Dynamic changes of NADH fluorescence images and NADH content during spreading depression in the cerebral cortex of gerbils

Abstract

To elucidate the changes in the mitochondrial redox state during spreading depression (SD), tissue NADH content was measured in 20 anesthetized gerbils by the enzymatic cycling assay in a small cortical region (0.30±0.07 mg) where the direct-current (DC)-potential was measured. Sequential imaging of NADH fluorescence with a CCD camera and continuous monitoring of DC-potential and regional CBF were also performed in another 5 gerbils. Biphasic fluorescence waves propagating at the rate of 3 mm/min were observed using the CCD camera. An initial narrow (1.6±0.4 mm) wave, which showed a modest increase in fluorescence (108±6.4%), was observed simultaneously with the onset of negative DC-deflection. During depolarization, CBF was unchanged and tissue NADH content increased to 25.3±7.9 μmol/kg brain, which was higher than the value in the sham-control (11.0±2.5 μmol/kg brain). At 30 s after the deflection, a subsequent wide (7.0±2.1 mm) wave, which showed a moderate decrease in fluorescence (87.1±5.7%), was observed simultaneously with the increase in CBF and repolarization in DC-potential. Then NADH fluorescence recovered along with normalization of CBF at 152.2±38.6 s after the onset of DC-deflection. Tissue NADH concentration sampled at 120 s after the deflection was 11.6±4.6 μmol/kg brain. Since NADH fluorescence is absorbed by hemoglobin, the initial increase and subsequent decrease in fluorescence seem to have been induced by increases in NADH content and CBF, respectively. These findings indicate that the mitochondrial redox state transiently inclines to the reduction side synchronous to the onset of DC-deflection and that it normalizes within 120 s after deflection.