| Psychological stress is one of stresses and refers to the body’s stress reaction both onphysical and psychological to objective requirements and environment. It can be dividedinto chronic psychological stress and acute psychological stress according to the durationof the stress factors’ function, and it’s severity of the hazard is related to patients’psychological quality and tolerance, externally manifested as emotional and behavioraldisorders, even organic disease severely. Many studies indicate that, when people haveexperienced major cataclysmic event or emotional trauma, the shadow caused by themajor events will not quickly disappear. Some people might be affected by disasters andmajor events for their lifetimes and may be hurt over and over again in the forms ofnightmare or recalls of traumatic events repeatedly, and they are tend to deny or avoidevents related to traumatic events. These patients alway start to suffer from depressionafter several months or years since a traumatic incident happened. If the symptom of stressdisorder lasts for more than3months, it will transform into chronic stress disorder,whichmay be reduced after treatments, but will not disappear. If untreated, some patients will get serious functional disabilities.Major traumatic event is usually part of acute stress, but its effect can be chronic.Nowadays, most people face long-term and common events in city life, which causesinvisible pressure to them, such as learning and working competition, the pressure ofemployment, children education, supporting parents and so on. When their actual abilitiescan’t match environmental requirements, they will be prone to in depression, even getdifferent degrees of body lesions, such as stomach ulcers and cardiovascular diseases.Clinical symptoms of TMJ disorder include joint pain, joint movement disorder and jointsnapping, which is related to many factors, and psychological-social factors (stress,anxiety, depression, etc.) can’t be ignored and even can be the cause of jaw musclestructure abnormality and dysfunction seperatedly, further led to TMJ disorders in functionor structure. In reverse, psychological stress become a new feature of chronicpsychological stress, which increase the patient’s degree of anxiety or depression, so, it isimportant to interrupt this vicious cycle for the treatment of TMJ disorder. We need tomake it clear if common life stress on individual life can be removed along with thedisappearance of stress factors. They are worth studying for us that how long will it take toreturn to normal levels after completely being divorced from stress environment and if therecovery time is propotional to the exposure time.The project is mainly to observe the effect differences among different times of stressexposure and prognosis to rats’ general state and TMJ condylar cartilage through theestablishment of chronic unpredictable mild stress (chronic unpredictable mild stress,CUMS).This study is divided into two parts:Part I: Study on CUMS impact on behavior and natural prognosis in rats.The model consisted of7soft stress factors which were arranged randomly and onefactor was applied to rats daily, one week as a cycle, which was uninterruptedlyundertaken8weeks and12weeks.144SD male rats were divided into8-week-stress group and12-week-stress group in accordance with the stress time.8-week-stress group was divided into groups ofpost-stressed0week, post-stressed2weeks, post-stressed4weeks and post-stressed8weeks according to recovery time; in the same way,12-week-stress group was divided intogroups of post-stressed0weeks,2weeks,4weeks,8weeks and12weeks according tothe recovery time, and each group had a corresponding blank control group with the sametime point. All recovery groups of8-week-stress group and12-week-stress grouprespectively accept the chronic unpredictable mild stress, while all of the rats in blankcontrol groups do not accept any stress. After the stress, the rats were fed in accordancewith the standards of SPF animal breeding, rats were anesthetized, taken blood fromeyeballs and then sacrificed after behavioral tests at the prescribed time points for eachgroup.Measure the rats’ weight once a week during the stress and after the stress and draw aline chart on the weight. The sucrose preference test, open-field test were performed toevaluate the behavior of rats after stresses. After taking blood, measure the concentrationof stress hormone cortisol and adrenocorticotropic hormone in rats’ serum by enzymelinked immunosorbent assay (ELISA), by which to observe the changes in body conditionand recovery. The results shows that, CUMS causes obvious effects on sucrose prefersignificantly smaller than control groups, and sucrose preference decreases after8weeks’and12weeks’ stress. Open-field test shows that the total travel velocity and total traveldistance decrease, central residence time increases for rats of8-week-stress group and12-week-stress group. Serum ELISA test showed that concentration of serum cortisol andadrenocorticotropic hormone increases. The weight of rats increases slowly after removalof the stress and maintains at a low level until the end of the experiment; Sucrosepreference significantly goes higher after2weeks’ recovery for rats having experienced8weeks’ stress and reaches the the same level with that of thecontrol group after4weeks’ recovery. As for sucrose preference of12-week-stress group,there is no obvious changes after2weeks’ recovery, somewhat increase after4weeks,reach the same level with the control group.8-week-stress group and12-week-stressgroup can reach the same level with the control group respectively after natural8weeks’ recovery and12weeks’ recovery in aspects of central residence time, total movingdistance and total rate of movement in open-field experiment. The concentration of serumCORT and ACTH is recovered rapidly, which just takes four weeks to reach normal level.Under the same stress, the longer duration of stress, the longer of the time of animalbehavior indexes recovery.Part II: Study on the effect of chronic unpredictable mild stress on TMJ condyle andnatural outcome of the condyle in了ratsMethod of establishing animal model is the same as the first part, the animal are killedafter anesthesia at corresponding time points and the tissue and the TMJ with the articulardisc around temporomandibular joint are removed for testing through methods of scanningelectron microscope, HE staining, immunohistochemistry and real time PCR testing.The results are as follows:1. Electron microscope images show that condylar cartilage surfaces of rats appearlesion for both8-week-stress group and12-week-stress group. Condyle surface collagenfibers are disorganized and cartilage cells are shed for8-week-stress group, but lesions on12-week-stress group is heavier and cartilage cells are exposed and hurt. HE stainingresults confirm that degeneration disease (necrosis, fibrosis, hyperplasia) is found oncondylar cartilage and the extent of damage is increased with the extension of stress timeand diseased regions are in physiological function part. Cartilage surface fiber graduallybecomes thicker and is organized regularly and flat during8weeks’ recovery for8-week-stress group. While cartilage cell hyperplasia and collagen fiber and proteoglycanincrease, deep structure are covered by collagen fiber and surface becomes flat, but is notcompletely recovered during12weeks’ recovery for12-week-stress group. The resultshows that the longer the stress, the more severe cartilage damage, the more incompleterecovery.2. The mRNA expression levels of IL-1α,MMP-3and TIMP-1in condylar cartilage forrats in8-week-stress group and12-week-stress group increase and expression is in directproportional to the stress time. The overall mRNA expression of IL-1and MMP-3is gradually decreased to normal level, and TIMP-1has been maintained at a higher level at12weeks after removed stress.3. Immunohistochemical staining shows Protein expression quantity of inflammatorycytokines interleukin-1α (IL-1α), matrix metalloproteinase-3(MMP-3), matrixmetalloproteinase reagent-1(TIMP-1) in condylar cartilage is higher than that of controlgroups at the same points (P <0.05) for8-week-stress group and12-week-stress group.During natural recovery of8weeks and12weeks, the protein expression quantity of IL-1α,MMP-3, TIMP-1decreases, but still is higher than normal levels, especially TIMP-1hasbeen maintained at a high level after recovery of12weeks.All in all, CUMS can cause serious typical depression on rats, such as loss of weight,lowing of sucrose preference, decrease of moving velocity and moving distance andelongating of center movement in open field test, CORT and ACTH concentration rise,and degenerative disease on TMJ condyle cartilage. After removal of stress factors, eachtarget of rats’ body and TMJ condyle cartage is recovered, depression state on body canreturn to normal levels during observation, organic injury of condylar cartilage showedremarkable reparative changes,but has not yet been fully restored by the end of theobservation. The recovery of stress index is proportional with the duration of stress. Thesituation of repair is time-related with stress, the longer stress time, the more incompleterepair. |
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