Use of Regenerating Skeletal Muscle During Voluntary Locomotion: Effects of Physical Training.

Abstract

Hypotheses were tested concerning the reinnervation and use of grafted skeletal muscle during voluntary locomotion and on the effects of training on changing these parameters. In rats, one soleus (SOL) muscle was transplanted with a SOL nerve implant; the other was sham-operated for control. In one experiment, muscle use was assessed qualitatively by measuring glycogen depletion after a 45 minute run to exhaustion. Cholinergic innervation was estimated by choline acetyltransferase (ChAT) activity. At 28 days after transplantation the decrease in glycogen content in grafts was greater (56%) than that at 7 days (25%) and did not differ from control (60%). ChAT activity increased from 10% (day 7) to 50% (day 28) of control values. In a second experiment, four weeks of endurance running commencing 28 days after transplantation did not significantly effect graft ChAT activity, and all grafts attained values equal to control. In a third experiment, electromyography (EMG) was used to quantitatively estimate muscle use. At 56 days after transplantation, trained and non-trained animals were run at 2 speeds and 3 grades while EMG's were recorded. EMG activity of control SOL muscles did not change with speed but increased significantly (12%) with an increase in grade. EMG activity of grafts from non-trained animals was identical to control SOL muscles at all speeds and grades. EMG activity of grafts from trained animals was 35% lower than their contralateral controls and 27% lower than grafts and control muscles of non-trained animals. These data show that SOL grafts were reinnervated and used within the first 28 days after transplantation. At 56 days, grafts from untrained animals were used similar to control SOL muscles but grafts from trained animals were used less. Since at 56 days ChAT activity of grafts was equal to control values, the lower EMG activity of the grafts from the trained animals was not attributed to deficient innervation. Since training began at the nadir of the growth curve, it is likely that synergists were used to maintain force output. This became a learned pattern that was continued even after the grafts matured.