Influence of severe hypercapnia upon cerebral cortical metabolism, CSF electrolyte concentrations and EEG in the cat

The interconnections between EEG, intermediary and energy metabolism of the brain cortex and CSF potassium level are studied during severe hypercapnia in anaesthetized, artificially ventilated cats. Hypercapnic animals were ventilated with 40 to 50% to CO2 in oxygen. During severe hypercapnia the EEG becomes isoelectric. The CSF potassium concentration is raised and the changes in metabolism suggest an acidosis-induced inhibition of phosphofructokinase and, probably, of hexokinase. The energy charge potential remains unchanged whereas the cortical ATP concentration increases slightly. It is assumed that the changes in P-creatine and creatine levels are related to the pH-dependency of creatine phosphokinase. Recovery animals were ventilated with 40% CO2 in O2 and subsequently with room air. After termination of CO2 inhalation the EEG reappears, the CSF potassium concentration normalizes, and the inhibition of the glycolytic enzymes disappears. The energy charge potential shows a small decrease. It is not possible to trace back the disappearance of the EEG to only one of the recorded parameters. Cortical P-creatine levels, CSF potassium concentration, changes in membrane permeability and cortical amino acid concentrations are considered in this context.