Long term functional improvement of dystrophic mouse leg muscles upon early immobilization.

The long term effects of immobilization of one hindleg, during the second postnatal week, were investigated in dystrophic ReJ 129 dy/dy strain of mice. The muscles of the immobilized limb were compared with those of the contralateral, non-treated side and with those of naturally dystrophic age-mates, after 1, 2 and 3 months of remobilization. It appeared that the experimental animals made better use of their remobilized leg than of the contralateral leg for locomotion. The remobilized muscles were significantly less atrophic than the contralateral muscles and they also contained more muscle fibres. It is concluded that during postnatal growth and differentiation the dystrophic muscle fibres pass through a sensitive period. Immobilization during this period prevents the majority of the muscle fibres from becoming affected. Remobilization induces pathological features in the muscles, but they remain less damaged than the non-immobilized muscles.