Epidural perfusion cooling protects against spinal cord ischemia in rabbits. An evaluation of cholinergic function.

The protective effect of regional epidural spinal cord cooling was evaluated in a rabbit spinal cord ischemia model. Hypothermia was performed by the continual perfusion of 2-4 degrees C cold saline in the epidural space around the ischemic lumbar segments, 4 min before and during ischemia. The spinal cord was deeply hypothermic (21 degrees C) throughout the whole ischemic period. Ischemia was induced by the occlusion of the abdominal aorta for 40 min under normothermic or hypothermic conditions. Recovery of motor and sensory functions, spinal cord-evoked potentials, and motor-evoked potentials were then evaluated up to 24 h postischemia. After this period, choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities were measured, in particular, zones of the lumbar spinal cord. AChE was also investigated histochemically. Animals in the normothermic group displayed fully developed spastic paraplegia with near complete loss of spinal somatosensory and motor-evoked potentials. AChE histochemistry showed extensive necrotic changes affecting lumbosacral gray matter. These changes corresponding with the pronounced losses of ChAT and AChE activities indicated irreversible injury of the spinal cord. In contrast, after hypothermic ischemia, animals survived without any sign of neurological impairment with almost full recovery of the spinal cord-evoked potentials. ChAT and AChE activities in the gray matter showed near control values corresponding with histochemical analysis of fully preserved gray matter. Hypothermia under the present experimental conditions efficiently protected the spinal cord against ischemic injury.