Involvement of myod and myogenin in response to exercise in paralyzed rats

Paralysis due to spinal cord transection leads to muscle fiber atrophy and changes in muscle fiber phenotype in muscles distal to the site of injury. Exercise of affected hindlimbs can modify these changes. To gain insight into the mechmsms underlying the effects of exercise on paralyzed muscle the hypothesis was tested that muscle specific transcription factors are involved in the early response to exercise. Rats (adult Sprague-Dawley) underwent a T10 spinal transection. Five days after transection animals were exercised on a motor-driven bicycle for 6Ü minutes daily. Transected/exercised rats (TXE) were sacrificed 12 or 24 hours after the onset of exercise. Control non-transected (CON) and transected only (TX) rats were sacrificed at similar time points. Soleus and extensor digitorum longus (EDL) muscles were dissected and quick frozen in liquid nitrogen. Muscles were cut in 9 m sections and immunocytochemistry was performed with antibodies against MyoD, myogenin, MEF2C and proliferating cell nuclear antigen (PCNA). No staining was observed in CON and TX muscles with MyoD, PCNA, and MEF2C, but soleus of CON showed some low level myogenin staining. TX and CON EDL did not show any myogenin staining. At 12 hours after exercise MyoD staining could be detected in soleus, but was more evident in EDL muscles. No increase in myogenin was observed 12 hours after exercise, however, 24 hours after exercise an increase in myogenin could be seen in soleus with an even more pronounced increase in EDL No reactivity was observed in any muscle with PCNA or MEF2C Results indicate that the expression of MyoD and myogenin is associated with the response to exercise in paralyzed rats and that the response is muscle specific.