Dynamic Imaging of Somatosensory Cortical activity in the Rat Visualized by Flavoprotein Autofluorescence

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Abstract
We used autofluorescence of mitochondrial flavoproteins to image cortical neural activity in the rat. Green autofluorescence in blue light was examined in slices obtained from rat cerebral cortex. About half of the basal autofluorescence was modulated by the presence or absence of O2 or glucose in the medium. Repetitive electrical stimulation at 20 Hz for 1 s produced a localized fluorescence increase in the slices. The amplitude of the increase was 27 ± 2 % (mean ±s.d., n= 35). Tetrodotoxin or diphenyleneiodonium, an inhibitor of flavoproteins, blocked the autofluorescence responses. The autofluorescence responses were not observed in slices perfused with calcium‐, glucose‐ or O2‐free medium. In the primary somatosensory cortex of rats anaesthetized with urethane (1.5 g kg−1, i.p.), an activity‐dependent increase in autofluorescence of 20 ± 4 % (n= 6) was observed after electrical cortical stimulation at 100 Hz for 1 s, and an increase of 2.6 ± 0.5 % (n= 33) after vibratory skin stimulation at 50 Hz for 1 s applied to the plantar hindpaw. These responses were large enough to allow visualization of the neural activity without having to average a number of trials. The distribution of the fluorescence responses after electrical or vibratory skin stimulation was comparable to that of the cortical field potentials in the same rats. The fluorescence responses were followed by an increase in arterial blood flow. The former were resistant to an inhibitor of nitric oxide synthase, while the latter was inhibited. Thus, activity‐dependent changes in the autofluorescence of flavoproteins are useful for functional brain imaging in vivo.