Imaging functional neural circuits in zebrafish with a new GCaMP and the Gal4FF-UAS system.

Measurement of the activity of neuronal ensembles is an essential step to understand how the neuronal network is organized and functioning. Electrical excitation of neurons causes calcium influx via voltage-gated calcium ion channels, which can be monitored by calcium imaging using fluorescent calcium probes. DNA-encoded calcium indicators (DECIs) such as cameleon and GCaMP have been developed to specifically label a subpopulation of neurons. However, in many cases, DECIs that had been developed and tested in vitro did not always show expected performance in vivo. It is necessary to increase its sensitivity and also to adjust its dynamic range to the physiological conditions. In our recent study, we developed an improved version of GCaMP and tested its performance in vivo using transgenic zebrafish. By combining the new GCaMP with targeted gene expression via the Gal4FF-UAS system, we successfully imaged the activity of the spinal motor circuit during spontaneous contractions of zebrafish larvae. Further we report here that heptanol, a gap junction blocker, could alter the spatiotemporal activation pattern of the motor circuit. Thus, we demonstrate that calcium imaging with GCaMP is powerful to analyze neuronal activities under normal and pharmacologically perturbed conditions.