Astrocytic GABA receptors

GABA receptors are distributed widely throughout the central nervous system on a variety of cell types. It has become increasingly clear that astrocytes, both in cell culture and tissue slices, express abundant GABA A receptors. In astrocytes, GABA activates Cl − ‐specific channels that are modulated by barbiturates and benzodiazepines; however, the neuronal inverse agonist methyl‐4‐ethyl‐6, 7‐dimethoxy‐β‐carboline‐3‐car‐boxylate enhances the current in a subpopulation of astrocytes. The properties of astrocytic GABA A receptors, therefore, are remarkably similar to their neuronal counterparts, with only a few pharmacological exceptions. In stellate glial cells of the pituitary pars intermedia, GABA released from neuronal terminals activates postsynaptic potentials directly. The physiological significance of astrocytic GABA A ‐receptor activation remains unknown, but it may be involved in extracellular ion homeostasis and pH regulation. At present, there is considerably less evidence for the presence of GABA B receptors on astrocytes. The data that have emerged, however, indicate a prominent role for second‐messenger regulation by this receptor. © 1994 Wiley‐Liss, Inc.