Glutamate-, kinate- and NMDA-evoked membrane currents in identified glial cells in rat spinal cord slice

The effect of L-glutamate, kainate and N-methyl-D-aspartate (NMDA) on membr ane currents of astrocytes, oligodendrocytes and their respective precursor s was studied in acute spinal cord slices of rats between the ages of postn atal days 5 and 13 using the whole-cell patch-clamp technique. L-glutamate (10(-3) M), kainate (10(-3) M), and NMDA (2x10(-3) M) evoked inward current s in all glial cells. Kainate evoked larger currents in precursors than in astrocytes and oligodendrocytes, while NMDA induced larger currents in astr ocytes and oligodendrocytes than in precursors. Kainate-evoked currents wer e blocked by the AMPA/kainate receptor antagonist CNQX (10(-4) M) and were, with the exception of the precursors, larger in dorsal than in ventral hor ns, as were NMDA-evoked currents. Currents evoked by NMDA were unaffected b y CNQX and, in contrast to those seen in neurones, were not sensitive to Mg 2+. In addition, they significantly decreased during development and were p resent when synaptic transmission was blocked in a Ca2+-free solution. NMDA -evoked currents were not abolished during the block of K+ inward currents in glial cells by Ba2+; thus they are unlikely to be mediated by an increas e in extracellular K+ during neuronal activity. We provide evidence that sp inal cord glial cells are sensitive to the application of L-glutamate, kain ate and transiently, during postnatal development, to NMDA.