Dopamine Mediates Circadian Rhythms of Rod–Cone Dominance in the Japanese Quail Retina

Abstract

A circadian clock modulates the functional organization of the Japanese quail retina. Under conditions of constant darkness, rods dominate electroretinogram (ERG) b-wave responses at night, and cones dominate them during the day, yielding a circadian rhythm in retinal sensitivity and rod-cone dominance. The activity of tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis, also exhibits a circadian rhythm in the retina with approximately threefold higher levels during the day than at night. The rhythm of tyrosine hydroxylase activity is opposite in phase to the circadian activity of tryptophan hydroxylase, the first enzyme in the melatonin biosynthetic pathway. We tested whether dopamine may be related to the physiological rhythms of the retina by examining the actions of pharmacological agents that effect dopamine receptors. We found that blocking dopamine D2 receptors in the retina during the day mimics the nighttime state by increasing the amplitude of the b-wave and shifting the retina to rod dominance. Conversely, activating D2 receptors at night mimics the daytime state by decreasing the amplitude of the b-wave and shifting the retina to cone dominance. A selective antagonist for D1 dopamine receptors has no effect on retinal sensitivity or rod-cone dominance. Reducing retinal dopamine partially abolishes rhythms in sensitivity and yields a rod-dominated retina regardless of the time of day. These results suggest that dopamine, under the control of a circadian oscillator, has a key role in modulating sensitivity and rod-cone dominance in the Japanese quail retina.

Effects of Dopamine Depletion on Visual Sensitivity of Zebrafish

“…A rhythm in ERG sensitivity to light was also demonstrated, but the extent of threshold variation was only ϳl.0 log unit, suggesting that regulation of visual sensitivity by the circadian clock mechanism occurs at several different levels in the visual system (Li and Dowling, 1998). Several studies have suggested that dopamine is a circadian clock modulator in the retina (Besharse and Iuvone, 1983;Kolbinger et al, 1990;McCormack and Burnside, 1992;Manglapus et al, 1999). We measured behaviorally as well as by ERG the visual sensitivity of DA-IPC-depleted animals as a function of time of day.…”

Molecular Mechanisms, Biological Actions, and Neuropharmacology of the Growth-Associated Protein GAP-43

“…GAP-43 is present in tyrosine hydroxylase-positive retinal amacrine cells, suggesting that the protein may be involved in the release of dopamine from the terminals of these cells located in the inner plexiform layer [46]. The release of dopamine in the retina has been implicated in light/dark adaptation [58]. The levels of released dopamine increase in almost all retinae with light adaptation, and dopamine mimics the effects of light in many instances [98].…”

D2-like dopamine receptors promote interactions between calcium and chloride channels that diminish rod synaptic transfer in the salamander retina

“…For example, dopamine-mediated suppression of rod output might involve other actions of D 2 /D 4 dopamine receptor activation in photoreceptors, such as inhibition of Na + /K + -ATPase activity (Shulman & Fox, 1996), increased rod/cone coupling , Manglapus et al, 1999, and inhibition of I h in rods (Akopian & Witkovsky, 1996). There may also be contributions from other neuromodulators known to influence rod function, such as nitric oxide, somatostatin, or adenosine (Kurenny et al, 1994;Akopian et al, 2000;Stella et al, 2002).…”