Corticomotor evoked potentials in acute and chronic blunt spinal cord injury in the rat: correlation with neurological outcome and histological damage.

Somatosensory evoked potentials (SSEPs) and corticomotor evoked potentials (CMEPs) were utilized to study acute and chronic blunt spinal cord trauma. Rats, anesthetized with ketamine hydrochloride, were subjected to parasagittal craniectomies and midthoracic laminectomies. SSEPs were cortically recorded and CMEPs were transcortically produced using epidural ball and disc electrodes. SSEPs were elicited and CMEPs were recorded via hindlimb percutaneous needle electrodes. After control records, animals were subjected to a 50-g/cm impact to the dorsal cord surface using a modified weight drop technique. Evaluation of neurological injury was performed by SSEP and CMEP analysis and was compared with neurological assessments obtained before injury and 1 hour, 1 week, 3 weeks, and 6 weeks after injury. Neurohistopathological verification of each spinal cord lesion was performed at 6 weeks after injury. Animals subjected to a 50-g/cm cord impact showed no change in SSEP wave forms, but all components of the CMEP were greatly attenuated with this injury. Acutely, either very weak movement or no movement to noxious stimulation was present without vocalization. There was a spectrum of clinical recovery that correlated closely with the return and normalization of the amplitude of the CMEP in 100% of the animals tested. The eventual degree of clinical and CMEP improvement correlated well with the degree of histological damage present. The results of this study suggest that the CMEP is a reliable indicator of the initial degree of loss of neurological motor function in acute blunt spinal cord injury in the rat, as well as an accurate measure of the degree and extent of recovery. The rat model as outlined here is a simple and inexpensive system for evaluation both clinically and electrophysiologically of the degree of motor recovery from spinal cord injury. This model should prove useful in the evaluation of promising pharmacological agents for potential use in the treatment of acute spinal cord injury.