不同部位骨骼肌失神经支配后超微结构变化的实验研究

目的：探讨长期失神经支配后萎缩骨骼肌神经修复手术疗效欠佳的机制。方法：12例臂丛神经损伤后1、2、3、6、12和18个月患者，术中切取小指展肌和肱二头肌的失神经骨骼肌，以相同部位的正常骨骼肌作对照，观察失神经骨骼肌超微结构和计数肌卫星细胞数量变化。结果：失神经支配后2个月，骨骼肌细胞的超微结构基本正常，肌纤维周围无明显增生的胶原纤维，可见到运动终板，肌卫星细胞数量多；6个月，肌丝断裂，排列紊乱现象明显增多，细胞核体积变小，染色加深，细胞核固缩，肌纤维周边出现较多的成纤维细胞和脂肪细胞以及增生的胶原纤维；12个月后，未见类似运动终板的结构，肌卫星细胞体积缩小，数量减少，小指展肌较肱二头肌中肌卫星细胞含量下降速度快。结论：失神经经支配晚期骨骼肌纤维中运动终板消失和胶原增生以及肌卫星细胞含量的迅速下降可能是影响疗效的主要因素之一。     

Functional and morphological motor regeneration after different periods of denervation and following microsurgical suture of the peroneal nerve. Experimental study in the rabbit.

The morphological and functional recovery of the peripheral nerve, motor endplate, and muscle has been studied in rabbits after different periods of denervation of the muscles and secondary suture of the supplying nerve, by electrophysiological (electromyography and electroneurography) and histological methods (electron microscopy, including freeze fracture techniques and histochemistry). In rabbit peroneal nerve, 10 months of denervation appears as the critical interval. Longer periods of denervation are not followed by a sufficient functional recovery.     

A scanning electron microscopical and morphometrical analysis of neuromuscular junctions in different muscle fiber types in the zebra finch and rat

The differences of neuromuscular junctions (NMJs) between different muscle fibers had been examined with scanning electron microscopy and analyzed morphometrically. The anterior and posterior latissimus dorsi muscles of the zebra finch were compared. The former consisted exclusively of slow tonic fibers and the latter of fast twitch fibers. The former had numerous, small NMJs. The synaptic depressions were small in number. The latter had a large NMJ. The synaptic depressions were large in number, and subsynaptic folds were found. The extensor digitorum longus and soleus muscles in the rat were also compared. The former consisted mostly of fast twitch fibers whereas the latter consisted of slow twitch fibers (75%) and fast twitch fibers (25%). NMJ of slow twitch fiber was small and the subsynaptic folds had sparse, narrow slit-like and pit-like openings. NMJ of fast twitch fiber was large and the subsynaptic folds had numerous, wide and slit-like openings.     

A rat model of the post-polio motor unit.

We examined the long-term effects of muscle usage on a rat model of the post-polio motor unit. Isometric tensions, type I and type II muscle fiber areas, the incidence of collateral sprouting, and motor endplate morphology were examined following 1, 3, 6, and 9 months of partial denervation in rat plantaris muscle. Full morphologic and functional stability of the expanded motor units occurred at 6 months post-partial denervation. Fiber hypertrophy was observed, possibly the result of compensatory work hypertrophy due to muscle overuse. Following 9 months of partial denervation and muscle overuse, the twitch and tetanic tensions and type I and type II muscle fiber areas were significantly reduced as compared to sham controls; angulated myofibers and group atrophy also were seen. The percent collateral sprouting, the number of terminal branches per endplate, and the endplate area were all increased, possibly a compensatory response to a decreased synthesis of neurotrophic factor(s) and/or transmitter-related components. These aging-like changes seem to occur earlier in chronically stressed, overenlarged, and overworked motor units.     

Reinnervation of the trapezius muscle

The eleventh cranial nerve shoulder syndrome, which results from denervation of the trapezius muscle, contributes significantly to the postoperative morbidity of radical neck dissections. Multiple techniques exist for the reinnervation of muscles that have injured motor nerves. Reinnervation of denervated trapezius muscles was examined in the New Zealand white rabbit by use of three techniques of reinnervation: (1) neuromuscular pedicle transfer of the accessory nerve from the trapezius muscle, (2) direct accessory nerve implantation, and (3) neuromuscular pedicle transfer of the accessory nerve from the sternocleidomastoid muscle. The reinnervated trapezius muscles were examined grossly by direct nerve stimulation, electrophysiologically by evoked electromyography, and histologically by enzymatic muscle staining and silver-reducing nerve staining. The gross, electrophysiologic, and histologic results confirmed successful reinnervation of the trapezius muscle within 6 weeks of operation. No significant difference was observed between the various techniques of reinnervation.     

Sprint-Interval Training Induces Heat Shock Protein 72 in Rat Skeletal Muscles

Previous studies have demonstrated that endurance exercise training increases the level of heat shock proteins (HSPs) in skeletal muscles. However, little attention has been drawn to the effects of high intensity-short duration exercise, or sprint- interval training (SIT) on HSP72 level in rat skeletal muscles. This study performed to test the hypothesis that the SIT would induce the HSP72 in fast and slow skeletal muscles of rats. Young male Wistar rats (8 weeks old) were randomly assigned to a control (CON) or a SIT group (n = 8/group). Animals in the SIT group were trained (1 min/sprint, 6~10 sets/day and 5~6 days/week) on a treadmill for 9 weeks. After the training period, HSP72 levels in the plantaris (fast) and soleus (slow) muscles were analyzed by Western blotting method. Enzyme activities (hexokinase, phosphofructokinase and citrate synthase) and histochemical properties (muscle fiber type compositions and cross sectional area) in both muscles were also determined. The SIT resulted in significantly (p < 0.05) higher levels of HSP72 in both the plantaris and soleus muscles compared to the CON group, with the plantaris producing a greater HSP72 increase than the soleus (plantaris; 550 ± 116%, soleus; 26 ± 8%, p < 0.05). Further, there were bioenergetic improvements, fast-to-slow shift of muscle fiber composition and hypertrophy in the type IIA fiber only in the plantaris muscle. These findings indicate that the SIT program increases HSP72 level of the rat hindlimb muscles, and the SIT-induced accumulation of HSP72 differs between fast and slow muscles.

Key Points

• There is no study about the effects of high intensity but short duration exercise, or sprint-interval training (SIT) on heat shock protein 72 (HSP72) level in skeletal muscles.
• The SIT program (≤ 10 min·day^-1) accumulated HSP72 in rat skeletal muscles.
• The SIT-induced accumulation of HSP72 in the plantaris (fast) muscle was drastic compared to the soleus (slow) muscle and accompanied with the improvements of enzyme activities, fast-to-slow shift within fast muscle fiber type and muscle hypertrophy.

Key words: Hindlimb, treadmill running, enzyme activity, fiber type shift, hypertrophy     

Histological study of muscle in the experimental hypophosphatemic rat

Using hypophosphatemic rat maintained on a low phosphate diet as a model for human rickets and osteomalacia, the skeletal muscle was histochemically and electron microscopically examined, in comparison with specimens obtained from normal control animals. In muscles obtained from hypophosphatemic animals, the type 2 muscle fibers were increased in number, and the type 1 fibers were atrophic. Electron microscopic studies revealed some atypical structures of mitochondria with fusion of cristae in the muscle spindles of intrafusal muscle fibers. The presynapse, the secondary cleft, and the endplate plasm were significantly atrophic in the extrafusal neuromuscular junction. Mitochondrial vacuolization was observed in the presynapse. These results indicated the presence of immature muscle fibers, dysfunction of the energy metabolism of the mitochondria and neurogenic disorders in hypophosphatemic muscles.     

Characterization of the train-of-four response in fast and slow muscles: effect of d-tubocurarine, pancuronium, and vecuronium

The in vivo cat soleus and gastrocnemius muscles were used to compare isometric contraction strength and the train-of-four (T4) response (2 Hz for 2 s) of two muscle types (fast and slow) during onset of competitive neuromuscular blockade in order to determine the extent of the correlation between twitch depression and T4 fade. Prior to drug administration the muscles that were studied differed significantly in that the T4 ratio was 1.0 in the gastrocnemius and only 0.87 in the soleus. Three competitive neuromuscular-blocking agents were compared: d-tubocurarine, pancuronium, and vecuronium. d-Tubocurarine was found to produce a close correlation between the degrees of twitch strength depression and T4 for both muscles. However, these muscles demonstrated significantly different ED50 values (105 micrograms/kg for gastrocnemius, 150 micrograms/kg for soleus). Pancuronium also produced a similar relationship between twitch strength depression and T4 decrement for each muscle. In this case, however, there was little difference in their ED50 values for twitch depression (11.5 micrograms/kg for gastrocnemius, 13 micrograms/kg for soleus). The effects of vecuronium were quite different from the other two muscle relaxants. Although vecuronium produced a comparable correlation between twitch tension and T4 fade in fast muscle, no such relationship was found to exist in slow muscle. Even when the twitch strength was blocked to 18% of control, the soleus T4 response was depressed to only 75% of control. These results highlight major differences among competitive neuromuscular-blocking agents and suggest multiple sites of action.     

Growth factor may decrease muscle atrophy secondary to denervation

Despite modern microsurgical techniques, functional outcomes following brachial-plexus reconstruction and peripheral-nerve repair are usually unsatisfactory, because irreversible muscle atrophy develops before reinnervation occurs. Insulin growth factor-1 (IGF-1) has been shown to improve muscle regeneration after injury, and may have a role in muscle preservation following denervation. This study evaluated the histologic, immunohistochemical, and electrophysiologic differences between normal and denervated muscle over an 8-week time period, and also evaluated the effects of injecting IGF-1 into denervated muscle. Denervated mice gastrocnemius muscles demonstrated a decrease in muscle diameter, a decrease in muscle weight, early nuclear proliferation, and a decrease in fast twitch and maximum tetanic strength, compared to normal gastrocnemius muscle up to 8 weeks following denervation. Four weeks after denervated muscle was injected with IGF-1 at time zero, however, relative preservation of muscle diameter and weight, and maintenance of electrophysiologic contractile properties were observed. These preliminary data suggest that IGF-1 may prevent muscle atrophy secondary to denervation.     

Effects of testosterone replacement therapy on skeletal muscle after spinal cord injury

STUDY DESIGN: Randomized control. OBJECTIVE: To examine the effects of testosterone replacement therapy (TRT) on skeletal muscle 11 weeks after complete SCI. SETTING: Athens, Georgia USA. METHODS: Soleus (SOL), gastrocnemius (GA), tibialis anterior (TA), vastus lateralis (VL) and triceps brachii (TRI) muscles were taken from twelve young male Charles River rats 11 weeks after complete SCI (T-9 transection, n=8) or sham surgery (n=4). Rats received either TRT (two 5 cm capsules, n=4) or empty capsules (n=8) implanted at surgery. Muscle samples were sectioned and fibers analyzed qualitatively for myosin ATPase and quantitatively for succinate dehydrogenase (SDH), alpha-glycerol-phosphate dehydrogenase (GPDH) and actomyosin ATPase (qATPase) activities using standard techniques. RESULTS: SCI decreased average fiber size (49+/-4%) in affected muscles and the percentage of slow fibers in SOL (93+/-3% to 17+/-2%). In addition, there was a decrease in SDH and an increase in GPDH and qATPase activities across the four hind-limb muscles of the SCI animals. Fiber size in the TRI was increased (31+/-2%) by SCI while enzyme activities were not altered. Average fiber size across the four hind limb muscles was decreased by only 30% in TRT SCI animals and their SOL contained 39+/-2% slow fibers. TRT also attenuated changes in enzyme activities. There was no effect of TRT on the TRI relative to SCI. CONCLUSIONS: TRT was effective in attenuating alterations in myofibrillar proteins during 11 weeks of SCI in affected skelatal muscles. SPONSORSHIP: Supported by a grant from The National Institutes of Health (HD-33738) and HD-37645 to KV, and HD-39676 to GAD.     

Duration of succinylcholine and vecuronium blockade but not potency correlates with the ratio of endplate size to fibre size in seven muscles in the goat

Purpose

Muscles differ in their response to neuromuscular relaxants. This study investigated whether (1) the relative responses of muscles is inverted between succinylcholine (SUX) and vecuronium (VEC), and (2) differences in dose-response or duration of action are related to the morphology of fibres, endplates and acetylcholine receptors (AChR) in muscles.

Methods

In goats during thiopentone anaesthesia, the evoked EMC response to indirect train-of-four stimulation was monitored and the cumulative dose-response curves and duration of action of SUX and VEC in the diaphragm, cricoary-tenoideus dorsalis, thyroarytenoideus, transversus abdominis, rectus abdominis, soleus and gastrocnemius muscles were determined and related to their fibre composition, fibre size, endplate size, endplate to fibre size ratio, AChR number or AChR density by regression analysis.

Results

There were no differences in the ED₅₀s of SUX [range, 119 ± 11 (SE) to 159 ± 20 μg · kg^?1] or VEC [range, 2.8 ± 0.2 to 3.7 ± 0.8 μg · kg^?1] among muscles. With either drug, duration to 25% or 50% T₁ recovery was shortest at the laryngeal muscles and longest at abdominal muscles (P = 0.0001), and correlated directly with fibre size (r ≥ 0.40: P < 0.004) and inversely with the endplate to fibre size ratio (r ≥ 0.40; P < 0.008).

Conclusion

The results show that (I) the relative responses of muscles do not differ between depolarizing and non-depolarizing relaxants; (2) the duration of blockade is shorter in muscles composed of small fibres with large endplates relative to fibre size; and (3) there is no relation between fibre type composition and sensitivity to muscle relaxants.     

Insulin growth factor-1 decreases muscle atrophy following denervation

Despite modern microsurgical techniques for nerve repair, functional outcome following proximal injury is often unsatisfactory because irreversible muscle atrophy may develop before reinnervation occurs. Because insulin growth factor-1 (IGF-1) has been shown to improve muscle regeneration after injury, and may have a role in muscle preservation following denervation, the purpose of this investigation was to evaluate the histological, immunohistochemical, and electrophysiological differences between normal, denervated, and IGF-1-injected denervated muscle over an 8-week period. Denervated mice gastrocnemius muscles demonstrated a decrease in muscle weight, a decrease in myofiber diameter, an absence of muscle regeneration, an early increase in the number of neuromuscular junctions (NMJs), and a decrease in fast-twitch and maximum tetanic strength as compared to normal muscle up to 8 weeks following denervation. IGF-1-injected denervated muscle, on the other hand, sustained muscle diameter and muscle weight, maintained a smaller number of NMJs, and relatively sustained fast-twitch and maximum tetanic strength as compared to normal muscle over 8 weeks. These data suggest that IGF-1 may help prevent muscle atrophy and secondary functional compromise after denervation.     

Effects of sepsis on the neuromuscular blocking actions of d-tubocurarine on rat adductor and abductor laryngeal muscles

Purpose

We evaluated the effects of sepsis on the neuromuscular blocking actions of d-tubocurarine (dTc) in the lateral cricoarytenoid (LCA) and posterior cricoarytenoid (PCA) muscles, an adductor muscle and an abductor muscle of the vocal cords, respectively, in vitro.

Methods

Sepsis was induced in rats by cecal ligation and puncture (CLP) to elicit panperitonitis. Electromyograms (EMGs) and endplate potentials (EPPs) were recorded from the LCA and PCA muscles of CLP-operated septic rats and sham-operated nonseptic rats, using extracellular and intracellular microelectrodes, respectively.

Results

EMG and EPP (amplitude and quantum content) were depressed by dTc, but the dTc-induced neuromuscular blocking effects were attenuated by sepsis. The suppressive effects of dTc on EMG and EPP (amplitude and quantum content) were less intense in the LCA muscle than in the PCA muscle under both sepsis and nonsepsis conditions.

Conclusion

Our study shows that sepsis has a depressive effect on dTc-induced neuromuscular blocking actions at both the adductor and abductor muscles of vocal cords in the larynx.     

Effects of Succinylcholine Chloride on the Response of Fast and Slow Muscle in the Cat

Fast and slow muscle fibres differ histochemically, electrophysiologically and pharmacologically. In vivo, the effect of 0.05, 0.075 and 0.1 mg X kg-1 succinylcholine on the response of the indirectly stimulated gastrocnemius (fast) and soleus muscle (slow) to single, train-of-four and tetanic stimuli was studied. There was a significant difference between the response of the two muscles. Maximum twitch suppression occurred 2 min after injection and was more significant in the gastrocnemius than the soleus. The duration of the neuromuscular blockade was 9 min or more in both groups. The train-of-four ratio dropped below 0.7 in the gastrocnemius preparation at all doses and in the soleus when 0.1 mg X kg-1 succinylcholine was used. Sustained tetanus was achieved in both muscles at 5 and 10 min, respectively. There was evidence of fatigue in the soleus muscle at the 5-min observation suggestive of the presence of a phase II block, a phenomenon not observed in the gastrocnemius.     

Mechanism of the differential sensitivity in the rat adductor and abductor laryngeal muscles to a non-depolarizing neuromuscular blocker

We have compared the neuromuscular blocking effects of tubocurarine at pre- and postsynaptic sites in the lateral cricoarytenoid muscle (LCA) (one of the adductor muscles of the vocal cords) and in the posterior cricoarytenoid muscle (PCA) (sole abductor muscle of the vocal cords) of the rat. Fine wire electrodes were inserted into both muscles and evoked compound electromyographic (EMG) responses measured by supramaximal stimulation of the recurrent laryngeal nerves. End-plate potentials (EPP), mean quantal content and carbachol sensitivity to tubocurarine in both muscles were measured using intracellular microelectrodes. Tubocurarine produced a concentration-dependent reduction in the EMG responses, EPP amplitude, mean quantal content and carbachol sensitivity. The LCA muscle was more resistant to tubocurarine than the PCA muscle in EPP amplitude, mean quantal content and carbachol sensitivity, suggesting unequal pre- and postsynaptic sensitivity for inhibition of elicited acetylcholine release, reduction in EPP amplitude and loss of evoked muscle action potentials. Examination of muscle fibre composition demonstrated that the LCA muscle contained a significantly higher fraction of slow twitch muscle fibres than PCA muscle. However, the sizes of the fibres were similar in both muscles. We conclude that the mechanism of unequal sensitivity to a non-depolarizing neuromuscular blocker in the LCA and PCA muscles may be explained by differential sensitivities at the pre- and postsynaptic sites of the neuromuscular junction.      

Electromyographic findings in patients with low back pain due to unsuspected primary and metastatic spinal or paraspinal muscle disease

Electromyographic studies were performed on 16 patients with intractable low back pain and no antecedent history of malignancy or metastatic disease. In each case, electromyographic evidence of severe segmental denervation limited to the paraspinal muscles innervated by the posterior primary rami was found. Subsequent diagnostic studies in each patient revealed a primary neoplasm or tumor metastasis as the source of pain. Applying current knowledge of neuromuscular physiology, the electromyograph may prove to be a valuable aid to the early detection of remote metastasis to the spine and paraspinal muscle structures.     

Respiratory muscle fibres: specialisation and plasticity

Skeletal muscles are composed of fibres of different types, each type being identified by the isoform of myosin heavy chain which is expressed as slow 1, fast 2A, fast 2X, and fast 2B. Slow fibres are resistant to fatigue due to their highly oxidative metabolism whereas 2X and 2B fibres are easily fatiguable and fast 2A fibres exhibit intermediate fatigue resistance. Slow fibres and fast fibres are present in equal proportions in the adult human diaphragm while intercostal muscles contain a higher proportion of fast fibres. A small fibre size, abundance of capillaries, and a high aerobic oxidative enzyme activity are typical features of diaphragm fibres and give them the resistance to fatigue required by their continuous activity. Because of their fibre composition, intercostal muscles are less resistant to fatigue. The structural and functional characteristics of respiratory muscle fibres are not fixed, however, and can be modified in response to several physiological and pathological conditions such as training (adaptation to changes in respiratory load), adaptation to hypoxia, age related changes, and changes associated with respiratory diseases. The properties of respiratory muscle fibres can also be modified by pharmacological agents such as beta2 agonists and corticosteroids used for the treatment of respiratory diseases.     

Coexistence of fast and slow myosin isozymes in human external urethral sphincter. A preliminary report

Human external urethral sphincter muscle was isolated for biochemical research. Myosin samples were prepared and pyrophosphate gel electrophoresis and two-dimensional electrophoresis were performed. Assignment in pyrophosphate gel of myosin isozymes of human external urethral sphincter was carried out by making comparisons with those from human rectus abdominis muscle. Myosin light chains in human external urethral sphincter were identified using two-dimensional electrophoresis. Human external urethral sphincter, similar to other voluntary muscles, is composed of fast and slow twitch muscle fibers, since fast and slow myosin components were shown in both pyrophosphate gel and two-dimensional electrophoretograms.     

The characteristic phenotype of the masseter muscle fibers is established after birth]

Muscle biopsies were taken from the superficial portion of the M. masseter in 10 foetuses (aged between 12 and 38 weeks), in a child of 18 months and in an adult without any neuromuscular disease. Serial frozen sections were processed for immunocytochemistry using antibodies specific for the embryonic, foetal, slow and fast myosin heavy chains (MHCs). Diameter of the different types of fibers were measured with a Leitz ASM 68 K; the results have been expressed as average diameters and histograms. During foetal development, the masseter is formed from two successive generations of muscle fibers in a manner very similar to that which has been previously described for other skeletal muscles. After birth, a particular phenotype appears. This phenotype is characterised by the persistence of embryonic and foetal MHCs and by the presence of two distinct populations of fibers: small diameter fibers which coexpress embryonic, foetal and fast myosin isoforms but never express the slow MHC; large diameter fibers which express slow myosin either exclusively or in variable associations with the other isoforms.     

Fast and slow myosin as markers of muscle regeneration in mangled extremities: a pilot study

Mangled extremities were classically managed by amputation. But over the past few decades, with the advancement in surgical techniques, an increased number of limb salvages have been possible. As muscles usually get damaged in such grievous injuries, a thorough understanding of muscle regeneration may give a better insight into muscle healing in these injuries. Muscles are composed of slow and fast fibers which can be represented by slow and fast myosin, respectively. There are some animal studies which reported differential regeneration of slow and fast muscle fibers during muscle healing. We conducted this pilot study to find out whether the same holds true for muscle healing in mangled extremities also. This pilot study is designed in 15 patients with lower limb mangled extremities presenting to trauma center of PGIMER, Chandigarh, who were operated within 24 h of injury to see whether muscle healing in mangled extremities follows the same pattern. Biopsies were taken during initial surgery conducted within 24 h of injury and on the 7th day of injury when patient was posted again for secondary wound closure procedure or revision amputation. The biopsy samples were subjected to histopathological and immunohistochemistry examination using antibodies against fast and slow myosin. We found that the regenerating muscle fibers in the biopsy sample taken on the 7th day of injury showed only slow muscle fibers with the absence of fast muscle fibers when compared with the initial biopsy results showing differential regeneration of slow muscle fibers.