Dynamics of local shifts in oscillations and energy metabolism of the rabbit cerebral cortex during formation of a conditioned defensive reflex

Brain energy metabolism in different functional states or activities of humans and animals is characterized by dynamic changes in the degree of coupling between glycolysis and tissue respiration in different cell compartments (Fox et al., 1988; Fox, 1989; Pellerin et Magistretti, 1994; Prichard et al., 1991; Schur et al., 1999). These processes determine variations in the brain redox state (Siesjo, 1978) that can be potentiometrically recorded with implanted platinum electrodes as the brain tissue redox state potential E (Puppi et Fely, 1983). This potential was recorded in rat brain cortex with four pairs of platinum electrodes implanted into different symmetrical cortical region (one electrode of a pair being located in the cortical layers, another being located epidurally). In the course of defensive conditioning (after 5-15 combination of a bulb light and a weak electrodermal stimulation of a ear), E oscillations (6-10 per minute) appeared. In this period, stimuli combinations produced the generalized E shifts. Later on (with accumulation of stimuli combinations), the episodes of E increase were replaced by the episodes of E decrease. To the 200-400th combinations, E oscillations disappeared, and E shifts became local and stable. The findings suggest that conditioning shifts the balance between the main energy-producing systems in the brain tissue: at the initial stages of conditioning brain functions are predominantly supported by the energy obtained from tissue respiration, while during the realization of defensive conditioning glycolysis is the main source of energy.