Motor evoked potentials in a static load model of spinal cord injury in the rat

Motor evoked potentials (MEPs) are used to evaluate spinal cord injury. In this study, the effect of different grades of static load spinal cord injury on MEPs was examined. Rats (n = 27) were anesthetized, ventilated, and curarized. MEPs were elicited by the stimulation of the right sensorimotor cortex and recorded with a needle electrode placed in the epidural space on the left side at T10. The spinal cord injury was produced by gently placing a weight (20, 35, or 50 g) on the spinal cord at the level of T3. The compression time was 5 minutes. A group of rats in which laminectomies were performed but in which no weight was put on the spinal cord served as a control group. MEPs were recorded before, during, and after the spinal cord lesion was produced. The MEPs in the 0g group were stable. While the spinal cord was compressed, the MEP positive peak latencies increased and the amplitudes decreased and finally disappeared. MEP latencies and amplitudes correlated well with the weight used for spinal cord compression. During spinal cord compression, MEPs vanished, starting from peaks with a longer latency to peaks with a shorter latency. After decompression, the peaks reappeared in a reverse order. This study shows that MEPs are a good parameter for the functional integrity of spinal cord motor pathways in a static load type of injury model.