Low-Frequency Oscillations of Cortical Oxidative Metabolism in Waking and Sleep

Abstract

Summary:To study the changes in cortical oxidative me tabolism and blood volume during behavioral state tran sitions, we employed reflectance spectrophotometry of the cortical cytochrome c oxidase (cyt aa3) redox state and blood volume in unanesthetized cats implanted with bilateral cortical windows and EEG electrodes. Contin uous oscillations in the redox state and blood volume (�9/min) were observed during waking and sleep. These primarily metabolic oscillations of relatively high ampli tude were usually synchronous in homotopic cortical areas, and persisted during barbiturate-induced electro cortical silence. Their mean amplitude and frequency did not vary across different behaviorallEEG states, although the mean levels of cyt aa3 oxidation and blood volume Determinations of cortical energy consumption and blood flow in studies of cerebrovascular physi ology and higher cortical functions have revealed important features of cortical behavior after depar tures from the resting steady state. For example, it is now clear that experimental cortical "activation" by electrical, pharmacologic, or behavioral stimuli is followed by increases in cortical metabolism and/ or blood flow (Rosenthal and J obsis, 1971; Dymond and Crandall, 1976; Vern et aI., 1979; LaManna et Received May 29. 1987; accepted October 19, 1987 Abbreviations used: cyt aa3' cytochrome c oxidase (cy tochrome aa3) ; cyt min and max, minimal and maximal excur sions of cyt aa3 redox state, respectively; EMG, electromyog raphy; EOG, electrooculography; 590 min and max, minimal and maximal excursions of 590-nm signals, respectively; PMT, pho tomultiplier tube; REM, rapid eye movement. 215during rapid eye movement (REM) sleep significantly ex ceeded those during waking and slow-wave sleep. These data suggest the existence of a spontaneously oscillating metabolic phenomenon in cortex that is not directly re lated to neuroelectric activity. A superimposed increase in cortical oxidative metabolism and blood volume occurs during REM sleep. Experimental data concerning cerebral metabolism and blood flow that are obtained by clinical methods that employ relatively long sample ac quisition times should therefore be interpreted with cau tion. Key Words: Cortical blood flow-Cortical oxidative metabolism-Cytochrome aa3-Metabolic oscillations -Rapid eye movement sleep-Reflectance spectropho tometry.

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