Early immobilization of hindleg muscles of dystrophic mice: short-term and long-term effects.

Hindleg muscles of normal and dystrophic mice were immobilized unilaterally early during the postnatal period. After 1 week the casts were removed. Of one group of mice hindleg muscles were processed for histopathological and morphometrical evaluation at the end of the immobilization period. Hindlegs of other groups of mice were remobilized for various periods of time before the muscles were examined. In normal mice immobilization of calf muscles that were fixed in a shortened position resulted in atrophy of about 35% compared with untreated muscles. This was accompanied by a reduction in fibre number of about 15%. The antagonists that had been fixed extended, did not show those effects. Immobilization of dystrophic muscles minimized pathology in both agonists and antagonists, although atrophy developed. Upon remobilization the normal muscles resumed postnatal development. They did not deviate from normal, untreated muscles at the age of 3.5 months. Upon remobilization of dystrophic muscles pathology developed, but less severely than during the second and third postnatal week in untreated dystrophic muscles. Significant differences in morphometrical parameters compared with untreated dystrophic muscles were observed during the 3 months remobilization period studied.