EFFECT OF OUABAIN AND PHENOBARBITAL ON THE KINETICS OF CORTICAL METABOLIC TRANSIENTS ASSOCIATED WITH EVOKED POTENTIALS

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Abstract
—: Evoked potentials, shifts of the steady potential and spreading depression have been shown to be associated with transient changes in the oxidative metabolic activity of the cerebral cortex of cats. The metabolic activity is measured at the intact surface by intensity of the fluorescence emitted at 460 nm when the tissue is illuminated at 366 nm. The intensity of the fluorescence signal is related to the oxidationreduction level of intramitochondrial NADH which is, itself, related to the ATP/ADP ratio and the rate of oxygen consumption.In this study, the transient changes in metabolic activity with evoked potentials are separated into component parts by means of kinetic analysis. Ouabain (0.1 mM) introduced directly under the cortical surface, markedly slows the ‘on kinetics’ with no change in recovery metabolism. Phenobarbital delays the reduction of NAD+ (‘off kinetics’) with little effect on ‘on kinetics’.Thus, the transient fluorometric response to evoked potentials is confirmed as a measure of ATP breakdown and oxidative rephosphorylation. The rate of NADH oxidation is a measure of the rising ADP concentration due to the action of the Na‐K ATPase. The rate of return of the fluorescence to baseline levels (reduction of NADH) is a function of the respiratory chain.