Effects of fetal spinal cord tissue transplants and cycling exercise on the soleus muscle in spinalized rats

Studies were carried out to determine if an intraspinal transplant (Trpl) o f fetal spinal cord tissue or hind limb exercise (Ex) affected the changes in myosin heavy chain (MyHC) composition or myofiber size that occur follow ing a complete transection (Tx) of the lower thoracic spinal cord of the ad ult rat. In one group of animals, transplants were made acutely, whereas in a second group, daily cycling exercise was initiated 5 days after injury, with animals in both groups being sacrificed 90 days after injury. The sole us muscle is normally composed of myofibers expressing either type I (90%) or type IIa (10%) MyHC. Following a spinal transection, expression of type I MyHC isoform decreased (18% of myofibers), type IIa MyHC expression incre ased (65% of myofibers), and the majority of myofibers (80%) expressed type IIx MyHC. Most myofibers coexpressed multiple MyHC isoforms, Compared with Tx only, with Ex or with Trpl, there was a decrease in the number of myofi bers expressing type I or IIa isoforms but little change in expression of I Ix MyHC. Myofibers expressing the Ilb isoform appeared in several transplan t recipients but not after exercise. Transection resulted in atrophy of typ e I myofibers to approximately 50% of normal size, whereas myofibers were s ignificantly larger after exercise (74% of control) and in Trpl recipients (77% of control). Type IIa myofibers also were significantly larger in Trpl recipients compared with the Tx only group. Overall, the mean myofiber siz e was significantly greater after exercise and in Trpl recipients compared with myofibers in Tx only animals. Thus, although neither strategy shifted the MyHC profile towards the control, both interventions influenced the ext ent of atrophy observed after spinalization. These data suggest that pallia tive strategies can be developed to modulate some of the changes in hind li mb muscles that occur following a spinal cord injury. (C) 1999 John Wiley & Sons, Inc.