Long-term changes in spinal cord evoked potentials after compression spinal cord injury in the rat.

1. After traumatic spinal cord injury (SCI), histological and neurological consequences are developing for several days and even weeks. However, little is known about the dynamics of changes in spinal axonal conductivity. The aim of this study was to record and compare repeated spinal cord evoked potentials (SCEP) after SCI in the rat during a 4 weeks' interval. These recordings were used: (i) for studying the dynamics of functional changes in spinal axons after SCI, and (ii) to define the value of SCEP as an independent outcome parameter in SCI studies. 2. We have used two pairs of chronically implanted epidural electrodes for stimulation/recording. The electrodes were placed below and above the site of injury, respectively. Animals with implanted electrodes underwent spinal cord compression injury induced by epidural balloon inflation at Th8-Th9 level. There were five experimental groups of animals, including one control group (sham-operated, no injury), and four injury groups (different degrees of SCI). 3. After SCI, SCEP waveform was either significantly reduced or completely lost. Partial recovery of SCEPs was observed in all groups. The onset and extent of recovery clearly correlated with the severity of injury. There was good correlation between quantitated SCEP variables and the volumes of the compressing balloon. However, sensitivity of electropohysiological parameters was inferior compared to neurological and morphometric outcomes. 4. Our study shows for the first time, that the dynamics of axonal recovery depends on the degree of injury. After mild injury, recovery of signal is rapid. However, after severe injury, axonal conductivity can re-appear after as long as 2 weeks postinjury. In conclusion, SCEPs can be used as an independent parameter of outcome after SCI, but in general, the sensitivity of electrophysiological data were worse than standard morphological and neurological evaluations.