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H Maaswinkel, L Li; Olfactory Stimulation With Amino Acids Modulates Visual Sensitivity in Zebrafish . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4751.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: In fish, the ganglion cells of the terminal nerve (TN) - located in the olfactory bulb - project onto the dopaminergic interplexiform cells (DA-IPCs) of the inner retina. This study was undertaken to investigate the function of this connection. Methods: In a behavioral assay, based on visually mediated escape response, the effect of amino acids added to the swimming water on the visual threshold of zebrafish was investigated. The question which chemosensory system (olfaction, taste) is involved was addressed by performing the same behavioral test with bulbectomized fish. To determine if the DA-IPCs play a role, the fish were tested under the following conditions: intra-ocular injection of dopamine D1 or D2 antagonists, or 6-OHDA that destroys dopaminergic cells. Results: All four amino acids used in this study (methionine, arginine, alanine, aspartic acid) decreased the visual threshold necessary to detect a visual stimulus. This effect was dose dependent. The highest doses (10-4, 10-3 M) were always effective, whereas the lower doses (10-6, 10-5 M) reduced the visual threshold only for some of the amino acids, such as arginine. In total darkness, amino acids did not alter the spontaneous swimming behavior. After lesion of the olfactory bulb or destruction of the DA-IPCs by 6-OHDA, amino acids did not have any perceptible effect on visual threshold. Testing the fish after intra-ocular injection of either the dopamine D1 antagonist SCH23390 or the D2 antagonist sulpiride, we found that only the latter blocked the effect of amino acids on visual sensitivity. Conclusion: The results demonstrate that olfactory stimulation in zebrafish can modulate visual sensitivity. This effect was neither confounded by motivation nor by the taste system. The retinal dopaminergic system is crucial for this modulation. We suggest that the TN is involved, because it is the only direct connection from olfactory bulb to the retina in zebrafish so far described.
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