Evaluation of medial pterygoid muscle and brain structures related to orofacial nociception and emotional behavior in an animal model of chronic stress and masticatory hypofunction

Abstract

The patient presenting dental loss reveals an occlusal collapse influencing stomatognathic functions. Although stress is involved in the pathogenesis of chronic diseases and enable the masticatory muscle pain in patients, it is not well understood the mechanism by which muscle adapts to psychological and physiological stresses and which neural pathways are involved in orofacial muscle dysfunction due to stress and/or masticatory hypofunction. Among the orofacial musculoskeletal pain, it is possible to highlight those caused by temporomandibular disorders (TMD). This disorder has a multifactorial etiology, and malocclusion, trauma, inflammation and emotional stress are part of this range of causal factors. One of the most notable and recent areas that have been studied in relation to TMD is its involvement with emotional disturbances. This study aims to investigate the effect of variable chronic stress associated with unilateral extraction on the medial pterygoid muscle, brain and plasma corticosterone. The influence of pretreatment of animals with diazepam, a classical anxiolytic, will also be evaluated. Male Wistar rats will be used (200g) and they will be randomly divided into two groups: Malocclusion Groups (GM): rats exposed to left unilateral extraction and Group without Malocclusion (GS): rats without extraction. There will be the following subgroups (n = 8): no stress; chronic stress; no stress and treated with diazepam; chronic stress and treated with diazepam. The rats will be euthanized on the 24th day after the beginning of the experiment to obtain the medial pterygoid muscle to HE analysis, MET, MMPs, Laminin and ROS; specific brain regions for analysis of c-fos and fos-B and collection of blood for analysis of plasma corticosterone. (AU)