Signaling In Muscle Research Articles

The test-retest reproducibility of the multiple array probe Leiden in men with lower urinary tract symptoms.

We aimed to study the test-retest reliability of the Multiple Array Probe Leiden (MAPLe), a multiple electrode probe designed to acquire and discriminate electromyography signals in the pelvic floor muscles, in men with lower urinary tract symptoms (LUTS). Adult male patients with LUTS with sufficient knowledge of Dutch language, but without complications (e.g., urinary tract infection), or previous urologic cancer and/or urologic surgery were enrolled. In the initial study, next to physical examination and uroflowmetry, all men underwent MAPLe assessment at baseline and after 6 weeks. Second, participants were reinvited for a new assessment using a stricter protocol. A time interval of 2 h (M2) and 1 week (M3) after baseline (M1) allowed the calculation of the intraday agreement (M1 vs. M2), and the interday agreement (M1 vs. M3) for all 13 MAPLe variables. The outcomes of the initial study in 21 men suggested a poor test-retest reliability. The second study in 23 men showed a good test-retest reliability with intraclass correlations ranging from 0.61 (0.12-0.86) to 0.91 (0.81-0.96). The agreement was generally higher for the intraday determinations than for the interday determinations. This study revealed a good test-retest reliability of the MAPLe device in men with LUTS, when using a strict protocol. With a less strict protocol, the test-retest reliability of MAPLe was poor in this sample. To make valid interpretations of this device in a clinical or research setting, a strict protocol is needed.

Printed soft skin electrodes for seamless bio-impedance measurements

Bio-impedance measurements are widely used to assess various physiological parameters. Contemporary skin electrodes for bio-impedance measurements are cumbersome and novel electrode designs are needed to allow fast and easy placement, long-term stability and user comfort. This investigation introduces dry, printed, bio-compatible electrode arrays, made of screen-printed carbon and inkjet-printed PEDOT:PSS that measure bio-impedance non-invasively and stably. Two contact impedance measurements yield the lowest normalized values of soft electrodes reported to date. Four contact bio-impedance measurements from the radial, ulnar, common carotid and superficial temporal arteries were performed, demonstrating the ability to capture blood pulsation in different areas with small form factor. Owing to the unique properties of the printed electrodes reported here, we were able to demonstrate for the first time blood pulsation in the face, continuous blood pulsation measurement during simultaneous muscle activation and signal stability over many hours.

IRE1α arm of unfolded protein response in muscle-specific TGF-β signaling-mediated regulation of muscle cell immunological properties

Endoplasmic reticulum stress (ERS) and the unfolded protein response (UPR) are involved in various muscle pathological states. The IRE1α arm of UPR can affect immunological properties of myofiber through restraining p38 mitogen-activated protein kinases (MAPK) activation under inflammatory milieu. However, the relevant pathway molecules regulating the initiation of the IRE1α arm in myofiber remain unclear. In this work, expression of transforming growth factor-beta (TGF-β) and TGF-β receptor II (TGF-βr2), and UPR pathway activation were examined in cardiotoxin (CTX)-damaged mouse muscle, which revealed the activation of TGF-β signaling and UPR in CTX-damaged muscle and in regenerating myofibers. Using control or transgenic mice with TGF-βr2 deleted in skeletal muscle (SM TGF-βr2−/−) and the derived primary differentiating myogenic precursor cells (MPCs) treated with/without ERS activator or inhibitor, IRE1α pathway inhibitor, or TGF-β signaling activator, this study further revealed an essential role of intrinsic TGF-β signaling in regulating muscle cell to express inflammation-related molecules including H-2Kb, H2-Eα, TLR3, and special myokines. TGF-β signaling prompted UPR IRE1α arm and restrained p38 MAPK activation in myofiber under inflammatory milieu. This study uncovers a previously unrecognized function of TGF-β signaling acting as an upstream factor controlling myofiber immune capacities in the inflamed state through the UPR–IRE1α–p38 MAPK pathway.

Cell selectivity in succinate receptor SUCNR1/GPR91 signaling in skeletal muscle.

Succinate is released by skeletal muscle during exercise and activates SUCNR1/GPR91. Signaling of SUCNR1 is involved in metabolite-sensing paracrine communication in skeletal muscle during exercise. However, the specific cell types responding to succinate and the directionality of communication are unclear. We aim to characterize the expression of SUCNR1 in human skeletal muscle. De novo analysis of transcriptomic datasets demonstrated that SUCNR1 mRNA is expressed in immune, adipose, and liver tissues, but scarce in skeletal muscle. In human tissues, SUCNR1 mRNA was associated with macrophage markers. Single-cell RNA sequencing and fluorescent RNAscope demonstrated that in human skeletal muscle, SUCNR1 mRNA is not expressed in muscle fibers but coincided with macrophage populations. Human M2-polarized macrophages exhibit high levels of SUCNR1 mRNA and stimulation with selective agonists of SUCNR1 triggered Gq- and Gi-coupled signaling. Primary human skeletal muscle cells were unresponsive to SUCNR1 agonists. In conclusion, SUCNR1 is not expressed in muscle cells and its role in the adaptive response of skeletal muscle to exercise is most likely mediated via paracrine mechanisms involving M2-like macrophages within the muscle.NEW & NOTEWORTHY Macrophages but not skeletal muscle cells respond to extracellular succinate via SUCNR1/GPR91.

Changes in the Mechanical Properties of Fast and Slow Skeletal Muscle after 7 and 21 Days of Restricted Activity in Rats.

Disuse muscle atrophy is usually accompanied by changes in skeletal muscle structure, signaling, and contractile potential. Different models of muscle unloading can provide valuable information, but the protocols of experiments with complete immobilization are not physiologically representative of a sedentary lifestyle, which is highly prevalent among humans now. In the current study, we investigated the potential effects of restricted activity on the mechanical characteristics of rat postural (soleus) and locomotor (extensor digitorum longus, EDL) muscles. The restricted-activity rats were kept in small Plexiglas cages (17.0 × 9.6 × 13.0 cm) for 7 and 21 days. After this, soleus and EDL muscles were collected for ex vivo mechanical measurements and biochemical analysis. We demonstrated that while a 21-day movement restriction affected the weight of both muscles, in soleus muscle we observed a greater decrease. The maximum isometric force and passive tension in both muscles also significantly changed after 21 days of movement restriction, along with a decrease in the level of collagen 1 and 3 mRNA expression. Furthermore, the collagen content itself changed only in soleus after 7 and 21 days of movement restriction. With regard to cytoskeletal proteins, in our experiment we observed a significant decrease in telethonin in soleus, and a similar decrease in desmin and telethonin in EDL. We also observed a shift towards fast-type myosin heavy chain expression in soleus, but not in EDL. In summary, in this study we showed that movement restriction leads to profound specific changes in the mechanical properties of fast and slow skeletal muscles. Future studies may include evaluation of signaling mechanisms regulating the synthesis, degradation, and mRNA expression of the extracellular matrix and scaffold proteins of myofibers.

The mammalian insulin antagonist S961 does not exhibit insulin receptor antagonism in rainbow trout in vivo.

Due to their reported 'glucose-intolerant' phenotype, rainbow trout have been the focus of comparative studies probing underlying endocrine mechanisms at the organismal, tissue and molecular level. A particular focus has been placed on the investigation of the comparative role of insulin, an important glucoregulatory hormone, and its interaction with macronutrients. A limiting factor in the comparative investigation of insulin is the current lack of reliable assays to quantify circulating mature and thus bioactive insulin. To circumvent this limitation, tissue-specific responsiveness to postprandial or exogenous insulin has been quantified at the level of post-translational modifications of cell signalling proteins. These studies revealed that the insulin responsiveness of these proteins and their post-translational modifications are evolutionarily highly conserved and thus provide useful and quantifiable proxy indices to investigate insulin function in rainbow trout. While the involvement of specific branches of the intracellular insulin signalling pathway (e.g., mTor) in rainbow trout glucoregulation have been successfully probed through pharmacological approaches, it would be useful to have a functionally validated insulin receptor antagonist to characterize the glucoregulatory role of the insulin receptor pathway in its entirety for this species. Here, we report two separate in vivo experiments to test the ability of the mammalian insulin receptor antagonist, S961, to efficiently block insulin signalling in liver and muscle in response to endogenously released insulin and to exogenously infused bovine insulin. We found that, irrespective of the experimental treatment or dose, activation of the insulin pathway in liver and muscle was not inhibited by S961, showing that its antagonistic effect does not extend to rainbow trout.

Emerging role of TAK1 in the regulation of skeletal muscle mass.

Maintenance of skeletal muscle mass and strength throughout life is crucial for heathy living and longevity. Several signaling pathways have been implicated in the regulation of skeletal muscle mass in adults. TGF-β-activated kinase 1 (TAK1) is a key protein, which coordinates the activation of multiple signaling pathways. Recently, it was discovered that TAK1 is essential for the maintenance of skeletal muscle mass and myofiber hypertrophy following mechanical overload. Forced activation of TAK1 in skeletal muscle causes hypertrophy and attenuates denervation-induced muscle atrophy. TAK1-mediated signaling in skeletal muscle promotes protein synthesis, redox homeostasis, mitochondrial health, and integrity of neuromuscular junctions. In this article, we have reviewed the role and potential mechanisms through which TAK1 regulates skeletal muscle mass and growth. We have also proposed future areas of research that could be instrumental in exploring TAK1 as therapeutic target for improving muscle mass in various catabolic conditions and diseases.

Phosphoproteomics Profiling Defines a Target Landscape of the Basophilic Protein Kinases AKT, S6K, and RSK in Skeletal Myotubes.

Phosphorylation-dependent signal transduction plays an important role in regulating the functions and fate of skeletal muscle cells. Central players in the phospho-signaling network are the protein kinases AKT, S6K, and RSK as part of the PI3K-AKT-mTOR-S6K and RAF-MEK-ERK-RSK pathways. However, despite their functional importance, knowledge about their specific targets is incomplete because these kinases share the same basophilic substrate motif RxRxxp[ST]. To address this, we performed a multifaceted quantitative phosphoproteomics study of skeletal myotubes following kinase inhibition. Our data corroborate a cross talk between AKT and RAF, a negative feedback loop of RSK on ERK, and a putative connection between RSK and PI3K signaling. Altogether, we report a kinase target landscape containing 49 so far unknown target sites. AKT, S6K, and RSK phosphorylate numerous proteins involved in muscle development, integrity, and functions, and signaling converges on factors that are central for the skeletal muscle cytoskeleton. Whereas AKT controls insulin signaling and impinges on GTPase signaling, nuclear signaling is characteristic for RSK. Our data further support a role of RSK in glucose metabolism. Shared targets have functions in RNA maturation, stability, and translation, which suggests that these basophilic kinases establish an intricate signaling network to orchestrate and regulate processes involved in translation.

Magnetic resonance findings of Stewart-Treves Syndrome in primary limb lymphedema compared with pathology: A retrospective single-center study.

Stewart-Treves Syndrome in Primary Limb Lymphedema (STS-PLE) is an extremely rare malignant tumor. A retrospective analysis was conducted to elucidate the relationship between magnetic resonance imaging (MRI) findings and signs compared to pathology. Seven patients with STS-PLE were enrolled at Beijing Shijitan Hospital, Capital Medical University, from June 2008 to March 2022. All cases were examined by MRI. The surgical specimens were subjected to histopathological and immunohistochemical staining for CD31, CD34, D2-40, and Ki-67. There were two different types of MRI findings. One was mass shape (STS-PLE I type) in three male patients, and the other was the "trash ice" d sign (STS-PLE II type) observed in four female patients. The average duration of lymphedema (DL) of STS-PLE I type (18 months) was shorter than that of STS-PLE II type (31 months). The prognosis for the STS-PLE I type was worse than that for the STS-PLE II type. Regarding overall survival (OS), the STS-PLE I type (17.3 months) was three times shorter than that of the STS-PLE II type (54.5 months). For STS-PLE I type, the older the STS-PLE onset, the shorter the OS. However, there was no significant correlation in STS-PLE II type. MRI was compared to histological results to provide an explanation for the differences in MR signal changes, especially on T2WI. Against a background of dense tumor cells, the richer the lumen of immature vessels and clefts, the higher the T2WI MRI signal (taking muscle signal as the internal reference standard) and the worse the prognosis, and vice versa. We also found that younger patients with a lower Ki-67 index (<16%) had better OS, especially for the STS-PLE I type. Those with stronger positive expression of CD31 or CD34 had shorter OS. However, the expression of D2-40 was positive in nearly all cases, and seemed not to be associated with prognosis. In lymphedema, the richer the lumen of immature vessels and clefts based on dense tumor cells, the higher the T2WI signal on the MRI. In adolescent patients, the tumor often showed a "trash ice" sign (STS-PLE II-type) and prognosis was better than for the STS-PLE I type. While in middle-aged and older patients, tumors showed a mass shape (STS-PLE I type). The expression of immunohistochemical indicators (CD31, CD34, and KI-67) correlated with clinical prognosis, especially decreased Ki-67 expression. In this study, we determined it was possible to predict prognosis comparing MRI findings with pathological results.

Candesartan protects against unilateral peripheral limb ischemia in type-2 diabetic rats: Possible contribution of PI3K-Akt-eNOS-VEGF angiogenic signaling pathway

Type-2 diabetes (T2DM) is known to be highly associated with increased risk for vascular complications including peripheral arterial diseases (PAD). Critical limb ischemia (CLI) is the most advanced stage of PAD. Current therapeutic options for diabetic patients experiencing vascular complications are limited to surgical revascularization with no effective pharmacotherapy available for clinical settings. This study is dedicated to evaluate the angiogenic potential of candesartan an angiotensin-II receptor blocker in an experimental model of vascular complications associating T2DM. T2DM was induced in rats through feeding with high fat diet for 6 weeks, followed by injection with streptozotocin (STZ, 30 mg/kg; i.p). After establishment of T2DM, unilateral CLI was induced through the ligation and excision of superficial femoral artery. Candesartan treatment (10 or 30 mg/kg; orally) was initiated one day post CLI and thereafter once daily for up to 14 days. T2DM rats that underwent CLI demonstrated impaired angiogenic signaling, increased inflammation and apoptosis in gastrocnemius muscle (GC). Candesartan reversed ischemic insult in T2DM rats subjected to unilateral CLI and induced reparative angiogenesis that was evident by increase in p-PI3K/PI3K, p-Akt/Akt, p-eNOS/eNOS, p-VEGFR2/VEGFR2 ratios, and VEGF levels. Candesartan treatment also increased levels of HO-1; while decreased caspase-3 apoptotic marker and levels of inflammatory markers; NF-κB and TNF-α, all of which were accompanied by preserved histological manifestations of GC muscles. Candesartan was able to combat limb ischemia under diabetic conditions which could pave the way for its therapeutic utility for diabetic patients experiencing vascular complications in clinical setting.

A flexible carbon nanotube electrode array for acute in vivo EMG recordings.

Executing complex behaviors requires precise control of muscle activity. Our understanding of how the nervous system learns and controls motor skills relies on recording electromyographic (EMG) signals from multiple muscles that are engaged in the motor task. Despite recent advances in tools for monitoring and manipulating neural activity, methods for recording in situ spiking activity in muscle fibers have changed little in recent decades. Here, we introduce a novel experimental approach to recording high-resolution EMG signals using parylene-coated carbon nanotube fibers (CNTFs). These fibers are fabricated via a wet spinning process and twisted together to create a bipolar electrode. Single CNTFs are strong, extremely flexible, small in diameter (14-24 µm), and have low interface impedance. We present two designs to build bipolar electrode arrays that, due to the small size of CNTF, lead to high spatial resolution EMG recordings. To test the EMG arrays, we recorded the activity of small (4 mm length) vocal muscles in songbirds in an acute setting. CNTF arrays were more flexible and yielded multiunit/bulk EMG recordings with higher SNR compared with stainless steel wire electrodes. Furthermore, we were able to record single-unit recordings not previously reported in these small muscles. CNTF electrodes are therefore well-suited for high-resolution EMG recording in acute settings, and we present both opportunities and challenges for their application in long-term chronic recordings.NEW & NOTEWORTHY We introduce a novel approach to record high-resolution EMG signals in small muscles using extremely strong and flexible carbon nanotube fibers (CNTFs). We test their functionality in songbird vocal muscles. Acute EMG recordings successfully yielded multiunit recordings with high SNR. Furthermore, they successfully isolated single-unit spike trains from CNTF recordings. CNTF electrodes have great potential for chronic EMG studies of small, deep muscles that demand high electrode flexibility and strength.

Cold exposure alters lipid metabolism of skeletal muscle through HIF-1α-induced mitophagy

BackgroundIn addition to its contractile properties and role in movement, skeletal muscle plays an important function in regulating whole-body glucose and lipid metabolism. A central component of such regulation is mitochondria, whose quality and function are essential in maintaining proper metabolic homeostasis, with defects in processes such as autophagy and mitophagy involved in mitochondria quality control impairing skeletal muscle mass and function, and potentially leading to a number of associated diseases. Cold exposure has been reported to markedly induce metabolic remodeling and enhance insulin sensitivity in the whole body by regulating mitochondrial biogenesis. However, changes in lipid metabolism and lipidomic profiles in skeletal muscle in response to cold exposure are unclear. Here, we generated lipidomic or transcriptome profiles of mouse skeletal muscle following cold induction, to dissect the molecular mechanisms regulating lipid metabolism upon acute cold treatment.ResultsOur results indicated that short-term cold exposure (3 days) can lead to a significant increase in intramuscular fat deposition. Lipidomic analyses revealed that a cold challenge altered the overall lipid composition by increasing the content of triglyceride (TG), lysophosphatidylcholine (LPC), and lysophosphatidylethanolamine (LPE), while decreasing sphingomyelin (SM), validating lipid remodeling during the cold environment. In addition, RNA-seq and qPCR analysis showed that cold exposure promoted the expression of genes related to lipolysis and fatty acid biosynthesis. These marked changes in metabolic effects were associated with mitophagy and muscle signaling pathways, which were accompanied by increased TG deposition and impaired fatty acid oxidation. Mechanistically, HIF-1α signaling was highly activated in response to the cold challenge, which may contribute to intramuscular fat deposition and enhanced mitophagy in a cold environment.ConclusionsOverall, our data revealed the adaptive changes of skeletal muscle associated with lipidomic and transcriptomic profiles upon cold exposure. We described the significant alterations in the composition of specific lipid species and expression of genes involved in glucose and fatty acid metabolism. Cold-mediated mitophagy may play a critical role in modulating lipid metabolism in skeletal muscle, which is precisely regulated by HIF-1α signaling.

Astrocyte-mediated Transduction of Muscle Fiber Contractions Synchronizes Hippocampal Neuronal Network Development

Exercise supports brain health in part by enhancing hippocampal function. The leading hypothesis is that muscles release factors when they contract (e.g., lactate, myokines, growth factors) that enter circulation and reach the brain where they enhance plasticity (e.g., increase neurogenesis and synaptogenesis). However, it remains unknown how the muscle signals are transduced by the hippocampal cells to modulate network activity and synaptic development. Thus, we established an in vitro model in which the media from contracting primary muscle cells (CM) is applied to developing primary hippocampal cell cultures on a microelectrode array. We found that the hippocampal neuronal network matures more rapidly (as indicated by synapse development and synchronous neuronal activity) when exposed to CM than regular media (RM). This was accompanied by a 4.4- and 1.4-fold increase in the proliferation of astrocytes and neurons, respectively. Further, experiments established that factors released by astrocytes inhibit neuronal hyper-excitability induced by muscle media, and facilitate network development. Results provide new insight into how exercise may support hippocampal function by regulating astrocyte proliferation and subsequent taming of neuronal activity into an integrated network.

Interrogation of skeletal muscle activation in an intact system via a myofilament incorporated FRET biosensor.

It is important to understand the mechanisms involved in regulating skeletal muscle activation and contraction for advancing insights into acquired and inherited muscle disorders and for identifying potential targets for therapeutics. The field has elucidated many sarcomeric components needed for activation of contraction. We seek to expand this work using a fluorescent sarcomere biosensor that allows for monitoring of sarcomeric activation in live, intact skeletal muscles. This biosensor fuses fluorescent donor and acceptor proteins to the N- and C-terminals of fast skeletal troponin C protein, respectively. Using the biosensor, skeletal muscle activation is monitored in real time through Förster Resonance Energy Transfer (FRET) fluorescence. This system maintains all essential, physiological features of the muscle, including excitation-contraction coupling and load, which was not possible in reconstituted systems. Using a transgenic mouse line with the biosensor, we have demonstrated FRET fluorescence in intact muscles from transgenic animals, with the time to peak of the fluorescence preceding the force development and the biosensor kinetics uncoupled from intracellular calcium kinetics. Of note, the FRET signal has a prolonged return to baseline as compared to force in intact EDL muscles, something that is not observed in unloaded FDB myofibers, and which may be evidence of a “primed state” of myofilament activation. The “primed state” is uncoupled from Ca2+ and is modified using fast skeletal muscle specific small molecules that target either the thin filament or thick filament. As thick filament modulating small molecules could be detected by the TnC localized biosensor during single twitch contractions, this demonstrates intermyofilament signaling in live muscle. Additionally, the “primed state” duration can be impacted through varying stimulation protocols, including dual pulse stimulations. This unique phenomenon will be further investigated using mechanical and pharmacological manipulations.

Clinical, cellular and molecular approaches to oxidative stress in athletes' bodies: a systematic and integrative review

Introduction: Frequent physical exercises can cause a state of transient fatigue, thus increasing the regenerative capacity of the body and inducing an overcompensation of the biological systems involved. The state resulting from overtraining has negative consequences not only for physical performance but also for health and when this state occurs, reactive oxygen species (ROS) are synthesized in the body. Objective: It was to carry out a systematic and integrative review of the main clinical, cellular and molecular approaches to oxidative stress in athletes' bodies, as well as the main functions of antioxidants in mitochondria. Methods: The systematic review rules of the PRISMA Platform were followed. The research was carried out from October to December 2022 in Scopus, PubMed, Science Direct, Scielo, and Google Scholar databases. The quality of the studies was based on the GRADE instrument and the risk of bias was analyzed according to the Cochrane instrument. Results and Conclusion: A total of 127 articles were found, and a total of 67 articles were fully evaluated and 57 were included and developed in the present systematic review study. Considering the Cochrane tool for risk of bias, the overall assessment resulted in 7 studies at high risk of bias and 25 studies that did not meet the GRADE. Studies have shown that free radicals play important roles as regulators in muscle signaling processes. Oxidative stress reflects an imbalance between the production of reactive oxygen species and adequate antioxidant defense. The relationship between exercise and oxidative stress is extremely complex, depending on the mode, intensity, and duration of exercise. High levels of reactive oxygen species produced in skeletal muscle during exercise have been associated with muscle damage and impaired muscle function. Antioxidant supplementation may be warranted under specific conditions when athletes are exposed to high oxidative stress or do not meet dietary antioxidant requirements. Continuous aerobic exercise under moderate-intensity or high-intensity interval training can be recommended to increase the body's ability to maintain redox balance, especially for unhealthy individuals.

Investigation of Phase Shifts Using AUC Diagrams: Application to Differential Diagnosis of Parkinson's Disease and Essential Tremor.

This study was motivated by the well-known problem of the differential diagnosis of Parkinson's disease and essential tremor using the phase shift between the tremor signals in the antagonist muscles of patients. Different phase shifts are typical for different diseases; however, it remains unclear how this parameter can be used for clinical diagnosis. Neurophysiological papers have reported different estimations of the accuracy of this parameter, which varies from insufficient to 100%. To address this issue, we developed special types of area under the ROC curve (AUC) diagrams and used them to analyze the phase shift. Different phase estimations, including the Hilbert instantaneous phase and the cross-wavelet spectrum mean phase, were applied. The results of the investigation of the clinical data revealed several regularities with opposite directions in the phase shift of the electromyographic signals in patients with Parkinson's disease and essential tremor. The detected regularities provide insights into the contradictory results reported in the literature. Moreover, the developed AUC diagrams show the potential for the investigation of neurodegenerative diseases related to the hyperkinetic movements of the extremities and the creation of high-accuracy methods of clinical diagnosis.

Regulation of the endocannabinoid system by endurance and resistance exercise in hypoxia in human skeletal muscle.

Exercise modulates the circulating levels of the endocannabinoids ligands N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) and possibly the levels of their receptors and downstream signaling in skeletal muscle. The aim of the present study was to investigate the regulation of the endocannabinoid system by several exercise paradigms in human skeletal muscle. A second aim was to compare endocannabinoid regulation in healthy and prediabetic people in response to an acute endurance exercise. Blood and muscle samples were taken before and after resistance and endurance exercise in normoxia and hypoxia to measure plasma endocannabinoid levels as well as muscle protein expression of CB1, CB2, and downstream signaling. We found that: 1) an acute resistance exercise session decreased plasma 2-AG and N-palmitoylethanolamine (PEA) levels in normoxia; 2) 4 wk resistance training decreased plasma AEA, PEA, and N-oleoylethanolamine (OEA) levels in both normoxia and hypoxia; 3) an acute moderate-intensity endurance exercise increased plasma OEA levels in the healthy and prediabetic groups in normoxia and hypoxia, whereas plasma 2-AG levels increased in the healthy group and AEA in the prediabetic group only in normoxia. The expression of the cannabinoid receptors was only marginally regulated by acute exercise, hypoxia, and prediabetes and downstream signaling did not follow the changes detected in the endocannabinoid ligands. Altogether, our results suggest that resistance and endurance exercise regulate the levels of the endocannabinoid ligands and CB1 expression in opposite ways. The physiological impact of the changes observed in the endocannabinoid ligands in human skeletal muscle after exercise needs further investigation.NEW & NOTEWORTHY We are the first to analyze both endocannabinoids ligands and receptors in response to endurance and resistance exercise. In addition, no study before has compared both exercise paradigms regarding endocannabinoid tone, which is of interest as endocannabinoids regulate energy metabolism, and these are different between endurance and resistance exercise. Furthermore, we investigated whether the endocannabinoid tone was differently regulated in response to acute endurance exercise in prediabetic people. Linking exercise, endocannabinoids and (pre)diabetic people has never been done before.

Spatially and velocity-selective magnetization preparation for noncontrast-enhanced peripheral MR angiography.

The purpose of the current study was to develop spatially and velocity-selective (SVS) magnetization preparation pulses for noncontrast-enhanced peripheral MR angiography (MRA) to provide comparisons with velocity-selective (VS) MRA with comparison to velocity-selective (VS). VS preparation pulses were designed by concatenating multiple excitation steps, each of which was a combination of a hard RF pulse, VS unipolar gradient pulses, and refocusing RF pulses. SVS preparation pulses were designed by replacing the hard RF pulse with a sinc-shaped RF pulse combined with a symmetric tripolar gradient pulse (which does not perturb the velocity encoding by the VS unipolar gradient pulses). Numerical simulations were performed to verify the intended hybrid excitation selectivity of SVS pulses taking account of tissue relaxation, magnetic field errors, and eddy currents. In vivo experiments were performed in healthy subjects to verify the hybrid excitation selectivity, as well as to demonstrate the visualization of the entire peripheral arteries using six-station protocols. As demonstrated by numerical simulations, SVS preparation yielded a notch-shaped longitudinal magnetization (Mz )-velocity response within the spatial stopband (the same as VS preparation) and preserved the Mz of spins outside the stopband, regardless of its velocity. We confirmed these observations also through in vivo tests with good agreement in normalized arterial and muscle signal intensities. In six-station peripheral MRA experiments, the proposed SVS-MRA yielded significantly higher arterial signal-to-noise ratio (SNR) (51.6 ± 14.3 vs. 38.9 ± 10.9; p < 0.001) and contrast-to-noise ratio (CNR) (41.2 ± 13.0 vs. 31.3 ± 10.5; p < 0.001) compared with VS-MRA. The proposed SVS-MRA improves arterial SNR and CNR compared with VS-MRA by mitigating undesired presaturation of arterial blood upstream the imaging field of view.

Generation and analysis of synthetic surface electromyography signals under varied muscle fiber type proportions and validation using recorded signals.

The magnitude and duration of muscle force production are influenced by the fiber type proportion. In this work, surface electromyography (sEMG) signals of muscles with varied fiber type proportions, are generated. For this, relevant components of existing models reported in various literature have been adopted. Also, a method to calculate the motor unit size factor is proposed. sEMG signals of adductor pollicis (AP) and triceps brachii (TB) muscles are simulated from the onset of force production to muscle fatigue state at various percentages of maximal voluntary contraction (MVC) values. The model is validated using signals recorded from these muscles using well-defined isometric exercise protocols. Root mean square and mean power spectral density values extracted from the simulated and recorded signals are found to increase for TB and decrease for AP with time. A linear variation of the features with %MVC values is obtained for simulated and experimental results. The Bland-Altman plot is used to analyze the agreement between simulated and experimental feature values. Good agreement is obtained for the feature values at various %MVCs. The mean endurance time calculated using the model is found to be comparable to that of the experimental value. This method can be used to generate sEMG signals of different muscles with varying fiber type ratios under various neuromuscular conditions.

Potentiated respiratory metaboreflex in older males and females: afferent or efferent mechanisms?

Potentiated respiratory metaboreflex in older males and females: afferent or efferent mechanisms?