Role of Dopamine in Retinal Function

Excerpt

Dopamine (DA) is the major catecholamine in all vertebrate retinas including man. All vertebrates have dopaminergic neurons identified as amacrine cells (ACs) and interplexiform cells (IPCs), with great variations among different species. DA neurons are comparatively rare with density about 10-100 per mm², which means that they are less than 1% of all amacrine cells. In retinal circuitry DA serves principally as a neuromodulator, which reaches distant target cells by diffusion, and thus exerts a “volume transmission” mode of communication. Dopamine release appears to be circadian, with high release levels during the day in many species, and is a counterpart to the circadian rhythm in melatonin, which is released at night. Dopamine regulates voltage-gated ion channels and alters chemical and electrical synaptic transmission through five D₁-like and D₂-like G-protein-coupled receptors. DA is particularly associated with retinal circuitry reconfigurations with nighttime and daytime vision. DA actions are highly cell type, species and context dependent. DA acts through multiple intracellular pathways, in particular G-protein activated Adenylate Cyclase (AC) and Phospholipase C (PLC) pathways.