Oxidative metabolism, extracellular potassium and sustained potential shifts in cat spinal cord in situ.

Changes in the ratio of reduced/oxidized cytochrome a,a3 were measured by reflection spectrophotometry in decerebrate cat spinal cord during microelectrode monitoring of extracellular K+ and extracellular potential. In 'resting' cord, cytochrome a,a3 was approximately 60% reduced, compared to 30% in cerebral cortex and 1% in isolated mitochondria. Stimulation of a dorsal root or afferent nerve caused linearly correlated responses, consisting of oxidation of cytochrome a,a3, elevation of K+0 and a negative shift of potential. In spinal cord, unlike cerebral cortex, the local volume of blood increased upon stimulation. The rate of recovery of the oxidation response of cytochrome a,a3 was consistently faster in cord than in cortex. Pentobarbital (i.v.) in anesthetic dosage reduced the amplitude and slowed the rate of recovery of all 4 parameters, indicating that the optical signals originate from gray matter. It is speculated that the spinal cord, even more than cortex, may depend for its viability on the maintenance of PO2 above a certain level, and that much of the metabolic activity following stimulation is associated with the restoration of ionic gradients.