The Effect Of Treadmill Training On Igf-1 Levels In Rat Skeletal Muscle And Lumbar Spinal Cord Following Spinal Cord Injury

Abstract

Motor recovery following spinal cord injury (SCI) can be enhanced or accelerated by locomotor training. The underlying premise of locomotor training is that rhythmic loading of the limbs and force feedback from the hindlimb muscles induces task appropriate activity-dependent plasticity. Locomotor training has been shown to induce both muscle plasticity and neural recovery. However, the mechanisms involved in mediating neuromuscular plasticity following SCI are not well established. PURPOSE: To determine the impact of treadmill training on IGF-I levels in the rat soleus muscle and lumbar spinal cord following SCI. METHODS: Contusion SCIs were produced using a NYU impactor in all rats except controls. Animals were then randomly assigned into a treadmill training or untrained group. Rats in the training group were trained starting at 1 week post SCI for 5 days, 2 trials/day, and 20minutes/trial. The soleus muscle and a region from the lumbar spinal cord (L1 -L4) were dissected at 1 week post training. Real-time PCR was used to quantify IGF-I mRNA expression in the soleus muscle, while the IGF-I protein content in both the soleus and lumbar spinal cord were determined using an immunoassay. resULts: Compared to untrained SCI animals, one week of treadmill training resulted in a 32% improvement in locomotor (BBB) scores, a 38% increase in soleus strength, and a 32.8% increase in muscle fiber size. Training also resulted in a significant 2.8 fold increase in soleus muscle IGF-I mRNA and a similar 2.4 fold increase in IGF-I protein. Finally, treadmill training significantly increased IGF-I protein content in lumbar spinal cord by 40.1%. CONCLUSION: This study demonstrates that treadmill training results in a significant increase in IGF-I levels of both lower extremity muscles and the lumbar spinal cord, which may play a important role in neuromuscular plasticity following SCI. ACKNOWLEDGEMENTS: This work was supported by the Paralyzed Veterans of American Research Foundation (PVA # 2347) and R01HD42955.