Spreading depression, sustained potential shifts, and metabolic activity of cerebral cortex of cats
The oxidation level of intramitochondrial NADH of the intact cerebral cortex of cats was measured in situ by the fluorometric method of Jobsis et al. The extracellular electrical potential of the same site of the cortex was recorded with a dc coupled system. When the cortex was stimulated by repetitive electrical pulse trains either directly or by way of a thalamocortical afferent pathway, a linear correlation was found between the amplitude of the shift of the electrical potential of the activated gray matter in the negative direction and the increase of the rate of oxidative metabolism estimated by the fluorometric response of the tissue. From this observation, and from the relationship of electrical potential to extracellular K+ levels, it is concluded that a substantial fraction of the consumption of oxidative energy of the cortical gray matter is in some direct manner related to the ratio of extracellular over intracellular K+ activities. Spreading depression of the cortex was provoked by electrical and chemical stimulation, and occasionally 'spontaneous' episodes of spreading depression were observed. Spreading depression was always associated with large increases of the oxidative metabolism of the cortex, often exceeding even the metabolic responses associated with seizures. Complete depression of electrographic activity of the cortex and the associated shift of electric potential in the negative direction occurred well before the metabolic response reached its maximal level. It is concluded that a shortage of oxidizable substrate and hence, presumably, of oxidative energy turnover, plays no part in causing spreading depression of the cerebral cortex.
Journal of Neurophysiology
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