NMDA receptors are expressed in oligodendrocytes and activated in ischaemia

Glutamate-mediated damage to oligodendrocytes contributes to mental or physical impairment in periventricular leukomalacia (pre- or perinatal white matter injury leading to cerebral palsy), spinal cord injury, multiple sclerosis and stroke(1-4). Unlike neurons(5), white matter oligodendrocytes reportedly lack NMDA (N-methyl-D- aspartate) receptors(6,7). It is believed that glutamate damages oligodendrocytes, especially their precursor cells, by acting on calcium-permeable AMPA (alpha-amino-3-hydroxy-5-methyl- 4-isoxazole propionic acid)/kainate receptors alone(1-4) or by reversing cystine - glutamate exchange and depriving cells of antioxidant protection(8). Here we show that precursor, immature and mature oligodendrocytes in the white matter of the cerebellum and corpus callosum exhibit NMDA-evoked currents, mediated by receptors that are blocked only weakly by Mg(2+) and that may contain NR1, NR2C and NR3 NMDA receptor subunits. NMDA receptors are present in the myelinating processes of oligodendrocytes, where the small intracellular space could lead to a large rise in intracellular ion concentration in response to NMDA receptor activation. Simulating ischaemia led to development of an inward current in oligodendrocytes, which was partly mediated by NMDA receptors. These results point to NMDA receptors of unusual subunit composition as a potential therapeutic target for preventing white matter damage in a variety of diseases.