Robinson, Martha Rose; (2017) Spatial and temporal dynamics of retinal ganglion cells with different photoreceptor inputs. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The retina must operate over a wide range of light levels. Two classes of input cells, rods and cones, specialised to different light conditions evolved to achieve this task. This thesis examines how interactions between these two classes shape retinal output as the light level changes, and the extent to which loss of one class can alter processing of the remaining class. Retinal ganglion cell (RGC) receptive elds were characterised using multielectrode array recordings performed during presentation of spatiotemporal white noise across a 4.5 log10 light level range. Receptive fi eld properties were compared between wild-type mice, mice lacking functional cones (cpfl1 model of achromatopsia), and mice lacking functional rods (rd17 model of congenital stationary night blindness). The response of RGCs to otherwise identical stimuli changed with ambient light level. In low light conditions, wild-type RGCs had a longer latency to spike and were shifted towards higher temporal and lower spatial frequency tuning. Of those RGCs characterised at multiple light levels, 28% changed the polarity of their receptive fields between ON and OFF. These polarity switches occurred between every possible pair of light levels, and several cells were observed to switch multiple times. RGCs which switched polarity were identi ed in both rd17 and cpfl1 mice, indicating that at least some circuit mechanisms responsible are driven by a single photoreceptor cell class. Loss of function in one photoreceptor cell class altered visual processing of inputs from the remaining class. In low light conditions, RGCs in cpfl1 mice showed shorter latency to spike and a marked shift towards higher temporal frequency tuning, a receptive field property that is often understood as indicating tuning to visual motion. This difference in visual processing could result in behavioural differences, for instance these mice may exhibit better contrast sensitivity at temporal frequencies in low light conditions.

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