Fig. 5. Summary of key aspects of glucose metabolism during brain activation and probable roles of astrocytes in metabolite spreading and release from brain.

Increased functional activity stimulates fluxes of glucose into different pathways, leading to discordant brain images obtained with [1- and 6-¹⁴C]glucose compared to [¹⁴C]deoxyglucose; the magnitude of glucose utilization is greatly underestimated with [¹⁴C]glucose. Astrocytes have specialized metabolic compartments, and metabolites generated from labeled glucose can spread in neurons or astrocytes via intra- and extracellular routes, thereby influencing local levels of labeled metabolites. Gap junction-coupled astrocytes form a large syncytium and the endfeet interface with the major fluid transport systems in brain: blood, interstitial fluid, and cerebrospinal fluid.