Spinal cord dorsum potentials recorded in vivo after cold injury to the sural nerve in the rabbit

Evoked potentials were recorded in the spinal cord dorsum of rabbits during and after local cooling or freezing of the sural nerve. The potentials were elicited by stimulation through implanted bipolar electrodes distal and proximal to the site of cooling. Recordings were made with a unipolar electrode implanted dorsally into the epidural space.The first two negative deflections of the evoked field potentials (s- and n-potentials) decreased or disappeared during cooling to temperatures between 12 and 2 °C. Immediately following cooling the potentials were depressed by as much as 40% below that of controls. Gradual recovery of the nerve conduction velocity and of both potentials occurred between postoperative Days 20 and 60. Cooling of the nerve to between +2 and ?2 °C caused a 70–80% decrease in amplitude and the precooling values were not obtained within 90 days' follow-up. Local freezing of the sural nerve to ?45 °C resulted in disappearance of the cord dorsum potentials previously obtained by stimulation of the sural nerve with electrode distal to the site frozen. About 40% decrease occurred when stimulated proximal to the site frozen. A fast amplitude increase took place between days 50 and 100 and a slower increase between days 150 and 450 to values more than twice the preoperative amplitudes. A similar amplitude increase was obtained by stimulation of the nerve proximal to the site frozen.