Properties of GABA and Glutamate Responses in Identified Glial Cells of the Mouse Hippocampal Slice

In this study, the patch-clamp technique was applied to brain slices to test for the presence of GABAA and glutamate receptors in glial cells of an intact tissue preparation, the hippocampus from 9-12 day old mice. Two types of glial cells were studied in the CA1 stratum pyramidale, termed passive and complex cells, which were distinct by their characteristic pattern of voltage-dependent currents. Both cell types were previously identified as glial by combining electrophysiology with ultrastructural inspection (Steinhüser et al., 1992, Eur J Neurosci 4:472-484). A subpopulation of passive cells was positive, all complex cells were negative for immunocytochemical staining against glial fibrillary acidic protein, a marker of mature astrocytes. In both cell types, GABA activated currents compatible with GABAA-receptor mediated responses. The glutamate response in complex and in most of the passive cells was mediated by a ligand-gated ion channel and closely matched the pharmacology of the kainate receptor. Activation of glutamate receptors led to a transient decrease of the resting K+ conductance in complex cells and to an irreversible decrease in the passive cells. In three passive cells, glutamate-activated currents were most likely dominated by an electrogenic uptake. In a small group of passive cells NMDA-activated currents were observed. This study provides evidence that glial cells from an intact tissue express receptors for the most abundant transmitters in the central nervous system, glutamate, and GABA.