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M. M. Deshpande, W. D. Eldred; Dopamine and Light Adaptation Modulate Nitric Oxide Production in Mouse Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5194.
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Many changes in light adaptation are controlled by dopamine (DA), which is synthesized by amacrine cells and is released by light stimulation. Recently nitric oxide (NO), which activates the cyclic guanosine monophosphate (cGMP) signal transduction system, has also been implicated in the modulation of many of the same retinal pathways as DA. In teleost, a serial release of DA and NO has been proposed during light adaptation in the retina. The purpose of our study was to localize NO production in the dark adapted mouse retina, to determine the effect of light adaptation on NO production, and to examine the role of DA in NO production.
Mouse retinal slices were loaded with the NO sensitive fluorescent dye diaminofluorescein (DAF), stimulated, fixed in paraformaldehyde, and the NO induced fluorescence (NO-IF) was imaged using confocal microscopy.
In the dark, there was extensive NO-IF in synaptic boutons in the inner and the outer plexiform layers, in many somata in the inner nuclear layer and ganglion cell layer. NO-IF was rarely seen in the photoreceptors. We replicated in mice previous work done in other vertebrates in that NO levels in the light were higher than those in the dark. As in teleosts, we also showed that application of exogenous DA in the dark mimicked the effects of light. The D1 DA receptor (DAR) agonist SKF38393 induced ‘light-like’ response by increasing NO-IF in the dark. However, there are species differences. Whereas in the fish, the D1 DAR antagonist SCH23390 inhibited NO production in the light, we saw no effect of the same antagonist on light adapted mouse retina. Surprisingly, exogenous application of the selective D2 DAR antagonist spiperone or the D2 DAR agonist quinpirole resulted in qualitatively similar results; significantly reducing NO-IF in the retina, both in the dark and in the light.
These data suggest a complicated interaction of the various DA receptors and NO in the mouse retina. Although DA does modulate NO production, it is likely that the two interact at various stages of adaptation. Given the wide variety of retinal neurons capable of making NO, it is extremely probable that different biochemical pathways are activated in specific cell types such that only a part of this NO production is under the modulatory control of DA.
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