We investigated the influence of glutamate and agonists of its ionotropic receptors on ROS formation detected by fluorescent dye DCFDA in rat brain synaptosomes. Glutamate in concentration 10 and 100 ¦ÌM led to an increase of probe fluorescence pointing to free radical accumulation. This effect was mimicked by 100 ¦ÌM of NMDA or 100 ¦ÌM of kainate. Glutamate-induced ROS formation was sensitive to NMDA inhibitors MK-801 (10 ¦ÌM), NO synthase (NOS) inhibitor l-NAME (100 ¦ÌM) and NADPH oxidase inhibitors DPI (30 ¦ÌM) and not affected by mitochondrial uncoupler CCCP (10 ¦ÌM) and mitochondrial toxins rotenone (10 ¦ÌM) + oligomycin (5 ¦Ìg/ml). We also showed that 100 ¦ÌM of glutamate leads to a decrease of intrasynaptosomal mitochondrial potential monitored by fluorescent dye Rhodamine-123.
Hence, the depolarization of intrasynaptosomal mitochondria is not a primary cause of glutamate-induced ROS formation in neuronal presynaptic terminals. Activation of NMDA receptors might be responsible for a certain part of glutamate pro-oxidant action. Most likely, sources of glutamate-induced ROS formation in neuronal presynaptic terminals are NADPH oxidase and NOS activation.