Changes in diffuse reflectance intensity and autofluorescence for brain tissue in rats during loss of tissue viability

Abstract

To investigate the correlation between light scattering and tissue viability of brains, we performed measurements of multiwavelength diffuse reflectance and autofluorescence for brains during loss of tissue viability. As a model temporally losing tissue viability of brain, a perfused brain in a rat was used. Diffuse reflectance at 620 nm, which is an isosbestic point of cytochrome oxidase (cyt. ox.), showed that a triphasic, drastic change in light scattering occurred 220 - 300 s after starting perfusion. After this event, light scattering stayed at a higher level than that before this event. We observed a different behavior between the reflectance at 620 nm and that at 605 nm, showing that the tissue absorption at 605 nm was increasing. This is attributable to the reduction of heme a+a₃ in cyt. ox., which preceded the triphasic change in light scattering. An important difference was also found between the reflectance at 620 nm and that at 800 nm, indicating that the absorption decrease at 800 nm presumably due to the reduction of copper A in cyt. ox. coincided with the triphasic change in light scattering; the reduction of copper A in cyt. ox. indicates the decrease in ATP production. Change in fluorescence of NADH did not correlate either with change in light scattering or with the reduction of cytochrome oxidase. These findings suggest that light scattering is useful as an indicator of brain tissue viability.