Dynamics of Local Changes and Oscillations in Energy Metabolism in the Rabbit Cerebral Cortex during the Formation of a Conditioned Defensive Reflex

Brain energy metabolism associated with different functional states and different types of human and animal activity is accompanied by dynamic changes in the degree of linkage between glycolysis and oxidative phosphorylation in different cell compartments [20–23, 25]. These processes are reflected in the redox state of brain tissue [27] and can be recorded potentiometrically as changes in the redox state potential (E) of brain tissue [24]. Studies of E in the cortex of rabbits using implanted platinum electrodes showed that during the acquisition of a conditioned defensive reflex using a combination of a light and a mild electric shock to one of the rabbit's ears, cortical E showed oscillations with periods of several seconds after 5–15 combinations. This number of combinations started to be accompanied by generalized changes in E in the cortex, which, at 20–100 combinations, could be either an increase or a decrease in E. As the number of combinations increased, increases in E were gradually replaced by decreases. By 200–400 combinations, oscillations in E disappeared and the episodes of decreased E accompanying combinations acquired a stable local character. These results suggest that there is a change in the balance of the major sources of brain tissue energy supply during the formation and stabilization of a conditioned defensive reflex: at the initial stages of acquisition of the conditioned reflex a number of cortical points have an energy supply dominated by tissue respiration, while the main energy source for brain function during performance of the acquired conditioned defensive reflex is glycolysis.