The role of dopamine in fine-tuning cone- and rod-driven vision
Dopamine, one of the major neuromodulators in the retina, acts through dopamine D1, D2, and D4 G-protein-coupled receptors localized to many types of retinal neurons. This expansive expression pattern allows dopamine to regulate visual processing at different cellular sites of the retinal circuitry. One of the most extensively studied functions of dopamine is its role in mediating the shift from roddominant to cone-dominant vision at the transition from night to daylight. However, dopamine is also critical for the regulation of the rod-driven circuitry. Recent studies in the mouse demonstrated that dopamine enhances the light sensitivity of the rod bipolar cells which mediate vision under dim-to-moderate illumination. In this mechanism, dopamine acts via dopamine D1 receptors and induces a GABAergic input onto rod bipolar cells which evokes a sustained hyperpolarizing chloride current carried by the GABAC receptor channel. This sensitizing GABAergic input is crucial for increasing the light response amplitudes and extending the operational range of rod bipolar cells. These recent findings expanded the role of dopamine in retinal processing from its well-established function of supporting the transition between rod- and cone-dominant vision to enhancing light responses in the dark or under dim light.
