Energy and amino acid neurotransmitter metabolism in astrocytes

Abstract

Knowledge about the functional roles of astrocytes has developed enormously over the past 30 years and it is interesting to note that even a century ago Ramón y Cajal (1911) was concerned that it would take a long time until it could be elucidated how important astrocytes would be in maintaining basic elements of brain function. By now it is clear that astrocytes are of pivotal importance for ion homeostasis, intercellular communication, exchange of metabolites, and clearance of the extrasynaptic milieu of the neurotransmitters glutamate and gamma-aminobutyric acid (GABA) [reviewed in (Ransom et al., 2003; Newman, 2003; Hertz and Zielke, 2004)]. Actually it should be noted that perhaps the most pronounced feature of the human brain which distinguishes it from that of lower mammals is the complexity and number of the astrocytes (Oberheim et al., 2006). In this context it is also important to emphasize that the demonstration that astrocytes possess the machinery to release glutamate in an exocytotic fashion (Parpura et al., 1994; Parpura and Haydon, 2000; Haydon, 2001) has led to the term, the tripartite synapse (Araque et al., 1999; Volterra et al., 2002).