Neuronal activity occurs simultaneously and in a highly coordinated fashion in many different areas across the brain. Real-time visualization of large-scale neural dynamics in whole mammalian brains is hindered with the existing neuroimaging methods that are limited in their ability to image large tissue volumes at high speeds. Genetically encoded calcium indicators (GECIs) that modulate their fluorescence intensity as a function of intracellular calcium concentrations are powerful tools for the observation of large neuronal networks. Optoacoustic imaging has been shown capable of real-time three-dimensional imaging of multiple cerebral hemodynamic parameters in rodents. However, optoacoustic imaging of calcium activity deep in mammalian brain is hampered by strong blood absorption in the visible light spectrum as well as lack of activity labels excitable in the near-infrared window. We developed and validated an isolated whole mouse brain preparation labelled with genetically encoded calcium indicator GCaMP6f, which can closely resemble in vivo conditions and exhibit functional activity for several hours to several days. An optoacoustic imaging system coupled to a superfusion system was further devised and used for rapid volumetric monitoring of calcium dynamics in the brain evoked using an epilepsy-inducing drug. The new technique captures calcium fluxes as true 3D information across the entire brain with temporal resolution of 10ms and spatial resolution of 150µm, thus enabling large-scale neural recording at penetration depths and spatio-temporal resolution scales not covered with the existing neuroimaging techniques. The system could be readily adapted to work with future generations of far-red- and near-infrared GECIs.
Sven Gottschalk, Oleksiy Degtyaruk, Johannes Rebling, Benedict McLarney, Xose Luis Deán-Ben, Shy Shoham, and Daniel Razansky, "Volumetric optoacoustic mapping of fast neuronal activity in an isolated mouse brain model expressing genetically encoded calcium indicator (Conference Presentation)," Proc. SPIE 10481, Neural Imaging and Sensing 2018, 104810L (Presented at SPIE BiOS: January 30, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2289711.5751488531001.
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