ASTROCYTES REGULATE AMINO-ACID RECEPTOR CURRENT DENSITIES IN EMBRYONIC RAT HIPPOCAMPAL-NEURONS

Embryonic rat hippocampal neurons were cultured in a serum-fre e defin ed medium (MEM/N3) either directly on poly-D-lysine (PDL) or on a conf luent monolayer of postnatal cortical astrocytes, C6 glioma cells, or Rat2 fibroblasts. Neurons on PDL were grown in MEM/N3 or in MEM/N3 con ditioned for 24 h by astrocytes or C6 cells. Membrane capacitance (C-m ) and gamma-aminobutyric acid (GABA)-, glycine-, kainate-, and N-methy l-D-aspartate (NMDA)-induced currents were quantified using whole-cell patch-clamp recordings. C-m as well as the amplitude and the density of these currents in neurons cultured on astrocytes were significantly greater than those in neurons grown on PDL after 24 and 48 h. C6 cell s mimicked astrocytes in promoting C-m and GABA-, glycine-, and NMDA-e voked, but not kainate-evoked, currents. C-m and currents in neurons g rown on Rat2 cells were comparable to those in neurons on PDL. Astrocy tes maintained in culture for 3 months were noticeably less effective than freshly prepared ones just grown to confluence. Suppression of sp ontaneous cytoplasmic Ca2+ (Ca-c(2+)) elevations in astrocytes by 1,2- bis(2-aminophenoxy) ehane-N, N, N, N-tetraacetic acid acetoxymethyl es ter (BAPTA-AM) loaded intracellularly blocked the observed modulatory effects. Medium conditioned by either astrocytes or C6 cells mimicked the effects of direct coculture of neurons on these cells in promoting C-m and amino acid-evoked currents. Inclusion of antagonists at GABA and glutamate receptors in coculture experiments blocked the observed effects. Thus, diffusible substances synthesized and/or secreted by as trocytes in a Ca-c(2+)-dependent manner can regulate neuronal growth a nd aminoacid receptor function, and these effects may involve neuronal GABA and glutamate receptors. (C) 1997 John Wiley & Sons, Inc.