Magnetic motor evoked potential monitoring in the rat

Object. The authors conducted a study to provide an objective electrophysio logical assessment of descending motor pathways in rats. which may become a means for predicting outcome in spinal cord injury research. Methods. Transcranial magnetic motor evoked potentials (TMMEPs) were record ed under various conditions in awake, nonanesthetized, restrained rats. Nor mative data were collected to determine the reproducibility of the model an d to evaluate the effect of changing the stimulus intensity on the evoked s ignals. In addition, an experiment was per formed to determine if the TMMEP s produced were the result of auditory startle response (ASR) potentials el icited by the sound generated by the movement of the copper coil inside its casing during magnetic stimulation. Transcranial magnetic motor evoked potentials were elicited after magnetic stimulation. At 100% stimulus intensity, the mean forelimb onset latency wa s 4.2 +/- 0.39 msec, and the amplitude was 9.16 +/-. 3.44 mV. The hindlimb onset latency was 6.5 +/- 0.47 msec, and the amplitude was 11.47 +/- 5.25 m V. As the stimulus intensity was decreased, the TMMEP onset latency increas ed and the response amplitude decreased. The ASR potentials were shown to h ave longer latencies, smaller amplitudes, and were more variable than those of the TMMEPs. Conclusions. These experiments demonstrate that TMMEPs can be recorded in a wake, nonanesthetized rats. The evoked signals were easy to elicit and repr oduce. This paper introduces noninvasive TMMEPs as a new technique for moni toring the physiological integrity of the rat spinal cord.