NEUROTRANSMITTERS REGULATE ENERGY-METABOLISM IN ASTROCYTES - IMPLICATIONS FOR THE METABOLIC TRAFFICKING BETWEEN NEURAL CELLS

In recent years a vast array of experimental evidence has indicated th e presence of functional receptors for neurotransmitters on nonneurona l cells, in particular astrocytes. The two neurotransmitters vasoactiv e intestinal peptide (VIP) and noradrenaline (NA) exert profound, rece ptor-mediated, metabolic actions on astrocytes. Thus both neurotransmi tters stimulate glycogenolysis in primary astrocyte cultures, with EC( 50)S of 3 and 20 nM respectively. Astrocytes display basal glucose uti lization rates ranging between 3 and 9 nmol/mg prot/min, a value that is remarkably close to glucose utilization of cerebral cortical grey m atter as determined by the 2-deoxyglucose autoradiographic technique. NA markedly enhances glucose uptake and phosphorylation by astrocytes, with an EC(50) of 1 mu M. The metabolic substrate that is released by astrocytes is predominantly lactate and not glucose. Since lactate ca n support neuronal activity and synaptic function in vitro, the possib ility should be considered that glucose uptake by the brain parenchyma occurs predominantly into astrocytes which subsequently release lacta te for the use of neurons.