Abstract: ObjectiveTo investigate the rule of changes of the soleus mass and expression of myosin heavy chain (MHC) isoforms mRNA.Methods40 female Wistar rats were divided randomly into the control group and three spinal cord transection (ST) groups, ST7, ST15, and ST30 with 10 animals in each group. Rats in ST groups were subjected to a complete ST between T₈ and T₁₀ levels. The right soleus was dissected and weighed at 7, 15, 30 days after ST, and the expression of MHC mRNA isoforms was measured by semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR).ResultsThe Absolute and relative soleus masses in three ST groups were lower significantly than those of control group (P<0.05). The soleus mass in ST15 and ST30 groups were lower than that of ST7 group (P<0.05). The soleus of control group predominantly expressed MHC-I and some MHC-IIa, whereas the soleus began to express MHC-IIx and MHC-IIb after ST, except for MHC-I and MHC-IIa. ST induced consistently down-regulation of MHC-I mRNA and up-regulation of MHC-IIx and MHC-IIa at three time points after ST. The level of MHC-IIb mRNA expression was very low at three time points after ST.ConclusionST can influence the soleus mass at early stage after ST. ST induces a shift toward a faster muscle phenotype from slow to fast MHC isoform. MHC demonstrates plasticity in response to decrease neuromuscular activation.

Key words: spinal cord transection, soleus, muscle mass, myosin heavy chain, reverse transcriptase polymerase chain reaction (RT-PCR)