软食喂养对发育中大鼠咬肌乙酰胆碱受体亚基mRNA表达的影响

目的：检测不同硬度食物喂养下,大鼠在咀嚼形成的不同阶段,咬肌乙酰胆碱受体亚基mRNA（nicotinic acetylcholine receptor,nAchR）的表达变化。方法：40只出生后18d的大鼠,随机分为硬食组、软食组,分别喂养营养成分相同的固体、粉状鼠粮,于大鼠3w、4w、6w、9w龄时取表层咬肌,半定量RT-PCR方法检测nAchRγ/ε/δ亚基mRNA的表达变化情况。结果：3周时两组大鼠咬肌γ-nAchR mRNA表达均较低,软食组强于硬食组（p〈0.05）,4周时,硬食组没有γ-nAchR mRNA表达,软食组仍有微弱表达,6～9周两组均无γ-nAchR mRNA表达。两组大鼠ε-nAchR mRNA表达变化没有显著差异,4～9周表达均明显低于3周（p〈0.05）。3～9周龄两组大鼠咬肌δ-nAchR mRNA表达均呈下降趋势,软食组下降程度更为明显,9周时明显低于硬食组（p〈0.05）。结论：大鼠咬肌γ/ε-nAchR亚基转化在出生后3～4周完成,软食喂养可以延缓γ-nAchR的消亡与γ/ε-nAchR亚基转化,但不能阻止这一过程;软食喂养对不同nAchR亚基mRNA表达的影响具有选择性。     

食物硬度对离乳后大鼠咬肌神经营养因子3及其受体TrkC mRNA表达的影响

目的:检测不同硬度食物喂养下,大鼠在离乳后不同发育阶段咬肌神经营养因子3(Neurotrophin-3,NT-3)及其受体酪氨酸蛋白激酶C(Tyrosine kinase C,TrkC)的表达变化。方法:对出生后18d刚离乳的大鼠分别喂养固体、粉状鼠粮,于大鼠3w、4w、6w、9w龄时取表层咬肌,利用RT-PCR方法检测NT-3及其受体TrkC mRNA的表达变化情况。结果:在出生后3-9w内,粉、固体组大鼠咬肌NT-3 mRNA表达均明显下降(P<0.05),粉食组NT-3 mRNA在6w时表达低于固体组(P<0.05);TrkC mRNA在3-9w内持续下降,但粉、固体组间没有差异(P>0.05)。结论:粉食喂养能够降低离乳后大鼠咬肌NT-3 mRNA的表达,但对TrkC mRNA影响不大。     

咀嚼力降低对大鼠髁突软骨中Bax和Bcl-2 mRNA表达的影响

目的：探讨咀嚼力降低对发育期大鼠下颌髁突软骨中凋亡相关蛋白Bax和Bcl-2 mRNA表达水平的影响.方法：40只18 d雄性大鼠随机分为2组.一组喂以标准的硬食,另一组以粉末状软食喂养.于大鼠4周、5周、6周、7周龄时取其髁突软骨以RT-PCR方法检测其中Bax和Bcl-2mRNA的表达水平.结果：正常硬食组大鼠髁突软骨中Bax mRNA和Bcl-2 mRNA的表达均随时间延长而降低.软食对Bcl-2mRNA表达的影响不大,但却使Bax mRNA表达上调.软食组Bax mRNA与Bcl-2 mRNA的比值在6周和7周时明显高于硬食组p＜0.05）.结论：咀嚼力降低使发育期大鼠髁突软骨Bax mRNA表达水平和Bax mRNA/Bcl-2 mRNA的比值上升,但对Bcl-2 mRNA影响不大.     

功能矫形前伸下颌对大鼠咬肌TrkB表达影响的研究

目的：探讨功能矫形前伸大鼠下颌对青春期大鼠咬肌酪氨酸激酶受体-B（Tyrosine kinase receptor-B,TrkB）表达的影响。方法：将40只4周龄雄性SD大鼠随机分为实验组和对照组各20只,实验组大鼠佩戴自制的上颌功能矫治器,对照组不戴,分别在实验第3、7、14、21 d处死大鼠,通过免疫组织化学染色和RT-PCR检测两组大鼠咬肌中TrkB及其mRNA的表达。结果：实验3 d组、7 d组免疫组化阳性染色和mRNA的表达虽有增强,但与对照组相比,均无明显变化;实验14 d组、21 d组TrkB免疫组化阳性染色明显强于对照组,其mRNA表达结果亦同样高于对照组。结论：随着功能矫形前伸下颌时间的延长,TrkB表达含量逐渐增加,TrkB参与了咬肌在下颌前伸中的适应性改建活动。     

不同咀嚼负荷对幼兔髁突软骨内印度豪猪蛋白-人甲状旁腺激素相关蛋白通路表达的影响

目的 分析不同咀嚼负荷作用下,幼兔髁突软骨内印度豪猪蛋白（Ihh）-人甲状旁腺激素相关蛋白（PThrP）通路表达的差异性,探讨咀嚼应力负荷对髁突软骨Ihh-PThrP信号通路的影响。方法 选取10 d龄幼兔48只,随机分为硬食组和软食组,分别喂以同种颗粒状（硬食）和粉状（软食）,于饲养的第2、4、6、8周处死。采用苏木精-伊红（HE）染色、免疫组织化学、免疫印迹、实时定量荧光聚合酶链反应检测Ihh和PThrP mRNA和蛋白的动态变化。结果 HE染色显示硬食组髁突软骨厚度高于软食组的厚度;第2、4、6、8周,Ihh蛋白、PThrP蛋白和mRNA表达量在两组中呈递减趋势;软食组中Ihh和PThrP蛋白以及mRNA表达量显著低于硬食组。结论 较低的咀嚼负荷会造成髁突软骨生长因子Ihh和PThrP分泌减少,Ihh-PThrP通路表达迟缓,软骨发育受阻碍;适当的咀嚼负荷对髁突的正常发育有至关重要的作用。     

咀嚼力降低对发育期大鼠髁突软骨中细胞增殖和凋亡的影响

目的：研究咀嚼力降低对发育期大鼠下颌髁突软骨细胞增殖和细胞凋亡活性的影响。方法：40只18d雄性大鼠随机分为两组。一组喂以标准的硬食,另一组以粉末状软食喂养。于大鼠4周、5周、6周、7周龄时取其髁突软骨,分别采用免疫组织化学染色和TUNEL染色,观察髁突软骨中增殖细胞核抗原阳性细胞数和凋亡细胞数。结果：在4～7周,PCNA阳性细胞数在软、硬食组都逐步上升。但在各相同时间点,软、硬食组的PCNA阳性细胞数不存在统计学差异。在4～7周,硬食组大鼠髁突软骨中凋亡细胞数基本保持一致,而软食组凋亡细胞数随时间推移而降低,但在4周、5周、6周时,软食组的凋亡细胞数均明显多于同期硬食组（P〈0.05）。结论：咀嚼力降低对发育期大鼠髁突软骨中的细胞增殖活性影响不大,但却使细胞凋亡的数量增加,提示咀嚼力降低可能加速了髁突软骨中细胞的分化、成熟、凋亡,进而影响髁突的正常发育。     

功能矫治器前伸大鼠下颌后咬肌中BDNF表达变化的研究

目的:观察功能矫治器前伸青春期大鼠下颌对咬肌中脑源性神经营养因子(brain-derived neurotropic factor,BDNF)表达的影响.方法:将40只4周龄雄性SD大鼠随机分为实验3d组、7d组、14 d组、21 d组和同步正常对照组,共8组(n=5).实验组大鼠佩戴功能矫治器,建立下颌前伸动物模型;建模不同时间用免疫组织化学染色和RT-PCR检测各组大鼠咬肌中BDNF蛋白及其mRNA的表达水平.结果:与对照组相比,实验3d组、7d组BDNF蛋白和mRNA的表达均无显著性差异(P＞0.05);而实验14 d组、21 d组BDNF蛋白及mRNA表达水平均明显高于对照组(P＜0.05).结论:功能矫治器前伸下颌可使大鼠咬肌BDNF的表达水平随前伸时间的延长而逐渐增加,提示咬肌在下颌前伸中发生了适应性的改建活动.     

发育中大鼠咬肌乙酰胆碱酯酶含量的变化及功能负荷对其影响

目的:观察大鼠发育过程中咬肌神经肌肉接头乙酰胆碱酯酶含量的变化以及咬合功能负荷对其影响。方法:对出生后3周的大鼠分别喂食标准固体鼠粮及粉状鼠粮,利用乙酰胆碱酯酶染色观察咬肌乙酰胆碱酯酶的变化。结果:大鼠在出生后3-9周乙酰胆碱酯酶强度呈逐渐上升趋势,其中出生后4周、6周的乙酰胆碱酯酶含量较3周分别增加了7.53%与9.83%,与3周时有明显差异(P<0.05);两组性状食物喂养下,大鼠咬肌乙酰胆碱酯酶强度变化趋势相似,3周到6周均逐渐上升,明显强于3周时水平,9周表达有所下降,与3周时没有显著差异。方差分析显示,两种食物对于3-9周大鼠咬肌的乙酰胆碱酯酶含量的影响不具统计意义(P>0.05)。结论:大鼠咬肌乙酰胆碱酯酶含量随咀嚼形成而增加,咀嚼功能负荷变化对其影响不大。     

A型肉毒素对下颌骨发育的早期干预实验研究

目的:探讨咬肌注射A型肉毒素后对于下颌骨早期过度发育的干预影响。方法:3周龄SD雌性大鼠35只,体重60~80 g,随机取5只大鼠咬肌不作任何处理作为正常对照组(组1),随机取5只大鼠第4周时双侧咬肌注射花生油(癸酸诺龙溶剂)作为阴性对照组(组2),另25只大鼠进行A型肉毒素干预下颌骨发育实验。实验组25只大鼠分为5组(组3~组7),每组每周于双侧咬肌注射癸酸诺龙,其中4组(组4~组7)分别于4、5、6、7周进行干预,于双侧咬肌注射A型肉毒素1次,共2 U,7组35只动物于15周龄时取材,下颌骨进行Mirco-CT扫描,经软件重建三维模型后测量标志点进行分析。结果:标志点测量后,组3与组1和组2之间各项指标差异有显著性。组4、5、6、7各项指标与组1接近,与组3差异有显著性,各项指标均有减小,组1与组2各项指标差异无显著性。组5指标与组3差异具代表性。结论:大鼠青春期前咬肌注射癸酸诺龙可以使大鼠下颌骨在长度和高度上过度发育,咬肌注射A型肉毒素可早期干预大鼠下颌骨过度生长发育。大鼠5周龄时A型肉毒素干预最有效果。     

咀嚼力降低对发育期大鼠髁突发育的组织学影响

目的：探讨咀嚼力降低对断乳后大鼠下颌骨髁突尺寸和髁突软骨厚度的影响。方法：16只刚断乳的雄性大鼠随机分为两组。一组喂以标准的硬食,另一组以粉末状软食喂养。4w后,取每只大鼠的一侧髁突进行长度和宽度的测量,另一侧髁突进行组织学观察。结果：软食组大鼠的髁突长度、宽度和软骨层厚度均明显小于硬食组。结论：咀嚼力降低会导致下颌骨髁突生长减慢和髁突软骨厚度的变化。     

Differential gene expression of vascular endothelial growth factor isoforms and their receptors in the development of the rat masseter muscle

The capillary network in the masseter muscle develops dramatically with the differentiation of muscle fibres after birth, especially around weaning. Here, developmental changes in mRNA expression for four splicing variants of vascular endothelial growth factor (VEGF) and for two distinct VEGF receptors (Fms-like tyrosine kinase (Flt-1) and kinase insert domain-containing receptor/fetal liver kinase-1 (KDR/Flk-1)) were studied in rat masseter. The relative abundance of VEGF (120) mRNA was the highest, representing 35% of total VEGF mRNA on day 7 after birth and gradually decreased with age to become approximately 5% on day 37. In contrast, VEGF (188) mRNA was very low in the newborn rat, but increased sharply before weaning and reached 40-50% of the total on day 50. Neither VEGF (144) nor VEGF(164) mRNA showed any significant change in abundance after birth. The expression of KDR/Flk-1 mRNA was transiently high in the early postnatal stage and gradually decreased with age, Flt-1 mRNA was stably expressed at a constant level after birth. These findings suggest that different combinations of VEGF isoforms and their receptors regulate angiogenesis in the development of the masseter muscle.     

Adaptation of normal and hypofunctional masseter muscle after bite-raising in growing rats

The aim of this study was to analyze the effects of prolonged muscular elongation induced by bite-raising on the length of the muscle belly, sarcomeres and aponeurosis of the anterior deep masseter in the growing rat. Another aim was to determine the role of different functional conditions of this muscle in the adaptation process. Ninety-six young male rats were split into two groups: one was fed a hard diet and the other a soft diet to develop different functional capacities in the masticatory muscles. After 2 wk, half of the rats in both groups were fitted with an appliance that raised the bite by 2 mm. The measurements on the muscles were performed in situ. The insertion of the appliance stretched the anterior masseter muscle. After 4 wk, the vertical dentoskeletal dimension, the muscle belly, and the sarcomeres showed no difference in length among the groups. However, the aponeurosis was longer in the rats wearing the appliance compared to the controls, and among the bite block groups it was longer in the rats fed a hard diet. Length adaptation occurred in the aponeurosis. Clinically this may imply a need for reactivation of functional appliances to increase their efficiency, at a rate possibly depending on masseter muscles functional condition.     

Isometric muscle tension generated by masseter stimulation after prolonged alteration of the consistency of the diet fed to growing rats

The forces developed by the masseter muscle and the diet-related changes were studied in situ. The active tetanic tension was measured indirectly by recording the forces applied to the mandible in four different predetermined interincisal distances. The highest tension developed in all the experimental groups was with an interincisal distance of 11 mm. The tetanic tension was significantly lower in rats fed a soft diet than in those fed a normal diet. This difference might be due to the smaller muscle fibres in rats with decreased functional demand. The changes in the masticatory muscles may influence the tension applied to the facial skeleton and cause the alteration in the craniofacial growth previously found in rats fed a soft diet.     

Effects of the masticatory demand on the rat mandibular development

The influence of masticatory loading stimulus on mandibular development is not fully clear. In this paper, experimental alterations in the daily muscle use, caused by a changed diet consistency, were continuously monitored, while adaptations in bone and cartilage were examined. It is hypothesised that decreased muscular loading will result in a decrease in the growth factor expression and mandible growth. Fourteen 21‐day‐old Wistar strain male rats were randomly divided into two groups and fed on either a hard or soft diet for 14 weeks. An implanted radio‐telemetric device recorded continuously muscle activity of the superficial masseter muscle. Chondroblast proliferation in the condylar cartilage was identified by insulin‐like growth factor‐1 receptor (IGF‐1r) immunostaining. Furthermore, an X‐ray was taken for cephalometric analysis. In the soft‐diet group, the duty time of the superficial masseter muscle at higher activity levels was significantly lower than that in the hard‐diet group. This decrease in muscular loading of the jaw system was accompanied by: a significant reduction in (i) articular cartilage thickness, (ii) expression of IGF‐1r immunopositive cells and (iii) mandible ramus height. In conclusion, a decrease in masticatory demand during the growth period leads to insufficient mandibular development.     

Alterations in enzyme histochemical characteristics of the masseter muscle caused by long-term soft diet in growing rabbits

OBJECTIVE: Recently young people have an increasing tendency to intake an easily chewable diet and spend less time on mastication. The aim of the present study was to investigate the histochemical effects of long-term soft diet on the masseter muscle in growing rabbits. MATERIALS AND METHODS: Twelve young male Japanese white rabbits were divided into two groups (n = 6 each) at weaning (1 month after birth) and fed a solid diet (control group) or a powder diet (soft-diet group). The duration of the experimental period was 6 months. Masseter fibers from the superficial and the deep portions were histochemically defined as type 1, 2A, 2B, or 2C fibers. RESULTS: As compared with that of the control, the deep masseter of the soft-diet group showed a significantly lower ratio of type 1 fiber cross-sectional area to total area (6.3 and 10.1% for the soft-diet and control group, respectively), significantly more type 2A fibers (74.0%vs 50.3%) and significantly fewer type 2B fibers (4.3%vs 12.5%). However, fiber size did not differ between the two groups. NADH-tetrazolium-reductase (NADH-TR) of the masseter was less reactive in the soft-diet group, reflecting a lower oxidative capacity. CONCLUSIONS: These findings indicate that the alteration of the functional activities contributed to selective disuse influences on the type 1 and type 2B fibers, and a resultant increase in type 2A fibers. This study suggests that long-term alteration of jaw function induced by a soft diet can lead to adaptations of the masseter muscle.