Sensory Evoked Potentials for Selective Monitoring of the Rat Spinal Cord: A Cerebellar Evoked Potential to Assess Ventral Cord Integrity

The purpose of this study was to evaluate two types of ascending sensory evoked potentials (SEPs) in the rat and their capacity for selective monitoring of dorsal versus ventral spinal cord integrity. SEPs were elicited by direct sciatic nerve stimulation. A cerebellar evoked response was recorded over the paramedian lobule of the cerebellar hemisphere (CEP_pml) while somatosensory evoked potentials (SSEPs) were simultaneously recorded over the sensorimotor cortex.

All components of the CEP_pml and SSEP except the longest latency positive waves were present in each animal. At stimulus intensities of 3 to 10 mA, no significant changes in latency of the peaks were observed, but amplitudes of the longer latency responses tended to increase throughout this stimulation range. Unilateral sciatic stimulation resulted in bilateral cortical responses, larger ipsilaterally for the CEP_pml, and contralaterally for the SSEP. Selective spinal cord lesions demonstrated N9 and P14 of the CEP_pml to be mediated primarily through the ventral spinal cord, while P14 and N19 of the SSEP were conducted primarily through the dorsal columns. Sectioning of the cerebellar peduncles abolished N9 and P14 of the CEP_pml despite persistence of the SSEP. This study demonstrates that selective assessment of the ventral and dorsal spinal cord is possible in the rat by monitoring SEPs.