Date of Award

Spring 5-15-2020

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Neurosciences)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

The inner retina is a highly tractable location for the study of neural networks in the central nervous system and improving our understanding of the inner retina is important for the treatment of a number of ophthalmic diseases. This dissertation aims to improve understanding of the inner retina in two parts: first, a basic neuroscientific project concerning normal neuronal processing in the inner retina at a cellular level, and second, a translational ophthalmologic project regarding the development in the inner retina of a common disease. In mammals, modulation of the amplitude of dim visual signals primarily occurs at axon terminals of rod bipolar cells. While such effects are largely mediated by conventional inhibitory neurotransmitter receptors, excitatory amino acid transporter 5 (EAAT5) also contributes a significant unconventional inhibitory activity. EAATs clear glutamate from the synapse, but they also have an intrinsic glutamate-gated chloride conductance. EAAT5 in particular has very little glutamate reuptake activity, and primarily acts as an inhibitory glutamate-gated chloride channel. In my primary project I demonstrate the relative contribution of EAAT5-mediated inhibition onto rod bipolar cells in response to physiologically relevant stimuli in retinal slice explants. In this setting, I also compare the roles of autoinhibition, in which excitation of the cell leads to inhibition onto itself, and alloinhibition, which is driven by other bipolar cells. Contrary to prior reports, I found that EAAT-mediated inhibition can be elicited by dim light stimuli. I also found that while conventional inhibitors mediate nearly all alloinhibition onto rod bipolar cells, EAAT5 is the primary mediator of rod bipolar autoinhibition. Finally, in silico modeling demonstrates that EAAT5-mediated autoinhibition may have a substantial impact on postsynaptic excitation of the downstream AII amacrine cell. My combined results suggest that EAAT5 autoinhibition in rod bipolar cells modulates the rod signaling pathway, possibly tuned to prevent long-term changes in baseline depolarization while still allowing single-photon signals to pass in the dark and transient signals to pass in the twilight. Obesity predisposes humans to type 2 diabetes, which may result in diabetic retinopathy, commonly understood to be fundamentally a vascular pathology. In my secondary project I seek to characterize the course of electroretinographic dysfunction in a high-fat dietЩnduced model of diabetes in mice. Mice weaned to chow or to a high-fat diet were tested for electroretinographic dysfunction at 3, 6 and 12 months of age. There is no evidence of microvascular disease in these mice until 12 months. However, at as early as 6 months, high fat-fed mice demonstrated increased latencies and reduced amplitudes of oscillatory potentials compared with controls. These electroretinographic abnormalities were correlated with glucose intolerance. The results suggest that retinal disease in the diabetic milieu may progress through neuro-retinal stages long before the development of vascular lesions representing the classic hallmark of diabetic retinopathy, establishing a model for assessing novel interventions to treat eye disease.

Language

English (en)

Chair and Committee

Peter D. Lukasiewicz

Committee Members

Erik D. Herzog, Timothy E. Holy, Daniel Kerschensteiner, Steven J. Mennerick,

Download

Share

COinS