Application of endogenous autofluorescence signal for functional brain imaging

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We developed a method of neural imaging using activity-dependent changes in green fluorescence of flavoproteins excited by blue light. We observed an increase in endogenous green fluorescence in response to electrical stimulation in the slices of the rat auditory cortex. The amplitude of the peak increase, which was observed 2-3 s after the initiation of the repetitive electrical stimulation, was as large as about 30% at room temperature. They were also not observed in the slices perfused with medium lacking calcium, glucose or oxygen. These data indicate that the green fluorescent responses are attributed to the fluorescence of flavoproteins involved in the energy metabolism in mitochondria. In anesthetized rats with urethane, we observed clear images of the green fluorescent changes on the exposed surface of the auditory cortex following sound stimuli. These fluorescent changes were observed without using averaging, since they were much larger than the optical noises caused by heartb … More eats or breathing. We also tried to investigate spatial pattern of correlation between spontaneous neural activites using fluctuations in flavoprotein fluorescence. In the normal somatosensory cortex covered with agar, positive correlation around a ROI was observed in the fluorescence signals after correction for breathing movements. Tetanic stimulation applied around the ROI increased the magnitude of the positive correlation around the ROI. This method was also used to visualize learning-induced changes of neural activities in the rat primary somatosensory cortex. A water-deprived rat was trained to discriminate the frequency (20 Hz or 40 z) of floor vibration in a Skinner box. After this discrimination learning was achieved in consecutive 3-5 days, the somatosensory neural responses to the rewarded frequency were larger than that in response to the unrewarded frequency in all of the rats tested. In mice, the transparent skull of mice allowed trans-cranial autofluorescence imaging of cortical activites. Less