Dopamine and full-field illumination activate D1 and D2-D5-type receptors in adult rat retinal ganglion cells
ABSTRACT Dopamine can regulate signal generation and transmission by activating multiple receptors and signaling cascades, especially in striatum, hippocampus, and cerebral cortex. Dopamine modulates an even larger variety of cellular properties in retina, yet has been reported to do so by only D1 receptor-driven cyclic adenosine monophosphate (cAMP) increases or D2 receptor-driven cAMP decreases. Here, we test the possibility that dopamine operates differently on retinal ganglion cells, because the ganglion cell layer binds D1 and D2 receptor ligands, and displays changes in signaling components other than cAMP under illumination that should release dopamine. In adult rat retinal ganglion cells, based on patch-clamp recordings, Ca(2+) imaging, and immunohistochemistry, we find that 1) spike firing is inhibited by dopamine and SKF 83959 (an agonist that does not activate homomeric D1 receptors or alter cAMP levels in other systems); 2) D1 and D2 receptor antagonists (SCH 23390, eticlopride, raclopride) counteract these effects; 3) these antagonists also block light-induced rises in cAMP, light-induced activation of Ca(2+) /calmodulin-dependent protein kinase II, and dopamine-induced Ca(2+) influx; and 4) the Ca(2+) rise is markedly reduced by removing extracellular Ca(2+) and by an IP3 receptor antagonist (2-APB). These results provide the first evidence that dopamine activates a receptor in adult mammalian retinal neurons that is distinct from classical D1 and D2 receptors, and that dopamine can activate mechanisms in addition to cAMP and cAMP-dependent protein kinase to modulate retinal ganglion cell excitability. J. Comp. Neurol. 520:4032-4049, 2012. © 2012 Wiley Periodicals, Inc.
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ABSTRACT: In Caenorhabditis elegans, the dopamine transporter DAT-1 regulates synaptic dopamine (DA) signaling by controlling extracellular DA levels. In dat-1(ok157) animals, DA is not taken back up presynaptically but instead reaches extrasynpatic sites where it activates the dopamine receptor DOP-3 on choligeneric motor neurons and causes animals to become paralyzed in water. This phenotype is called swimming induced paralysis (SWIP) and is dependent on dat-1 and dop-3. Upstream regulators of dat-1 and dop-3 have yet to be described in C. elegans. In our previous studies, we defined a role for HLH-17 during dopamine response through its regulation of the dopamine receptors. Here we continue our characterization of the effects of HLH-17 on dopamine signaling. Our results suggest that HLH-17 acts downstream of dopamine synthesis to regulate the expression of dop-3 and dat-1. First, we show that hlh-17 animals display a SWIP phenotype that is consistent with its regulation of dop-3 and dat-1. Second, we show that this behavior is enhanced by treatment with the dopamine reuptake inhibitor, bupropion, in both hlh-17 and dat-1 animals, a result suggesting that SWIP behavior is regulated via a mechanism that is both dependent and independent of DAT-1. Third, and finally, we show that although the SWIP phenotype of hlh-17 animals is unresponsive to the dopamine agonist, reserpine, and to the antidepressant, fluoxetine, hlh-17 animals are not defective in acetylcholine signaling. Taken together, our work suggests that HLH-17 is required to maintain normal levels of dopamine in the synaptic cleft through its regulation of dop-3 and dat-1.G3-Genes Genomes Genetics 04/2014; 4(6). DOI:10.1534/g3.114.010819 · 2.51 Impact Factor
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ABSTRACT: Oxidative stress is widely implicated in the death of retinal ganglion cells associated with various optic neuropathies. Agonists of the dopamine D(1) receptor have recently been found to be potentially neuroprotective against oxidative stress-induced injury. The goal of this study was to investigate whether SKF83959, a next-generation high-affinity D(1) receptor agonist, could protect retinal ganglion cell 5 (RGC-5) cells from H(2)O(2)-induced damage and the molecular mechanism involved. We examined expression of the D(1) receptor in RGC-5 cells with reverse-transcription-PCR and immunoblotting and assessed neuroprotection using propidium iodide staining and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. In addition, we monitored the activation and involvement of members of mitogen-activated protein kinase family, extracellular signal-regulated kinase (ERK), p38 and c-Jun NH(2)-terminal kinase, with western blot and specific inhibitors. We found that the D(1) receptor was expressed in RGC-5 cells, but the sequence analysis suggested this cell line is from mouse and not rat origin. SKF83959 exhibited a remarkable neuroprotective effect on H(2)O(2)-damaged RGC-5 cells, which was blocked by the specific D(1) receptor antagonist, SCH23390. ERK and p38 were activated by SKF83959, and pretreatment with their inhibitors U0126 and SB203580, respectively, significantly blunted the SKF83959-induced cytoprotection. However, the specific c-Jun NH(2)-terminal kinase inhibitor, SP600125, had no effect on the SKF83959-induced protection. We conclude that SKF83959 attenuates hydrogen peroxide-induced injury in RGC-5 cells via a mechanism involving activation of the ERK and p38 pathways and the D(1) receptor is a potential molecular target for developing neuroprotective drugs.Molecular vision 12/2012; 18:2882-95. · 2.25 Impact Factor
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ABSTRACT: The polyunsaturated fatty acid, docosahexaenoic acid (DHA), participates in neurotransmission involving activation of calcium-independent phospholipase A2 (iPLA2), which is coupled to muscarinic, cholinergic and serotonergic neuroreceptors. Drug induced activation of iPLA2 can be measured in vivo with quantitative autoradiography using 14C-DHA as a probe. The present study used this approach to address whether a DHA signal is produced following dompaminergic (D)2-like receptor activation with quinpirole in rat brain. Unanesthetized rats were infused intravenously with 14C-DHA one minute after saline or quinpirole infusion, and serial blood samples were collected over a 20-minute period to obtain plasma. The animals were euthanized with sodium pentobarbital and their brains excised, coronally dissected and subjected to quantitative autoradiography to derive the regional incorporation coefficient, k*a marker of DHA signaling. Plasma labeled and unlabeled unesterified DHA concentrations were measured.BMC Neuroscience 10/2014; 15(1):113. DOI:10.1186/1471-2202-15-113 · 2.85 Impact Factor