Résumé :
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Introduction. Magnetic resonance (MR) techniques have proven their ability to investigate skeletal muscle function in situ. However, in animal research, the benefit provided by MR techniques in terms of non-invasiveness is lost because of the utilization of invasive procedures for inducing muscular contractions (via nerve stimulation) and for measuring force output (via attachment of a transducer to the muscle tendon). Required surgical preparation thus prohibits repeated investigations on the same animal. We have developed a new experimental setup allowing strictly non-invasive MR investigations of muscle function in contracting rat gastrocnemius muscle. In this study, we have compared its performance with that of a traditional invasive setup. Methods. The new setup integrates four non-invasive systems allowing prolonged anesthesia with control of the animal’s body temperature, transcutaneous electrical stimulation of the gastrocnemius muscle, force measurement with a dedicated ergometer, and two MR probes for 31-phosphorus spectroscopy and proton imaging. Muscle function was investigated in 20 rats through a fatiguing stimulation protocol, either with this new setup (n = 10 rats) or with a traditional setup (n = 10). Results. Muscle functional MR imaging demonstrated that transcutaneous stimulation specifically activated the gastrocnemius muscle. During the stimulation period, changes in isometric force production and energy metabolism (intramuscular pH and phosphorylated compounds) were similar for both setups. Conclusion. The non-invasive setup is then suitable for investigating skeletal muscle function in situ, allowing mechanical performance, energy metabolism, anatomy and physiology to be accessed strictly non-invasively in contracting rat gastrocnemius muscle. This non-invasive alternative makes surgical preparations obsolete and represents a major advance for the future investigations of skeletal muscle function in animal models. Longitudinal studies become readily feasible and each rat can serve as its own control, thus reducing inter-individual variability, workload and costs, hence opening up new perspectives in various research areas including pharmaceutical research.
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