Effects of Induced Hypothermia on Subcortical Evoked Potentials in the Cat

¹ From the Divisions of Neurosurgery and Neurology, School of Medicine, Western Reserve University and University Hospitals of Cleveland, Cleveland, Ohio

The effects of induced hypothermia in the unanesthetized immobilized cat on somatic afferent evoked potentials from the posteroventral lateral nucleus of the thalamus, periaqueductal midbrain reticular formation and dorsal column of the spinal cord were studied in 28 cats. At a rectal temperature of 23°C, marked depression of the responses recorded from all loci was demonstrable. The afferent midbrain reticular formation was demonstrated to be more sensitive to hypothermia than the thalamic relay nucleus. Augmentation of the spinal cord dorsal column evoked potentials was noted between 33°C and 25°C. Conduction time measurements indicated that between 37°C and 27°C the velocity of transmission along the nerve fibers is more affected than transmission across a synapse.