ASTROCYTIC GABA RECEPTORS

GABA receptors are distributed widely throughout the central nervous s ystem on a variety of cell types. It has become increasingly clear tha t astrocytes, both in cell culture and tissue slices, express abundant GABA(A) receptors. In astrocytes, GABA activates Cl--specific channel s that are modulated by barbiturates and benzodiazepines; however, the neuronal inverse agonist methyl-4-ethyl-6, 7-dimethoxy-beta-carboline -3-carboxylate enhances the current in a subpopulation of astrocytes. The properties of astrocytic GABA(A) receptors, therefore, are remarka bly similar to their neuronal counterparts, with only a few pharmacolo gical exceptions. In stellate glial cells of the pituitary pars interm edia, GABA released from neuronal terminals activates postsynaptic pot entials directly. The physiological significance of astrocytic GABA(A) -receptor activation remains unknown, but it may be involved in extrac ellular ion homeostasis and pH regulation. At present, there is consid erably less evidence for the presence of GABA(B) receptors on astrocyt es. The data that have emerged, however, indicate a prominent role for second-messenger regulation by this receptor. (C) 1994 Wiley-Liss, In c.