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Date of Award
Doctor of Philosophy (PhD)
Recognizing object motion is one of the essential visual functions for survival. Object motion information is first detected by the retina. Among approximately 30 different types of retinal ganglion cells (RGCs), some motion detecting RGCs (e.g. direction-selectivity, differential motion detection, edge detection) have been identified. However, except for the direction-selective retinal circuit, specific circuit components and underlying mechanisms of motion information processing in the retina are poorly understood. Recent findings show amacrine cells (ACs), inhibitory interneurons in the inner retina, often determine response properties of retinal outputs (e.g. direction selectivity). ACs are the most diverse neuronal class in the retina yet only a few types are thoroughly studied. Studying characteristics of specific AC types and their functional roles in the circuit is crucial to understanding how the retina processes object motion information. The second chapter of my thesis focuses on one type of AC, the VG3-AC, which expresses vesicular glutamate transporter 3 (VGluT3). In order to analyze VG3-ACs’ receptive field properties, I first examined light responses of VG3-ACs in the flat-mounted retina to broad sets of visual stimuli under 2-photon guidance in VGluT3-Cre transgenic mice. My results demonstrate that VG3-ACs detect object motion. Furthermore, I explored the functional role of VG3-ACs in the retinal circuit. The activation pattern of a RGC type called W3-RGC, also known as local edge detecting RGC, exactly corresponded to responses of VG3-ACs. Anatomical reconstruction of the circuit elicited the connectivity between VG3- ACs and W3-RGCs. Then, by comparing wild-type and VGluT3 knock-out mice, I demonstrated that W3-RGCs receive object motion sensitive (OMS) glutamatergic input from VG3-Acs. The fourth chapter of my thesis investigated whether motion processing in the retina can alter visually guided behaviors of the animal. Looming visual stimuli, also called approaching motion visual stimuli, evoke defensive behaviors of the animal. Brain networks that mediate this defensive response have recently been identified. In the retina, however, it is unknown whether a single or multiple neural circuits contribute to encoding looming stimulus detection to drive such a behavior. Recent optogenetic studies demonstrated VG3- ACs connect to several downstream RGCs. W3-RGC and OFFα-RGC are two RGC types considered to receive glutamatergic input from VG3-ACs and to detect looming stimulus. Thus, I tested the responses of VG3-ACs to approaching motion visual stimuli and compared them to the excitatory input W3- and OFFα-RGCs receive. Then, I examined whether removing VG3-ACs in the mature retinal circuit affects responses of W3-RGCs and OFFα - RGCs, and defensive behaviors of the animal. Overall, my thesis work reveals characteristics of the VG3-AC type, contributions of VG3-AC in motion information processing in retinal circuits and in animal’s defensive behavior, and underlying synaptic mechanisms of VG3-ACs in an aspect of their feature-selectively tuned excitatory input to downstream partners.
Chair and Committee
Peter Lukasiewicz, Steven J. Mennerick, Andreas H. Burkhalter, Martha W. Bagnall,
Kim, Tahnbee, "Motion processing in the mouse retina" (2017). Arts & Sciences Electronic Theses and Dissertations. 1118.
Available for download on Saturday, May 15, 2117