Astrocytes of the mouse neocortex express functional N-methyl-D-aspartate receptors.

In the brain, N-methyl-D-aspartate (NMDA)-type glutamate receptors are important elements for the manifestation of memory as well as mediators of neurotoxicity, and they are thought to be exclusive to neurons. To test for the expression of functional NMDA receptors on astrocytes, we generated transgenic mice in which glial fibrillary acidic protein (GFAP)-positive astrocytes are labeled by a green fluorescent protein and tested their responses to NMDA in acute cortical slices by patch-clamp recording and Ca imaging. The NMDA-evoked currents reversed at 0 mV; could be blocked by MK-801; persisted in the absence of synaptic transmission; were sensitive to Mg; and were accompanied by focal Ca elevation, indicating the presence of functional NMDA receptors. Furthermore, we detected mRNAs for NMDA receptor subunits in freshly isolated astrocytes purified by fluorescence-activated cell sorting. We conclude that processes of cortical astrocytes enwrapping synaptic regions express high densities of NMDA receptors that could be involved in neurone-glia signaling.