title: Chronic stress effects in contralateral medial pterygoid muscle of rats with occlusion alteration.
abstract: Temporomandibular disorder (TMD) has a high prevalence in our society, characterized by a severe pain condition of the masticatory muscles and temporomandibular joint. Despite the indication of multiple factor initiators of TMD, there is still controversy about its etiology and its pathophysiology is poorly understood. Using rats as experimental animals we investigated the effect of unpredictable chronic stress with or without unilateral molar extraction on the contralateral medial pterygoid muscle. Our hypothesis is that these two factors induce changes in morphology, oxidative metabolism and oxidative stress of muscle fibers. Young adult male Wistar rats (±200g) were divided into four groups: a group with extraction and unpredictable chronic stress (E+US); with extraction and without stress (E+C); without extraction and with unpredictable chronic stress (NO+US); and a control group without either extraction or stress (NO+C). The animals were subjected to unilateral extraction of the upper left molars, under intraperitoneal anesthesia with 4% Xylazine (10mg/kg) and 10% Ketamine (80mg/kg) on day zero. The rats of groups E+US and NO+US were submitted to different protocols of stress, from the 14th day after the extraction. The protocols were different every day for five consecutive days, which were repeated from the 6th day for five days more. Contralateral medial pterygoid muscles were obtained on the 24th day after the start of the experiment for morphological, metabolic, capillary density, and oxidative stress analysis. The data from capillary density showed a decrease of capillaries in animals subjected to dental extraction, compared with those without extraction and an increase of laminin expression in the group submitted to the unpredictable chronic stress when compared to the unexposed to stress. SDH test revealed a decrease of light fibers in the group submitted to unilateral extraction of molars, compared with this area in the control group. In E+US and NO+US groups, the deeply stained fibers increased compared to NO+C.·The exodontia factor was able to increase the ROS activity in muscle, whereas the stress factor does not significantly alter ROS in this tissue. It was concluded that both unpredictable chronic stress and the extraction induce metabolic and density of capillary changes in the contralateral medial pterygoid muscle to extraction, suggesting that these factors for a longer period of this experiment could induce muscle damage related to TMD.
authors.affiliation: Department of Morphology, Physiology and Basic Pathology, RibeirãoPreto Dentistry Faculty, University of São Paulo, RibeirãoPreto 14040-904, SP, Brazil.
authors.forename: Bruno Melo
authors.initials: BM
authors.lastname: Loyola
authors.affiliation: Department of Morphology, Physiology and Basic Pathology, RibeirãoPreto Dentistry Faculty, University of São Paulo, RibeirãoPreto 14040-904, SP, Brazil. Electronic address: glauce.nascimento@usp.br.
authors.forename: Glauce Crivelaro
authors.initials: GC
authors.lastname: Nascimento
authors.affiliation: Department of Physiology, Medical School, University of São Paulo, RibeirãoPreto 14040-900, SP, Brazil.
authors.forename: Rodrigo Alberto Restrepo
authors.initials: RA
authors.lastname: Fernández
authors.affiliation: Psychobiology Graduate Program, School of Philosophy, Science and Literature of RibeirãoPreto, University of São Paulo, RibeirãoPreto 14040-901, SP, Brazil.
authors.forename: Daniela Mizusaki
authors.initials: DM
authors.lastname: Iyomasa
authors.affiliation: Department of Dentistry, Tocantins Sciences Faculty, Tocantins 77818650, SP, Brazil.
authors.forename: Yamba Carla Lara
authors.initials: YC
authors.lastname: Pereira
authors.affiliation: Department of Morphology, Physiology and Basic Pathology, RibeirãoPreto Dentistry Faculty, University of São Paulo, RibeirãoPreto 14040-904, SP, Brazil; Psychobiology Graduate Program, School of Philosophy, Science and Literature of RibeirãoPreto, University of São Paulo, RibeirãoPreto 14040-901, SP, Brazil.
authors.forename: Christie Ramos Andrade
authors.initials: CR
authors.lastname: Leite-Panissi
authors.affiliation: Department of Morphology, Physiology and Basic Pathology, RibeirãoPreto Dentistry Faculty, University of São Paulo, RibeirãoPreto 14040-904, SP, Brazil.
authors.forename: João Paulo Mardegan
authors.initials: JP
authors.lastname: Issa
authors.affiliation: Department of Morphology, Physiology and Basic Pathology, RibeirãoPreto Dentistry Faculty, University of São Paulo, RibeirãoPreto 14040-904, SP, Brazil.
authors.forename: Mamie Mizusaki
authors.initials: MM
authors.lastname: Iyomasa
mesh_terms: D000818:Animals; D002196:Capillaries / Q000378:metabolism / Q000473:pathology; D002908:Chronic Disease; D003766:Dental Occlusion; D004195:Disease Models, Animal; D008297:Male; D008963:Molar; D018384:Oxidative Stress / Q000502:physiology; D010100:Oxygen / Q000378:metabolism; D011626:Pterygoid Muscles / Q000098:blood supply / Q000378:metabolism* / Q000473:pathology; D011897:Random Allocation; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism; D013315:Stress, Psychological / Q000378:metabolism* / Q000473:pathology; D013385:Succinate Dehydrogenase / Q000378:metabolism; D013705:Temporomandibular Joint Disorders / Q000378:metabolism; D014081:Tooth Extraction / Q000009:adverse effects*; D035501:Uncertainty
chemical_list: D017382:Reactive Oxygen Species; D013385:Succinate Dehydrogenase; D010100:Oxygen
keywords: Masticatory muscle; Metabolic activity; Oxidative stress; Temporomandibular disorder; Unpredictable chronic stress