Recent studies suggest that the neural retinal response to light is compromised in diabetes. Electroretinogram studies suggest that the dim light retinal rod pathway is especially susceptible to diabetic damage. The purpose of this study was to determine whether diabetes alters rod pathway signaling.

The retina is able to adjust its signaling over a wide range of light levels. A functional result of this is increased visual acuity at brighter luminance levels, such as during the day, due to changes in the organization of retinal receptive fields. This process is commonly referred to as light adaptation. These organizational changes have been shown to occur at the level of the ganglion cells, the output neurons of the retina, which have shifts in their excitatory center-inhibitory surround receptive fields that increase their sensitivity to small stimuli. Recent work supports the idea that light-adapted changes in ganglion cell spatial sensitivity are due in part to inner retinal signaling changes, possibly including changes to inhibition onto bipolar cells, the interneurons at the center of retinal signal processing. However, it is unknown how inhibition to the bipolar cells changes with light adaptation, how any changes affect the light signal or what mediates the changes to the bipolar cells that have been suggested by previous reports. To determine how light adaptation affects bipolar cell inhibition, the inhibitory inputs to OFF bipolar cells were measured. OFF bipolar cells, which respond to the offset of light, in particular may be involved in retinal adaptation as they bridge dim- and bright-light retinal pathways. Their inputs were compared between dark- and light-adapted conditions to determine how any inhibitory changes affects their output onto downstream ganglion cells. We found that there was a compensatory switch from primarily glycinergic-mediated inhibition to OFF bipolar cells in the dark to primarily GABAergic-mediated inhibition in the light. Since glycinergic and GABAergic inhibition perform very different roles and are mediated by morphologically different cells, it is likely this switch underlies a change in the spatial distribution of inhibition to these cells. We found that the spatial inhibitory input to OFF bipolar cells became significantly smaller and narrower with light adaptation, translating to smaller inhibitory surrounds of the OFF bipolar cell receptive fields. Through a model, our data suggested that the OFF bipolar cell output to downstream ganglion cells was stronger in the light, due to the narrowing and reduction in the spatial input, to small light stimuli. This would effectively be one way the retina could use to increase visual acuity. Additionally, we found that the inhibitory changes to OFF bipolar cells with light-adaptation are partially mediated by dopamine D1 receptor signaling. Dopamine is released in the light and has been shown to be an important modulator of retinal light-adaptation. However, there are likely other factors involved in mediating inhibitory changes to OFF bipolar cells. Through these studies, we show that light adaptation heavily influences inner retina inhibition and likely plays a prominent role in determining and shaping light signals under different ambient light conditions which may ultimately be one mechanism for increasing visual sensitivity and acuity.

Previous studies from our lab have shown that Activating protein-2 (AP-2) transcription factors, AP-2α and AP-2β are important in retinal development, specifically in the developing horizontal and post-mitotic amacrine cells. Conditional deletion of AP-2α and AP-2β from the retina of mice resulted in a variety of abnormalities including loss of horizontal cells, defects in the photoreceptor ribbons in which synapses failed to form, along with evidence that amacrine cell mosaic patterning may be disrupted. The current thesis examined the neural retina of these AP-2α and AP-2β conditional mice in greater detail using immunofluorescence of histological sections and whole retinas, and electroretinograms to measure retinal function in post-natal adult mice. Examining regularity of the amacrine cell mosaics of these double mutants showed the loss of AP-2α and AP-2β led to significant irregularities in the mosaic patterning of these cells as determined by Voronoi domain areas (P<0.01) and nearest-neighbour distances (P<0.03). No significant changes in amacrine population numbers were observed. Observed cellular changes in the double conditional knock out mice were reflected as a change in the retinal response to light as recorded by electroretinograms. For example, the b-wave amplitude, representative of the interneuron signal processing, was significantly affected in those mice lacking AP-2⍺ and AP-2β (P<0.0001). Taken together, the work presented in this thesis implicates the requirement of AP-2⍺ and AP-2β for the correct amacrine mosaic patterning and for the proper functional light response in the retina. / Thesis / Master of Applied Science (MASc)

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Local and global forms of inhibition control directionally selective ganglion cells (DSGCs) in the mammalian retina. Specifically, local inhibition arising from GABAergic starburst amacrine cells (SACs) strongly contributes to direction selectivity. In this thesis, I demonstrate that increasing ambient illumination leads to the recruitment of GABAergic wide-field amacrine cells (WACs) endowing the DS circuit with an additional feature: size selectivity. Using a combination of electrophysiology, pharmacology and light/electron microscopy, I demonstrate that WACs predominantly contact presynaptic bipolar cells, which drive direct excitation and feed-forward inhibition (through SACs) to DSGCs, therefore maintaining the appropriate balance of inhibition/excitation required for generating DS. This circuit arrangement permits high-fidelity direction coding over a range of ambient light levels, over which size selectivity is adjusted. Together, these results provide novel insights into the anatomical and functional arrangement of multiple inhibitory interneurons within a single computational module in the retina. / Graduate

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 91-101).

Glaucoma is a group of ocular disorders characterized by optic nerve damage that leads to vision loss and blindness. Damage to retinal ganglion cells (RGCs), particularly through axonal damage due to an increase in intraocular pressure (IOP), is a proposed mechanism behind glaucomatous injury. Other than increased IOP, vascular changes leading to ischemia are another explanation for glaucoma. A state of ischemia leads to a decrease in nutrients supplied to neurons of the retina and creates a hypoxic environment which is linked to cell death in both IOP- and non-IOP-related injury. Injury during glaucoma not only affects RGCs but also has secondary effects that impact the function of other cells in the retina like amacrine cells (ACs). To better understand how RGCs and ACs respond during glaucomatous injury, this study characterized the changes in viability of these cells under hypoxic conditions over time. With the use of a unique immunopanning technique, RGCs and two subpopulations of ACs (CD15+ and CD57+) were isolated from 12-week-old C57BL/6J mice and cultured for 6 to 9 days. After about a week of culturing, the three cell types were placed under either normoxic (n = 5) or hypoxic (n = 6) conditions, and cell viabilities were measured at 1-hour time intervals over 24 hours. RGC and AC isolations based on the immunopanning technique resulted in high yield and viability, confirming the findings of previous optimization studies. In response to hypoxic conditions, RGCs and the two subpopulations of ACs all experienced a decrease in cell viability over the course of 24 hours. Surprisingly, CD57+ cells showed increased susceptibility to injury and death during isolation. However, the remaining CD57+ cells that stayed alive in culture by the start of the time-course experiment were the most resilient to cell death during hypoxia, showing significantly higher cell viability compared with CD15+ and Thy1.2+ cells. The characterization of CD15+, CD57+, and Thy1.2+ cells in response to hypoxia highlights a difference in resilience across neuronal cell types in the retina. Although CD57+ exhibited greater resilience than its counterparts, the mechanism behind neuroprotection among these cells is still unknown and requires further study. / 2024-01-28T00:00:00Z

Previous studies from our lab have shown that the Activating Protein- 2 (AP-2) transcription factors, AP-2α and AP-2β, are important in retinal development. It was discovered that these are co-expressed in developing horizontal cells and postmitotic amacrine cells. To understand their role in retinogenesis, and the impact of their deletion on the adult retina, a double mutant mouse model was created, AP-2αKI/flox/AP-2β-/flox. The neural retina of the AP-2αKI/flox/AP-2β-/flox mice was examined in the current study using histological, immunofluorescent and electron microscopy (EM) techniques at embryonic, post-natal and adult stages. These double mutants displayed a variety of abnormalities in the inner retina. Loss of AP-2α and AP-2β at E10.5 led to a complete absence of developing and mature horizontal cells. This loss was associated with changes in the outer plexiform layer, which diminished from two to four months of age. There were also defects with photoreceptor ribbons in which triad synapses failed to form, and instead led to rudimentary, spherical-shaped ribbons. There was also significant retraction of photoreceptor axons. Furthermore, this study was able to infer a role of AP-2α and AP-2β as acting upstream of the Onecut-1 protein, which targets Lim1 and Prox1 to direct horizontal cell genesis. Examining amacrine cells of the double mutants shows evidence that AP-2α and AP-2β are involved in the mosaic arrangement pattern of amacrine cell bodies and axons. Previous work on embryonic double mutants displayed clustering of amacrine cells. This study observed abnormalities in the dendrites of the inner plexiform layer, which consists of amacrine cell processes. Taken together, the work presented in this thesis implicates the redundant requirement of both AP-2α and AP-2β in development of horizontal cells and patterning of amacrine cells in the neural retina. / Thesis / Master of Health Sciences (MSc)

No description available.

Inherited retinal degenerative diseases can affect various components of the retina leading to blindness. Five different mutant strains of chicken have been studied extensively as potential models for inherited retinal degeneration. The Smoky Joe (SJ) chicken is a sixth genetically blind strain of White Leghorns that shows various degrees of blindness at hatch and by 8 weeks post-hatch, have complete blindness for those that are homozygous. The objective of this study was to characterize the retinal degeneration in these birds by histology, both during embryonic and post-hatch development, and to the retinal function using electroretinograms (ERG). For both embryonic and post-hatch development, a significantly lower number of cells were found in the retina of blind birds compared to sighted (both p<0.0001). The significant contributor to cell number decrease was the loss of amacrine cells located in the inner nuclear layer. Photoreceptors were also found to potentially decrease in number, but at a later stage. ERG recordings revealed decreases in amplitudes of b-waves and oscillatory potentials in blind birds, but not in sighted. Both histology and ERG findings support the idea that the inner retinal cells are affected. The results indicate that degeneration in the Smoky Joe retina occurs mostly within the inner nuclear layer affecting amacrine cells. This hampers the functional capacity of the retina, causing blindness.