| Summary: | Information on the direction of movement of objects in the visual field is vital for visually guided behaviours including prey capture and predator avoidance. The optic tectum is important for producing such visually guided behaviours in zebrafish. Understanding the functional properties of subtypes of neurons within this tectal circuit is vital to understanding the processing responsible. Superficial inhibitory interneurons (SINs) are located in the superficial optic tectum and have laminar arborisations; ablation of these neurons has been shown to perturb prey capture behaviour. In this thesis, the receptive field properties of SINs in the zebrafish optic tectum were characterised. A subset of SINs were found to be direction selective, forming three different direction selective (DS) populations with preferred directions mirroring those of DS retinal ganglion cell (DSGC) inputs to the tectum. Furthermore, the spatial frequency (SF) and temporal frequency (TF) tuning properties of SINs were also characterised, finding that these neurons are selective for smaller moving objects. Comparing SIN DS responses to those of DSGC and tectal neuron populations, SINs have much narrower DS tuning. This narrow DS tuning was insensitive to injection of GABA-A receptor antagonists into the tectum, indicating that GABA-A receptor mediated inhibition is not involved. The role of GABAergic inhibition in generating the properties of DS populations in the tectum was also probed using drug injections, finding that both DS tectal neurons and DSGC properties were not significantly altered when GABA signalling is perturbed. This characterisation of SIN function has identified a narrowly tuned inhibitory interneuron in the tectal circuit, exhibiting band pass filtering for small moving objects. This functional characterisation of SIN receptive field properties indicates a possible role of these SINs in a size selective circuit, possibly relating to prey capture behaviours.
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