Circadian regulation of retinomotor movements. I. Interaction of melatonin and dopamine in the control of cone length.

Abstract

In lower vertebrates, cone retinomotor movements occur in response to changes in lighting conditions and to an endogenous circadian clock. In the light, cone myoids contract, while in the dark, they elongate . In order to test the hypothesis that melatonin and dopamine may be involved in the regulation of cone movement, we have used an in vitro eyecup preparation from Xenopus laevis that sustains light-and dark-adaptive cone retinomotor movement . Melatonin mimics darkness by causing cone elongation . Dark-and melatonin-induced cone elongation are blocked by dopamine . Dopamine also stimulates cone contraction in dark-adapted eyecups. The effect of dopamine appears to be mediated specifically by a dopamine receptor, possibly of the D2 type . The dopamine agonist apomorphine and the putative D2 agonist LY171555 induced cone contraction . In contrast, the putative D, agonist SKF38393-A and specific a,-, a2-, and /3-adrenergic receptor agonists were without effect . Furthermore, the dopamine antagonist spiroperidol not only blocked light-induced cone contraction, but also stimulated cone elongation in the light. These results suggest that dopamine is part of the light signal for cone contraction, and that its suppression is part of the dark signal for cone elongation . Melatonin may affect cone movement indirectly through its influence on the dopaminergic system .

The expression of L‐type voltage‐gated calcium channels in retinal photoreceptors is under circadian control

“…The circadian oscillators in photoreceptors are endogenous and able to function independently in the absence of other retinal inputs (Cahill and Besharse 1993;Thomas et al 1993;Ko et al 2001). Photoreceptor circadian oscillators regulate retinomotor movement (Pierce and Besharse 1985;Burnside 2001), outer segment disc shedding and membrane renewal (LaVail 1980;Besharse and Dunis 1983), morphological changes at synaptic ribbons (Adly et al 1999), gene expression (Korenbrot and Fernald 1989;Pierce et al 1993;Haque et al 2002), and the gating behavior of ion channels (Ko et al 2001) among other photoreceptor activities. Importantly, photoreceptors are more sensitive to intense light damage at night than during the day, even in animals that have been maintained in constant darkness (DD) for several days after circadian lightdark (LD) cycle entrainment (Vaughan et al 2002).…”

Circadian rhythms of behavioral cone sensitivity and long wavelength opsin mRNA expression: a correlation study in zebrafish

“…A variety of visual behaviors, such as photoreceptor cell disk shedding (Young, 1967;LaVail, 1976;Besharse et al, 1988;Bassi and Powers, 1990), rod and cone myoid movement (Pierce and Besharse, 1985;Dearry and Burnside, 1986), retinal pigment epithelium granule migration (Bruenner and Burnside, 1986), opsin expression (Korenbrot and Fernald, 1989;Pierce et al, 1993), and retinal sensitivity (Barlow, 1983;Powers, 1986, 1987), display robust day-night rhythms. In frogs, for example, the expression of rod opsin mRNA fluctuates between the day and night; it is high in the day and low at night.…”

Functional interaction of melatonin receptors and D1 dopamine receptors in cultured chick retinal neurons

“…Melatonin is synthesized in and released from photoreceptor cells (e.g., Redburn and Mitchell, 1989;Iuvone et al, 1990;Cahill and Besharse, 1992;Zawilska and Iuvone, 1992;Thomas et al, 1993;Wiechmann and Craft, 1993), and dopamine is synthesized in amacrine and interplexiform cells (reviewed in Ehinger, 1977;Iuvone, 1986). In retina, melatonin activates rod photoreceptor disk shedding (Besharse and Dunis, 1983;Besharse et al, 1984) and promotes dark-adaptive retinomotor movements (Cheze and Ali, 1976;Pang and Yew, 1979;Pierce and Besharse, 1985). In contrast, dopamine inhibits rod photoreceptor disk shedding (Pierce and Besharse, 1986;Besharse et al, 1988) and promotes light-adaptive retinomotor movements (Pierce and Besharse, 198.5;Dearry and Burnside, 1986).…”