Optical scatter imaging detects mitochondrial swelling in living tissue slices

Mitochondrial swelling is observed in neuronal injury and is a key event in many pathways to cell death. Currently, there is no technique for directly measuring mitochondrial size changes within living tissue slices with a field of view of several millimeters. In this paper, we test our hypothesis that Mie light-scatter theory can be used to study mitochondrial swelling in living tissue sections. Using a unique dual-angle scatter ratio (DASR) optical imaging system previously demonstrated to be sensitive to latex particle size changes and N-methyl-D-aspartate (NMDA) treatment of hippocampal slices, we studied mitochondrial swelling induced by 500 microM NMDA treatment of hippocampal slices. We observed a strong (R(2) = 0.73) and significant (P < 0.000005) correlation between the electron microscopy-determined diameters of swollen, intact mitochondria and the DASR imaging. We examined the robustness of the technique by evaluating the correlation between the dual-angle scatter ratio and the diameter of the dendrites, observed to swell, in NMDA-treated slices and found no correlation (R(2) = 0.06). The advantage of DASR imaging over electron microscopy or other methods of studying mitochondrial swelling is the sensitivity of DASR imaging to mitochondrial swelling over a large field of view (>9 mm(2)) in an intact tissue slice. This novel technique may allow for the study of regional changes in mitochondrial swelling and recovery as sequential events within a single specimen. This technique will eventually be useful in studying the efficacy of stroke and other disease therapies targeting mitochondrial swelling.