T-scope V4: miniaturized microscope for optogenetic tagging in freely behaving animals

Abstract

A miniaturized microscope (i.e., miniscope) enables the imaging of neuronal activity using calcium sensors while simultaneously manipulating that activity using opsins in freely moving animals. However, many miniscopes use light-emitting diodes with broadband emission, leading to unintentional opsin stimulation by light intended solely for calcium sensor activation (a phenomenon referred to as "biological crosstalk"). To address this issue, we previously developed a miniscope including a port for chosen light sources, such as lasers, by restructuring the open-source UCLA Miniscope v3. However, targeting the same neuronal soma for both excitable opsin stimulation and calcium sensor imaging remained a challenge. Here, we integrated features from the UCLA Miniscope v4 into our new T-scope V4 miniscope. In optogenetic tagging experiments, we demonstrated that a 445-nm blue laser can be used to image neuronal activity with the calcium sensor GCaMP6s without inadvertently stimulating the ChrimsonR opsin, allowing for simultaneous neuronal activity imaging and manipulation in freely moving mice. Thus, the T-scope V4 can serve as a powerful tool for probing causal relationships between neuronal activity and its function in living animals.