Synaptic potentials recorded in brain slices and their modification by changes in the level of tissue ATP.

Abstract

Postsynaptic responses to electrical stimulation were recorded in olfactory cortex slices maintained in vitro, and their modification by changes in the level of tissue ATP was examined. A slight decrease in the ATP level caused by lowered oxygen tension markedly affects the synaptic transmission. Thus when ATP is decreased by 20%, the amplitude of the synaptic potential already diminishes by 93%. With inhibitors of oxidative phosphorylation, reduction of ATP and suppression of synaptic potential occur to the same extent as that induced by lowered oxygen tension. In contrast, decrease of ATP caused by the inhibition of glycolytic pathway affects the transmission to a lesser extent. With chlorpromazine and phenobarbitone, synaptic transmission is affected more than is expected from the reduction of ATP. When ATP is reduced by various means, the post-tetanic potentiation and frequency potentiation are enhanced. With the reduced ATP level, the post-tetanic potentiation develops and also declines more rapidly than with the normal level of ATP. Reduction of ATP and of the potential caused by anoxia or cyanide can be recovered when the normal metabolic condition of the slice is restored. However, if slices are incubated anaerobically in a glucosefree medium, an irreversible fall in both ATP and the synaptic potential occurs. In contrast with the decrease, increase of ATP up to about 135% of the normal level does not affect transmission.