PROJECT SUMMARY Dopamine is a neuromodulator with a critical role in vascular diseases of the eye. Our recent studies show that dopamine can directly signal to the vasculature via dopamine receptors and act as a developmental timing cue for hyaloid vascular regression through its regulation of VEGF. Here, we now extend these studies to the retina vasculature. Our preliminary data show that increasing dopamine signaling in the developing retina decreases vascular density, while decreasing dopamine causes vasculature overgrowth. We further identify retinal ganglion cells as novel dopamine producing cells and show that they directly modulate vascular growth. This is an important finding because dopamine was previously thought to be produced only by a subset of amacrine cells. To understand the mechanisms by which RGCs become dopaminergic and the vascular pathways through which they signal, we propose three experimental aims. We test whether dopamine has a direct (Aim 1) or indirect (Aim 2) effect on retinal vascular cells using vascular and neuron cell-specific strategies to remove dopamine receptors. We also ask whether dopamine and VEGFA function in trophic feedback within the retina to establish causation. In Aim 3, we determine the neuronal mechanisms by which RGC-derived dopamine modulates the vasculature through examination of the temporal and genetic pathways that regulate these unique cells. Identification of a dopaminergic-RGC dependent mechanism for modifying vasculature development and homeostasis is unexpected, so when completed this work will change the way we understand dopamine signaling and its distinct cellular roles. This work will also guide future efforts aimed at developing new therapeutic options to target retina vasculopathies.