A circadian clock in the fish retina regulates dopamine release via activation of melatonin receptors

Circadian Rhythm of Contrast Sensitivity Is Regulated by a Dopamine–Neuronal PAS-Domain Protein 2–Adenylyl Cyclase 1 Signaling Pathway in Retinal Ganglion Cells

“…In the retina of Drd2 Ϫ / Ϫ mice, the amplitude of the Per1 transcript rhythm is reduced (Yujnovsky et al, 2006). Dopamine, via D1 receptors, entrains the clock regulating Per2::LUC reporter expression in the inner retina (Ruan et al, 2008). In photoreceptor cells of Xenopus, the administration of the D 2 /D 4 receptor agonist quinpirole can shift the circadian rhythm of melatonin release (Cahill and Besharse, 1991).…”

“…However, a time delay in the activation of clock and clock-controlled genes is not uncommon. For example, in the mouse retina, there is an ϳ8 h delay from the time at which Bmal1 transcript level peaks to the time that Per1 and Per2 levels peak (Ruan et al, 2006;Storch et al, 2007). Additionally, in the chicken retina, the Aanat gene, which is another clock-controlled gene regulated by NPAS2, peaks over 6 h after the peak of Npas2 transcript level (Haque et al, 2010).…”

“…In the mammalian retina, the rhythmic transcript expression of the Drd4 gene, which encodes the D4R, persists in constant darkness (Jackson et al, 2011), and there is evidence that dopamine itself modulates retinal clocks (Ruan et al, 2008). Hence, we tested the hypothesis that contrast sensitivity is rhythmic and modulated by clock components.…”

“…However, the underlying cellular and molecular mechanisms through which retinal dopamine modulates contrast sensitivity have not been elucidated. Dopamine secretion, as well as synthesis and metabolism, is controlled by light and modulated by the circadian clock (Iuvone et al, 1978;Doyle et al, 2002;Ribelayga et al, 2004). The circadian clock is an autonomous oscillator responsible for regulating physiology and behavior, thereby conferring adaptive advantage to living organisms by allowing them to anticipate regular changes in their environment.…”

Functional Heterogeneity of Retinal Dopaminergic Neurons Underlying Their Multiple Roles in Vision

“…Despite the description of retinal DA cells 3 decades ago (Dowling and Ehinger, 1975) and the importance of retinal dopamine for visual function, the regulation of retinal dopamine secretion has remained unclear. Experiments attempting to define the stimulus conditions for dopamine release have yielded widely varying results suggesting that dopamine secretion can be stimulated by prolonged darkness or steady and flickering illumination, and it can also be mediated by the retinal circadian clock in a light-independent manner (Bauer et al, 1980;Mangel and Dowling, 1985;Umino et al, 1991;Weiler et al, 1997;Nir et al, 2000;Doyle et al, 2002a,b;Ribelayga et al, 2004).…”