Electrophysiological subtypes and prognosis of Guillain–Barré syndrome in Northeastern China

Introduction: The dystrophic features in hindlimb skeletal muscles of female mdx mice are unclear. Methods: We analyzed force‐generating capacity and force decline after lengthening contraction‐induced damage (fragility). Results: Young (6‐month‐old) female mdx mice displayed reduced force‐generating capacity (?18%) and higher fragility (23% force decline) compared with female age‐matched wild‐type mice. These 2 dystrophic features were less accentuated in young female than in young male mdx mice (?32% and 42% force drop). With advancing age, force‐generating capacity decreased and fragility increased in old (20 month) female mdx mice (?21% and 57% force decline), but they were unchanged in old male mdx mice. Moreover, estradiol treatment had no effect in old female mdx mice. Conclusions: Female gender–related factors mitigate dystrophic features in young but not old mdx mice. Further studies are warranted to identify the beneficial gender‐related factor in dystrophic muscle. Muscle Nerve, 2013     

Use of evans blue dye to compare limb muscles in exercised young and old mdx mice

Evans blue dye (EBD) is used to mark damaged and permeable muscle fibers in mouse models of muscular dystrophy and as an endpoint in therapeutic trials. We counted EBD‐positive muscle fibers and extracted EBD from muscles sampled throughout the hindlimbs in young adult and old mdx mice to determine if the natural variability in morphology would allow measurement of a functional improvement in one limb compared to the contralateral limb. Following one bout of rotarod or treadmill exercise that greatly increased serum creatine kinase levels, the number of EBD⁺ muscle fibers in 12–19‐month‐old mdx mice increased 3‐fold, EBD in the muscles increased, and, importantly, contralateral pairs of muscles contained similar amounts of EBD. In contrast, the intra‐ and interlimb amounts of EBD in 2–7‐month‐old mdx mice were much too variable. A therapeutic effect can more readily be measured in old mdx mice. These results will be useful in the design of therapy protocols using the mdx mouse. Muscle Nerve, 2010     

Characterization of neuromuscular synapse function abnormalities in multiple Duchenne muscular dystrophy mouse models

Duchenne muscular dystrophy (DMD) is an X‐linked myopathy caused by dystrophin deficiency. Dystrophin is present intracellularly at the sarcolemma, connecting actin to the dystrophin‐associated glycoprotein complex. Interestingly, it is enriched postsynaptically at the neuromuscular junction (NMJ), but its synaptic function is largely unknown. Utrophin, a dystrophin homologue, is also concentrated at the NMJ, and upregulated in DMD. It is possible that the absence of dystrophin at NMJs in DMD causes neuromuscular transmission defects that aggravate muscle weakness. We studied NMJ function in mdx mice (lacking dystrophin) and wild type mice. In addition, mdx/utrn^+/? and mdx/utrn^?/? mice (lacking utrophin) were used to investigate influences of utrophin levels. The three Duchenne mouse models showed muscle weakness when comparatively tested in vivo, with mdx/utrn^?/? mice being weakest. Ex vivo muscle contraction and electrophysiological studies showed a reduced safety factor of neuromuscular transmission in all models. NMJs had ~ 40% smaller miniature endplate potential amplitudes compared with wild type, indicating postsynaptic sensitivity loss for the neurotransmitter acetylcholine. However, nerve stimulation‐evoked endplate potential amplitudes were unchanged. Consequently, quantal content (i.e. the number of acetylcholine quanta released per nerve impulse) was considerably increased. Such a homeostatic compensatory increase in neurotransmitter release is also found at NMJs in myasthenia gravis, where autoantibodies reduce acetylcholine receptors. However, high‐rate nerve stimulation induced exaggerated endplate potential rundown. Study of NMJ morphology showed that fragmentation of acetylcholine receptor clusters occurred in all models, being most severe in mdx/utrn^?/? mice. Overall, we showed mild ‘myasthenia‐like’ neuromuscular synaptic dysfunction in several Duchenne mouse models, which possibly affects muscle weakness and degeneration.     

Effect of voluntary physical activity initiated at age 7 months on skeletal hindlimb and cardiac muscle function in mdx mice of both genders

Introduction: The effects of voluntary activity initiated in adult mdx (C57BL/10ScSc‐DMD^mdx/J) mice on skeletal and cardiac muscle function have not been studied extensively. Methods: We studied the effects of 3 months of voluntary wheel running initiated at age 7 months on hindlimb muscle weakness, increased susceptibility to muscle contraction?induced injury, and left ventricular function in mdx mice. Results: We found that voluntary wheel running did not worsen the deficit in force‐generating capacity and the force drop after lengthening contractions in either mdx mouse gender. It increased the absolute maximal force of skeletal muscle in female mdx mice. Moreover, it did not affect left ventricular function, structural heart dimensions, cardiac gene expression of inflammation, fibrosis, or remodeling markers. Conclusion: These results indicate that voluntary activity initiated at age 7 months had no detrimental effects on skeletal or cardiac muscles in either mdx mouse gender. Muscle Nerve 52 : 788–794, 2015     

Exercise increases utrophin protein expression in the mdx mouse model of Duchenne muscular dystrophy

Introduction: Duchenne muscular dystrophy (DMD) is a lethal genetic disease caused by mutations in the dystrophin gene resulting in chronic muscle damage, muscle wasting, and premature death. Utrophin is a dystrophin protein homologue that increases dystrophic muscle function and reduces pathology. Currently, no treatments that increase utrophin protein expression exist. However, exercise increases utrophin mRNA expression in healthy humans. Therefore, the purpose was to determine whether exercise increases utrophin protein expression in dystrophic muscle. Methods: Utrophin protein was measured in the quadriceps and soleus muscles of mdx mice after 12 weeks of voluntary wheel running exercise or sedentary controls. Muscle pathology was measured in the quadriceps. Results: Exercise increased utrophin protein expression 334 ± 63% in the quadriceps relative to sedentary controls. Exercise increased central nuclei 4 ± 1% but not other measures of pathology. Conclusions: Exercise may be an intervention that increases utrophin expression in patients with DMD. Muscle Nerve 49 : 915–918, 2014     

Functional in situ assessment of muscle contraction in wild‐type and mdx mice

Introduction: Reports of muscle testing are frequently limited to maximal force alone. The experiments reported here show that force generation and relaxation rates can be obtained from the same experiments and provide a more complete functional characterization. Methods: Partial in situ testing was performed on the tibialis anterior of young wild‐type (WT) mice, young mdx mice, and old mdx mice. Force, force generation rate, and relaxation rates were measured during a fatigue test, 2 frequency–force tests, and a passive tension test. Results: We measured increased force but decreased force generation rate in WT compared with mdx muscles, and increased force but decreased relaxation rate of old compared with young mdx muscles. Young mdx muscles were the most sensitive to increases in passive tension. Conclusions: These measurements offer an improved understanding of muscle capability and are readily acquired by further analysis of the same tests used to obtain force measurements. Muscle Nerve 53: 260–268, 2016     

Effect of constitutive inactivation of the myostatin gene on the gain in muscle strength during postnatal growth in two murine models

Introduction: The effect of constitutive inactivation of the gene encoding myostatin on the gain in muscle performance during postnatal growth has not been well characterized. Methods: We analyzed 2 murine myostatin knockout (KO) models, (i) the Lee model (KO^Lee) and (ii) the Grobet model (KO^Grobet), and measured the contraction of tibialis anterior muscle in situ. Results: Absolute maximal isometric force was increased in 6‐month‐old KO^Lee and KO^Grobet mice, as compared to wild‐type mice. Similarly, absolute maximal power was increased in 6‐month‐old KO^Lee mice. In contrast, specific maximal force (relative maximal force per unit of muscle mass was decreased in all 6‐month‐old male and female KO mice, except in 6‐month‐old female KO^Grobet mice, whereas specific maximal power was reduced only in male KO^Lee mice. Conclusions: Genetic inactivation of myostatin increases maximal force and power, but in return it reduces muscle quality, particularly in male mice. Muscle Nerve 55 : 254–261, 2017     

Physical exercise during muscle regeneration improves recovery of the slow/oxidative phenotype

Introduction: As skeletal muscle mass recovery after extensive injury is improved by contractile activity, we explored whether concomitant exercise accelerates recovery of the contractile and metabolic phenotypes after muscle injury. Methods: After notexin‐induced degeneration of a soleus muscle, Wistar rats were assigned to active (running exercise) or sedentary groups. Myosin heavy chains (MHC), metabolic enzymes, and calcineurin were studied during muscle regeneration at different time points. Results: The mature MHC profile recovered earlier in active rats (21 days after injury) than in sedentary rats (42 days). Calcineurin was higher in the active degenerated than in the sedentary degenerated muscles at day 14. Citrate synthase and total lactate dehydrogenase (LDH) activity decreased after injury and were similarly recovered in both active and sedentary groups at 14 or 42 days, respectively. H‐LDH isozyme activity recovered earlier in the active rats. Conclusions: Exercise improved recovery of the slow/oxidative phenotype after soleus muscle injury. Muscle Nerve 55 : 91–100, 2017     

Gender differences in contractile and passive properties of mdx extensor digitorum longus muscle

Introduction: Duchenne muscular dystrophy (DMD) is a severe, muscle‐wasting disease caused by mutations in the dystrophin gene. The mdx mouse is the first and perhaps the most commonly used animal model for study of DMD. Both male and female mdx mice are used. However, it is not completely clear whether gender influences contraction and the passive mechanical properties of mdx skeletal muscle. Methods: We compared isometric tetanic forces and passive forces of the extensor digitorum longus muscle between male and female mdx mice. Results: At age 6 months, female mdx mice showed better‐preserved specific tetanic force. Interestingly, at 20 months of age, female mdx muscle appeared stiffer. Conclusions: Our results suggest that gender may profoundly influence physiological measurement outcomes in mdx mice. Gender should be considered when using the mdx model. Muscle Nerve, 2012     

Evidence of mdx mouse skeletal muscle fragility in vivo by eccentric running exercise

Duchenne muscular dystrophy is an X-linked devastating disease due to the lack of expression of a functional dystrophin. Unfortunately, the dystrophin-deficient mdx mouse model does not present clinical signs of dystrophy before the age of 18 months, and the role of dystrophin in fiber integrity is not fully understood. The fragility of the skeletal muscle fibers was investigated in transgenic mice expressing β-galactosidase under the control of a muscle specific promoter. Adult mdx/β-galactosidase (dystrophin-negative) and normal/β-galactosidase (dystrophin-positive) mice were submitted to one short session of eccentric, downhill running exercise. The leakage of muscle enzymes creatine kinase and β-galactosidase was investigated before, 1 h after, and 3 days after the running session. A significant and transient rise in the level of these enzymes was noted in the serum of mdx mice following the exercise session. Thus, the lack of dystrophin in the mdx model led to local microdamages to the exercised muscle allowing leakage of proteins from the fibers. The peak leakage was transient, suggesting that muscle fiber lesions were rapidly repaired following this short, noninvasive eccentric running session. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:567–576, 1998.     

Effects of a CRF2R agonist and exercise on mdx and wildtype skeletal muscle

Corticotrophin-releasing factor 2 receptor (CRF2R) agonists prevent muscle atrophy due to immobilization, denervation, and corticosteroid-induced muscle atrophy in wildtype mice. We hypothesized that a CRF2R agonist will increase skeletal muscle mass in mdx mice. Mdx (C57BL/10ScSn-Dmd(mdx)) and wildtype (C57BL/6) mice were divided into four groups: sedentary placebo, sedentary CRF2R agonist, exercised placebo, and exercised CRF2R agonist. Mice exercised on a treadmill twice weekly for 30 min (8-12 m/min, 8 weeks). Muscle and heart weights, serum creatine kinase, and gamma-glutamyltransferase activities were measured. The CRF2R agonist increased extensor digitorum longus and soleus muscle weights (P < 0.05) in wildtype and mdx mice. Sedentary mdx CRF2R and exercised mdx placebo mice had lower serum creatine kinase activity than sedentary mdx placebo mice. CRF2R-treated mice had decreased heart weights compared to placebo-treated mice. We conclude that CRF2R agonists should be further evaluated as a potential therapy for dystrophinopathies.     

Exercise-induced muscle growth is muscle-specific and age-dependent

Introduction: Sarcopenia, and the importance of satellite cells (SCs) in muscle growth led us to examine the effects of exercise and age on SC activation and gene expression. Methods: Eight‐ and 18‐month‐old mice were either sedentary or underwent 3 weeks of exercise (N = 24). Body mass, distance traveled, and grip strength were recorded at weekly intervals. The extensor digitorum longus (EDL), tibialis anterior (TA), gastrocnemius (GAST), and quadriceps (QUAD) muscles were analyzed along with muscle fiber area, SC activation, neuronal nitric oxide synthase (NOS‐I), MyoD, and myostatin protein content. Results: Older mice demonstrated decreased body mass, grip strength, and fiber area, but these changes were not affected by exercise. The QUAD muscle from young mice demonstrated an exercise‐induced increase in SC activation and NOS‐I and downregulation of myostatin. Conclusions: Exercise‐induced activation of SCs and regulation of gene expression are muscle‐specific and age‐dependent. Perturbed sensitivity to exercise in older mice provides insight into sarcopenia and potential treatments. Muscle Nerve, 2011     

Statin-associated changes in skeletal muscle function and stress response after novel or accustomed exercise

Introduction: The most common side effect of statins, myopathy, is more likely in exercisers. We investigated the interaction of statin treatment with novel vs. accustomed exercise on muscle function, heat shock protein (Hsp) expression, and caspase activation. Methods: Mice received daily cerivastatin or saline for 2 weeks, with/without wheel running (RW) (novel/sedentary). Accustomed groups completed 2 weeks of RW before statins. At 4 weeks, plantarflexor isometric force, Hsp25, αB‐crystallin, caspase‐3 and ‐9, and plasma creatine kinase (CK) were quantified. Results: Statins reduced force in sedentary and novel groups, compared with saline, by 15% and 27%, respectively. Muscle fatigability increased 21% and 30% with statins compared with saline in sedentary and novel groups, respectively. Accustomed exercise prevented statin‐associated force loss and increased fatigability. CK did not correlate with functional outcomes. RW increased Hsp protein in all groups. Conclusion: Our results suggest that exercise prior to statin treatment can protect against decrements in muscle function. Muscle Nerve 2011     

An octaguanidine-morpholino oligo conjugate improves muscle function of mdx mice

Introduction: Skeletal muscles of mdx mice lack functional levels of dystrophin due to a mutation in Dmd exon 23. Morpholino antisense oligomers can induce expression of a truncated dystrophin by redirecting splicing to skip processing of exon 23. Methods: We tested whether systemic administration of Vivo‐Morpholino, an octaguanidine delivery moiety–Morpholino conjugate that targets exon 23 (VMO23), restored function to muscles of mdx mice. Results: Extensor digitorum longus (EDL) muscles of mdx mice were weaker, less powerful, and showed greater functional deficits after eccentric contractions than normal. VMO23 treatment normalized EDL force and power of mdx mice and eliminated their exaggerated sensitivity to eccentric contractions. Diaphragm muscle strips from mdx mice also produced lower‐than‐normal force and power, and these variables were restored to normal, or near‐normal, levels by VMO23 treatment. Conclusion: These results provide a functional basis for continuing development of VMO23 as a treatment for Duchenne muscular dystrophy. Muscle Nerve, 2011     

Truncated dystrophins can influence neuromuscular synapse structure

Duchenne muscular dystrophy (DMD) is characterized by muscle degeneration and structural defects in the neuromuscular synapse that are caused by mutations in dystrophin. Whether aberrant neuromuscular synapse structure is an indirect consequence of muscle degeneration or a direct result of loss of dystrophin function is not known. Rational design of truncated dystrophins has enabled the design of expression cassettes highly effective at preventing muscle degeneration in mouse models of DMD using gene therapy. Here we examined the functional capacity of a minidystrophin (minidysGFP) and a microdystrophin (microdystrophin^ΔR4–R23) transgene on the maturation and maintenance of neuromuscular junctions (NMJ) in mdx mice. We found that minidysGFP prevents fragmentation and the loss of postsynaptic folds at the NMJ. In contrast, microdystrophin ^ΔR4–R23 was unable to prevent synapse fragmentation in the limb muscles despite preventing muscle degeneration, although fragmentation was observed to temporally correlate with the formation of ringed fibers. Surprisingly, microdystrophin^ΔR4–R23 increased the length of synaptic folds in the diaphragm muscles of mdx mice independent of muscle degeneration or the formation of ringed fibers. We also demonstrate that the number and depth of synaptic folds influences the density of voltage-gated sodium channels at the neuromuscular synapse in mdx, microdystrophin^ΔR4–R23/mdx and mdx:utrophin double knockout mice. Together, these data suggest that maintenance of the neuromuscular synapse is governed through its lateral association with the muscle cytoskeleton, and that dystrophin has a direct role in promoting the maturation of synaptic folds to allow more sodium channels into the junction.     

Clenbuterol reduces degeneration of exercised or aged dystrophic (mdx) muscle

Evidence of dystrophic muscle degeneration in the hind limb muscles of young (20-week-old) treadmill-exercised or aged (87-week-old) sedentary mdx mice was greatly reduced by treatment with clenbuterol, a beta(2)-adrenoceptor agonist. Daily treadmill exercise for 10 weeks increased the size of regions within the mdx plantaris but not the soleus or gastrocnemius muscles, in which necrotic muscle fibers or the absence of fibers was observed. Clenbuterol reduced the size of these abnormal regions from 21% of total muscle cross-sectional area to levels (4%) found in sedentary mdx mice. In addition, the muscles obtained from aged clenbuterol-treated mdx or wild-type mice did not display the extensive fibrosis or fiber loss observed in untreated mdx mice. These observations are consistent with a mechanism of dystrophic muscle degeneration caused by work load-induced injury that is cumulative with aging and is opposed by beta(2)-adrenoceptor activation. Optimization of beta(2)-agonist treatment of muscular dystrophy in mdx mice may lead to a useful therapeutic modality for human forms of the disease.     

Combined XIL‐6R and urocortin‐2 treatment restores MDX diaphragm muscle force

Introduction: Duchenne muscular dystrophy (DMD) is characterized by progressive muscle degeneration leading to immobility, respiratory failure, and premature death. As chronic inflammation and stress are implicated in DMD pathology, the efficacy of an anti‐inflammatory and anti‐stress intervention strategy in ameliorating diaphragm dysfunction was investigated. Methods: Diaphragm muscle contractile function was compared in wild‐type and dystrophin‐deficient mdx mice treated with saline, anti‐interleukin‐6 receptor antibodies (xIL‐6R), the corticotrophin‐releasing factor receptor 2 (CRFR2) agonist, urocortin 2, or both xIL‐6R and urocortin 2. Results: Combined treatment with xIL‐6R and urocortin 2 rescued impaired force in mdx diaphragms. Mechanical work production and muscle shortening was also improved by combined drug treatment. Discussion: Treatment which neutralizes peripheral IL‐6 signaling and stimulates CRFR2 recovers force‐generating capacity and the ability to perform mechanical work in mdx diaphragm muscle. These findings may be important in the search for therapeutic targets in DMD. Muscle Nerve 56 : E134–E140, 2017     

Low‐intensity running exercise enhances the capillary volume and pro‐angiogenic factors in the soleus muscle of type 2 diabetic rats

Introduction: We determined the effects of low‐intensity exercise on the three‐dimensional capillary structure and associated angiogenic factors in the soleus muscle of Goto‐Kakizaki (GK) diabetic rats. Methods: Four groups of male rats were studied: sedentary nondiabetic (Con), exercised nondiabetic control (Ex), sedentary GK, and exercised GK (GK+Ex). Rats in the Ex and GK+Ex groups were subjected to chronic low‐intensity running on a treadmill (15 m/min, 60 min/session, 5 sessions/week for 3 weeks). Results: Although mean capillary volume and diameter were lower in the GK compared with all other groups, low‐intensity exercise increased both of these measures in GK rats. Mitochondrial markers, i.e., SDH activity and PGC‐1α expression, and the levels of angiogenic factors were higher in the GK+Ex than all other groups. Exercise increased vascular endothelial growth factor (VEGF) protein levels and the VEGF‐to‐TSP‐1 ratio, an indicator of angiogenesis, in GK rats. Conclusions: Combined, the results indicate that low‐intensity exercise reduces some of the microcirculatory complications in type 2 diabetic muscles. Muscle Nerve 51: 391–399, 2015