The accessory optic system (AOS) integrates binocular visual information to drive compensatory eye and body movements in response to optic flow. Recently, we showed, by optical imaging in the AOS homolog of larval zebrafish, the pretectal area, the existence of different types of direction-selective (DS) neurons (Kubo et al., 2014). So-called “simple cells” responded to moving gratings presented to one or two eyes, either nasal- or temporalward, or a combination of these stimuli. “Complex cells”, on the other hand, encoded either translational or rotational motion. Simple responses can be generated by feedforward monocular DS inputs (e. g. from retinal ganglion cells). Complex response types, however, combine information from both eyes, requiring DS inhibitory connections. From this analysis, Kubo et al. (2014) were able to predict a wiring diagram of the optic-flow responsive circuit.
To test the predictions, we established a novel optogenetic method, combining functional characterization with morphological analysis of individual cells. In FuGiMA (Function-guided inducible morphological analysis), a cell of a specific response type is identified by regressor-based correlation of in vivo GCaMP6s imaging data with the expected neuronal activity. Next, paGFP is activated in the identified cell, enabling the visualization of its morphology.
We successfully reconstructed neurons with simple and complex response types. Registering the cells to a reference brain, we are now exploring if cells of the same response type have similar projection patterns. In parallel, we are also mapping inhibitory and excitatory cells in the pretectal area.