Thinking with and without oxygen: energy metabolism in vertebrate brains

Abstract

A survey of the information available on the biochemical differences between anoxia-sensitive brains of mammals and anoxia-tolerant brains of aquatic turtles reveals that the latter maintain membrane ion gradients, ATP concentrations, and, to a limited extent, electroencephalographic (EEG) activity, while metabolic rate is depressed during prolonged anoxia. In contrast, mammalian brains are unable to maintain ATP concentrations, ion gradients, and EEG activity during ischemia or anoxia despite a dramatic (albeit transient) Pasteur effect. This evidence indicates that rates of ATP utilization decrease during anoxia in anoxia-tolerant brains, while they are maintained (and not matched by glycolytic ATP production) in anoxia-sensitive brains. The implications with respect to possible mechanisms of "metabolic arrest" and the evolution of anoxia tolerance in vertebrate brains are discussed.