Chapter 17: Regulatory role of astrocytes for neuronal biosynthesis and homeostasis of glutamate and GABA

Abstract

Publisher Summary The chapter discusses an overview of the current status of the knowledge about transmembrane fluxes of glutamate, glutamine and GABA, and their apparent metabolic interconversions. The glutamine synthesizing enzyme glutamine synthetase (GS) is localized in astrocytes and not in neurons. As a consequence of this, there exists a cycling of glutamate, glutamine, and presumably GABA between neurons and astrocytes, and this cycling is defined as the glutamate/glutamine cycle. Regardless of whether the precursor for transmitter glutamate is glutamine or a tricarboxylic acid constituent, a communication between neurons and astrocytes must take place as the astrocytes control the availability of these metabolites. Transmitter GABA is synthesized from glutamate by the action of glutamate decarboxylase, which is found only in GABAergic neurons. However, it appears that in the brain in vivo in synaptosomes, as well as in cultured GABAergic neurons glutamine is a better precursor for GABA than glutamate.