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UBC Theses and Dissertations

The retinorecipient pretectal projections to the oculomotor cerebellum in zebra finch (Taeniopygia guttata) and Anna’s hummingbird (Calypte anna) Azargoon, Sarina

Abstract

A major visual signal for control of posture and movement is optic flow - the global motion across the retina due to relative motion between an organism and its environment. In birds, the pretectum and accessory optic system of the midbrain consist of neurons that are sensitive to optic flow. The retinal recipient nuclei for these key pathways are the lentiformis mesencephali (LM) and the nucleus of the basal optic root (nBOR). Over a decade, research from pigeons (Columba livia) revealed that both retinal recipient optic flow nuclei send projections to the cerebellum. The vestibulocerebellum (folium IX) receives strong input from both LM and nBOR. The oculomotor cerebellum (folia VI-VIII) also received LM input. Recently, the inputs to the vestibulocerebellum and the oculomotor cerebellum were measured in two additional species, Anna's hummingbirds (Calypte anna) and zebra finches (Taeniopygia guttata). The midbrain-cerebellar pathways differed among species in several unexpected ways. The hummingbird oculomotor cerebellum received half of it inputs from the LM and half from two other midbrain areas, the nucleus laminaris precommisuralis (LPC) and the nucleus principalis precommisuralis (PPC). In the zebra finch, the oculomotor cerebellum received 75% of its inputs from LPC and PPC. Thus, the recent work suggests important roles for LPC and PPC in oculomotor control. This result is surprising because in the pigeon, these two nuclei represent only 7.9% of the inputs to the oculomotor cerebellum. Relatively little is known about either LPC or PPC. The goal of my thesis was to answer two questions about these circuits: 1) Do LPC and PPC neurons of zebra finches and hummingbirds that project to oculomotor cerebellum also receive retinal inputs? 2) Do retinal ganglion cells of hummingbirds and zebra finches project to other brain regions not currently described for birds? Both questions were addressed by injecting Cholera Toxin B with different fluorophores into the oculomotor cerebellum and the eye. These experiments revealed a novel one-synapse pathway from the eye to the cerebellum in LPC, but not in PPC. I also confirmed a second one-synapse pathway through the area pretectalis that had been proposed from earlier single injection studies.

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