RETARDED MYOGENIC CELL REPLICATION IN REGENERATING SKELETAL-MUSCLES OF OLD MICE - AN AUTORADIOGRAPHIC STUDY IN YOUNG AND OLD BALBC AND SJL J MICE/

The patterns of skeletal muscle precursor cell replication after crush injury were compared by the use of autoradiographic techniques, in yo ung (4-week-old) and old (39-week-old) BALBc and SJL/J mice, Similar c omparisons were made between cut and crush lesions in old BALBc muscle . Muscle precursor cell replication commenced at 18-24 h after injury in both young and old muscles from both strains of mice. In young BALB c muscle the peak of myogenic activity at 60 h was 36 h earlier than i n old mice. SJL/J muscle responded more rapidly than did BALBc: in you ng SJL/J the peak myogenic activity was at 46 h (14 h earlier than in young BALBc muscle), and in old SJL/J muscle the peak activity at 72 h was 24 h earlier than in old BALBc muscle. In all mice (both young an d old) myogenic cell replication was substantially reduced by 120 h af ter injury. A comparison of the timing of muscle precursor cell replic ation in cut and crush lesions in old BALBc mice revealed a more rapid response in the cut lesion; this difference between the lesions is co mparable with data from identical lesions in 6-8-week-old BALBc mice ( McGeachie and Grounds 1987). However, the peak of myogenic replication in the older mice in the present study was some 26-36 h later than in the younger 6-8-week-old mice. These experiments show that, whilst mu scle precursor cell replication commences at approximately the same ti me (about 24 h) after injury in young and old mice, the peak level of activity is delayed by some 24-36 h in old mice. In addition, the SJL/ J mouse strain responds more rapidly and prolifically to muscle injury than does the BALBc strain.