Effect of cerebral ischemia and hypercapnia on cerebral pH studied with 31P-NMR and electrical activity in rat brain.

The activity of electroencephalogram (EEG) and cortical somatosensory evoked potential (SEP) was suppressed during cerebral ischemia in rats subjected to the 4-vessel occlusion. Considerable variations were demonstrated in the decrease of phosphocreatine and ATP concentration during ischemia among the rats measured with 31P-NMR, accompanied with cerebral acidification. Hypercapnia, induced in the rats studied by the inhalation of a gas mixture of 30-40% CO2, suppressed the activity of EEG and cortical SEP. The cerebral acidification observed during the ischemia was more severe than that under the hypercapnia, implying that cerebral acidification is one of the possible causes for the decrease in the electrical activity of the brain during ischemia.