Visualization of Neuronal Activity in Zebrafish Spinal Neurons with an Improved GCaMP

Akira Muto1, Masamichi Ohkura2, Tomoya Kotani1,Junichi Nakai2, Koichi Kawakami1

1)National Institute of Genetics, Mishima, Japan, 2)Saitama University Brain Science Institute, Saitama, Japan

 Calcium imaging with DNA-coded calcium indicators is a powerful means for monitoring the activity of genetically identified neurons. We developed GCaMP-HS, an improved version of GCaMP2, and created transgenic zebrafish carrying the GCaMP-HS gene downstream of the Gal4-recognition sequence, UAS. We used this tool to study the spinal motor circuits. In a gene trap screen, we identified the SAIGFF213A transgenic fish that expressed Gal4FF, a modified version of Gal4, in a subset of spinal neurons including the CaP primary motor neurons. Zebrafish shows the earliest behavior, spontaneous contractions at 17-27 hpf. We imaged calcium signals in the SAIGFF213A;UAS:GCaMP-HS double transgenic embryos at these stages. We observed periodic and synchronized activation of a set of ipsilateral motor neurons located on the right and left trunk in accordance with actual muscle movements. The activation on the right and left sides occurred alternately. Further, the synchronized and periodic activities of the neurons were already present at the onset of spontaneous contractions. This study thus demonstrated the activity of an entire CaP motor neuron network. GCaMP-HS in combination with the Gal4FF-UAS system provides an excellent tool to study functional neural circuits in vertebrate.