Measurements of Glycogen Metabolism in the Living Brain

To maintain brain function, the combustion of glucose for the generation of energy (ATP) is essential, yet the brain maintains fuel storage in the form of glial glycogen. Although brain glycogen levels are lower than those in the liver, they exceed the normal free glucose concentration in brain several-fold. Under normoxic conditions, when a partial glucose supply deficit is present, brain glycogen can provide fuel for extended periods of time. Brain glycogen metabolism is active, but comparatively slow, consistent with a role of an emergency fuel with neuroprotective effects. The classical analysis with biochemical means requires tissue extraction; brain glycogen metabolism can be measured directly in the living brain only by 13C NMR spectroscopy. This chapter reviews the insights gained into brain glycogen metabolism in the living brain to-date and reviews potential roles for brain glycogen in the context of neuro-glial metabolism, hypoglycemia and neuroprotection.