Optical characterization of heme a + a3 and copper of cytochrome oxidase in blood-free perfused rat brain.

For the precise examination of the optical characteristics of cerebral tissue, we prepared hemoglobin-free perfused rat heads, from which trace amounts of blood were completely removed. In this preparation at 30 degrees C, the redox responses of the cytochrome oxidase components, heme a + a3 and copper, were followed spectrophotometrically in visible and near-infrared regions, and were correlated with the changes in neural activity as monitored by electroencephalography (EEG). During the aerobic-anaerobic transition, there was clear dissociation of the time courses of the reduction of heme a + a3 and copper; the reduction of heme a + a3 preceded the reduction of copper. The EEG activity decreased earlier than the reduction of heme a + a3. Pentylenetetrazole administration in normoxia caused the partial reduction of heme a + a3 but not of copper. The redox behaviors of cytochrome oxidase components in the brain were identical to those observed in isolated mitochondria. The usefulness of brain preparation for bridging the in vivo and in vitro studies is documented where various circulatory parameters could be controlled artificially.