Optometry and Vision Sciences - Theses
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ItemWide-field ganglion cells in primate retina( 2011)The anatomical circuitry involving distinct neuronal types within the retina, form the basis for the functional properties of ganglion cells. Such properties ultimately represent the nature of visual information carried by these cells for further processing in subsequent areas of the visual system, and are therefore crucial to our understanding of the visual system as a whole. The projects outlined in chapters 2, 3 and 4 investigate the anatomical connections of a group of ganglion cell types (wide-field ganglion cells) retrogradely labelled and photo-filled in the retina of the common marmoset (Callithrix jacchus). This animal model is ideal for our purposes, as ganglion cell types identified in marmoset retina to date, have closely resembled those of Old world primate species. Chapter 1 outlines the anatomical connectivity, morphological features and physiological properties of retinal neurons. Chapter 2 investigates the density and distribution of synaptic inputs onto the two dendritic tiers of small bistratified ganglion cells with the aim of elucidating the retinal connectivity behind their blue-ON/yellow-OFF chromatic responses. The density of presumed bipolar and amacrine cell inputs onto small bistratified cells were measured. All cells analysed showed a consistent pattern, where bipolar input to the inner tier is approximately fourfold greater than bipolar input to the outer tier. This structural asymmetry of bipolar input may help to balance the weight of cone signals from the sparse S cone array against inputs from the much denser M/L cone array. Chapter 3 investigates the density and distribution of synaptic inputs onto two wide-field ganglion cell types with largely contrasting morphological features. Large sparse cells have sparsely branching dendritic trees that are narrowly stratified close to the ganglion cell layer. Broad thorny cells have densely branching dendritic trees broadly stratified within the center of the inner plexiform layer. The density of presumed synaptic inputs was similar for the two cell types, indicating that the larger number of synapses on broad thorny cells may be attributable to the larger membrane surface area of this cell type. Synaptic input density was comparable to previous values for midget and parasol ganglion cells, suggesting that functional differences between these cell types do not arise from variation in synaptic input densities. Chapter 4 investigates the contribution of wide-field ganglion cells to the retinal circuitry subserving foveal vision. The fovea is a region of the retina specialised for high acuity photopic vision, in which the role of the midget pathway has been implicated. The question of whether wide-field ganglion cell types and their neural partners are present within the first 1mm of the foveola was examined. Bipolar cells were immuno-labelled in vertical sections of marmoset and macaque retina. At least three types of wide-field ganglion cells previously described in peripheral retina were present at the fovea. A subset of bipolar cells likely to be involved in providing inputs onto wide-field ganglion cells at the fovea was also found, supporting the view that retinal pathways involving wide-field ganglion cells contribute to foveal vision.