Abstract: The metabolite lactate (L-lactate) can be generated and released by diverse brain cells, including neurons, astrocytes, and oligodendrocytes (Kann, 2023; Rae et al., 2024). Lactate productton usually requires the degradation of glucose (D-glucose) – and glycogen in astrocytes – to pyruvate by glycolysis and subsequent conversion of pyruvate to lactate by the enzyme lactate dehydrogenase (Dienel, 2019; Rae et al., 2024). Lactate production occurs when local glycolysis exceeds oxidative phosphorylation in mitochondria, a complex metabolic process that requires the tricarboxylic acid cycle for pyruvate utilization, the respiratory chain and molecular oxygen as an electron acceptor to finally enable adenosine-5′- triphosphate (ATP) generatton (Dienel, 2019; Kann, 2023). Lactate production is generally favored during hypoxia (anaerobic glycolysis). Alternattvely, lactate is generated in the presence of oxygen (aerobic glycolysis), for example, in astrocytes or in neuronal structures that miss mitochondria like a fraction of presynaptic terminals in pyramidal cell axons (Magistretti and Allaman, 2018; Kann, 2023). Aerobic glycolysis in neurons and glial cells usually results in some net lactate efffux from the acttve brain to the blood circulatton (Dienel, 2019). By contrast to lactate, glucose is also required for essential processes such as build-up of glycogen and management of oxidattve stress (Dienel, 2019; Kann, 2023).