Diabetes causes deficits in vision and global retinal activity that happen prior to the end-stage vascular growth and edema of diabetic retinopathy. Several studies have shown that decreases in retinal function predict vascular changes, suggesting that diabetic retinopathy may be a neurovascular disease, where direct damage to retinal neurons contributes to the progression of diabetic retinopathy. However, it is unknown what causes this retinal dysfunction. Decreases measured in human and animal models with electroretinograms are population measurements and thus could be due to deficits in retinal neuronal signaling or loss of retinal neurons. To address this major knowledge gap, we are proposing to investigate the progression of direct neuronal damage in diabetes and differentiate between retinal neuronal dysfunction and retinal cell death as the causes. Previous in vivo studies have identified potential decreases in the activity or survival of retinal photoreceptors that sense light, bipolar cells that receive inputs from photoreceptors, amacrine cells that feedback input onto bipolar cells and ganglion cells that are the output of the retina. As bipolar cells receive inputs from photoreceptors and amacrine cells, changes in the activity or cell loss of bipolar cells or ganglion cells may be an important mechanism of retinal dysfunction in early diabetes. We will use an innovative approach with mouse lines that express fluorescent proteins in specific retinal bipolar cells and the STZ model of diabetes, which kills pancreatic beta cells, to investigate the mechanisms of diabetic retinal damage in vitro over multiple time points. In Aim 1 we will determine which specific retinal neurons have a dysfunctional physiological response in diabetes and test a potential treatment to prevent this dysfunction, using single cell electrophysiology recordings of the responses of targeted bipolar cells and ganglion cells to light. In Aim 2 we will determine what changes in the mechanisms of neuronal signaling explain the physiological changes measured in Aim 1 in the targeted bipolar cells. In Aim 3 we will determine if the diabetes induced changes in neuronal signaling are accompanied or preceded by changes in morphology, survival and/or receptor expression, using the fluorescent protein expression of our targeted bipolar cells and immunohistochemistry techniques. These studies will be the first to make physiological measurements from individual retinal cell types in the intact retina from a diabetic mouse model, where it is possible to determine what neuronal mechanisms have changed due to diabetes. The illustration of the mechanisms of diabetic retinal neuronal damage will test one therapeutic target (dopamine deficiency) and suggest others, such as therapies that reverse changes in neuronal activity or promote neuronal survival that can be used in a time window where retinal damage from diabetes may not be irreversible. This will provide a foundation for future studies to determine if these direct neuronal changes correlate with vascular changes and how preventing neuronal changes would affect the end-stage of diabetic retinopathy.