Functional brain imaging with improved GCaMPs in zebrafish

â—‹Akira Muto1, Junichi Nakai2,Koichi Kawakami1

1)Natl. Inst. of Genet., Mishima, Shizuoka, Japan,
2)Brain Sci. Inst., Saitama, Japan

Imaging of the brain activity in behaving animal enhances our understanding of how the brain works and how animal behaviors are generated. Calcium imaging with DNA-encoded calcium indicators has a great potential to study function of genetically identified neural circuits or a population of neurons in vivo. Recent progress in the improvement of GCaMP demonstrated that transgenic zebrafish of an improved GCaMP is suited for the analysis of the spinal neural circuit (Muto et al., 2011). We extended this approach by making further-improved GCaMPs and testing them in several brain regions. Introduction of the GCaMPs into specific cells were realized by mating UAS:GCaMP transgenic fish with another fish of specific GAL4 lines. Calcium imaging with the improved GCaMPs revealed spontaneous neuronal activities in almost all areas of the brain tested, such as forebrain, habenula, tectum, cerebellum and spinal cord at larval stage. Stimulus-driven responses were also observed in the tectum, the visual center in teleost fish. Tectal neurons showed ON- and OFF-responses to the changes in brightness of an object presented on a PC display. They also showed direction selectivity to a moving object. To examine how a natural object is represented in the brain, we showed zebrafish larvae living paramecia and imaged the brain activity in the tectum. The activity on the neuropil of the tectum indeed moved around in accordance with the topographic map of retinotectal projection. Our results demonstrate that the improved GCaMPs are sensitive enough to report neuronal responses to natural stimuli in behaving animal.