Dopamine D1 receptor activation contributes to light-adapted changes in retinal inhibition to rod bipolar cells

Michael D. Flood; Johnnie M. Moore-Dotson; and Erika D. Eggers, University of Arizona.  This study was conducted with IRRF support – Erika D. Eggers.  (15 AUG 2018, Vol 120, Issue 2)

ABSTRACT: Dopamine modulation of retinal signaling has been shown to be an important part of retinal adaptation to increased background light levels, but the role of dopamine modulation of retinal inhibition is not clear.  This team previously showed that light adaptation causes a large reduction in inhibition to rod bipolar cells, potentially to match the decrease in excitation after rod saturation.  This study determined how dopamine D1 receptors in the inner retina contribute to this modulation.  It was found that D1 receptor activation significantly decreased the magnitude of inhibitory light responses from rod bipolar cells. Whereas D1 receptor blockade during light adaptation partially prevented this decline.  To determine what mechanisms were involved in the modulation of inhibitory light responses, the effect of D1 receptor activation on spontaneous currents and currents evoked from electrically stimulating amacrine cell inputs to rod bipolar cells was measured.  D1 receptor activation decreased the frequency of spontaneous inhibition with no change in event amplitudes, suggesting a presynaptic change in amacrine cell activity in agreement with previous reports that rod bipolar cells lack D1 receptors.  Additionally, it was found that D1 receptor activation reduced the amplitude of electrically evoked responses, showing that D1 receptors can modulate amacrine cells directly.  These results suggest that D1 receptor activation can replicate a large portion but not all of the effects of light adaptation, likely by modulating release from amacrine cells onto rod bipolar cells.

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