Functional properties of muscle transplanted between normal and dystrophic mice

Modification of the phenotypic expression of murine dystrophy: a morphological study

The extensor digitorum longus muscles of 4-6-week-old normal mice (129 ReJ) and dystrophic mice (129 ReJ dy/dy) were orthotopically transplanted. Grafted muscles were examined 1, 3, 7, 14, 20, 50, and 100 days post-transplantation. The myofibers of both types of grafts underwent a similar time course of necrosis and regeneration. Other than during the initial necrotic response, no evidence of necrotic myofibers was found in either type of grafted muscle. At 100 days post-transplantation, the grafted normal and dystrophic muscles were essentially similar, except that the dystrophic graft was of smaller size. Based on a comparison of the number of myofibers found at the 100-day grafts' widest girths [631 +/- 59 SEM, for normal grafts (Bourke and Ontell, 1984); 631 +/- 74 SEM, for dystrophic grafts], it is suggested that the regenerative capability of traumatized 4-6-week-old dystrophic muscle is similar to that of traumatized normal muscle. At 100 days post-transplantation, the grafted dystrophic muscle appeared "healthier" than untraumatized muscle from age-matched dystrophic mice, having less variation in myofiber diameter, better fascicular organization, and less connective tissue. The transplantation system demonstrates the possibility of modifying the expression of genetic programming of myopathic disorders using environmental manipulation.

Use of mononuclear precursor cells to insert allogeneic genes into growing mouse muscles

Our long-term aim is to use allografts of normal muscle precursor cells to insert donor myonuclei, containing a normal genome, into the growing defective muscle fibers of young animals with inherited myopathies. In the present article, we have used isoenzyme variants of glucose-6-phosphate isomerase (GPI) as genetic markers of host and donor genomes in the mouse. We show that mononucleated cells, prepared by enzymatic disaggregation of neonatal donor muscle, 39 can be used to introduce donor GPI genes into muscle fibers of growing muscles of young hosts. The expression of both donor and host GPI genes in the resulting mosaic muscle fibers leads to the formation of a "hybrid" GPI isoenzyme dimer. Such hybrid GPI was found in 10 of 102 host muscles examined. Our results indicate that grafts of muscle precursor cells can be used to alter the genetic constitution of both normal and mildly myopathic muscle.

Freely transplanted peroneus longus muscle in the cat reinnervated by a single nerve: physiological properties

Physiological properties (tetanic tension, single twitch, fatigability) of free autologous muscle transplants in cats were examined in vivo five months after transplantation. After 2 weeks denervation the peroneus longus muscle was placed isometrically in the abdomen with the omentum around the muscle and with the proximal end of a cut branch of the femoral nerve attached to the muscle. (In one case a sensory nerve was used.) Five months after transplantation the function of the muscle was controlled in vivo by nerve stimulation. In the case when a sensory nerve was connected to the muscle no contraction was obtained upon indirect or direct stimulation. All the other muscles contracted when the nerve was stimulated. The mean maximum tetanic tension was 16% of the mean for the control. The twitch-time was about the same as in the control muscle but the contraction time was longer and the half relaxation time shorter compared with the control. The transplanted muscles fatigued more slowly than the normal peroneus longus muscles. In spite of the unphysiological placement of the muscles in the abdomen where they have no natural function to fulfil, they became reinnervated and contracted as late as five months after transplantation.

Tests of skeletal muscle function in children

The contractile properties of a large proximal muscle (quadriceps femoris) and a small distal muscle (adductor pollicis) have been measured in normal children and children with neuromuscular disorders. The method of stimulating the quadriceps femoris to contract, previously evaluated in adults, was found to be acceptable to children. In normal children a number of indices of muscle function were found to be similar to those in adults. A small study of the function of the adductor pollicis using supramaximal stimulation of the ulnar nerve was carried out in boys with Duchenne dystrophy. Decreased contractile force and prolonged relaxation times from a tetanic stimulation were noted in both the proximal and distal muscles of the boys with Duchenne dystrophy.