大鼠比目鱼肌质量、肌重-体质量比及其肌纤维构成比与年龄相关的变化

目的:观测SD大鼠比目鱼肌质量、肌重-体质量比及其肌纤维构成比随年龄增长的变化。方法:取4、18、25月和30月龄雄性SD大鼠比目鱼肌各5块,通过H-E染色和免疫荧光方法,观测比目鱼肌纤维形态、肌肉质量、肌重-体质量比及其肌纤维构成比与年龄相关的变化。结果:比目鱼肌内肌纤维横截面的形态随年龄增长变得不规则,肌纤维和肌束之间的结缔组织逐渐增多。30月龄SD大鼠体质量较18月和25月龄低;30月龄SD大鼠肌重和肌重-体质量比较其余年龄组均明显减小。SD大鼠比目鱼肌内慢肌纤维所占比例各年龄组比较无差别;而快肌纤维所占比例随年龄增长呈下降趋势,但到30月龄其所占比例较25月龄高;同时,自18月龄开始,比目鱼肌内新生和杂合肌纤维出现的几率增加。结论:30月龄SD大鼠比目鱼肌质量、肌重-体质量比均较其余年龄组明显下降,提示该肌肉在老年晚期其承重和维持体态姿势的功能受损,但其骨骼肌纤维仍具有再生的能力。     

睫状神经营养因子对大鼠去神经骨骼肌的营养作用

目的：通过测定SD大鼠坐骨神经离断后比目鱼肌（SOL）和趾长伸肌（EDL）肌纤维横截面积,观察持续给睫状神经营养因子（CNTF）对神经骨骼肌萎缩的影响。结果：SD大鼠坐骨神经离断后,持续给0．2mg/kg.d的CNTF20天后,损伤侧SOL和EDL肌纤维横截面积分别比实验对照组高27％（P＜0．01）和14％,SOL肌纤维横截面积比EDL增加的幅度大,而给予0．05mg/kg.d的CNTF20天后,动物肌纤维横截面积与实验对照组无明显差异。结论：CNTF可显著改善坐骨神经离断后SD大鼠骨骼肌的萎缩,并且CNTF效应的强弱与用药剂量和肌肉类型有关,0．2mg/kg.dCNTF作用明显强于0．05mg/kg.dCNTF,慢肌（SOL）比快肌（EDL）对CNTF更敏感。     

慢性低氧大鼠膈肌纤维截面积变化

本文通过建立慢性常压和减压低氧大鼠模型,采用肌球蛋白ATP酶（mATP酶）组化方法将肌纤维分为I、ⅡA和ⅡB三种类型和显示毛细血管,用计算机图象分析系统测定肌纤维横截面积（CSA）和毛细血管密度变化,观测慢性低氧大鼠膈肌不同类型纤维CSA变化,探讨其与毛细血管密度变化的关系。慢性低氧大鼠肌纤维CSA均不同程度缩小,CSA缩小与毛细血管密度增加显著相关。隔肌CSA缩小使毛细血管相对密度增加,有利于氧运输和弥散,膈肌氧化能力增强。     

慢性低氧大鼠膈肌纤维横截面积变化

本文通过建立慢性常压和减压低氧大鼠模型 ,采用肌球蛋白ATP酶 (mATP酶 )组化方法将肌纤维分为Ⅰ、ⅡA和ⅡB三种类型和显示毛细血管 ,用计算机图象分析系统测定肌纤维横截面积 (CSA)和毛细血管密度变化 ,观测慢性低氧大鼠膈肌不同类型纤维CSA变化 ,探讨其与毛细血管密度变化的关系。慢性低氧大鼠肌纤维CSA均不同程度缩小 ,CSA缩小与毛细血管密度增加显著相关。膈肌CSA缩小使毛细血管相对密度增加 ,有利于氧运输和弥散 ,膈肌氧化能力增强。     

小圆肌和大圆肌的肌纤维型分布研究

目的：探讨小圆肌和大圆肌的肌纤维型分布特征和构成比例及其相关生理功能,为骨骼肌运动生理和临床应用提供形态学数据.方法：选取4例16～40岁（均死于非神经肌性疾病）死后12 h内的国人尸体两侧小圆肌和大圆肌,在肌腹中部取材共16块立即置入液氮,随后作恒冷箱冰冻横切片（-20℃,厚10 μm）,用肌球蛋白ATP酶法染色,研究两肌的肌纤维分型分布、测定各肌I型（慢缩）、Ⅱ型（快缩）肌纤维的构成比例.结果：（1）小圆肌和大圆肌的肌纤维分成Ⅰ型、Ⅱ型,两型肌纤维呈棋盘格式混杂分布;（2）两肌的Ⅰ型肌纤维平均百分率分别为57.9%和55.0%;（3）同型肌纤维的分布频率在左、右侧别之间比较差异无统计学意义（P＞0.05）.结论：小圆肌和大圆肌以I型肌纤维分布稍占优势,为国人肌纤维型提供基础资料.     

有氧运动对发育期大鼠骨骼肌肌纤维影响的研究

目的观察有氧运动对发育期大鼠骨骼肌肌纤维的形态学影响。方法本实验以雄性发育期(3-13周龄)wistar大鼠为研究对象,采用动物跑台,以坡度5%,速度15m/min的运动负荷,进行有氧运动训练,1h/d,5d/w。在训练3周(3周运动组,T3W)、6周(6周运动组,T6W)和9周(3周运动组,T9W)后,取大鼠腓肠肌内侧头进行冰冻切片,琥珀酸脱氢酶(SDH)胆碱酯酶(AchE)联合染色法,光镜下观察各型肌纤维的变化。结果各运动组各型肌纤维的横截面积、平均直径呈进行性增长,其中T6W组和T9W组的红肌、中间肌纤维的横截面积和平均直径都显著高于各对照组(P<0.05,P<0.01),T3W组、T6W组和T9W组白肌纤维的横截面积和平均直径显著高于各对照组(P<0.01)。各运动组红肌纤维百分比未见明显变化(P>0.05);T6W组和T9W组的中间肌纤维百分比较T3W组显著增加(P<0.01),分别增加10.31%和10.60%,而白肌纤维的百分比显著降低(P<0.01),分别降低11.19%和11.03%。结论有氧运动对发育期大鼠骨骼肌各型肌纤维有明显的促增长作用,并可引起白肌纤维向中间肌纤维的转变,肌纤维的形态结构不仅同运动方式及运动负荷有关,同时还与发育的年龄有着密切的相关。     

实验大鼠斜方肌肌纤维型组成及分布研究

目的探讨大鼠斜方肌的肌纤维型组成和分布,借以了解该肌功能。方法取成年SD大鼠斜方肌升部肌组织进行冰冻切片(8μm厚),采用Guth-Samaha肌球蛋白ATP酶组织化学染色法并稍做改良,对其进行肌纤维分型研究。结果SD大鼠斜方肌经肌球蛋白ATP酶组织化学染色后可明确分出2种肌纤维型,即白色的Ⅰ型纤维(慢缩纤维)和深褐色的Ⅱ型纤维(快缩纤维),2种肌纤维在肌内呈棋盘样均匀分布;图像分析计数其Ⅰ型纤维占(48.8±6.9)%,Ⅱ型纤维比例为(51.2±6.9)%,2者比较差异无统计学意义(P>0.05)。结论SD大鼠斜方肌2型肌纤维所占比例均等,与其维持颈背部姿势的作用一致。     

肌苷对尾部悬吊大鼠比目鱼肌梭内、外肌纤维肌球蛋白重链表达的影响

目的探讨肌苷注射液对尾部悬吊大鼠比目鱼肌(SOL)梭内、外肌纤维肌球蛋白重链(MHC)表达的影响。方法采用大鼠尾部悬吊法建立后肢骨骼肌废用模型,用免疫组化染色法检测肌苷注射液对大鼠SOL梭内、外肌纤维MHC表达的影响。结果尾部悬吊14d后,大鼠SOL肌梭内、外肌纤维中快缩型MHC的表达均有增加;而在吊尾期间注射肌苷后,SOL肌梭内、外肌快缩型MHC的表达没有明显变化。结论肌苷注射液对尾部悬吊大鼠SOL肌梭内、外肌纤维MHC表型的转化有明显的对抗作用。     

人四肢骨骼肌两型肌纤维的横切面积研究

目的 为查清人四肢骨骼肌两型肌纤维的横切面积和直径。方法 用死后２４ｈ内男性尸体５具（年龄２１￣２８岁）,分别取双侧上、下肢２９块肌共４８块肌组织,作恒冷箱冰冻横切片。以肌球蛋白ＡＴＰ酶组织化学染色（ｐＨ９．４）,将肌纤维分为Ｉ型和Ⅱ型。用网形测微尺测量两型肌纤维的横切面积和直径。结果 人四肢不同骨骼肌的肌纤维粗细各不相同,其平均横切面积范围在１７８０￣４７６０μｍ＾２之间,平均直径为４７．６￣７     

大鼠胸深肌肌纤维型的组成及分布

目的探讨SD大鼠胸深肌的肌纤维型组成和分布,借以了解该肌功能。方法采用Guth-Samaha肌球蛋白ATP酶组织化学染色法并稍做改良,对成年SD大鼠胸深肌冰冻切片进行肌纤维分型研究。结果大鼠胸深肌经肌球蛋白ATP酶组织化学染色后可明确分出2型肌纤维,即明亮色白的Ⅰ型纤维(慢缩纤维)和幽暗深褐的Ⅱ型纤维(快缩纤维),并且,两种纤维在肌内呈棋盘样均匀分布;图像分析仪下计数Ⅱ型纤维达到65%±6%,而Ⅰ纤维仅占35%±5%,前者明显高于后者(P<0.01)。结论大鼠胸深肌以Ⅱ型纤维为主,属于力量和速度型肌。     

Histochemical responses of human soleus muscle fibers to long-term bedrest with or without countermeasures

Effects of 2- or 4-month bedrest in -6 degrees head-down tilt position with or without countermeasures on the histochemical properties of fiber phenotype and cross-sectional area (CSA) were studied in human soleus. The CSAs in slow fibers decreased approximately 32% during 4-month bedrest. This reduction was normalized after 1-month recovery. Although the reduction of percent slow fibers was not significant statistically, the percent intermediate fibers was significantly elevated 4 months after bedrest. Such shift in fiber type was not normalized following 1-month recovery. Effects of wearing an anti-g Penguin suit which has a modest, but continuous resistance at the knee and ankle (Penguin-1) or with knee resistance without loading on the ankle (Penguin-2) for 10 consecutive hours daily were also investigated during approximately 2 months of bedrest. The subjects performed knee extension and flexion for the last 15 min of each hour while in a supine position in bed. Bedrest-induced fiber atrophy was prevented in the Penguin-1 group but not the Penguin-2 group. Transformation of fiber type was not prevented in either Penguin suit group. It is suggested that long-term bedrest causes an atrophy and a shift of fiber phenotype toward fast-twitch type in human soleus. Data also indicated that loading on the muscle is an effective countermeasure for prevention of fiber atrophy but not fiber-type transformation.     

Adult and developmental myosin heavy chain isoforms in soleus muscle of aging Fischer Brown Norway rat

Fiber type shifts in aging skeletal muscle have been studied with myofibrillar ATPase histochemistry and gel electrophoresis, but less commonly with immunohistochemistry. Immunohistochemical study of myosin heavy chains (MHCs) in single myofibers yields additional information about aged skeletal muscle. Furthermore, many studies of aging rodent skeletal muscle have been performed on fast-MHC-predominant muscle and in several different strains. The aim of this study was to evaluate immunohistochemically MHC characteristics in the slow-MHC-predominant soleus muscle in the Fischer Brown Norway F1 hybrid aging rat (FBN). Three age groups of FBN rats were studied: 12 months, 30 months, and 36 months. Soleus muscles were excised, quick-frozen, and stained immunohistochemically for slow, fast, developmental, and neonatal MHC isoforms. Cross-sections were evaluated for the number and cross-sectional areas of fibers expressing each isoform. Single myofibers in soleus muscles of the aged rats showed significantly greater amounts of coexpression of slow and fast MHC than did younger animals. This change began by 30 months of age, but did not reach statistical significance until 36 months of age. The soleus from 36-month-old rats also expressed greater amounts of developmental MHC than did the other groups. These developmental MHC-positive myofibers also coexpressed either slow or slow and fast MHC. The age-related increase in MHC coexpression of slow with fast isoforms may indicate a fiber type shift suggestive of denervation that outpaces reinnervation. The developmental MHC-positive fibers provide evidence of ongoing myofiber remodeling in the oldest rats in the midst of the fiber degeneration of aging.     

The role of neural and mechanical influences in maintaining normal fast and slow muscle properties

The relative importance of neural and mechanical influences in maintaining normal slow and fast muscle properties remains unclear. To address this issue, we studied the effects of 10 days of hindlimb unloading (HU) with or without tenotomy and/or denervation on the cross-sectional area (CSA), myosin heavy chain (MHC) expression (immunohistochemistry) and composition (gel electrophoresis), and myonuclear number in soleus and plantaris fibers in adult male Wistar rats. In general, the adaptations in fiber type and size were similar using either single fiber gel or immunohistochemical analyses. HU resulted in atrophy of type I and I+IIa/x MHC fibers in the soleus and in type I, I+IIa/x, IIa/x, IIa/x+IIb, and IIb MHC fibers in the plantaris. Addition of tenotomy and/or denervation in HU rats had minimal effects on fiber CSA in the soleus, but fiber CSA in the plantaris further decreased, particularly in fibers expressing only fast MHCs. HU resulted in a de novo appearance of type I+IIa/x+IIb and IIa/x+IIb MHC fibers in the soleus and of type I+IIa/x+IIb MHC fibers in the plantaris.Tenotomy and/or denervation in HU rats had no further effect on the fiber type composition of either muscle. Mean myonuclear number/mm of type I fibers was decreased in the soleus of HU rats, and increased in type I and I+IIa/x fibers in HU plus tenotomy (HU+Ten) rats. In the plantaris, mean myonuclear number/mm of type IIa/x, IIa/x+IIb, and IIb fibers was lower after HU with or without tenotomy and/or denervation. Mean cytoplasmic volume/myonucleus ratio of type I and I+IIa/x fibers in the soleus of the HU group tended to be smaller than in controls. The largest decrease was noted in the HU+Ten group. In the plantaris, this ratio was unaffected by HU alone, but was decreased by addition of tenotomy and/or denervation when all fiber types were combined. These data indicate that the major cause of fiber atrophy and adaptations in myonuclear domain size in the slow soleus of HU rats is the chronic reduction in force generation, whereas the elimination of neuromuscular contact via denervation results in additional fiber atrophy and adaptations in myonuclear domain size in the fast plantaris.     

Tapering of the intrafascicular endings of muscle fibers and its implications to relay of force

The geometric shape of the filamentous, intrafascicular type of muscle fiber ending was reconstructed as a basis for understanding the pattern in relay of the fiber's force to the muscle tendon. Single motor units (MUs) identified physiologically as being fast and slow, respectively, were isolated in cat tibialis muscles and glycogen-depleted for recognition in cross sections of the muscle frozen at its L_o. Serial measurements of cross-sectional area (CSA) using an image processing system were made along 14 intrafascicular endings of MU fibers and an additional seve, nondepleted fibers identified histochemically as slow. Comparison of coefficients of variation for the linear relation of the CSAs and of the equivalent diameters with length along the taper indicated that in both fast and slow fibers the areas bore a closer relationship, that is, the taper had the equivalent of a parabolic, rather than a conical outline. The implications of these two conformations to relay of the fiber's contractile force to surrounding structures are displayed graphically. © 1993 Wiley-Liss, Inc.     

Expression and functional implications of troponin T isoforms in soleus muscle fibers of rat after unloading

The expression pattern of troponin T (TnT) isoforms was studied in rat soleus muscle fibers in control and after hindlimb unloading (HU) conditions. To determine the functional consequence of TnT expression, the fibers were also examined for their calcium activation characteristics. With regard to TnT expression, four populations of fibers were distinguished in control muscle. Slow fibers expressing only slow isoforms of TnT (TnT1s, 2s, 3s ) were predominant (54%). Hybrid slow fibers (16%) differed from slow fibers by the additional expression of two TnTf isoforms. Hybrid fast fibers (22%) expressed slow and fast isoforms of TnT while fast fibers (8%) expressed only fast TnT isoforms. The expression of the other regulatory protein isoforms was checked for each population. The contractile experiments revealed steeper slopes of the tension/pCa relationship from hybrid slow fibers expressing fast TnT in a completely slow molecular environment. The expression of TnTs in hybrid fast fibers did not modulate the intrinsic co-operativity. After HU, the fast population was increased and reached 55%. The slow population decreased to 41% and a very small amount of hybrid slow fibers remained (4%). These data demonstrated the implication of TnT isoforms in the calcium activation properties and, more particularly, in the modulation of co-operativity within the myofibrillar lattice. Regulation of TnT expression appeared as a very fast and complete process compared to moderate changes of TnC and TnI.     

Targeting functional subtypes of spinal motoneurons and skeletal muscle fibers in vivo by intramuscular injection of adenoviral and adeno-associated viral vectors

We report that functional subtypes of spinal motoneurons and skeletal muscle fibers can be selectively transduced using replication-defective adenoviral (ADV) or adeno-associated (AAV) viral vectors. After intramuscular injection in adult rodents, ADV vectors transduced both fast-twitch and slow-twitch skeletal muscle fibers. Intramuscular injection of ADV vectors also caused transduction of spinal motoneurons and dorsal root ganglion cells. However, only neurons innervating the injected muscle were transduced, as shown by co-injection of a retrograde axonal tracer. In adult male rats it is therefore possible to transduce fast or slow spinal motoneurons and muscle fibers selectively since in these animals, the extensor digitorum longus and soleus muscles contain almost exclusively fast or slow motor units, respectively. In rats, AAV vectors transduced muscle fibers in the predominantly fast extensor digitorum longus but not in the predominantly slow soleus muscle. We did not observe any transduction of spinal motoneurons following intramuscular injection of AAV vectors. These results show that physiologically and clinically important subpopulations of cells in the neuromuscular system can be selectively transduced by viral vectors.     

Effect of hypobaric hypoxia on rat soleus muscle fibers and their innervating motoneurons: a review

Mammalian skeletal muscle fibers are classified into three basic types based on their enzyme histochemical profiles: fast-twitch glycolytic (FG), fast-twitch oxidative glycolytic (FOG), and slow-twitch oxidative (SO) types. The type-shift of fibers from FOG to SO in the slow soleus muscle of rats occurs during postnatal growth. Our previous studies have demonstrated that hypoxic exposure inhibits a growth-related type-shift of fibers from FOG to SO in the rat soleus muscle, irrespective of the duration and age at which the animals are exposed to hypoxia. Our previous studies have also revealed that a high percentage of FOG fibers in the soleus muscle of the hypoxia-adapted rats is found only under hypoxic conditions. Furthermore, we have found that these adaptations in fibers of the rat soleus muscle correspond well with those in motoneurons at the ventral horn of the spinal cord that innervate the muscle fibers.     

Motoneuron and muscle-unit properties after long-term direct innervation of soleus muscle by medial gastrocnemius nerve in cat

1. This study addresses the following questions. 1) In a previous experiment, when the combined lateral gastrocnemius-soleus nerve was cross-innervated by the medial gastrocnemius (MG) nerve, was the predominance of slow muscle units in soleus muscle a result of selective routing of slow motor axons into soleus? 2) Is MG-nerve-induced conversion of soleus muscle fibers from slow to fast more complete at very long (18 mo vs. 9-11 mo) postoperative times? 3) Do MG motoneurons that cross-innervate soleus muscle recover their normal membrane electrical properties at very long postoperative times? 2. The proximal portion of approximately one-third of the MG nerve was coapted directly with the distally isolated soleus nerve. The MG muscle remained innervated by the unoperated portion of the MG nerve. At 6, 10, or 18 mos postoperative, motoneuron and/or muscle-unit properties were determined for MG motoneurons innervating MG, soleus, or neither muscle, and for axotomized soleus motoneurons. 3. In the partially denervated MG muscle, the proportions of motor units of each type were normal. This suggests that the population of MG motor axons that had been directed to the soleus nerve also contained a representative distribution of MG motoneuron types. 4. Most motor units (74%) in cross-innervated soleus (Xsoleus) were type S (based on muscle-unit contractile properties), in spite of the soleus nerve's having been cross-connected by approximately 75% fast MG motoneurons. Thus, even at very long postoperative times, slow soleus muscle units resisted conversion by fast MG motoneurons. 5. Thirty-two percent of MG motoneurons that had been cross-connected to soleus nerve elicited no measurable muscle contraction, compared with approximately 10% in previous reinnervation experiments in which the MG nerve was coapted with the MG or lateral gastrocnemius-soleus nerve. Thus MG motoneurons may be disadvantaged in their ability to innervate soleus muscle fibers. 6. It appears that at long postoperative times, those fast MG motoneurons tha had innervated large soleus muscle units had failed to convert those muscle fibers to fast types and had failed also to recover their normal motoneuron electrical properties. Conversion and recovery did occur for fast MG motoneurons that innervated small soleus muscle units and for slow MG motoneurons.     

Abnormal distribution of fiber types in the slow-twitch soleus muscle of the C57BL/6J DY2J/DY2J dystrophic mouse during postnatal development

The postnatal development of extrafusal fibers in the slow-twitch soleus muscle of genetically dystrophic C57BL/6J dy^2J/dy^2J mice and their normal age-matched controls was investigated by histochemical and quantitative methods at selected ages of 4, 8, 12, and 32 weeks. The majority of fibers in the soleus consisted of two kinds, fast-twitch oxidative-glycolytic (FOG) and slow-twitch oxidative (SO), according to reactions for alkaline-stable and acid-stable myosin ATPase and the oxidative enzyme, NADH-tetrazolium reductase. A minor population of fibers, stable for both alkaline- and acid-preincubated ATPase, but variable in staining intensity for NADH-TR, were designated “atypical” fibers. With age, the normal soleus exhibited a gradual increase in the number and proportion of SO fibers and a reciprocal, steady decline in the percentage of FOG fibers. Atypical fibers were numerous at 4 weeks, but were substantially diminished at later ages. Since total extrafusal fiber number remained relatively constant between the periods examined, this change in relative proportions reflects an adaptive transformation of fiber types characteristic of normal postnatal growth. A striking alteration in the number and distribution of fiber types was associated with the dystrophic soleus. At 4 weeks an 18% reduction in total fiber number was already noted. Subsequently, by 32 weeks a further 22% diminution in overall fiber number had occurred. With age, the absolute number and proportion of dystrophic SO fibers were drastically reduced. In contrast, the percentage of dystrophic FOG fibers increased significantly while their absolute numbers between 4 and 32 weeks remained relatively constant. Atypical fibers in the dystrophic solei were found in elevated numbers at all age groups, particularly at 12 weeks. They may, in part, represent attempts at regeneration or an intermediate stage in fiber-type transformation. Microscopically, both of the major fiber types appeared affected, albeit differently, by the dystrophic process. We suggest that a failure or retardation in the normal postnatal conversion of fiber types within the soleus muscle occurs in this murine model for muscular dystrophy.     

Scanning electron microscope study of neuromuscular junctions in different muscle fiber types in the zebra finch and rat

Examination by scanning electron microscopy revealed differences between neuromuscular junctions in the muscle fibers of the zebra finch (bird) and rat. The neuromuscular junctions between the anterior and posterior latissimus dorsi muscles of the zebra finch were compared. The junctions of the former, exclusively slow tonic fibers, were small and numerous along the long axis of a single muscle fiber. The synaptic depressions per junction were few. The junctions of the latter, exclusively fast twitch fibers, were large and consisted of more synaptic depressions than the former. Junctional folds were occasionally found in some depressions. The neuromuscular junctions between the extensor digitorum longus and soleus muscles of the rat were also compared. The former consisted almost entirely of fast twitch muscle fibers, whereas the latter consisted of both slow twitch fibers (75%) and fast twitch fibers (25%). The junctions in the extensor digitorum longus muscle were almost all labyrinthine gutters containing exclusively slit-like junctional folds. In the soleus muscle, two types of junctions were observed. One type was similar to that of the extensor digitorum longus muscle; the other was characterized by labyrinthine gutters containing sparse, narrow slit-like and pit-like junctional folds. We suggest from these structural differences of the subneural apparatuses that the junction of the fast twitch muscle is characterized by the subneural apparatus containing numerous slit-like junctional folds, and that of the slow twitch muscle fiber characterized by the apparatus containing sparse, narrow slit-like and pit-like junctional folds.