[Changes of motor evoked potentials after spinal cord injuries in rats].

Aim: Study on the relationship between the degraded spinal cord injuries and the changes of the motor evoked potentials (MEP) to prove the diagnosis and prognosis value of MEP.

Methods: After injury at T8-T9 cord using modified Allen's weight-drop method, 27 male SD rats were divided randomly into control group (n = 5), group A (50 gcf, n = 8), group B (70 gcf, n = 8) and group C (100 gcf, n = 6). MEPs elicited by monopolar transcortical stimulation were recorded continuously before injury, just after injury, 15 minutes, 1 hour, 3 hours and 6 hours after injury. The rate of the size of the bleeding or necrosis area to the total cord was also calculated.

Results: MEP had no significant change in the control group. The amplitude of MEP's early components in group A or group B decreased or even obliterated after SCI, and then partially recovered, while the late components were lost without any recovery signals. All animals in group C showed no MEP waves excepting 2 rats had recovery signals. The size of the cord injuries area increased according to the dropping force and was correlated significantly with the amplitude of the largest peaks of scMEP 1 hour after SCI (r = -0.821).

Conclusion: The scMEP changes after SCI are correlated with the injury forces and the pathological changes in the cord, which indicates that scMEP can be used as an objective index for the cord functional monitoring.