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Received September 29, 2005
Revised October 10, 2005
Accepted after revision October 19, 2005
1 Univ of Notre Dame
* To whom correspondence should be addressed. E-mail: li.78{at}nd.edu.
The vertebrate retina receives centrifugal input from the brain. In zebrafish, the major centrifugal input originates in the terminal nerve (TN). TN cell bodies are located in the olfactory bulb and/or ventral telencephalon. The TN projects axons to the retina where they branch in the inner plexiform layer (IPL) and synapse onto several inner retinal cell types, including dopaminergic interplexiform cells (DA-IPCs). This olfactoretinal centrifugal input plays a role in modulating retinal ganglion cell (RGC) activity, likely via dopamine-mediated Ca2+ signaling pathways. Normally, dopamine inhibits RGC firing by decreasing the inward Ca2+ current. Olfactory stimulation with amino acids decreases dopamine release in the retina, thereby reducing dopaminergic inhibition of RGCs. This model of olfacto-visual integration was directly tested by recording single-unit RGC activity in response to olfactory stimulation in the presence or absence of dopamine receptor blockers. Stimulation of the olfactory neurons increased RGC activity. However, this effect diminished when the dopamine D1 receptors were pharmacologically blocked. In isolated RGCs, the application of dopamine or dopamine D1 receptor agonist decreased voltage-activated Ca2+ current and lowered Ca2+ influx. Together, the data suggest that olfactory input has a modulatory effect on RGC firing, and that this effect is likely mediated by dopamine D1 receptor-coupled Ca2+ signaling pathways.
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