Is Brain Lactate Metabolized Immediately after Neuronal Activity through the Oxidative Pathway?

In the central nervous system, lactate is formed under both aerobic and anaerobic conditions. The question is whether the generated lactate after neural excitation by glutamate is immediately metabolized. It has been hypothesized that lactate is formed after glutamate uptake in the glia, then released into the intercellular compartment and subsequently used by neurones (the so-called astrocyte–neuron lactate shuttle; Pellerin and Magistretti, 1994). In two recent reports (Schurr, 2006; Aubert et al, 2005), the question was addressed whether lactate could serve as a substrate for oxidative metabolism during nerve cell activation under aerobic conditions in vivo. Aubert et al (2005) designed a mathematical model to show that the time course of extracellular changes of lactate levels during enhanced neural activity could be interpreted as aerobic metabolism. Schurr (2006) summarized the arguments favouring the idea that in the functioning brain, lactate is the major end product of both aerobic and anaerobic glycolysis and that lactate subsequently serves as an oxidative substrate. For both reports, the results shown by Hu and Wilson (1997) are crucial. In that study, the perforant pathway of the rat was simulated for 5 secs once or repeatedly and the time course of extracellular lactate, oxygen, and glucose in the dentate gyrus of the rat brain was measured with