Effects of moderate‐ and high‐intensity chronic exercise on brain‐derived neurotrophic factor expression in fast and slow muscles

Introduction: Brain‐derived neurotrophic factor (BDNF) protein expression is sensitive to cellular activity. In the sedentary state, BDNF expression is affected by the muscle phenotype. Methods: Eighteen Wistar rats were divided into the following 3 groups: sedentary (S); moderate‐intensity training (MIT); and high‐intensity training (HIT). The training protocol lasted 8 weeks. Forty‐eight hours after training, total RNA and protein levels in the soleus and plantaris muscles were obtained. Results: In the plantaris, the BDNF protein level was lower in the HIT than in the S group (P < 0.05). A similar effect was found in the soleus (without significant difference). In the soleus, higher Bdnf mRNA levels were found in the HIT group (P < 0.001 vs. S and MIT groups). In the plantaris muscle, similar Bdnf mRNA levels were found in all groups. Conclusions: These results indicate that high‐intensity chronic exercise reduces BDNF protein level in fast muscles and increases Bdnf mRNA levels in slow muscles. Muscle Nerve 53: 446–451, 2016     

Tongue muscle plasticity following hypoglossal nerve stimulation in aged rats

Introduction: Age‐related decreases in tongue muscle mass and strength have been reported. It may be possible to prevent age‐related tongue muscle changes using neuromuscular electrical stimulation (NMES). Our hypothesis was that alterations in muscle contractile properties and myosin heavy chain composition would be found after NMES. Methods: Fifty‐four young, middle‐aged, and old 344/Brown Norway rats were included in this study. Twenty‐four rats underwent bilateral electrical stimulation of the hypoglossal nerves for 8 weeks and were compared with control or sham rats. Muscle contractile properties and myosin heavy chain (MHC) in the genioglossus (GG), styloglossus (SG), and hyoglossus (HG) muscles were examined. Results: Compared with unstimulated control rats, we found reduced muscle fatigue, increased contraction and half‐decay times, and increased twitch and tetanic tension. Increased type I MHC was found, except for in GG in old and middle‐aged rats. Conclusion: Transitions in tongue muscle contractile properties and phenotype were found after NMES. Muscle Nerve, 2013     

Interaction of thyroid state and denervation on skeletal myosin heavy chain expression

The goal of this study was to examine the effects of altered thyroid state and denervation (Den) on skeletal myosin heavy chain (MHC) expression in the plantaris and soleus muscles. Rats were subjected to unilateral denervation (Den) and randomly assigned to one of three groups: (1) euthyroid; (2) hyperthyroid; (3) and hypothyroid. Denervation caused severe muscle atrophy and muscle-type specific MHC transformation. Denervation transformed the soleus to a faster muscle, and its effects required the presence of circulating thyroid hormone. In contrast, denervation transformed the plantaris to a slower muscle independently of thyroid state. Furthermore, thyroid hormone effects did not depend upon innervation status in the soleus, while they required the presence of the nerve in the plantaris. Collectively, these findings suggest that both thyroid hormone and intact nerve (a) differentially affect MHC transformations in fast and slow muscle; and (b) are important factors in regulating the optimal expression of both type I and IIB MHC genes. This research suggests that for patients with nerve damage and/or paralysis, both muscle mass and biochemical properties can also be affected by the thyroid state. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20: 1487–1496, 1997     

Absence of developmental and unconventional myosin heavy chain in human suprahyoid muscles

Introduction: Contradictory reports of the myosin heavy chain (MHC) composition of adult human suprahyoid muscles leave unresolved the extent to which these muscles express developmental and unconventional MHC. Methods: By immunohistochemistry, separation sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE)‐Coomassie, separation SDS‐PAGE‐Western blot, and mRNA PCR, we tested for conventional MHCI, MHCIIA, MHCIIX, developmental MHC embryonic and MHC neonatal, and unconventional MHC alpha‐cardiac, MHC extraocular, and MHC slow tonic in adult human anterior digastric (AD), geniohyoid (GH), and mylohyoid (MH) muscles. Results: By separation SDS‐PAGE‐Coomassie and Western blot, only conventional MHC are present. By immunohistochemistry all muscle fibers are positive for MHCI, MHCIIA, or MHCIIX, and fewer than 4 fibers/mm² are positive for developmental or unconventional MHC. By PCR, mRNA of MHCI and MHCIIA dominate, with sporadically detectable MHC alpha‐cardiac and without detectable mRNA of other developmental and unconventional MHC. Conclusions: We conclude that human suprahyoid muscles AD, GH, and MH are composed almost exclusively of conventional MHC isoforms. Muscle Nerve 49:534–544, 2014     

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     

Excess post-exercise oxygen consumption is not associated with mechanomyographic amplitude after incremental cycle ergometry in the quadriceps femoris muscles

Introduction: The purpose of this study was to understand the relationship between the mechanical activities of the three superficial quadriceps muscles and excess post‐exercise oxygen consumption (EPOC) after incremental cycle ergometer exercise. Methods: Twelve healthy male volunteers had mechanomyographic (MMG) and electromyographic (EMG) activity of the superficial quadriceps muscles recorded 30 minutes before incremental cycle ergometry and 60 minutes after the exercise work bout. Results: The results indicate significant time‐constant values for EPOC and MMG amplitude for the three superficial quadriceps muscles during the 60‐minute post‐exercise recovery period. For EMG amplitude no decay patterns were found for the three muscles. In addition, there were no mean differences between the MMG values for the three muscles that were significantly different from EPOC. Conclusions: These results suggest that EPOC after exercise could not be exclusively attributed to elevated activity of the working muscles. Muscle Nerve 44: 432–438, 2011     

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     

Measurement of intramuscular fat by muscle echo intensity

Introduction: The aim of this study was to compare ultrasound echo intensity (EI) with high‐resolution T₁‐weighted MRI and to establish calibration equations to estimate percent intramuscular fat from EI. Methods: Thirty‐one participants underwent both ultrasound and MRI testing of 4 muscles: rectus femoris (RF); biceps femoris (BF); tibialis anterior (TA); and medial gastrocnemius (MG). Results: Strong correlations were found between MRI percent fat and muscle EI after correcting for subcutaneous fat thickness (r = 0.91 in RF, r = 0.80 in BF, r = 0.80 in TA, r = 0.76 in MG). Three types of calibration equations were established. Conclusions: Muscle ultrasound is a practical and reproducible method that can be used as an imaging technique for examination of percent intramuscular fat. Future ultrasound studies are needed to establish equations for other muscle groups to enhance its use in both research and clinical settings. Muscle Nerve 52 : 963–971, 2015     

Apoptosis in young and old denervated rat skeletal muscle

Introduction: We investigated the apoptotic response to different degrees of denervation in young and older rats randomized into control (C), partial (PD), and complete denervation (CD) of muscles innervated by the sciatic nerve. Methods: Muscle wet weight to body weight (MWW/BW), myosin heavy chain (MHC) isoforms, and fiber cross‐sectional area were determined in gastrocnemius and soleus muscles. Apoptotic responses were determined by changes in myonuclei and expression of Bcl‐2 and BAX. Results: PD and CD resulted in significant reductions in MWW/BW and FCSA in both young and older rats. Older controls had greater apoptotic responses than young controls. Apoptotic responses were greater in PD and CD than in C in both age groups. No statistical interaction between denervation and age group was seen. Conclusions: Older age was associated with increased level of apoptosis, but older muscle was not more vulnerable to the effect of denervation. Muscle Nerve 55 : 262–269, 2017     

Intermuscular relationship of human muscle fiber type proportions: slow leg muscles predict slow neck muscles

Introduction: Our aim in this study was to examine whether the muscle fiber type proportions in different muscles from the same individual are interrelated. Methods: Samples were excised from five skeletal muscles in each of 12 human autopsy cases, and the fiber type proportions were determined by immunohistochemistry. We further examined the intermuscular relationship in fiber type proportion by reanalyzing three previously published data sets involving other muscles. Results: Subjects demonstrated a predominantly high or low proportion of type 1 fibers in all examined muscles, and the overall difference between individuals was statistically significant (P < 0.001). Accordingly, the type 1 fiber proportions in most muscles were positively correlated (median r = 0.42, range ?0.03–0.80). Similar results were also obtained from the three reanalyzed data sets. Conclusions: We suggest the existence of an across‐muscle phenotype with respect to fiber type proportions; some individuals display generally faster muscles and some individuals slower muscles when compared with others. Muscle Nerve, 2012     

Apigenin inhibits sciatic nerve denervation–induced muscle atrophy

Introduction: Apigenin (AP) has been reported to elicit anti‐inflammatory effects. In this study, we investigated the effect of AP on sciatic nerve denervation–induced muscle atrophy. Methods: Sciatic nerve–denervated mice were fed a 0.1% AP‐containing diet for 2 weeks. Muscle weight and cross‐sectional area (CSA), and the expression of atrophic genes and inflammatory cytokines in the gastrocnemius were analyzed. Results: Denervation significantly induced muscle atrophy. However, values for muscle weight and CSA were greater in the denervated muscle of the AP mice than the controls. AP suppressed the expression of MuRF1, but upregulated both myosin heavy chain (MHC) and MHC type IIb. AP also significantly suppressed expression of tumor necrosis‐alpha in the gastrocnemius and soleus muscles, and interleukin‐6 expression in the soleus muscle. Discussion: AP appears to inhibit denervation‐induced muscle atrophy, which may be due in part to its inhibitory effect on inflammatory processes within muscle. Muscle Nerve 58 : 314–318, 2018     

Increase of Cardiotrophin‐1 immunoreactivity in regenerating and overloaded but not denervated muscles of rats

The original report by Pennica et al. on Cardiotrophin‐1 (CT‐1) states that it markedly stimulates hypertrophy in cardiac myocytes both in vitro and in vivo and is predominantly expressed in the early mouse embryonic heart tube. CT‐1 is a member of the interleukin‐6 superfamily and past studies have shown that it exerts trophic effects on neurons, glial cells and their precursors, and is expressed during myogenesis. Thus CT‐1 is associated with physical and pathological changes in skeletal muscle. In this study, we examined whether CT‐1 is expressed in mechanically overloaded, regenerating, and denervated muscles of rats using immunohistochemistry. In the overloaded plantaris muscles at 1 and 3 days postsurgery, CT‐1 immunoreactivity was detected in the mononuclear cells that had infiltrated the extracellular space. CT‐1 immunoreactivity was also observed in the mononuclear cells invading the extracellular space at 2, 4, and 6 days after a bupivacaine injection and in degenerative and necrotic muscle fibers at 2 days postinjection. In the denervated muscles, the CT‐1 immunoreactivity did not change in intensity during the entire period of the denervation (2, 7, and 14 days postsurgery). The cells invading extracellular space and in necrotic muscle fibers possessing CT‐1 immunoreactivity might be muscle precursor cells (satellite cells) or migrating macrophages undergoing phagocytosis. Using double‐immunostainings for anti‐CT‐1/antic‐met, anti‐CT‐1/ anti‐M‐cadherin, and anti‐CT‐1/anti‐ED1, we found that satellite cells and macrophages exhibited CT‐1 immunoreactivity in the damaged muscles after bupivacaine injection. We therefore believe that CT‐1 plays a key role in regeneration and hypertrophy in the skeletal muscle of rats.     

New mouse model of skeletal muscle atrophy using spiral wire immobilization

Introduction: Disuse‐induced skeletal muscle atrophy is a serious concern; however, there is not an effective mouse model to elucidate the molecular mechanisms. We developed a noninvasive atrophy model in mice. Methods: After the ankle joints of mice were bandaged into a bilateral plantar flexed position, either bilateral or unilateral hindlimbs were immobilized by wrapping in bonsai steel wire. Results: After 3, 5, or 10 days of immobilization of the hip, knee, and ankle, the weight of the soleus and plantaris muscles decreased significantly in both bilateral and unilateral immobilization. MAFbx/atrogin‐1 and MuRF1 mRNA was found to have significantly increased in both muscles, consistent with disuse‐induced atrophy. Notably, the procedure did not result in either edema or necrosis in the fixed hindlimbs. Conclusions: This method allows repeated, direct access to the immobilized muscle, making it a useful procedure for concurrent application and assessment of various therapeutic interventions. Muscle Nerve 54 : 788–791, 2016     

Mitochondrial DNA deletions and depletion within paraspinal muscles

G. R. Campbell, A. Reeve, I. Ziabreva, T. M. Polvikoski, R. W. Taylor, R. Reynolds, D. M. Turnbull and D. J. Mahad (2013) Neuropathology and Applied Neurobiology 39, 377–389 Mitochondrial DNA deletions and depletion within paraspinal muscles Aims: Although mitochondrial abnormalities have been reported within paraspinal muscles in patients with axial weakness and neuromuscular disease as well as with ageing, the basis of respiratory deficiency in paraspinal muscles is not known. This study aimed to determine the extent and basis of respiratory deficiency in paraspinal muscles from cases undergoing surgery for degenerative spinal disease and post mortem cases without a history of spinal disease, where age‐related histopathological changes were previously reported. Methods: Cervical and lumbar paraspinal muscles were obtained peri‐operatively from 13 patients and from six post mortem control cases (age range 18–82 years) without a neurological disease. Sequential COX/SDH (mitochondrial respiratory chain complex IV/complex II) histochemistry was performed to identify respiratory‐deficient muscle fibres (lacking complex IV with intact complex II activity). Real‐time polymerase chain reaction, long‐range polymerase chain reaction and sequencing were used to identify and characterize mitochondrial DNA (mtDNA) deletions and determine mtDNA copy number status. Mitochondrial respiratory chain complex subunits were detected by immunohistochemistry. Results: The density of respiratory‐deficient fibres increased with age. On average, 3.96% of fibres in paraspinal muscles were respiratory‐deficient (range 0–10.26). Respiratory deficiency in 36.8% of paraspinal muscle fibres was due to clonally expanded mtDNA deletions. MtDNA depletion accounted for further 13.5% of respiratory deficiency. The profile of immunohistochemically detected subunits of complexes was similar in respiratory‐deficient fibres with and without mtDNA deletions or mtDNA depletion. Conclusions: Paraspinal muscles appeared to be particularly susceptible to age‐related mitochondrial respiratory chain defects. Clonally expanded mtDNA deletions and focal mtDNA depletion may contribute towards the development of age‐related postural abnormalities.     

Knee extensor fatigue resistance of young and older men and women performing sustained and brief intermittent isometric contractions

Introduction: Susceptibility to muscle fatigue during aging could depend on muscle activation patterns. Methods: Young (mean age, 22 years) and older (mean age 70 years) men and women completed two fatigue tests of knee extensor muscles using voluntary and electrically stimulated contractions. Results: Older subjects displayed a shift to the left of the torque‐frequency relationship and held a sustained voluntary isometric contraction at 50% maximal strength for significantly longer than young (P < 0.001). Young and old showed similar fatigue during electrically induced, intermittent isometric contractions (1‐s on, 1‐s off for 2 min), but women fatigued less than men (P = 0.001). Stronger muscles fatigued more quickly, and slower contractile properties were associated with longer sustained contractions. Conclusions: The slowing and weakness of older muscle was associated with superior fatigue resistance during sustained isometric contractions. Young and old showed similar fatigue following a series of brief, intermittent contractions, but women fatigued less than men. Muscle Nerve 50 : 393–400, 2014     

Quantitative muscle ultrasound and quadriceps strength in patients with post‐polio syndrome

Introduction: We investigated whether muscle ultrasound can distinguish muscles affected by post‐polio syndrome (PPS) from healthy muscles and whether severity of ultrasound abnormalities is associated with muscle strength. Methods: Echo intensity, muscle thickness, and isometric strength of the quadriceps muscles were measured in 48 patients with PPS and 12 healthy controls. Results: Patients with PPS had significantly higher echo intensity and lower muscle thickness than healthy controls. In patients, both echo intensity and muscle thickness were associated independently with muscle strength. A combined measure of echo intensity and muscle thickness was more strongly related to muscle strength than either parameter alone. Conclusions: Quantitative ultrasound distinguishes healthy muscles from those affected by PPS, and measures of muscle quality and quantity are associated with muscle strength. Hence, ultrasound could be a useful tool for assessing disease severity and monitoring changes resulting from disease progression or clinical intervention in patients with PPS. Muscle Nerve 51 : 24–29, 2015     

Contractile properties of slow and fast skeletal muscles from protease activated receptor‐1 null mice

Introduction: Protease‐activated receptors (PARs) may play a role in skeletal muscle development. We compared the contractile properties of slow‐twitch soleus muscles and fast‐twitch extensor digitorum longus (EDL) muscles from PAR‐1 null and littermate control mice. Methods: Contractile function was measured using a force transducer system. Fiber type proportions were determined using immunohistochemistry. Results: Soleus muscles from PAR‐1 null mice exhibited longer contraction times, a leftward shift in the force–stimulation frequency relationship, and decreased fatiguability compared with controls. PAR‐1 null soleus muscles also had increased type 1 and decreased type IIb/x fiber numbers compared with controls. In PAR‐1 null EDL muscles, no differences were found, except for a slower rate of fatigue compared with controls. Conclusions: The absence of PAR‐1 results in a slower skeletal muscle contractile phenotype, likely due to an increase in type I and a decrease in type IIb/x fiber numbers. Muscle Nerve 50: 991–998, 2014     

Recovery of reinnervating rat muscle after cast immobilization

We evaluated the recovery of the reinnervating rat plantar flexor muscles after different periods of casting and then decasting the lower extremities. Four groups of 4-month-old, female Wistar rats underwent bilateral crush-denervation of the sciatic nerve at the sciatic notch. Two weeks after nerve crush, the hind legs of three groups of rats were immobilized with bilateral casts at the knee and ankle joints and the fourth group was a control group. Of the three casted groups, one was mobilized after 1 week and another group after 3 weeks of casting. The third experimental group remained casted until the end of 6 weeks. Six weeks after the nerve crush, all groups were evaluated for muscle weights of the soleus, plantaris, and gastrocnemius; absolute amounts of the myofibrillar, sarcoplasmic, and stromal proteins in the gastrocnemius; the fiber diameters and percent composition of type I and type II fibers in the soleus and plantaris; and the isometric contractile properties of the soleus muscle. Compared with the denervated control group, the experimental groups revealed the following: (i) Four weeks of casting caused a reduction in wet weight (range 30.6 to 40.4%, P less than 0.01) in the soleus, plantaris, and gastrocnemius muscles. Decasting led to an earlier recovery of the soleus than of the plantaris and gastrocnemius muscles. (ii) The myofibrillar protein returned to control values with 3 weeks of decasting but the stromal protein remained significantly elevated and the sarcoplasmic protein significantly depressed regardless of the period of mobilization. (iii) Except for the type I fibers in the plantaris, the remainder of the muscle fibers in the soleus and plantaris decreased in size due to casting. Only the type I muscle fibers of the soleus increased in size with longer periods of mobilization. (iv) Four weeks of casting significantly altered the maximum isometric twitch tension (-42.3%), contraction time (+17.1%), maximum tetanic tension (-38.1%), and half-fatigue time (+40.5%) in the soleus. The reinnervating soleus muscle appears to recover from the effects of casting sooner than the plantaris or gastrocnemius muscles.