A strictly noninvasive MR setup dedicated to longitudinal studies of mechanical performance, bioenergetics, anatomy, and muscle recruitment in contracting mouse skeletal muscle
Résumé
MR techniques have proven their ability to investigate skeletal muscle function in situ. Their benefit in terms of noninvasiveness is, however, lost in animal research, given that muscle stimulation and force output measurements are usually achieved using invasive surgical procedures, thereby excluding repeated investigations in the same animal. This study describes a new setup allowing strictly noninvasive investigations of mouse gastrocnemius muscle function using (1)H-MRI and (31)P-MR spectroscopy. Its originality is to integrate noninvasive systems for inducing muscle contraction through transcutaneous stimulation and for measuring mechanical performance with a dedicated ergometer. In order to test the setup, muscle function was investigated using a fatiguing stimulation protocol (6 min of repeated isometric contractions at 1.7 Hz). T(2)-weighted imaging demonstrated that transcutaneous stimulation mainly activated the gastrocnemius. Moreover, investigations repeated twice with a 7-day interval between bouts did show a high reproducibility in measurements with regard to changes in isometric force and energy metabolism. In conclusion, this setup enables us for the first time to access mechanical performance, energy metabolism, anatomy, and physiology strictly noninvasively in contracting mouse skeletal muscle. The possibility for implementing longitudinal studies opens up new perspectives in many research areas, including ageing, pharmaceutical research, and gene and cell therapy.