Our understanding of hemodynamic signals, blood perfusion and oxygen saturation (sO2), recorded through fiber-based instruments is limited. To address this, a potential method can be to simultaneously acquire hemodynamic signals with widely used fluorescence fiber photometry signals. We report a novel System for the Simultaneous Measurement of Fluorescence and Hemodynamics (SSMFH) from deep brain regions of freely moving rodents. SSMFH has been developed by modifying our previous white light reflectance single fiber system (SFS) that enabled measurement of blood perfusion and oxygen saturation from freely moving rodents. SSMFH has been designed to be easily integrated with a commercial fluorescence fiber photometry system for time-locked measurement of both hemodynamics and fluorescence signals. SSMFH can be additionally synchronized to behavioral monitoring cameras and other behavioral equipment during experiments. In contrast to previous work in the literature, SSMFH enables hemodynamic recordings from deep brain regions using a wide spectral range (∼ 545nm to 700nm) without the need for injection of an activity-independent fluorescent reporter. The details of the design will be presented along with data to illustrate proof-of-concept through an animal experiment. GCaMP-based fiber photometry and its relation to neuronal activity is well understood. Hemodynamic measurement with simultaneous and co-localized GCaMP based neuronal activity recording can help in understanding variations in in-vivo hemodynamic signals. SSMFH can be used to correct fluorescence measurements which are affected by blood absorption changes.
Oxygen saturation (sO2) and blood perfusion in brain tissue have been known to be modulated with cellular activity in the brain. A single fiber system (SFS) has previously been shown to enable sO2 measurements from localized deep brain regions in freely moving animals. Reflectance spectra (RSF) obtained through the SFS can be used to understand changes in blood perfusion and fit to an empirical model to extract sO2. The sO2 extracted is dependent on the shape of RSF and thus relatively resistant to noise as compared to blood perfusion which is dependent on the magnitude of RSF at specific wavelengths. While slow changes in sO2 have been shown to be robust, sources of certain relatively rapid temporal variations observed in the sO2 signal remains unclear. Potential sources could be variations in cellular activity in the brain or noise due to motion artifacts. In this work, we have described the design of new experiments focused to investigate the effects of motion artifacts on RSF and sO2. Computer simulations and mathematical modelling have been used to explain the experimental findings. Results suggest that the motion artifacts mainly arise from the fiber/brain interface and appear to offset RSF. Using the interpretation from a mathematical model, we also propose a motion artifact correction algorithm which can potentially be used for comparison of perfusion signals.
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