The redox potential (E) is a useful measure of the intensity and quality of shifts in energy metabolism. Brain E depends on the ratio of the rates of processes occurred in two compartments of energy metabolism - the glycolysis compartment, in which glucose is split without oxygen, and the oxidative metabolism compartment. The present report describes recording of local changes in E using platinum electrodes implanted into several points in the cortex. In these conditions, decreases in E correspond to local increases in the rates of glycolytic processes in the tissue surrounding the electrode and are related to mitochondrial processes, while increases in E correspond to local acceleration of processes in oxidative metabolism in the tissues around the electrode. Our previous studies in rats showed that during episodes of slow-wave sleep (SWS), metabolically active points of the rat cerebral cortex show significant decreases in E, and it was suggested that these are associated with increases in the rate of glycolysis. At the same time, E showed characteristic oscillations lasting 20-40 sec with amplitudes of tens of millivolts. The experiments reported here demonstrated that slow oscillations in E developing during SWS are created by regular episodes of ECoG arousal occurring during SWS, accompanied by startling of the animal, decreases in E, and inhibition of respiration. We suggest that a homeostasis system operates during SWS to maintain the animal's level of consciousness at a particular level and that this, like any system with feedback, operates in an oscillatory fashion. The role of glycolysis in supplying energy to the cerebral cortex to support the elevated level of consciousness increases.

Freely mobile mongrel male rats weighing 300-350 g were used for studies of changes in the oxidative-reductive (redox) state of brain tissue during cycles of waking, slow-wave sleep, and paradoxical sleep, by recording the potential of the oxidative-reductive state of brain tissue with platinum electrodes implanted into the cerebral cortex ad hippocampus. Electromyograms were also recorded from the cervical muscles, and overall movement activity was also recorded. A common platinum reference electrode was implanted into the nasal bones. These experiments showed that in rats, episodes of waking and paradoxical sleep occurred on the background of increases in the oxidation-reduction potential state of brain tissue at a series of brain points, which we termed "metabolically active." Transitions from waking and paradoxical sleep to slow-wave sleep were accompanied by decreases in the potential of the redox state. The magnitude of changes in the tissue redox state varied up to 100 mV. It is suggested that transitions from waking and paradoxical sleep to slow-wave sleep are accompanied by dynamic changes in the balance of brain tissue energy metabolism between the main energy sources. Oxidative phosphorylation dominates in waking and paradoxical sleep, while aerobic glycolysis dominates slow-wave sleep. We suggest that this latter should be interpreted as a decrease in the potential of the tissue redox state and the formation within the tissue of oscillations during slow-wave sleep. Formation of oscillations is typical for acceleration of glycolytic processes. Recently published data suggest that the major compartment or aerobic glycolysis is the astroglia.

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This article is devoted to an analysis of the factors forming slow changes in the potential of a metallic electrode coming into direct contact with living tissue. Data are presented in this paper according to which, the electrochemical activity of the tissue also participates, in addition to electrical activity, in the formation of the electrode potential. The article is in the nature of a discussion.

The oxidative-reductive (redox) potential (E) of brain tissue depends on the ratio of the speeds of processes occurring in the glycolysis (the evolutionarily ancient energy compartment operating without oxygen) and oxidative metabolism (evolutionarily younger and energetically more efficient) compartments. E in the cortex was recorded using implanted platinum electrodes. A conditioned defensive reflex (CDR) was developed by combination of a light and electrocutaneous stimulation (ECS) of the ear. The results showed that after a series of combinations of the light and the ECS, the light started to elicit a change in E. By 200 combinations, the brain developed both increases and decreases in E during combinations. As the number of combinations increased, increases in E were gradually replaced by decreases. We believe that this dynamic of the balance of the major sources of brain energy supply suggests that formation of the CDR may involve a significant role for subcellular structures receiving energy from oxidative metabolism formed at the relatively young evolutionary level, while the major source of energy for brain function during performance of the acquired CDR is the older evolutionary compartment - glycolysis.