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 t o test for the presence of GABA(A) and glutamate receptors in glial ce lls of an intact tissue preparation, the hippocampus from 9-12 day old mice. Two types of glial cells were studied in the CA1 stratum pyrami dale, termed passive and complex cells, which were distinct by their c haracteristic pattern of voltage-dependent currents. Both cell types w ere previously identified as glial by combining electrophysiology with ultrastructural inspection (Steinhauser 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 fib rillary acidic protein, a marker of mature astrocytes. In both cell ty pes, GABA activated currents compatible with GABA(A)-receptor mediated responses. The glutamate response in complex and in most of the passi ve cells was mediated by a ligand-gated ion channel and closely matche d the pharmacology of the kainate receptor. Activation of glutamate re ceptors led to a transient decrease of the resting K+ conductance in c omplex cells and to an irreversible decrease in the passive cells. In three passive cells, glutamate-activated currents were most likely dom inated by an electrogenic uptake. In a small group of passive cells NM DA-activated currents were observed. This study provides evidence that glial cells from an intact tissue express receptors for the most abun dant transmitters in the central nervous system, glutamate, and GABA.