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T.A. Blute, S. Cahoon, P.B. Cook, W.D. Eldred; Dopamine Modulates Nitric Oxide Levels in the Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5147.
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Purpose: Light adaptation in the retina is known to involve changes in levels of dopamine and nitric oxide, but the interactions between these messengers remains unclear. Therefore we examined the effects of blocking D1 dopamine receptors on light-induced increases in nitric oxide production in the dark-adapted retina. Methods: Retinas from dark-adapted larval tiger salamanders were isolated and sliced under infra-red optics, the slices loaded with diaminofluorescein, washed, and transferred to light-tight boxes for stimulation. When appropriate, 15µM of the D1 dopamine receptor antagonist SCH-23390 was included in the Ringers. Following stimulation, the slices were fixed in 4% paraformaldehyde and then the NO-induced fluorescence (NO-IF) was imaged using confocal microscopy. Results: Control, dark-adapted retinas had strong NO-IF in the OPL, concentrated in horizontal cell somata and processes, but low levels in amacrine cells and the IPL. Flashing light (3Hz, 20µW, 660nm) increased NO-IF in numerous amacrine and ganglion cells. SCH23390 increased the NO-IF in unstimulated, dark-adapted slices but strongly decreased the NO-IF stimulated by flashing light. Conclusions: Antagonism of D1 dopamine receptors altered NO-IF in both dark-adapted and light-stimulated retinas. Blocking D1 receptors in the dark shifted the pattern of NO-IF to resemble that seen with light stimulation, while blocking D1 receptors in the light shifted the pattern of NO-IF production towards the pattern seen in the dark. This suggests that dopamine actively suppresses the production of NO in the dark-adapted retina and stimulates the production of NO in the light-adapted retina.
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