Brain Imaging with New GCaMPs

Akira Muto、Koichi Kawakami

Division of Molecular and Developmental Biology, National Institute of Genetics

Why we behave as we do, or why animals behave as they do? To answer this fascinating question, we have chosen zebrafish as a model system. It is the brain activity that creates behaviors. Therefore, visualization of the brain function can be the first step to understanding of the brain-behavior connection. Neuronal activity can be monitored by measuring calcium influx that is coupled with generation of electrical signals in the neurons. Calcium imaging with DNA-encoded calcium indicators, such as GCaMP, is a powerful means because it allows us to monitor the activity of genetically identified neurons. Recently we developed an improved GCaMP, GCaMPHS, and demonstrated visualization of the activity in the spinal neurons during a motor behavior (Muto et al., 2011). Here we have further modified the GCaMP and generated UAS:GCaMP transgenicfish. To observe neuronal activities in a visual behavior, the UAS:GCaMP was expressed in GAL4 enhancer/gene trap lines with specific expression patterns. Our imaging study using artificial visual stimuli revealed a functional retinotopic map in accordance with the well established retinotectal projection. Next, we asked how natural visual stimuli are represented in the brain. One of the vision-guided behaviors in zebrafish larvae is feeding with paramecia. We observed that the neuronal activity driven by the visual input of a moving paramecium also moved around on the neuropil showing the functional retinotopy. We also observed spontaneous activities in the forebrain, habenula and cerebellum, although their roles remain to be elucidated. The improved GCaMPs, in combination with the Gal4-UAS system will be an excellent tool to study brain functions in animal behavior, from sensory perception, cognition, to motor outputs.

Muto A, Ohkura M, Kotani T, Higashijima S, Nakai J, Kawakami K. Genetic visualization with an improved GCaMP calcium indicator reveals spatiotemporal activation of the spinal motor neurons in zebrafish. Proc Natl Acad Sci U S A. 2011 Mar 29;108(13):5425-30.