A red herring in the zebrafish retina: regional specializations among retinal ganglion cells in zebrafish larva linked to chromatic encoding of prey stimuli

In the study of vision and visual ecology, the larval zebrafish is a widely used model organism for speculative and translational research due to its genetic accessibility, amenability to non-invasive in vivo recording techniques, and repertoire of well-studied and stereotyped visually guided behaviors. Yet, although a great deal is known about zebrafish outer retinal circuitry and visual brain areas, the retinal ganglion cells (RGCs), which transmit information from photoreceptors to arborization fields in tectum and pretectum, remain incompletely understood. In particular, recent research has demonstrated the existence of a specialized area within the ventrotemporal region which appears to serve as a prey detection unit, but how the inner retina computes prey-related signals is unknown. In this thesis, we use in vivo two-photon imaging and photolabeling to create an anatomical and functional profile of ventrotemporally-positioned RGCs. We also compare the structure and physiology of this neuronal population to those in other retinal regions, and use the results of our analyses to probe chromatic preferences of the 7 dpf larval retina in terms of kinematic output. We show that the function, distribution, and morphologies of ventrotemporal RGCs differs substantially from the rest of the retina, and that their feature-response set appears to match chromatic components of prey-like stimuli capable of eliciting hunting behaviors. Taken together, our results strongly suggest that prey-responsive RGCs viewing the upper-frontal visual field are highly specialized for short-wavelength chromatic computations necessary for detecting prey stimuli in natural settings.