DEVELOPMENT AND IMPROVEMENT OF ULTRA-THIN FLUORESCENCE ENDOSCOPE IMAGING SYSTEM (U-FEIS) AND ITS APPLICATION TO NEURAL ACTIVITY RECORDING IN BEHAVING MICE

In vivo recordings of neural activity in behaving animals are essential for understanding the relationship between neural activity and brain function. We developed an ultra-thin fluorescence endoscope imaging system (U-FEIS) that enables the recording of neural activity under conditions that are difficult to achieve with conventional in vivo imaging systems. U-FEIS employs an image fiber (0.45 mm diameter, 10,000 pixels) as an endoscope, allowing minimally invasive access to deep brain regions and enabling recordings from multiple regions in behaving mice. Additionally, U-FEIS employs a straightforward optical configuration comprising excitation light sources, cameras, and associated components, which can be readily adapted to various experimental setups.
In calcium imaging using genetically encoded calcium indicators during behavioral tasks, it is often difficult to distinguish genuine neural activity from motion artifacts. This issue can be addressed by simultaneously monitoring activity-dependent and activity-independent fluorescent signals. Since the original U-FEIS was a single-wavelength imaging system, we modified it to enable dual-wavelength imaging of two fluorescent proteins, such as GCaMP and DsRed, and evaluated the performance of the improved system.
We first assessed the spatial resolution of the dual-wavelength U-FEIS using fluorescent microspheres and performed dual-wavelength imaging in the CA1 region of the mice during head-fixed locomotion. Our results demonstrate that the dual-wavelength U-FEIS provides sufficient spatial resolution to resolve neuronal cell bodies and enables reliable recording of neural activity. Furthermore, motion correction based on signals from the two channels highlights the importance of careful analysis and interpretation when recording neural activity with fluorescent proteins during behavior.