Glial-neuronal interactions and brain energy metabolism

Abstract

Golgi, more than a century ago, suggested that glial cells provide nutritive support for neurons. He based this on his microscopic observations that glial cells are positioned between blood vessels and neurons, and their endfeet intimately surround blood vessels (Andriezen, 1893; Cajal, 1995). The anatomic arrangement of astrocytes, neurons and capillaries suggested that nutrients might be taken up preferentially by astrocytes. Astrocytes would then ‘share’ these nutrients with nearby neurons (Figure 11.1A). This old idea gained a degree of modern plausibility as more was learned about brain energy metabolism, and it was discovered that astrocytes are the only cells in the mammalian brain that contain significant glycogen (Cataldo and Broadwell, 1986a), the storage form of glucose. These refinements in the evolution of the nutritive hypothesis are shown in Figure 11.1B. The transfer of energy substrate (e.g. glucose or monocarboxylates) occurs across brain extracellular space (ECS), which is so narrow that molecules released from one cell diffuse almost instantly to adjacent cells (Nicholson, 1995). A crucial permissive feature of this scheme is that nearly every neuron in the brain shares common ECS with adjacent astrocytes.