Disuse atrophy alterations in normal and low temperature environments during hindlimb unloading in Syrian hamsters

This study examined whether a hypothermic environment reduces experimentally-induced atrophy of skeletal muscle, as judged by histochemical findings. The hind limbs of hamsters in a hypothermic group were suspended and flexed into plantar positions at the ankle joint, and housed for one week at 8 to 12 degree celsius in a temperature-controlled room, while the normothermic group was housed at 23 to 25 degree celsius. Hypothermia did not significantly alter the average caloric intake, and the animals from the hypothermic group lost a significant amount of body weight when compared with the normothermic group. The hypothermic group retained more muscle wet-weight and myofibers cross-sectional area in the soleus and gastrocnemius muscles compared with the normothermic group. Our results indicate that a hypothermic environment inhibits short-term muscle atrophy. This inhibition may be caused by the increased caloric intake combined with a state similar to hibernation in low-temperature environments.     

Early ultrastructural events of skeletal muscle damage following cardiotoxin-induced injury and glycerol-induced injury

In this study, we investigated the early changes of skeletal muscle damage in response to injuries induced by cardiotoxin (CTX) and glycerol by using both light microscopy and transmission electron microscopy. Normal, non-dystrophic, adult male mice were used in this study. Tibialis anterior (TA) muscles were injected either with CTX or glycerol. Samples were collected at intervals starting from 1 h up to 4 days after injury. Injured muscles were subjected to both histological and ultrastructural analyses. CTX-induced injury caused mitochondrial accumulation and swelling followed by lysis, while glycerol-induced injury caused accumulation of vesicles with focal disruption of the basal lamina, indicating that the injuries have different mechanisms of damage to myofibers. Moreover, inflammatory cells, including neutrophils and macrophages, were recruited earlier and in larger numbers after CTX-induced injury than after glycerol-induced injury. On the other hand, satellite cells (SCs) activation started at 6 h after both injuries, as indicated by an increase in both the length and cytoplasmic-to-nuclear ratio. However, there were significantly longer SCs with a higher cytoplasmic-to-nuclear ratio in the CTX-injured muscles than in the glycerol-injured muscles at day 4. In conclusion, our results demonstrated a difference between CTX and glycerol in their damage to myofibers; CTX damages myofiber mitochondria, while glycerol damages the myofiber cell membrane and alters osmosis. In addition, CTX-induced injury caused earlier and more extensive inflammatory infiltration than did glycerol-induced injury. This study is the first study to shed light on the early events following skeletal muscle injury induced by CTX and glycerol.     

Dependence of residual dipolar couplings on foot angle in H MR spectra from skeletal muscle

Foot dorsi and plantar flexion affects the pennation angle of skeletal muscle fibers and changes the fiber direction with respect to the main magnetic field, thereby affecting MR spectrum of the muscle. In order to analyze the effect that foot flexion has on the MR spectrum, tibialis anterior (TA) and soleus muscles were studied in humans and rats. Localized MRS was performed at different foot angles in clinical and pre-clinical settings using a 3 T MRI/MRS GE Excite HD and 7 T Bruker Clinscan scanner, respectively. In this study we show the effect of foot angle variation on total Creatine (tCr) resonance of ¹H spectrum at 3.03 and 3.93 ppm for TA and soleus muscles. In addition to this, we observe a 4-line splitting pattern for methylene resonance of tCr in the rat TA spectrum for a specific foot angle. This observation is attributed to the individual splitting of creatine and phosphocreatine of the tCr signal. Novel hydrogel application is demonstrated and used to support our in vivo observations and for the first time splitting of individual resonances of Cr and PCr has been shown in an in vitro set-up.     

NMR relaxation times of skeletal muscle: Dependence on fiber type and diet

Skeletal muscles are composed of a mixture of different types of muscle fibers. Previous NMR studies of muscle have typically used muscles of mixed fiber composition and have not taken into account factors such as the dietary history of the experimental animal. In this paper we present evidence that the T₁ and T₂ relaxation times of two of the major types of skeletal muscle fiber are not significantly different under normal conditions. Following dietary manipulation of the rabbits (limiting potassium intake or increasing cholesterol consumption), the T₁ and T₂ relaxation times of psoas and soleus muscles were significantly different. The change in relaxation times of psoas muscles following dietary manipulation can be only partially explained by shifts in muscle water content. The results suggest that changes in diet are capable of inducing changes in water bonding and structuring in muscle tissues. Our results indicate that diet must be added to the growing list of environmental factors that can cause NMR contrast changes. Also, NMR measurements of muscles rich in one fiber type or another could be of value for detecting changes in body composition.     

Orientational dependence of trimethyl ammonium signal in human muscles by (1)H magnetic resonance spectroscopic imaging

(1)H magnetic resonance spectroscopic imaging (MRSI) was used to investigate the effect of orientation on spectral characteristics of trimethyl ammonium (TMA) in human muscle at rest. Four different muscles in the healthy calf were studied: soleus, gastrocnemius, tibial posterior and anterior. The data demonstrate that muscle orientation can profoundly change apparent spectral characteristics of proton metabolites. In particular, muscle orientation can cause concerted changes in the spectral pattern of TMA/methyl (tCr) and methylene (Cr2) protons of creatine for a given muscle, a switch of TMA/tCr spectral patterns among different muscles and changes in the T(2) of TMA. A significant correlation was detected between TMA/tCr peaks and the Cr2 peak splitting (r=.62, P<.001). In vivo (1)H MRSI has the potential to simultaneously evaluate the orientation of muscle fibers and biochemical changes induced by a disease process or physiological activity.     

Estimation of Time-Frequency Muscle Synergy in Wrist Movements

Muscle synergy analysis is a kind of modularized decomposition of muscles during exercise controlled by the central nervous system (CNS). It can not only extract the synergistic muscles in exercise, but also obtain the activation states of muscles to reflect the coordination and control relationship between muscles. However, previous studies have mainly focused on the time-domain synergy without considering the frequency-specific characteristics within synergy structures. Therefore, this study proposes a novel method, named time-frequency non-negative matrix factorization (TF-NMF), to explore the time-varying regularity of muscle synergy characteristics of multi-channel surface electromyogram (sEMG) signals at different frequency bands. In this method, the wavelet packet transform (WPT) is used to transform the time-scale signals into time-frequency dimension. Then, the NMF method is calculated in each time-frequency window to extract the synergy modules. Finally, this method is used to analyze the sEMG signals recorded from 8 muscles during the conversion between wrist flexion (WF stage) and wrist extension (WE stage) movements in 12 healthy people. The experimental results show that the number of synergy modules in wrist flexion transmission to wrist extension (Motion Conversion, MC stage) is more than that in the WF stage and WE stage. Furthermore, the number of flexor and extensor muscle synergies in the frequency band of 0–125 Hz during the MC stage is more than that in the frequency band of 125–250 Hz. Further analysis shows that the flexion muscle synergies mostly exist in the frequency band of 140.625–156.25 Hz during the WF stage, and the extension muscle synergies appear in the frequency band of 125–156.25 Hz during the WE stage. These results can help to better understand the time-frequency features of muscle synergy, and expand study perspective related to motor control in nervous system.     

Simulation study of a magnetocardiogram based on a virtual heart model: effect of a cardiac equivalent source and a volume conductor

In this paper,we present a magnetocardiogram(MCG) simulation study using the boundary element method(BEM) and based on the virtual heart model and the realistic human volume conductor model.The different contributions of cardiac equivalent source models and volume conductor models to the MCG are deeply and comprehensively investigated.The single dipole source model,the multiple dipoles source model and the equivalent double layer(EDL) source model are analysed and compared with the cardiac equivalent source models.Meanwhile,the effect of the volume conductor model on the MCG combined with these cardiac equivalent sources is investigated.The simulation results demonstrate that the cardiac electrophysiological information will be partly missed when only the single dipole source is taken,while the EDL source is a good option for MCG simulation and the effect of the volume conductor is smallest for the EDL source.Therefore,the EDL source is suitable for the study of MCG forward and inverse problems,and more attention should be paid to it in future MCG studies.     

Anisotropy of ultrasonic propagation and scattering properties in fresh rat skeletal muscle in vitro

The anisotropy of frequency-dependent backscatter coefficient, attenuation, and speed of sound is assessed in fresh rat skeletal muscle within 5 h post-mortem. Excised rat semimembranosus and soleus muscles are measured in 37 degrees C Tyrode solution, with the muscle fibers at 90 degrees and 45 degrees orientations to the incident sound beam. Reflected and through transmission signals from either a 6- or 10-MHz focused transducer give frequency dependent information in the 4-14 MHz range. The attenuation coefficient in each muscle is consistently a factor of 2.0 +/- 0.4 lower for propagation perpendicular to the fibers than at 45 degrees, whereas speed of sound shows a much milder anisotropy, and is slightly faster for the 90 degrees orientation. The largest anisotropy is seen in the backscatter coefficient, most notably in the semimembranosus where the magnitude at 90 degrees is over an order of magnitude greater than at 45 degrees, with the frequency dependence in both cases giving a power law between 1.5 and 2.0.     

Effect of Immobilization on Insoluble Collagen Concentration and Type I and Type III Collagen Isoforms of Rat Soleus Muscle

Immobilization is often associated with decreased muscle elasticity. This condition is known as muscle contracture; however, the mechanism remains unclear. The purpose of this study was to clarify the mechanism governing muscle contracture in rat soleus muscle by identifying changes in ankle joint mobility, insoluble collagen concentration and type I and type III collagen isoforms following 1- and 3-week immobilizations. Following a 1-week immobilization, range of motion (ROM) of dorsiflexion declined to 90% of the control value; additionally, ROM dropped to 67.5% of the control value after a 3-week immobilization. This finding suggested that ankle joint mobility decreases in conjunction with extended periods of immobilization. Insoluble collagen concentration in soleus muscles, which was unchanged after 1 week of immobilization, increased 3 weeks after immobilization. These results may be indicative of collagen fibers with strong intermolecular cross-links contained in the muscle was made increased relatively by 3 weeks of immobilization. Therefore, the change in intermolecular cross-links may be significant in terms of progress of muscle contracture with longer periods of immobilization. On the other hand, the ratio of type III to type I collagen isoforms in muscular tissue increased following a 1-week immobilization; moreover, this ratio remained constant after 3 weeks of immobilization. These data suggested that muscle immobilization may induce type III collagen isoform expression. The increase in the ratio of type III to type I collagen isoforms do not change in parallel with the increase in the limitation in ROM; however, this phenomenon probably is not closely related to the progress of muscle contracture. The change of collagen isoform in immobilized muscle may be involved in the mechanism governing the progression of muscle fibrosis.     

Differences in muscle thickness and echo intensity between stroke survivors and age- and sex-matched healthy older adults

Objective: The stroke survivors exhibit change in muscle quantity and quality compared to healthy older adults. This study aimed to compare the muscle thickness (MT) and echo intensity (EI) values of individual muscles between stroke survivors and age- and sex-matched healthy older adults. Methods : In total, 27 stroke survivors and 34 healthy older adults participated in this study. The MT and EI values of the following muscles were assessed from transverse ultrasound images: rectus abdominis (RA), external oblique, internal oblique, transversus abdominis, rectus femoris, vastus intermedius (VI), vastus lateralis (VL), vastus medialis (VM), tibialis anterior (TA), gastrocnemius (Gas), and soleus (Sol). The MT and EI values of these muscles were compared between stroke survivors and healthy older adults. Results : The MT values of the VL, VM, and RA on the non-paretic sides were significantly higher and those of the TA, Gas, and Sol on the paretic sides were significantly lower in the stroke survivors than in the healthy older adults (P < 0.05). The EI values of the VI, VL, VM, TA on the paretic sides and those of the Gas on both the paretic and non-paretic sides were significantly higher in the stroke survivors than in the healthy older adults (P < 0.05). Conclusion : Stroke survivors seem to develop muscle hypertrophy of the non-paretic thigh muscles owing to a compensatory strategy. In addition, the lower-leg muscles on the paretic side of stroke survivors tend to show both quantitative and qualitative muscle changes.     

Nuclear microscopy of normal and necrotic skeletal muscle fibers: an intracellular elemental microanalysis

The in situ total elemental composition and elemental concentrations present in mouse soleus (type I) and gastrocnemius (type IIA) muscle fibers were analyzed by using nuclear microscopy (NM). Elemental changes in necrotic fibers, induced by intramuscluar injection with snake venom (Pseudechis australis), were also studied 3 h post-injection. Nuclear microscopy is a new method based on nuclear technology that utilizes the interaction between a million-electron-volt nuclear particle beam and the muscle sample (in the case of the present study). Elemental analysis was done at the parts per million (ppm) level of sensitivity on unfixed, rapidly frozen and unstained single fast- and slow-twitch muscle fibers with imaging capabilities of μm spatial resolution and in multi-elemental mode. In total, 12 different intracellular elements were mapped, co-localized and analyzed in single normal and necrotic skeletal muscle fibers from mice. Elements such as potassium, sulfur, phosphorus, chlorine and sodium were found in concentrations from 1000 to 18 000 ppm. Unlike conventional electron-probe X-ray microanalysis, NM also detected and analyzed the trace elements such as magnesium, calcium, iron and zinc that were found in concentrations of 50 to 1000 ppm. Other elements — copper, manganese and rubidium — were also detected in concentrations of less than 50 ppm. The trace elements calcium, iron and zinc were more abundant in the soleus than the gastrocnemius (the level of iron was statistically significant). Calcium, sodium and chlorine were significantly elevated in venom-induced necrotic soleus muscle fibers.     

Technical evaluation of in vivo abdominal fat and IMCL quantification using MRI and MRSI at 3 T

OBJECTIVES: The objectives of this study were to develop protocols that measure abdominal fat and calf muscle lipids with magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS), respectively, at 3 T and to examine the correlation between these parameters and insulin sensitivity. MATERIALS AND METHODS: Ten nondiabetic subjects [five insulin-sensitive (IS) subjects and five insulin-resistant (IR) subjects] were scanned at 3 T. Visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) were segmented semiautomatically from abdominal imaging. Intramyocellular lipids (IMCL) in calf muscles were quantified with single-voxel MRS in both soleus and tibialis anterior muscles and with magnetic resonance spectroscopic imaging (MRSI). RESULTS: The average coefficient of variation (CV) of VAT/(VAT+SAT) was 5.2%. The interoperator CV was 1.1% and 5.3% for SAT and VAT estimates, respectively. The CV of IMCL was 13.7% in soleus, 11.9% in tibialis anterior and 2.9% with MRSI. IMCL based on MRSI (3.8+/-1.2%) were significantly inversely correlated with glucose disposal rate, as measured by a hyperinsulinemic-euglycemic clamp. VAT volume correlated significantly with IMCL. IMCL based on MRSI for IR subjects was significantly greater than that for IS subjects (4.5+/-0.9% vs. 2.8+/-0.5%, P=.02). CONCLUSION: MRI and MRS techniques provide a robust noninvasive measurement of abdominal fat and muscle IMCL, which are correlated with insulin action in humans.     

Measurement of excitation-contraction coupling time in lower extremities

Objective: The aim of this study was to apply a novel method to measure excitation-contraction coupling time (ECCT) in normal soleus muscles. Methods: We performed simultaneous recordings of soleus compound muscle action potential (CMAP) and foot movement-related potential (MRP), and measured ankle plantar flexion torque in 36 healthy subjects. We calculated ECCT and examined the relations between CMAP, MRP, ECCT and ankle plantar flexion torque. Results: Statistical analyses established reference ranges (mean ± SE) for CMAP (13.4 ± 0.9 mV), MRP (5.3 ± 0.4 m/s²), ECCT (5.2 ± 0.1 ms), torque (85.9 ± 6.4 Nm) and torque/body weight (1.4 ± 0.1 Nm/kg). The torque showed a positive linear correlation with CMAP (p = 0.041) and a negative linear correlation with ECCT (p = 0.045). Conclusion: Soleus ECCT can be recorded easily, and is useful to assess the impairment of E-C coupling in muscles of the lower extremities.     

Metabolic profile of dystrophic mdx mouse muscles analyzed with in vitro magnetic resonance spectroscopy (MRS)

Duchenne muscular dystrophy (DMD) is a recessive X-linked form of muscular dystrophy characterized by progressive and irreversible degeneration of the muscles. The mdx mouse is the classical animal model for DMD, showing similar molecular and protein defects. The mdx mouse, however, does not show significant muscle weakness, and the diaphragm muscle is significantly more degenerated than skeletal muscles. In this work, (1)H magnetic resonance spectroscopy (MRS) was used to study the metabolic profile of quadriceps and diaphragm muscles from mdx and control mice. Using principal components analysis (PCA), the animals were separated into groups according to age and lineages. The classification was compared to histopathological analysis. Among the 24 metabolites identified from the nuclear MR spectra, only 19 were used by the PCA program for classification purposes. These can be important key biomarkers associated with the progression of degeneration in mdx muscles and with natural aging in control mice. Glutamate, glutamine, succinate, isoleucine, acetate, alanine and glycerol were increased in mdx samples as compared to control mice, in contrast to carnosine, taurine, glycine, methionine and creatine that were decreased. These results suggest that MRS associated with pattern recognition analysis can be a reliable tool to assess the degree of pathological and metabolic alterations in the dystrophic tissue, thereby affording the possibility of evaluation of beneficial effects of putative therapies.     

Effect of tetrasodium tripolyphosphate on the freeze-concentrated glass-like transition temperature of sugar aqueous solutions

The freeze-concentrated glass-like transition temperatures (Tg2), so-called ante-melting temperature or ice-melting temperature of tripolyphosphate-sugar aqueous solutions prepared with various sugars (ribose, sorbitol, glucose, maltose, sucrose, and trehalose) were investigated by using differential scanning calorimetry to evaluate the effect of tetrasodium tripolyphosphate on the Tg2 of sugar aqueous solutions. The Tg2 of tripolyphosphate-sugar aqueous solutions were higher than those of tripolyphosphate or sugar aqueous solutions and converged in a narrow temperature range of 238 to 243 K. Furthermore, a study of the Tg2 of tripolyphosphate-glucose aqueous solutions adjusted to various ratios indicated that the Tg2 increment depended on the ratio and that another glass-like transition appeared at a temperature below the Tg2 by increasing the ratio of tripolyphosphate. The drastic increase in the Tg2 of sugars with the addition of tripolyphosphate will be useful for improving the cryostabilization of biomaterials.     

Low-level laser therapy (LLLT) reduces inflammatory infiltrate and enhances skeletal muscle repair: Histomorphometric parameters

Low level laser therapy (LLLT) has been suggested as an effective therapeutics in inflammatory processes modulation and tissue repairing. However, there is a lack of studies that analyze the anti-inflammatory effects of the infrared lasers in muscular skeletal injury. The aim of this study was to investigate the effects of low-level laser therapy 904 nm in the repair process of skeletal muscle tissue. Swiss mice were submitted to cryoinjury and divided in test (LLLT-treated) and control groups. Histological sections were stained with hematoxylin-eosin to assess general morphology and inflammatory influx, and Picrossirus to quantify collagen fibers deposition. Our results showed significant reduction in inflammatory infiltrated in irradiated mice after 4 days of treatment compared to control (p = 0.01). After 8 days, the irradiated group showed high levels at regenerating myofibers with significant statistically differences in relation at control group (p < 0.01). Collagen deposition was significantly increased in the final stages of regeneration at test group, when compared with control group (p = 0.05). Our data suggests that LLLT reduces the inflammatory response in the initial stages of injury and accelerates the process of muscular tissue repair.     

Electrooptic effect of water in electric double layer at interface of GaN electrode

We determined the Pockels constant of water in the electric double layer (EDL) at the GaN electrode interface. For a positive (negative) bias, the difference transmittance showed a blue (red) shift in the interference fringes in the visible. This was caused by a negative (positive) refractive index change both in the EDL of water and in the space charge layer (SCL) of the GaN. The latter was associated with the blue shift in the absorption edge in the UV due to the band population effect in the GaN. The voltage drops took place within the interfacial layer at a ratio of about 3: 1 for the SCL vs EDL at the modulation frequency of f = 20 Hz, estimated from the frequency dependence of the impedance. The Pockels constant of water in the EDL was determined to be r ₁₃ = 0:63 × 100 pm/V for the GaN electrodes. This is three times smaller than that at the surface of the indium tin oxide (ITO) electrode.     

In vivo T1 characterization of genetically induced muscle atrophy

In vivo spin-lattice relaxation times, T1, of water and lipid protons of normal and atrophic muscles were measured, using the spatially resolved spectroscopy (SPARS) sequence, in a genetic avian model of myopathy. These T1 values were compared with those of the hypertrophic muscles. Although the water T1 values of muscles were elevated in both types of lesions, the atrophic muscles showed a greater increase (54%) than the hypertrophic muscles (22%). The water T1 differentiation between the atrophic and hypertrophic muscles appeared to depend upon their bound water fractions that were calculated on the basis of the Fast Proton Diffusion model. The lipid T1 values of muscles were higher in the atrophic line of chickens compared to their genetic controls. In contrast, the lipid T1 values of muscles of the hypertrophic chickens and their controls were essentially identical. This suggests that the lipid T1 values may potentially complement the water T1 values in the differential diagnosis of muscle disorders.     

Effects of aging and maternal protein restriction on the muscle fibers morphology and neuromuscular junctions of rats after nutritional recovery

Changes in the nutritional status of mothers may predispose their offspring to neuromuscular disorders in the long term. This study evaluated the effects of maternal protein restriction during pregnancy and lactation on the muscle fibers and neuromuscular junctions (NMJs) of the soleus muscle in the offspring of rats at 365 days of age that had undergone nutritional recovery. Wistar rats were divided into two groups: control (CG) – the offspring of mothers fed a normal protein diet (17%) and restricted (RG) – offspring of mothers fed a low protein diet (6%). After lactation, the male pups received standard chow ad libitum. At 365 days, samples of soleus muscle were collected for muscle fiber analysis (HE staining, NADH-TR reaction and ultrastructure), intramuscular collagen quantification (picrosirius red staining) and NMJs analysis (non-specific esterase technique). The cross-sectional area of type I fibers was reduced by 20% and type IIa fibers by 5% while type IIb fibers increased by 5% in the RG compared to the CG. The percentage of intramuscular collagen was 19% lower in the RG. Disorganization of the myofibrils and Z line was observed, with the presence of clusters of mitochondria in both groups. Regarding the NMJs, in the RG there was a reduction of 10% in the area and 17% in the small diameter and an increase of 7% in the large diameter. The results indicate that the effects of maternal protein restriction on muscle fibers and NMJs seem to be long-lasting and irreversible.     

Spectral pattern of total creatine and trimethyl ammonium in multiple sclerosis

Fatigue and impairment mobility are frequent problems in multiple sclerosis (MS). Despite its enormous potential, in vivo (1)H MRS of skeletal muscles for MS patients is a largely unexplored field. One fundamental question remains unanswered: whether MS can cause observable proton metabolite changes. High quality two-dimensional in vivo (1)H MRS reveals that the spectral pattern of total creatine (tCr) and trimethyl ammonium (TMA) of soleus muscles of MS patients can be distinctively different from that of healthy volunteers, and in vivo (1)H MRS of skeletal muscles has a potential to become a useful tool in MS study.