMJ pain. The TMJ formalin test was used as an experimental assay in the rat. Intra-TMJ 0.5% formalin induced a significant nociceptive behavior in naive female rats and gonadectomized male rats but not in naive male rats, suggesting that naive male rats have a lower risk for development of TMJ pain. The finding that the serum level of testosterone but not of estrogen and progesterone significantly decreased in gonadectomized male rats suggests that testosterone is the hormone underlying the decreased naive male rat's risk for development of TMJ pain. The magnitude of the nociceptive behaviors induced by intra-TMJ 1.5% formalin was similar in gonadectomized and naive male rats. Therefore, in contrast to the protective role of testosterone in TMJ pain development, testosterone, at physiological serum levels, does not appear to modulate acute persistent TMJ pain induced by the TMJ injection of 1.5% formalin. At a supraphysiological serum level, however, testosterone significantly attenuated 1.5% formalin-induced nociception in male rats but not in female rats. This antinociceptive effect was not mediated by estrogen derived from testosterone aromatization, because estrogen administration did not affect 1.5% formalin-induced TMJ nociception in gonadectomized male rats.
  
  
  CONCLUSIONS
  The present findings not only help to explain the lower prevalence of TMJ pain in males versus females but also show that testosterone reduces TMJ pain at supraphysiological serum levels.
authors.affiliation: Laboratory of Orofacial Pain, Department of Physiology, Faculty of Dentistry of Piracicaba, University of Campinas-Unicamp, São Paulo, Brazil.
authors.forename: Luana
authors.initials: L
authors.lastname: Fischer
authors.forename: Juliana T
authors.initials: JT
authors.lastname: Clemente
authors.forename: Cláudia H
authors.initials: CH
authors.lastname: Tambeli
mesh_terms: D000704:Analysis of Variance; D000728:Androgens / Q000627:therapeutic use*; D000818:Animals; D002369:Castration; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D005260:Female; D005557:Formaldehyde; D008297:Male; D010146:Pain / Q000209:etiology* / Q000517:prevention & control*; D010147:Pain Measurement; D051381:Rats; D017208:Rats, Wistar; D012737:Sex Factors; D013705:Temporomandibular Joint Disorders / Q000139:chemically induced / Q000150:complications*; D013739:Testosterone / Q000627:therapeutic use*
chemical_list: D000728:Androgens; D005557:Formaldehyde; D013739:Testosterone