大鼠比目鱼肌肌纤维总数、横截面积及其内慢肌纤维和快肌纤维横截面积与年龄相关的变化

目的 探讨SD大鼠比目鱼肌的形态学特征随年龄增长的变化情况。方法 4、18、25和30月龄雄性SD大鼠比目鱼肌各5块,通过HE染色、琥珀酸脱氢酶（SDH）活性检测和免疫组织化学方法,观测比目鱼肌纤维形态、数目、肌肉横截面积及其内慢肌纤维和快肌纤维分布特征、横截面积与年龄相关的变化。 结果 比目鱼肌内肌纤维形状随年龄增长变得不规则,并伴以肌纤维劈裂和簇聚。30月龄较4月龄大鼠的比目鱼肌纤维总数减少（P＜0.05）,而且其与其余年龄组大鼠的肌肉横截面积比较亦明显减小（P＜0.01）。仅4月龄和25月龄大鼠比目鱼肌内慢肌纤维横截面积相比无差别（P＞0.05）,而快肌纤维横截面积则表现为18月龄和25月龄比较无差异（P＞0.05）。结论 30月龄SD大鼠比目鱼肌纤维总数、肌肉横截面积及其内慢肌纤维和快肌纤维横截面积与其他年龄组大鼠相比差异显著,提示在衰老后期骨骼肌功能可能会发生明显变化。     

重组人睫状神经营养因子对大鼠坐骨神经再生长的影响

目的: 观察重组人睫状神经营养因子(CNTF)对大鼠坐骨神经再生长的影响,并与神经生长因子(NGF)的作用进行比较。方法: 随机将动物分成正常对照组、模型组、CNTF给药小剂量组(48 μg/kg)、中剂量组(216 μg/kg)、大剂量组(1 080 μg/kg)、NGF 给药组(20 μg/kg),每组各10只。模型组采用大鼠坐骨神经切断再缝合法造成坐骨神经损伤模型,给药组采用不同药物剂量对神经损伤部位肌肉注射给药45 d后,测定神经动作电位潜伏期和传导速度。结果: 与模型组相比较,CNTF各给药组神经动作电位潜伏期显著缩短(P<0.01),传导速度显著增快(P<0.01);同时,216 μg/kg、1 080 μg/kg CNTF组和NGF组对神经动作电位潜伏期的影响无显著差别(P>0.05),但是216 μg/kg、1 080 μg/kg CNTF组的神经动作电位传导速度比NGF组显著增快(P<0.01)。结论: CNTF对大鼠坐骨神经再生具有一定的促进作用,而且其作用可能优于NGF。     

脂肪源性干细胞促进大鼠受损坐骨神经传导及脊髓脑源性神经营养因子和睫状神经营养因子的表达

目的:探讨脂肪源性干细胞(ADSCs)对坐骨神经损伤大鼠神经传导功能以及脊髓脑源性神经营养因子(BDNF)和睫状神经营养因子(CNTF)表达的影响。方法:将第4代ADSCs移植入脱细胞神经移植物(ANA)中,构建组织工程神经。大鼠随机分为正常组、杜氏改良Eagle培养基营养混合物F12(DMEM)组和ADSC组。DMEM组和ADSC组均建立坐骨神经损伤模型,后用相应的组织工程神经桥接损伤神经的断端。术后6周采用神经电生理记录仪检测各组大鼠坐骨神经传导速度和波幅,采用免疫荧光和Real-time PCR检测各组大鼠脊髓脑源性神经营养因子(BDNF)、睫状神经营养因子(CNTF)蛋白和mRNA的表达。结果:ADSC组大鼠坐骨神经传导速度、波幅和脊髓BDNF和CNTF蛋白及mRNA表达均显著高于DMEM组。结论:ADSCs可增加坐骨神经传导速度和波幅、上调脊髓BDNF和CNTF的表达。     

神经生长颗粒对大鼠腓总神经横断损伤的修复作用

目的 研究神经生长颗粒(NGG)对大鼠腓总神经横断损伤的修复作用.方法 SD大鼠50只,随机分为NGG高、中、低剂量组(剂量分别为5.2g生药/kg、2.6g生药/kg、1.3g生药/kg)、弥可保组(剂最为625μg/kg)、空白对照组.行大鼠腓总神经横断缝合术,术后每日灌胃给药.于术后2周、3周、4周行足迹实验,测定展趾功能,术后4周行电生理检测,测定复合肌动作电位和神经干动作电位检测,组织形态学分析,测定再生有髓神经纤维数、髓鞘厚度和胫前肌肌纤维截面积,观察NGG对大鼠腓总神经损伤的修复作用.结果 与空白对照组相比,NGG组展趾功能、复合肌动作电位和神经干动作电位波幅及恢复率、再生有髓神经纤维计数、髓鞘厚度及胫前肌横截面积均显著增高,且呈剂量依赖的量效关系.结论 NGG有利于轴突生长和髓鞘形成,可以促进大鼠损伤神经修复和神经功能的恢复.     

脐带间充质干细胞移植可延缓大鼠失神经肌肉的萎缩

背景：周围神经断伤后生长缓慢,失神经支配的肌肉萎缩及运动终板纤维化,导致肢体功能不可逆障碍。脐带间充质干细胞已经广泛应用于多学科研究,但应用于周围神经损伤中延缓大鼠失神经肌肉萎缩鲜有报道。 目的：观察异种异基因脐带间充干细胞移植于大鼠离断坐骨神经断端,延缓失神经肌肉萎缩的效果。 方法：新鲜脐带采集于健康足月产妇,分离鉴定脐带间充质干细胞。制备大鼠坐骨神经SunderlandⅣ度损伤模型,去神经束5 mm,神经外膜修复,5 mm小间隙移植脐带间充质干细胞模型,对照组仅在小间隙内注入同体积生理盐水。测定大鼠坐骨神经功能指数,小腿三头肌湿质量,坐骨神经干潜伏期、动作电位传导速度、波幅,以及骨骼肌纤维横截面积维持率。 结果与结论：造模后4,8及12周,脐带间充质干细胞组大鼠坐骨神经功能指数、右侧小腿三头肌湿质量及骨骼肌纤维横截面积维持率均显著高于对照组(P < 0.05)。造模后12周肌电图显示,脐带间充质干细胞组大鼠坐骨神经干潜伏期显著低于对照组,动作电位传导速度及波幅显著高于生理盐水对照组(P < 0.001)。提示脐带间充质干细胞移植于大鼠离断的坐骨神经断端,可促进神经生长,延缓失神经肌肉萎缩,维持失神经肌肉形态及功能。中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程全文链接：     

牛膝活性提取物对大鼠坐骨神经横断的修复作用

目的:研究牛膝活性提取物(ABPPk)对大鼠坐骨神经横断的修复作用.方法:SD大鼠随机分为5组,ABPPk低、中、高剂量组(剂量分别为2.5、5.0、10.0 mg/kg),阳性对照组(弥可保,0.13mg/kg),生理盐水组(阴性对照).行大鼠左侧坐骨神经横断缝合术,术后每日腹腔注射给药.于术前1d和术后1、7、14、21、28 d行热痛阈实验,测定大鼠热痛阈值;术后7、14、21、28d行足迹实验,测定大鼠坐骨神经功能指数;术后28 d行电生理检测,测定大鼠复合肌动作电位;透射电镜观察大鼠再生有髓神经纤维的髓鞘厚度和髓鞘板层数目;行Masson三色染色观察大鼠腓肠肌肌纤维横截面.结果:与生理盐水组相比,ABPPk中、高剂量组大鼠热痛阈值、坐骨神经功能指数、复合肌动作电位幅度、再生有髓神经纤维髓鞘厚度、板层数目及腓肠肌肌纤维横截面积均增高,各剂量组之间呈量效关系.结论:ABPPk有利于轴突再生和髓鞘形成,能促进大鼠周围神经损伤后功能和形态的恢复.     

被动训练促进失神经肌萎缩模型大鼠骨骼肌结构和功能的恢复

文题释义：肌肉萎缩：是指横纹肌营养障碍,肌肉纤维变细甚至消失等导致的肌肉体积缩小。多由肌肉本身疾患或神经系统功能障碍所致,病因主要有：神经源性肌萎缩、肌源性肌萎缩、失用性肌萎缩和其他原因性肌萎缩。肌肉营养状况除肌肉组织本身的病理变化外,更与神经系统有密切关系。脊髓疾病常导致肌肉营养不良而发生肌肉萎缩。 肌卫星细胞：是一类存在于肌细胞基底膜与肌膜之间的成体干细胞,作为肌源性干细胞在肌肉组织损伤后,能够在激活后发挥良好的增殖、分化能力,在骨骼肌损伤的修复和再生过程中发挥重要作用。 背景：炎症细胞或炎性因子参与失神经损伤后骨骼肌肌卫星细胞的增殖和分化,在失神经骨骼肌肌组织病理过程中起着重要的作用。 目的：研究被动康复训练对失神经萎缩大鼠骨骼肌结构、功能以及肌动蛋白和炎症因子表达的影响。 方法：将30只SD大鼠平均分为假手术组、模型组和训练组,模型组及训练组大鼠暴露坐骨神经并剪断,假手术组只暴露而不剪断坐骨神经。造模后2个月始用自制滚筒对训练组大鼠进行被动康复训练2个月,用肌肉湿质量比和BBB评分评估肌肉萎缩的程度及运动功能,苏木精-伊红染色观察肌纤维微细结构及横截面积,免疫组化染色检测各组腓肠肌肌动蛋白及肿瘤坏死因子α、白细胞介素6及白细胞介素1β表达。实验经沈阳医学院实验动物福利伦理委员会的审批,批准文号为SYYXY2015010601。结果与结论：①训练组BBB评分高于模型组;②训练组腓肠肌湿质量高于模型组但肌纤维的横截面积却低于模型组(P < 0.001,P < 0.05),训练组腓肠肌肌动蛋白表达高于模型组(P < 0.001);③训练组炎症因子肿瘤坏死因子α、白细胞介素6及白细胞介素1β的表达水平低于模型组(P < 0.001或P < 0.05);④结果说明,被动训练有助于失神经萎缩肌肉结构和功能的恢复,降低炎症因子的水平防止肌肉的进一步萎缩,提高骨骼肌的肌力。 ORCID: 0000-0002-9303-8651(王世杨) 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

运动训练对大鼠肾上腺睫状神经营养因子表达的影响

目的研究大鼠游泳运动训练对大鼠肾上腺睫状神经营养因子(CNTF)表达的影响。方法成年SD大鼠分四组,除正常组外,三个负重组分别给予占体重1%、3%、5%负重,进行6周游泳训练,每天1h,取各组大鼠肾上腺,用RT-PCR研究CNTF mRNA水平变化。结果肾上腺能检测到CNTF mRNA表达,与正常组比较,轻度和中度负重组肾上腺CNTF mRNA表达明显增加(P<0.05)。结论轻、中度负重游泳训练明显增加肾上腺CNTF基因水平,提示CNTF可能与游泳负重导致机体的神经内分泌调节有关。     

低频电刺激对坐骨神经损伤大鼠不同类型骨骼肌萎缩及内源性胰岛素样生长因子1表达的影响

背景：低频电刺激可以缓解骨骼肌的萎缩,但对肌纤维类型的影响尚不清楚,同时内源性胰岛素样生长因子1在萎缩后的肌纤维中的表达与电刺激的关系尚无公识。 目的：观察低频电刺激对坐骨神经损伤大鼠不同类型骨骼肌纤维萎缩情况及内源性胰岛素样生长因子1表达的影响。 方法：将健康雄性SD大鼠随机分为3组,切断模型组和电刺激组大鼠左侧坐骨神经制备失神经支配模型,适应5 d后,对电刺激组大鼠损伤侧腓肠肌施以2 Hz的电刺激,2次/d,每次持续20 min,正常组和模型组常规饲养。30 d后,取大鼠腓肠肌腹部,检测其肌纤维直径和数量;免疫组织化学法检测肌组织中胰岛素样生长因子1的水平。 结果与结论：失神经支配后,大鼠腓肠肌Ⅰ、Ⅱ型肌纤维直径减小,Ⅰ型肌纤维数比例增大。与模型组比较,电刺激组大鼠腓肠肌Ⅰ、Ⅱ型肌纤维直径有所增大,尤以Ⅰ型肌纤维直径增大更明显(P < 0.05)。同时,电刺激组大鼠腓肠肌中胰岛素样生长因子1的表达也明显高于模型组(P < 0.05)。提示,2 Hz的电刺激可促进胰岛素样生长因子1的表达,减轻Ⅰ型肌纤维的萎缩。     

miRNA-206及miRNA-26a在周围神经卡压后骨骼肌纤维化过程中的表达

目的 探讨大鼠坐骨神经慢性卡压损伤后其支配的腓肠肌组织内miRNA-206、miRNA-26a的表达变化及其意义。方法 2020年5月至2020年7月，选取50只成年雄性SD大鼠；大鼠右侧后腿采用Mackinnon建立的坐骨神经卡压模型方法对坐骨神经行硅胶管卡压术，作为手术组（实验组）；对大鼠左侧后腿仅分离暴露坐骨神经，作为假手术组（对照组）。于卡压术后2、4、6、8、10周时间点随机取大鼠10只，取其双后腿腓肠肌，观察腓肠肌组织萎缩及纤维化程度，并行组织形态学观察，RT-PCR定量测定miRNA-206、miRNA-26a、转化生长因子-β（TGF-β）、Ⅰ型胶原蛋白（COL-Ⅰ）的表达。结果 坐骨神经慢性卡压损伤后，手术组与假手术组相比，腓肠肌组织湿重明显减轻，肌肉横截面积变小，肌肉组织胶原纤维增生，miRNA-206及miRNA-26a的表达先降低后升高，4周时表达最低，后表达逐渐升高；TGF-β及COL-Ⅰ含量升高，两组比较差异统计学意义（P＜0.05）。结论 周围神经慢性卡压损伤可致支配骨骼肌发生纤维化病变，TGF-β及COL-Ⅰ表达升高，miRNA-206及miRNA-26a在此过程中表达先降低后升高，提示miRNA-206及miRNA-26a在周围神经卡压致骨骼肌萎缩及纤维化过程中起到重要作用。     

Corticotropin releasing factor 2 receptor agonists reduce the denervation-induced loss of rat skeletal muscle mass and force and increase non-atrophying skeletal muscle mass and force

Of the two corticotropin releasing factor receptors known, corticotrophin releasing factor 2 receptor (CRF2R) is expressed in skeletal muscle. The function of this receptor in skeletal muscle is at present unknown. In order to better understand the role of the CRF2R in skeletal muscle, we treated rats with CRF2R agonists and evaluated the effect of these agents on normal and denervated muscle mass. Rats treated with the non-selective CRFR agonist, sauvagine, did not demonstrate any significant and consistent change in non-denervated and denervated fast twitch [tibialis anterior (TA) or extensor digitorum longus (EDL)] or slow/mixed twitch [medial gastrocnemius (MG) or soleus] fiber muscle mass. In adrenalectomized rats, sauvagine treatment resulted in no significant and consistent change in non-denervated fast or slow/mixed twitch fiber muscles but did cause a significant and consistent increase in denervated fast twitch (TA and EDL) but not slow/mixed twitch muscle mass. Interestingly adrenalectomy had no effect on the degree of muscle atrophy. Rats treated with the CRF2R selective agonist urocortin 2 demonstrated an increase in non-denervated and denervated fast and slow/mix twitch fiber muscle mass. The urocortin 2 induced increase in muscle mass was accompanied by an increase in muscle fiber cross-sectional area and muscle absolute force. These studies demonstrated that activation of the CRF2R decreased the level of skeletal muscle mass, force, and myocyte cross-sectional area loss resulting from sciatic nerve damage and increased the mass, force and myocyte cross-sectional area of normal (non-atrophying) skeletal muscle. In addition, we also observed that removal of the adrenals increased the effectiveness of the non-selective CRFR agonists sauvagine, presumably via the removal of the pro-atrophy influence of adrenal produced corticosteroids. These results demonstrate that pharmacological modulation of the CRF2R may be a viable method to treat skeletal muscle atrophy.     

Exercise improves skeletal muscle insulin resistance without reduced basal mTOR/S6K1 signaling in rats fed a high-fat diet

Exercise improves high-fat diet (HFD)-induced skeletal muscle insulin resistance, but the mechanism is unresolved. This study aims to explore whether the improvement in response to exercise is associated with mTOR/S6K1 signaling and whether the signaling changes are muscle-specific. Male SD rats (150–180 g) were used for this study. After the experimental period, 6 weeks of exercise improved HFD-impaired intraperitoneal glucose tolerance and insulin-stimulated 2-deoxyglucose uptake in soleus (SOL) and extensor digitorum longus (EDL) muscles. Furthermore, 6 weeks of the HFD resulted in a reduced type I fiber ratio of SOL, an increased type I ratio of EDL, and a reduced fiber size of EDL, whereas exercise increased type I fiber ratio of SOL as well as type I fiber cross-sectional areas of EDL. However, the HFD had a main effect on basal cytosolic phosphorylation of S6K1 on Thr³⁸⁹ content in SOL, which was also influenced by a significant interaction between the diet and exercise in EDL. Exercise had no direct effect on the basal phosphorylation of Akt on Ser⁴⁷³, mTOR on Ser²⁴⁴⁸, S6K1 on Thr³⁸⁹ content in SOL. On the contrary, exercise prevented HFD-induced decrease in basal phosphorylation of S6K1 on Thr³⁸⁹ content in EDL. These results indicate that 6 weeks of HFD and exercise lead to alterations in fiber type shift, fiber size, and basal phosphorylation of S6K1 on Thr³⁸⁹ content in a muscle-specific pattern. Exercise prevents HFD-induced skeletal muscle insulin resistance, which is not associated with a reduced basal phosphorylation of mTOR/S6K1 alteration in the muscles.     

外源性睫状神经营养因子干预缺损神经再生及运动功能的恢复*

背景：睫状神经营养因子作为生物活性因子家族的成员,因其生物活性的多效性而备受基础与临床研究的重视。 目的：探讨睫状神经营养因子对缺损神经再生及其运动功能恢复的影响及相关因素。 方法：40只大鼠建立高位神经缺损模型后随机数字表法均分成4组,3个实验组分别将不同质量浓度10,20,40 mg/L的外源性睫状神经营养因子液0.2 mL注入神经再生室内,对照组注入等量的生理盐水。两组干预后检测坐骨神经功能指数、神经肌肉动作电位、神经再生及其靶器官的形态学变化。 结果与结论：治疗后4周,各组坐骨神经功能指数差异无显著性意义(P > 0.05)。治疗后8,12周,各实验组的坐骨神经功能指数、运动神经传导速度、腓肠肌湿质量及截面积残存率均明显高于对照组(P < 0.05),各组神经远段再生的有髓神经纤维数量、直径、截面积及髓鞘厚度均小于自体神经近段(P < 0.05),其中以40 mg/L质量浓度指标变化最为显著(P < 0.05)。说明在修复缺损神经过程中,向由可降解生物膜形成的神经再生室内加入一定浓度的外源性睫状神经营养因子,对受损神经的结构再生与运动功能恢复有一定的促进作用。关键词：睫状神经营养因子;坐骨神经功能指数;运动神经传导速度;坐骨神经;神经再生 doi:10.3969/j.issn.1673-8225.2012.21.002     

Muscle-specific effects of hindlimb suspension and clenbuterol in mature male rats

Anabolic agents are useful tools for probing the mechanisms by which muscle fibers perceive and respond to disuse. beta(2)-Adrenergic agonists exert protective, and/or reparative, effects on atrophying muscle tissue. The effects of one such agent, clenbuterol (Cb), were examined on muscle mass, total protein content, and myofibrillar protein content in selected hindlimb muscles [adductor longus (ADL), extensor digitorum longus (EDL), plantaris (PLAN), soleus (SOL)] of mature male rats, under different loading conditions. Pair-fed rats were divided into four experimental groups: vehicle- and Cb-treated nonsuspended, vehicle- and Cb-treated hindlimb suspended (HLS). Experiments lasted 14 days, during which the rats received subcutaneous injections of 1 mg/kg Cb or 1 ml/kg vehicle. HLS induced significant atrophy in all muscles, except the EDL, in a generally fiber type-related pattern. However, myofibrillar protein content was affected in a more regional pattern. Cb treatment of nonsuspended rats induced hypertrophy in all muscles, in a generally uniform pattern. However, myofibrillar protein content was affected in a more fiber type-related pattern. Cb treatment of HLS rats reduced or eliminated HLS-induced atrophy in all muscles, in a muscle-specific pattern. Overall, the ADL and SOL were most susceptible to HLS-induced atrophy. The PLAN had the greatest magnitude of Cb-induced sparing of atrophy. The results show that, in mature male rats, Cb exerts anabolic effects that are load-dependent and muscle-specific. Responses to this drug cannot be reliably predicted by fiber-type composition alone.     

Ubiquitin targeting of rat muscle proteins during short periods of unloading

AIM: The ubiquitin-proteasome system is known to be involved in many situations leading to skeletal muscle atrophy. However, the cellular mechanisms triggering the atrophic process initiation are still poorly understood. For short periods of rat hindlimb unloading, we assessed the specific ubiquitin targeting of sarcoplasmic or myofibrillar proteins in slow and fast rat muscle types. METHODS: Adult Sprague Dawley rats were randomly assigned to three groups: control, hindlimb-unloaded for 4 days (HU4) and hindlimb-unloaded for 8 days (HU8). In fractionated extracts from soleus (SOL) and Extensor Digitorum Longus (EDL) muscles, the relative contents of free and conjugated ubiquitin were quantified by immunoblotting. RESULTS: Hindlimb unloading of short durations resulted in a preferential atrophy of slow-twitch fibres and bound ubiquitin levels were increased by 37 and 68% in the soleus myofibrillar fraction after respectively 4 and 8 days. The ubiquitin conjugation was shown to principally affect the high molecular weight proteins. Free and conjugated ubiquitin levels remained unchanged in sarcoplasmic fraction from SOL muscle after 8 days HU. For the fast muscle (EDL), ubiquitin contents were approximately twofold lower in control conditions, and did not significantly change during the hindlimb unloading periods considered. CONCLUSION: The postural SOL muscle was shown to contain higher constitutive sarcoplasmic ubiquitin levels than the phasic EDL. The high response to unloading of the slow twitch fibres rich SOL muscle was accompanied by a specific conjugation of its myofibrillar proteins that may participate in the initiation of skeletal muscle remodelling consequent to disuse.     

Overexpression of inducible 70-kDa heat shock protein in mouse improves structural and functional recovery of skeletal muscles from atrophy

Heat shock proteins play a key regulatory role in cellular defense. To investigate the role of the inducible 70-kDa heat shock protein (HSP70) in skeletal muscle atrophy and subsequent recovery, soleus (SOL) and extensor digitorum longus (EDL) muscles from overexpressing HSP70 transgenic mice were immobilized for 7 days and subsequently released from immobilization and evaluated after 7 days. Histological analysis showed that there was a decrease in cross-sectional area of type II myofiber from EDL and types I and II myofiber from SOL muscles at 7-day immobilization in both wild-type and HSP70 mice. At 7-day recovery, EDL and SOL myofibers from HSP70 mice, but not from wild-type mice, recovered their size. Muscle tetanic contraction decreased only in SOL muscles from wild-type mice at both 7-day immobilization and 7-day recovery; however, it was unaltered in the respective groups from HSP70 mice. Although no effect in a fatigue protocol was observed among groups, we noticed a better contractile performance of EDL muscles from overexpressing HSP70 groups as compared to their matched wild-type groups. The number of NCAM positive-satellite cells reduced after immobilization and recovery in both EDL and SOL muscles from wild-type mice, but it was unchanged in the muscles from HSP70 mice. These results suggest that HSP70 improves structural and functional recovery of skeletal muscle after disuse atrophy, and this effect might be associated with preservation of satellite cell amount.     

Effects of growth hormone on skeletal muscle. II. Studies on regeneration and denervation in adult rats

The effects of human recombinant growth hormone (rhGH) on regenerating skeletal muscle after ischaemic necrosis and on denervated skeletal muscle were studied in normal adult rats. One group of rats was treated with 4 IE rhGH daily by subcutaneous injections, while control rats were injected with saline. The treatment with rhGH resulted in increased levels of insulin-like growth factor-I (IGF-I) in serum. Ischaemic necrosis was achieved in the extensor digitorum longus (EDL) muscle by cutting the supplying vessels and nerve fascicles at the entrance into the muscle. The wet weight and DNA: protein ration in the regenerating muscle were determined 2 and 4 weeks after the operation. The weight of the regenerating muscles in the rats treated with rhGH during the period of study was larger than in the control rats, while the DNA:protein ratio did not differ significantly between the groups. Denervation of the EDL and soleus muscles followed by subsequent reinnervation was obtained by freezing the sciatic nerve with a forceps chilled in liquid nitrogen. Rats treated with rhGH during the period of denervation and reinnervation, i.e. during the 4 weeks after the freezing of the sciatic nerve, revealed increased weight of both the reinnervated and normal muscles compared to corresponding muscles of control rats. Denervation of the EDL and soleus muscles without subsequent reinnervation was achieved by cutting the sciatic nerve at the level of the thigh. Four weeks after denervation the muscles showed atrophy, mainly affecting type 2 fibres in the EDL muscle and both type 1 and type 2 fibres in the soleus muscle.     

Slow- and fast-twitch rat hind limb skeletal muscle phenotypes 8 months after spinal cord transection and olfactory ensheathing glia transplantation

Paralysed skeletal muscle of rats with spinal cord injury (SCI) undergoes atrophy and a switch in gene expression pattern which leads to faster, more fatigable phenotypes. Olfactory ensheathing glia (OEG) transplants have been reported to promote axonal regeneration and to restore sensory-motor function in animals with SCI. We hypothesized that OEG transplants could attenuate skeletal muscle phenotypic deterioration and that this effect could underlie the functional recovery observed in behavioural tests. A variety of morphological, metabolic and molecular markers were assessed in soleus (SOL) and extensor digitorum longus (EDL) muscles of spinal cord transected (SCT), OEG-transplanted rats 8 months after the intervention and compared with non-transplanted SCT rats and sham-operated (without SCT) controls (C). A multivariate analysis encompassing all the parameters indicated that OEG-transplanted rats displayed skeletal muscle phenotypes intermediate between non-transplanted and sham-operated controls, but different from both. A high correlation was observed between behaviourally tested sensory-motor functional capacity and expression level of slow- and fast-twitch hind limb skeletal muscle phenotypic markers, particularly the histochemical glycerol-3-phosphate dehydrogenase activity (−0.843, P < 0.0001) and the fraction of variant 2s of the slow regulatory myosin light chain isoform (0.848, P < 0.0001) in SOL. Despite the mean overall effect of OEG transplants in patterning skeletal muscle protein expression towards normal, in 6 out of 9 animals they appeared insufficient to overcome fibre type switching and to support a consistent and generalized long-term maintenance of normal skeletal muscle characteristics. The interplay of OEG and exercise-mediated neurotrophic actions is a plausible mechanism underlying OEG transplantation effects on paralysed skeletal muscle.     

Pathologic changes and contractile properties of the diaphragm in corticosteroid myopathy in hamsters: comparison to peripheral muscle

Corticosteroids have been shown to produce a myopathy of peripheral skeletal muscle, characterized predominantly by Type II fiber atrophy. To determine if similar histologic and histochemical changes occur in the diaphragm and whether the in vitro contractile properties of this muscle are adversely affected by steroids, we studied two groups of hamsters. The experimental group received triamcinolone while a control group received saline, both given daily for 3 wk as i.m. injections. Soleus (Sol) and extensor digitorum longus (EDL) muscles and costal diaphragm muscle sections were stained for histologic (hematoxylin and eosin, modified Gomori trichrome) and histochemical (myosin ATPase, succinate dehydrogenase [SDH]) analysis. Muscle fiber proportions and cross-sectional areas (CSA) were measured from myosin ATPase sections. In vitro studies of isometric contractions were carried out on small strips of costal diaphragm, measuring maximal isometric twitch (Pt) and tetanus (Po) tensions, time to peak tension (TTP), half relaxation time (1/2 RT), force-frequency relationship, and fatigue characteristics (60 Hz tetani; duty cycle, 0.5). Triamcinolone treatment resulted in no change in muscle fiber proportions. There was no effect on Type I fiber CSA; however, there was Type IIa (Sol, EDL) and Type IIb (diaphragm, EDL) fiber atrophy in triamcinolone-treated animals. Pt and Po (normalized for weight) of diaphragm strips were not different. There was a prolongation in TTP and 1/2 RT, a left shift in the force-frequency curve, and a reduced fatiguability of triamcinolone-treated diaphragm (P less than 0.05). We conclude that a steroid myopathy could be explained by a loss of muscle mass (Type IIb fiber atrophy) rather than an intrinsic impairment in contractile function.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of chronic corticosterone treatment on the morphology of rat neuromuscular junctions

This study examined the effects of chronic corticosterone (CORT) treatment on the morphology of two physiologically different muscles. Nerve terminals from the slow twitch soleus (SOL) and fast twitch extensor digitorum longus (EDL) of Fischer 344 rats were stained using the zinc iodide osmium (ZIO) technique. Nerve terminal area, perimeter, and longitudinal extent length were measured using computer-aided morphometry. Slow and fast muscle fibers from animals which received 5-10 mg CORT per day for 3 months were atrophied compared with controls. Treated animals failed to gain weight during the study, while controls gained 37%. Adrenal weights in treated animals were 30% less than controls, after correction for body weight. Morphological parameters for SOL nerve terminals were generally larger in the CORT group, while EDL nerve terminals from the CORT group did not differ significantly from controls. Soleus nerve terminal area was 43% greater, perimeter 14% longer, and longitudinal extent length 18% longer than the control nerve terminals. This study demonstrates a greater effect of CORT treatment on slow twitch muscle than has been demonstrated in previous studies. Changes in the nerve terminal morphology of the SOL were also greater than in previous studies and suggest that a functional adaptation or remodelling may occur following CORT treatment to maintain the neuromuscular interface during the enhanced catabolic effects of the steroid. These steroid-induced stress changes are similar in some respects to those observed in aging and disuse studies of the vertebrate neuromuscular junction. This suggests that glucocorticoid hormones may play an etiological role in the homeostasis of the neuromuscular junction in response to various stimuli.