Neuroenergetics and synaptic activity: the glutamatergic synapse. Whatever the type of synapses, most of the brain energy in the rodent is used for reversing Na+ and K+ fluxes provoked by action potentials (47% of brain ATP consumed) and postsynaptic currents (34%). The reversion of ion fluxes is mediated by the neuronal Na+/K+ ATPase. About 10% of brain ATP is expended at the level of the glutamatergic synapse for the recycling of glutamate released in the synaptic left since it is coupled to Na+ influx and astrocytic Na+/K+ ATPase activation. Glucose, the main energy substrate, is translocated from blood via endothelial cells of the blood-brain barrier (BBB) by a glucose transporter GLUT1 (55 kDa isoform), and is then taken up by astrocytes via GLUT1 (45 kDa isoform) and by neurons via GLUT3. In astrocytes, part of the pyruvate produced from glucose is converted to lactate which is an alternative energy substrate for neurones during neuronal activation.