Résumé :
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Introduction. The aim of this study was to set up an in vivo and non-invasive follow-up of the skeletal muscle function in small rodents. In this purpose we developed ahome-made torquemeter based on previous studies in the literature. The reproducibility and sensitivity of our set up was assessed and the device was used to comparethe ankle dorsal and plantar flexion torque of a Myotonic Dystrophy type 1 mouse model (DMSXL) with wild-type mice in vivo over 2 months. Method. Anaesthetized micewere placed in a standardized position in a home-made torquemeter to measure the ankle flexion and extension torque. Removable subcutaneous electrodes insertedat the level of the Tibialis Anterior or of the Gastrocnemius induced the ankle flexion or extension, respectively. The resulting isometric maximal torque was measured,as well as contraction relaxation and fatigue resistance.Results. The torque recorded in c57bl6 wild-type mice at 4 and 6 months of age was respectively 1.88±0.18N.mm and 2.02±0.17 N.mm for dorsal flexion and 6.50±0.82 N.mm and 6.90±0.67 N.mm for plantar flexion of the ankle (n=4). These values are in agreement withthe literature. We didn't find any significant difference between right and left legs, validating the intra-individual reproducibility. In DMSXL mice (n=4) at 4 and 6 monthsof age, the torque for dorsal and plantar flexion was reduced by 25% compared to control c57bl6 mice. The same decrease was observed when torque was normalizedwith the leg length (20-25%). However no significant difference was seen when torque was normalized with body mass. Half-relaxation time was similar in DMSXL andcontrol mice, suggesting the absence of myotonia in these muscle groups. Moreover a test for resistance to fatigue didn't show any difference between DMSXL andcontrol mice.Conclusion. The set-up described here allows in vivo longitudinal studies of the ankle dorsal and plantar flexion in almost non-invasive conditions. Thesensitivity is sufficient to discriminate DMSXL mice from control animals and the efficacy of therapeutic approaches on muscle function is planned to be tested in vivo ina long term follow up.
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