ANALYSIS OF ION-CHANNEL EXPRESSION BY ASTROCYTES IN RED NUCLEUS BRAIN-STEM SLICES OF THE RAT

The red nucleus (RN) has been widely used to study the formation and r emodeling of synaptic connections during development and in post-lesio n plasticity. Since glial cells are thought to contribute to synaptic plasticity, and information on functional properties of brain stem gli a is missing, we analyzed voltage-gated ion channels as well as glutam ate receptors expressed by glial cells of the RN. The patch-clamp tech nique was applied to identified cells in acute brain stem slices of 5- to 12-day-old rats. Based on their pattern of membrane currents, two types of glial cells could be distinguished. A first type was characte rized by passive, symmetrical currents. The second population of cells , which was the focus of the present study, expressed a complex patter n of voltage-gated channels. These cells could be labeled with antibod ies against glutamine synthetase and S100 beta, suggesting an astrogli a origin. Depolarizing voltage steps activated transient and delayed r ectifier K+ currents as well as Na+ currents. In addition, a subset of cells expressed Ba2+ sensitive inward rectifier K+ currents activated by hyperpolarization. All ''complex'' glial cells analyzed possessed ionotropic glutamate receptors of the lpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid (AMPA) subtype, while functional kainate and N -methyl-D-aspartate (NMDA) receptors could not be detected. Receptor a ctivation blocked outward rectifying K+ currents, similar to previous observations in glial cells of the hippocampus and the corpus callosum . (C) 1997 Wiley-Liss, Inc.