Metabolic Changes in Masseter Muscle of Rats Submitted to Acute Stress Associated with Exodontia

Clinical evidence has shown that stress may be associated with alterations in masticatory muscle functions. Morphological changes in masticatory muscles induced by occlusal alterations and associated with emotional stress are still lacking in the literature. The objective of this study was to evaluate the influence of acute stress on metabolic activity and oxidative stress of masseter muscles of rats subjected to occlusal modification through morphological and histochemical analyses. In this study, adult Wistar rats were divided into 4 groups: a group with extraction and acute stress (E+A); group with extraction and without stress (E+C); group without extraction and with acute stress (NO+A); and control group without both extraction and stress (NO+C). Masseter muscles were analyzed by Succinate Dehydrogenase (SDH), Nicotinamide Adenine Dinucleotide Diaphorase (NADH) and Reactive Oxygen Species (ROS) techniques. Statistical analyses and two-way ANOVA were applied, followed by Tukey-Kramer tests. In the SDH test, the E+C, E+A and NO+A groups showed a decrease in high desidrogenase activities fibers (P < 0.05), compared to the NO+C group. In the NADH test, there was no difference among the different groups. In the ROS test, in contrast, E+A, E+C and NO+A groups showed a decrease in ROS expression, compared to NO+C groups (P < 0.05). Modified dental occlusion and acute stress - which are important and prevalent problems that affect the general population - are important etiologic factors in metabolic plasticity and ROS levels of masseter muscles.     

两种赋形剂载体中姜黄素干预慢性应激大鼠抑郁样行为和肌肉炎性反应的作用研究

目的:从抑郁样行为和肌肉炎性反应角度,研究姜黄素在由可可脂和花生油两种赋形剂载体时,对慢性应激大鼠的干预作用。方法:分别制备以可可脂和花生油为赋形剂的姜黄素制剂,使用SD雄性大鼠50只随机分为空白对照组、模型对照组、姜黄素可可脂组、姜黄素花生油组、阳性对照组,除空白对照组外,各组均采用束缚、噪音声刺激、冰水浴刺激、夹尾疼痛刺激等方法持续6周建立慢性应激大鼠模型,在维持模型刺激条件的基础上分别给予各种设计药物,连续用药7 d后在考察各组模型动物悬尾挣扎时间、机械痛阈、糖水偏好的行为学变化,然后使用Elisa试剂盒法检测各组大鼠脑中5五羟色胺(5-HT)和多巴胺(DA)含量,制作大鼠咬肌组织的HE染色切片观察肌肉病理变化,检测咬肌组织中高迁移率族蛋白B1(HMGB-1)、白介素1β(IL-1β)、白介素6(IL-6)、肿瘤坏死因子α(TNF-α)水平。结果:与模型组相比,两种姜黄素均能显著降低应激大鼠抑郁样行为,改善脑内5-HT和DA含量的作用较阳性对照组弱,咬肌病理切片中两种姜黄素组可明显减少应激大鼠咬肌组织血管周围的炎性反应。两种姜黄素能显著降低咬肌组织中的IL-1β、IL-6、TNF-α水平(P<0.05),其中姜黄素可可脂组作用最明显。结论:两种姜黄素制剂对抗慢性应激大鼠的抑郁样症状均有治疗作用,均可降低咬肌中炎性因子HMGB-1、IL-1β、IL-6、TNF-α水平,其中可可脂作为赋形剂时作用较显著,在姜黄素的抗抑郁制剂研究中具有较好的开发潜力。     

Electromyographic evaluation of masseter and anterior temporalis muscles in rest position of edentulous patients with temporomandibular disorders, before and after using complete dentures with sliding plates

Objectives: This study was performed with the purpose of investigating electromyographic (EMG) activity of the anterior temporalis and masseter muscles in edentulous individuals with temporomandibular disorder (TMD), before and after using sliding plates on complete dentures in the mandibular rest position. Background: Edentulous patients may present TMD, which is characterised by pain in temporomandibular joints, masticatory and neck muscles, uncoordinated and limited mandible movements, joint sounds and an altered occlusal relationship. It is imperative to offer treatment in order to re‐establish stomatognathic system structures before submitting the individual to any definitive restorative treatment. Materials and methods: The patients were edentulous for at least 10 years. EMG recordings were made before the insertion of the dentures (0 months) and also after using the sliding plates at the fourth month, 9th month and 12th month, using computerised electromyography K6‐I/ EMG Light Channel Surface. EMG evaluations of the muscles were performed under the following clinical conditions: rest position with dentures (R1), rest position without dentures (R2), rest position with dentures post‐activity (chewing) (R3), rest position without dentures post‐activity (chewing) (R4). Results: All patients obtained remission of muscular fatigue and reduced pain in stomatognathic system structures. Temporalis muscle showed significant increase in EMG activity compared with initial values (p < 0.01). Masseter muscles showed significantly lower mean values (p < 0.01) compared with initial values. Conclusion: The sliding plates allowed the process of neuromuscular deprogramming, contributing to muscular balance of the masticatory system, and are therefore indicated to be used before the fabrication of definitive complete dentures in patients with TMD.     

Changes in masticatory muscle activity in children with cerebral palsy

The objective of the study was to determine whether children with cerebral palsy (CP) have abnormal bilateral masseter and temporal muscle activation during mastication. The muscular activity of 32 children aged between 7 and 13 years was assessed during the task of non-habitual mastication by means of surface electromyograms. During non-habitual mastication, the amplitude of all assessed muscles in the inactive period and the amplitude of the Right Masseter and Left Temporal muscles in the active period of children with CP was greater (p < 0.05) in relation to the group of children with Typical Development (TD). Considering each muscle individually, only the duration of the active period of Right Masseter and Right Temporal muscles in children with CP was lower (p < 0.05) than in the TD children. Considering the four analyzed muscles, the duration of time of general active period, when at least one muscle should be activated, was higher in children with CP (p < 0.05) than in children with TD showing greater time variation in inactivation (p < 0.05). The higher muscle activity during the phases of the masticatory cycle, with longer duration of the active period and with greater variability between the muscles to inhibit this activity show greater difficulty in coordinating the muscles of mastication in children with CP compared to children with TD.     

The level of serotonin in the superficial masseter muscle in relation to local pain and allodynia.

The aim of this study was to investigate if serotonin is present in the human masseter muscle and if so, whether it is involved in the modulation of local muscle pain or allodynia. Thirty-five patients with pain and tenderness of the masseter muscle as well as ten healthy individuals were included in the study. Of the patients, 18 suffered from fibromyalgia and 17 had localized myalgia, e.g. myofascial pain in the temporomandibular system. The participants were examined clinically with special consideration to the masseter muscle and the pressure pain threshold as well as tolerance levels of this muscle were assessed. Intramuscular microdialysis was performed in order to sample serotonin and a venous blood sample was collected for analysis of the serum level of serotonin. Serotonin was present in the masseter muscle and the level was significantly higher in the initial sample than in the sample collected during steady state. The level of serotonin in the masseter muscle in relation to the level of serotonin in the blood serum was calculated. This fraction of serotonin was higher in the patients with fibromyalgia than in healthy individuals and high level of serotonin was associated with pain as well as allodynia of the masseter muscle. In conclusion, the results of this study show that serotonin is present in the human masseter muscle both immediately following puncture and in a subsequent steady state and that it is associated with pain and allodynia. The origin of the serotonin seems partly to be the blood, but our results indicate that peripheral release also occurs.     

The activity of jaw elevator muscles during peanut chewing in patients with temporomandibular joint and muscle pain dysfunction syndrome

A synchronized system of EMG and jaw motion tracking device was used to observe some chewing parameters of jaw elevator muscles in 15 patients with temporomandibular joint and muscle pain dysfunction syndrome (TMJ) and 15 normal subjects. Duration of tooth contact (DTC), duration of muscle contraction before tooth contact (DMC), total duration of muscle contraction (DTM) and velocity of jaw movement during peanut chewing were observed. Symptoms of the TMJ patients included pain and tenderness at joints and muscles, and limitation and clicking at joints during jaw movements. It was found that the TMJ patients needed more numerous breaking off strokes before trituration at the occlusal level. There was a longer DMC in the earlier trituration period and TMJ patients had longer DMC than in normals. No difference was found between right and left side chewing or between temporalis and masseter muscles. DTM in the TMJ group was only slightly longer than in normals and the difference between early and late chewing periods was statistically not significant. DTC was only slightly shorter in the TMJ group while the difference between early and late chewing periods in both groups was significant. The average and maximum closing velocities were significantly lower in the TMJ group in both right and left chewing. The difference in the opening phase was not as significant. It was concluded that DMC and jaw closing velocity are more sensitive parameters than DTM and DTC on the diagnosis of TMJ dysfunction with or without occlusal interference. DTM and DTC are parameters more closely related to the influence of occlusal factors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Discrimination of muscle tension in chronic pain patients and healthy controls.

The purpose of this study was to assess the perception of muscle tension in chronic pain patients and healthy controls. Twenty chronic back pain patients, 20 patients who suffered from temporomandibular pain and dysfunction, and 20 healthy controls were instructed to produce eight different levels of muscle contraction in either the m. masseter or the m. erector spinae. Each level was produced three times; trials were presented in random order. Analyses of the accuracy and the sensitivity of discrimination of muscle tension levels revealed that the patients were less able to perceive muscle contraction levels correctly and that they underestimated their actual levels of muscle tension. Patients and controls did not differ in the extent to which they contracted muscles not involved in the task. Patients suffering from musculoskeletal disorders seem to display a genuine deficit in discrimination of muscle tension that is related to neither local physiological changes at the site of pain, lack of motivation, in-attention, nor fatigue.     

Altered Pain Sensitivity in Elderly Women with Chronic Neck Pain

Background

Age-related changes occur in both the peripheral and central nervous system, yet little is known about the influence of chronic pain on pain sensitivity in older persons. The aim of this study was to investigate pain sensitivity in elders with chronic neck pain compared to healthy elders.

Methods

Thirty elderly women with chronic neck pain and 30 controls were recruited. Measures of pain sensitivity included pressure pain thresholds, heat/cold pain thresholds and suprathreshold heat pain responses. The pain measures were assessed over the cervical spine and at a remote site, the tibialis anterior muscle.

Results

Elders with chronic neck pain had lower pressure pain threshold over the articular pillar of C5-C6 and decreased cold pain thresholds over the cervical spine and tibialis anterior muscle when compared with controls (p < 0.05). There were no between group differences in heat pain thresholds and suprathreshold heat pain responses (p > 0.05).

Conclusion

The presence of pain hypersensitivity in elderly women with chronic neck pain appears to be dependent on types of painful stimuli. This may reflect changes in the peripheral and central nervous system with age.     

腰腹肌运动联合超声波对非特异性下腰痛的治疗效果及机制

为了解腰腹肌运动联合超声波治疗的效果,本研究对腰腹肌运动联合超声波治疗非特异性下腰痛进行了探讨。研究显示,治疗4周后,腰腹肌运动+超声波治疗组的疼痛评分(0.73)显著低于超声波治疗组(1.22)(p<0.05)。腰腹肌运动+超声波治疗组的立位体前屈活动幅度(2.35 cm)显著低于超声波治疗组(6.23 cm)(p<0.05)。腰腹肌运动+超声波治疗组的屈伸肌总功和屈伸肌峰值力矩比显著高于超声波治疗组(p<0.05)。腰腹肌运动+超声波治疗组的Oswestry功能障碍指数问卷表(ODI)评分显著低于超声波治疗组(p<0.05)。治疗4周后,腰腹肌运动+超声波治疗组的血清超氧化物歧化酶(SOD)和过氧化氢酶(CAT)水平显著高于超声波治疗组,而丙二醛(MDA)水平显著低于超声波治疗组(p<0.05)。为了进一步考察运动联合超声波疗法对下腰痛的治疗机制,本研究建立了完全弗氏佐剂诱导的腰椎间盘退变大鼠模型。采用阿利新蓝染色检测大鼠椎间盘纤维环区和髓核区蛋白多糖的水平,并采用免疫组化染色检测蛋白聚糖和Ⅱ型胶原的表达,发现运动联合超声波治疗可明显提高大鼠蛋白多糖、Ⅱ型胶原和蛋白聚糖水平。本研究表明,与超声波治疗相比,腰腹肌运动联合超声波治疗可更大程度地降低非特异性下腰痛患者的疼痛,提高肌肉功能和腰椎功能,增强血清抗氧化能力,并减少氧化应激损伤。此外,该联合疗法可明显提高腰椎间盘退变大鼠椎间盘中的蛋白多糖、Ⅱ型胶原和蛋白聚糖水平。     

Absent effect of zinc deficiency on the oxidative stress of erythrocytes in chronic uremic rats

Both anemia and zinc deficiency are commonly observed in patients with chronic uremia. Oxidative stress of red blood cells (RBC) has been suggested to participate in the development of anemia in these patients with chronic uremia due to reduced life span of RBC. Whether zinc deficiency aggravates the effect of oxidative stress on RBC of chronic uremia is still not understood. We thus performed the study to determine the influence of zinc deficiency on the oxidative stress of RBC in uremic rats. Zinc deficiency was induced by long-term dietary zinc deficiency. Five-sixth nephrectomy (5/6 Nx) was used to produce chronic uremia. Experiment was carried out in the following five groups: normal control (NL), chronic uremia (Nx), chronic uremia + dietary zinc deficiency (Nx-D), Nx-D + zinc supplement (Nx-DZ) and Chronic uremia + pair-fed (Nx-PF). Osmotic fragility and lipid peroxidation of RBC were used to evaluate the oxidative stress of RBC. Five weeks after 5/6 nephrectomy (Nx), 5/6 Nx rats present a syndrome of uremia to elevate the levels of plasma creatinine and urea, and reduce the level of plasma zinc (1.12 +/- 0.08 vs 1.35 +/- 0.05 ug/ml). But they does not find to produce anemia and to increase osmotic fragility and lipid peroxidation in RBC. Dietary zinc deficiency in Nx-D group produced severe anorexia and reduced plasma zinc and selenium levels and the activity of RBC-GPX. Yet in Nx-D rats, osmotic fragility and susceptibility of lipid peroxidation in red cells did not increase, because of the increase of plasma copper level (1.85 +/- 0.3 vs 1.41 +/- 0.05 microg/ml) and RBC-SOD activity (1.95 +/- 0.27 vs 0.78 +/- 0.05 unit/g Hb). Zinc supplement in Nx-D rats (Nx-DZ group) recovered the appetite and normalized the levels of plasma zinc, copper and selenium. Food restriction in 5/6 Nx rats (Nx-PF group) decreased plasma copper level and increased osmotic fragility of RBC and elevated the susceptibility of lipid peroxidation after stressing RBC with H2O2 Because Nx-PF rats presented a lower RBC-SOD activity (0.44 +/- 0.11 vs 0.78 +/- 0.05 unit/g Hb) and a lower plasma copper level. We further found a positive relationship (r=0. 802,p<0.01) between plasma copper level and RBC-SOD activity in normal and uremic rats. This study suggests that RBC-SOD activity may play an important role in preventing RBC oxidative stress. Plasma copper level may be a marker of RBC-SOD activity. We conclude, in chronic uremia, zinc deficiency doses not result in RBC oxidative stress as plasma copper level is normal, but may affect the absorption of intestinal nutrition.     

Oxidative stress contributes to muscle atrophy in chronic kidney disease patients

Abstract

Objectives

Patients with chronic kidney disease have impaired muscle metabolism, resulting in muscle atrophy. Oxidative stress has previously been identified as a significant contributor to muscle atrophy in other populations, but the contribution in chronic kidney disease is unknown. The aim of this study was to investigate the association between oxidative stress, grip strength, and lean mass in patients with chronic kidney disease.

Methods

This is a cross-sectional study of 152 participants with stage 3 or 4 chronic kidney disease. Outcome measures include grip strength, lean mass, plasma total F2-isoprostanes, inflammation, peak oxygen uptake, and standard clinical measures.

Results

Thirty four (22.4%) chronic kidney disease patients had elevated oxidative stress levels (plasma F2-isoprostanes >250 pg/ml), with 82% of patients below age-predicted grip strength normative values. There was a significant negative association between plasma F2-isoprostanes and grip strength (r = ?0.251) and lean mass (r = ?0.243). There were no associations with inflammation markers. Multiple linear regression identified plasma F2-isoprostanes as a significant predictor of grip strength independent of other predictors: sex, diabetes status, body mass index, body fat percent, and phosphate (adjusted r² = 69.5, P < 0.001).

Discussion

Plasma F2-isoprostanes were independently associated with reduced strength in chronic kidney disease patients.     

The Effect of Social Stress on Chronic Pain Perception in Female and Male Mice

The current investigations on social stress primarily point to the negative health consequences of being in a stressful social hierarchy. The repetitive nature of such stressors seems to affect behavioral response to pain both in rodents and humans. Moreover, a large discrepancy in the possibility of social stresses affecting pain perception in the two genders exists. The present study examined the effect of chronic social stress on nociceptive responses of both sexes by implementing of food deprivation, food intake inequality and unstable social status (cage-mate change every 3 days) for a period of 14 days in 96 Balb/c mice. In this regard we injected 20 µl formalin 2% into the plantar surface of hind paw at the end of stress period and scored pain behaviors of all subjects, then serum concentrations of proinflammatory cytokines were measured. Our results showed that there was significant difference in chronic phase of formalin test following implementation of food deprivation and inequality (P<0.05) as compared to control group, so that pain perception was decreased considerably and this decline in inequality exposed subjects was well above isolated ones (P<0.05); whereas unstable social situation did not affect pain perception. Moreover, IL-1 and IL-6 concentrations in serum of stressed mice of both genders were well above control group (p<0.05). Finally, despite chronic pain perception in control and unstable male subjects was larger than females; the decrease of chronic pain perception in male stressed animals (poverty and inequality experienced subjects) was much more than stressed females. These results revealed that although food deprivation and social inequality can induce hypoalgesia, some socioeconomic situations like social instability don''t affect pain sensation, whereas there were similar increases of proinflammatory cytokines level in all socially stressed subjects. In addition, males display larger hypoalgesic responses to inequality as compared with females.     

The effect of postural correction on muscle activation amplitudes recorded from the cervicobrachial region

In clinical practice, postural correction is a common treatment approach for individuals with neck and shoulder pain. As chronic static muscle use is thought to be associated with the onset of some neck and shoulder pain syndromes, it is important to understand the impact a postural correction program might have on muscle activation amplitudes in the neck and shoulder regions. Normalized surface electromyographic data were recorded from the levator scapulae, upper trapezius, supraspinatus, posterior deltoid, masseter, rhomboid major, cervical erector spinae, and sternocleidomastoid muscles of the dominant side of each of eighteen healthy subjects. Subjects performed five repetitions of each of four seated typing postures (habitual, corrected, head-forward and slouched) and four standing postures (habitual, corrected, and head-forward and slouched). Repeated-measures analysis of variance models (α = 0.05) revealed that in sitting postural correction tended to decreased the level of muscle activation required in all muscles studied during seated computer work, however this finding was not statistically significant. Corrected posture in sitting did, however produce a statistically significant reduction in muscle activity compared to forward head posture. Corrected posture in standing required more muscle activity than habitual or forward head posture in the majority of cervicobrachial and jaw muscles, suggesting that a graduated approach to postural correction exercises might be required in order to train the muscles to appropriately withstand the requirements of the task. A surprising finding was that muscle activity levels and postural changes had the largest impact on the masseter muscle, which demonstrated activation levels in the order of 20% maximum voluntary electrical activation.     

Eotaxin in serum of patients with asthma or chronic obstructive pulmonary disease: relationship with eosinophil cationic protein and lung function

This study was undertaken to investigate the correlation between the serum ECP and the serum eotaxin level, and disease activity as evaluated with pulmonary function in patients with asthma or chronic obstructive pulmonary disease (COPD). 20 patients with stable asthma and 15 patients with COPD, and 15 subjects of the control group took part in this study. The analysis of ECP was performed according to the manufacturer's directions (Pharmacia Diagnostics AB, Uppsala, Sweden). The ELISA test was used to measure eotaxin levels in sserum (kits from R&D, USA). The levels of ECP were 16.9+/-6.3 microg/L in patients with asthma, 15.1+/-9.3 microg/L in patients with COPD and 11.8+/-6.2 microg/L in the control group (P<0.05). There was no significant difference in the asthma ECP level compared with the ECP level in COPD. There was a significant difference between the ECP plasma level in asthma compared with the ECP plasma level in the control group (p<0.05). The levels of eotaxin were 175.8+/-49.3 pg/mL in the control group. There was a correlation of ECP and the eotaxin level in asthma patients (r=+0.5, p<0.05). The percentage fall in FEV1 correlated with eotaxin level in asthma (r=-0.3, p<0.05) and with the eotaxin level in COPD (r=-0.5, p<0.05). Serum outcomes of eotaxin and ECP levels appear to be a useful indicator of atopic asthma, and might provide complementary data disease monitoring. Therefore, further investigations are required to clarify whether serum eotaxin measurements have a role in the clinical evaluation in COPD.     

A型肉毒毒素不同注射方式治疗单纯性咬肌肥大患者的疗效及对咬肌厚度的影响

摘要 目的：探讨A型肉毒毒素不同注射方式治疗单纯性咬肌肥大患者的疗效及对咬肌厚度的影响。方法：选择2014年6月-2016年6月在我院接受治疗的单纯性咬肌肥大患者84例,根据随机数字表法将患者均分为研究组和对照组,两组各42例,其中对照组进行单次注射A型肉毒毒素,研究组给予连续注射A型肉毒毒素。所有患者在治疗前、治疗后1个月、治疗后3个月、治疗后6个月、治疗后9个月、治疗后12个月,采用超声对进行咬肌厚度进行检测;在治疗后12个月调查两组患者对治疗效果的主观评价,同时邀请两名专家对患者的治疗效果进行评价。记录患者在治疗后出现的不良反应。结果：研究组在治疗后9个月、治疗后12个月的咬肌厚度显著低于对照组,差异有统计学意义（P<0.05）,对照组患者的咬肌厚度在治疗后1个月至治疗后6个月逐渐降低,治疗后6个月达到最低值,在治疗后9个月和治疗后12个月开始回升。研究组患者的咬肌厚度在治疗后一直呈下降的趋势,并在治疗后12个月达到最低值。两组治疗后的各个时间点的咬肌厚度均低于治疗前,差异有统计学意义（P<0.05）。研究组患者本人的主观评价和专家评价为A、B、C的比例均显著低于对照组,D、E的比例均显著高于对照组,差异有统计学意义（P<0.05）。两组患者不良反应发生情况无统计学差异（P>0.05）。结论：与单次注射相比,A型肉毒毒素连续注射能更好的降低咬肌厚度,同时患者对治疗效果的主观评价和专家的评价较好,且不良反应少,临床上治疗咬肌肥大时可选用连续注射A型肉毒毒素的方式。     

不同咬合板接触点对颞下颌关节紊乱病咀嚼肌肌电的影响

目的:探讨不同咬合板接触点对颞下颌关节紊乱病(Tempromandibular disorders, TMD)咀嚼肌肌电的影响分析。方法:选取陕西中医药大学附属医院自2016年3月～2019年3月间收治的颞下颌关节紊乱病患者40例,按照佩戴咬合板接触点不同分为两组,A组(18例)咬合板与下前牙呈点状均匀接触;B组(22例)咬合板与对颌牙功能尖呈点状接触,对比佩戴前、后1个月时两组患者双侧颞肌前束(Temporal anterior, TA)和咬肌(Masseter muscle, MM)肌电电位变化。结果:静息状态戴咬合板前两组TA、MM两项指标差异无统计学意义(P0.05),戴板1个月后两组TA、MM指标均明显下降,组间对比B组患者TA显著高于A组,MM显著低于A组(P0.05);咬紧状态下戴板一个月后两组患者TA、MM值均明显升高(P0.05),组间对比A组TA、MM值略高于B组,但对比无统计学意义(P0.05);戴板后两组视觉模拟评分(Visual analogue scale, VAS)均明显下降,A组评分显著低于B组(P0.05)。结论:下前牙和舌侧平板呈点状均匀接触的咬合板治疗TMD可更好改善咬肌功能,缓解疼痛症状。     

Mandible position and activation of submental and masseter muscles during sleep.

Movement of the mandible could influence pharyngeal airway caliber because the mandible is attached to the tongue and to muscles that insert on the hyoid bone. In normal subjects and patients with obstructive sleep apnea (OSA) we measured jaw position during sleep with strain gauges, as well as masseter and submental electromyograms, airflow, esophageal pressure, oximetry, electroencephalograms, and electrooculograms. Jaws of patients with OSA were open more than those of normal subjects at end expiration and opened further at end inspiration, particularly at the termination of apneas when the masseter and submental muscles contracted. Masseter activation occurred only in patients with OSA and in a pattern similar to that of submental muscles. Jaw opening at end expiration could narrow the upper airway, whereas opening at end inspiration could reflect efforts to expand the airway with tracheal tug and with submental muscle activation and efforts to open the mouth to allow mouth breathing. Masseter contraction does not close the jaw but may serve to stabilize it.     

Impact of muscle injury and accompanying inflammatory response on thermoregulation during exercise in the heat.

This study examined whether muscle injury and the accompanying inflammatory responses alter thermoregulation during subsequent exercise-heat stress. Sixteen subjects performed 50 min of treadmill exercise (45-50% maximal O(2) consumption) in a hot room (40 degrees C, 20% relative humidity) before and at select times after eccentric upper body (UBE) and/or eccentric lower body (LBE) exercise. In experiment 1, eight subjects performed treadmill exercise before and 6, 25, and 30 h after UBE and then 6, 25, and 30 h after LBE. In experiment 2, eight subjects performed treadmill exercise before and 2, 7, and 26 h after LBE only. UBE and LBE produced marked soreness and significantly elevated creatine kinase levels (P < 0.05), but only LBE increased (P < 0.05) interleukin-6 levels. In experiment 1, core temperatures before and during exercise-heat stress were similar for control and after UBE, but some evidence for higher core temperatures was found after LBE. In experiment 2, core temperatures during exercise-heat stress were 0.2-0.3 degrees C (P < 0.05) above control values at 2 and 7 h after LBE. The added thermal strain after LBE (P < 0.05) was associated with higher metabolic rate (r = 0.70 and 0.68 at 2 and 6-7 h, respectively) but was not related (P > 0.05) to muscle soreness (r = 0.47 at 6-7 h), plasma interleukin-6 (r = 0.35 at 6-7 h), or peak creatine kinase levels (r = 0.22). Local sweating responses (threshold core temperature and slope) were not altered by UBE or LBE. The results suggest that profuse muscle injury can increase body core temperature during exercise-heat stress and that the added heat storage cannot be attributed solely to increased heat production.     

The expression of myogenic regulatory factors and muscle growth factors in the masticatory muscles of dystrophin-deficient (MDX) mice

The activities of myogenic regulatory factors (MRF) and muscle growth factors increase in muscle that is undergoing regeneration, and may correspond to some specific changes. Little is known about the role of MRFs in masticatory muscles in mdx mice (the model of Duchenne muscular dystrophy) and particularly about their mRNA expression during the process of muscle regeneration. Using Taqman RT-PCR, we examined the mRNA expression of the MRFs myogenin and MyoD1 (myogenic differentiation 1), and of the muscle growth factors myostatin, IGF1 (insulin-like growth factor) and MGF (mechanogrowth factor) in the masseter, temporal and tongue masticatory muscles of mdx mice (n = 6 to 10 per group). The myogenin mRNA expression in the mdx masseter and temporal muscle was found to have increased (P < 0.05), whereas the myostatin mRNA expressions in the mdx masseter (P < 0.005) and tongue (P < 0.05) were found to have diminished compared to those for the controls. The IGF and MGF mRNA amounts in the mdx mice remained unchanged. Inside the mdx animal group, gender-related differences in the mRNA expressions were also found. A higher mRNA expression of myogenin and MyoD1 in the mdx massterer and temporal muscles was found in females in comparison to males, and the level of myostatin was higher in the masseter and tongue muscle (P < 0.001 for all comparisons). Similar gender-related differences were also found within the control groups. This study reveals the intermuscular differences in the mRNA expression pattern of myogenin and myostatin in mdx mice. The existence of these differences implies that dystrophinopathy affects the skeletal muscles differentially. The finding of gender-related differences in the mRNA expression of the examined factors may indicate the importance of hormonal influences on muscle regeneration.     

Myosin heavy chain protein and gene expression in the masseter muscle of adult patients with distal or mesial malocclusion

The aim of this study was to determine the amount of myosin heavy chain (MyHC) proteins and MyHC mRNA in muscles of patients with different positions of the mandible. Ten adult patients for orthognathic surgery were divided into two groups: distal and mesial malocclusion. The mRNA expression of two MyHC isoforms of the anterior and posterior part of the right and left side of the human masseter muscle was analysed with a competitive RT-PCR assay. An exogenous template that includes oligonucleotide sequences specific for sarcomeric MyHC isoforms (1 and 2x) was constructed and utilized as competitor. Different isoforms of the MyHC protein were identified by Western blot analysis. In the total mRNA pool of the masseter muscle, the MyHC 1 mRNA level was 25.5 +/- 7.6% and the MyHC 2x mRNA was 2.5 +/- 1.2%. The anterior part of the masseter muscle from patients with distal occlusion contained more type 1 and 2x MyHC mRNA, as compared to patients with mesial occlusion (P < 0.05). No difference in the protein distribution was observed. The differences in mRNA expression may be caused by the enforced stress of the masticatory muscle in distal occlusion because of the disadvantageous pivot.