The role of lactate in brain metabolism

According to the astrocyte-neurone-lactate shuttle (ANLS) hypothesis, activated neurones use lactate released by astrocytes as their energy substrate. The hypothesis, based largely on in vitro experiments, postulates that lactate is derived from the uptake by astrocytes of synaptically released glutamate. The time course of changes in lactate, derived from in vivo experiments, is incompatible with the ANLS model. Neuronal activation leads to a delayed rise in lactate followed by a slow decay, which greatly outlasts the period of neuronal activation. The present review proposes that the uptake of stimulated glutamate release from astrocytes, rather than synaptically released glutamate, is the source of lactate released following neuronal activation. This rise in lactate occurs too late to provide energy for neuronal activity. Furthermore, there is no evidence that lactate undergoes local oxidative phosphorylation. In conclusion, under physiological conditions, there is no evidence that lactate is a significant source of energy for activated neurones.