Résumé :
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Dynamic in vivo nuclear magnetic resonance (NMR) imaging and spectroscopic investigations of metabolism, perfusion and/or oxygenation has existed in humans for many years, including in interleaved combinations of these1 and serves for clinical investigations of pathology. Technological transfer to mice remains a challenge, despite the manifest interest in investigating muscle function in models of disease. A recurrent issue is obtaining reproducible non-invasive electrostimulation (ES) of rodent muscle. Set-ups have been proposed for fully non-invasive (FNI)2 or minimally invasive (MI)3 ES in mice. The present work aimed at comparing repeated ES of calf muscles by FNI per-cutaneous copper wire electrodes secured to skin with adhesive conductive gel, to MI ES with silver wire electrodes, inserted subcutaneously, in terms of1) muscle damage, assessed at 24hrs post-ES by- T2 NMRI maps - histological analysis of excised Gastrocnemius muscles2) metabolic reproducibility of exercise by- multi-parametric functional NMR1, 3 - force measurementsTwelve FVB mice investigated in a Bruker 4T NMR system underwent [2min moderate exercise -10min recovery] repeated 12 times. ES (120?s, 50Hz pulses, 0.5s trains every 2.5s) required 2mA intensity for supra-maximal contractions in MI protocol, but 5mA for reproducible ES in FNI.The FNI protocol elicited a greater output force, phosphocreatine (PCr) depletion and maximum perfusion, while PCr recovery time and end exercise pH were identical to MI. Variance moderately increased only for maximum perfusion. Despite higher sollicitation, T2 at 24h of ES leg showed no increase after FNI, while MI ES provoked a small T2 elevation in muscle (p=0.09) and occasional subcutaneous enhancement, suggestive of oedema from subcutaneous electrode placement. In histology, at most 10% randomly distributed necrotic myofibers were seen in MI protocol, and even less in FNI (< 5% in 1 mouse, 3/4 mice had 0-6 countable necrotic fibers).Although unavoidably less selective than needle nervous ES4, fully atraumatic surface electrodes are an improvement over subcutaneous electrodes in reducing lesions and installation time while still procuring reproducible stimulation of mouse muscles for NMR evaluation of vascular and metabolic function in mice. 1. P.G. Carlier, et al., Magn Reson Med, 2005. 54; 2. B. Giannesini, et al., Magn Reson Med, 2010. 64; 3. C. Baligand, et al., NMR Biomed, 2010. epub; 4. H.M.D. Feyter, et al. 15th ISMRM. 2007. Berlin
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