Regulation of energy metabolism by neurotransmitters in astrocytes in primary culture and in an immortalized cell line

Evidence suggests that astrocytes might play an important role in cerebral energy metabolism. A recently developed cell line, called DI TNC₁, displays several characteristic features of astrocytes. Thus, we have investigated in these cells a number of parameters related to energy metabolism. First, glycogen, the major energy reserve in the brain, is present in these cells and its levels are influenced by the glucose content of the growth medium and the presence of serum. Second, several neurotransmitters including noradrenaline and vasoactive intestinal peptide (VIP) induce a glycogenolytic response. Their effect on glycogen is paralleled by a similar effect on the formation of cyclic AMP, which is presumably the second messenger involved. Third, noradrenaline stimulates glucose utilization (as reflected by 2-deoxyglucose uptake) in DI TNC₁ cells, an effect which is mimicked by the second messenger arachidonate. Interestingly, two actions of neurotransmitters, which are well characterized in primary astrocytes, are absent in DI TNC₁ cells. These are the noradrenaline- and VIP-induced resynthesis of glycogen and the glutamate-stimulated glycolysis. In summary, the observations reported here lend further support to the concept that astrocytes are important for the control of brain energy metabolism. In addition, DI TNC₁ cells might represent an interesting preparation to help decipher some of the astrocytic functions related to energy metabolism.