Visualization of mitochondria in living cultured neurons using mitochondrial-targeted DsRed2. A. Embryonic mouse primary cerebral cortical neuron transfected with mitoDsRed plasmid. The cell body (lower left) containing numerous mitochondria is overexposed to show individual mitochondria in fine distal processes (arrows). Scale bar = 7 μm. B. NSC34 motor neuron-like cells transfected with mitoDsRed plasmid showing vast numbers of mitochondria forming a network in the cytoplasm surrounding the nucleus (asterisk). Scale bar = 6 μm. C. Mouse cerebral cortical astrocytes expressing mitochondrial-targeted DsRed show mitochondria as long vermiform, ellipsoid, or round organelles. Asterisks identify nucleus. Scale bar = 6 μm. D. NSC34-motor neuron transfected with Thy1-mitoDsRed plasmid. Cell body fluorescence is bright due to numerous mitochondria and overexposure, while individual mitochondria in a long dendrite (arrow) can be discerned. Scale bar = 6 μm. E-G. Embryonic mouse primary spinal cord neuron transfected with Thy1-mitoDsRed plasmid and shown at different exposures to reveal red fluorescent mitochondria in the cell body (E, asterisk marks the nucleus) and distal processes (F and G, arrows). Scale bar = 6 μm. H and I. NMDA receptor activation by quinolinic acid causes mitochondrial pathology as seen directly in living cultured primary cortical neurons by Thy1-mitoDsRed. Mouse cortical neurons treated with PBS (vehicle) show numerous individual mitochondria distributed throughout the dendritic arborization (H, arrows). Neurons treated with 100 μM quinolinic acid undergo mitochondrial swelling (arrows) and dendrite retraction by 4 hours (I). Scale bars = 6 μm. Images are representative of at least 3 different cell culture experiments.