Rhythmic changes in metabolism of dopamine in the chick retina: the importance of light versus biological clock

Abstract

Rhythmic changes in dopamine (DA) content and metabolism were studied in retinas of chicks that were adapted to three different lighting conditions: 12-h light : 12-h dark (LD), constant darkness (DD) and continuous light (LL). Retinas of chicks kept under LD conditions exhibited light-darkdependent variations in the steady-state level of DA and the two metabolites of DA, i.e. 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA). Concentrations of DA, DOPAC and HVA were high in light hours and low in dark hours of the LD illumination cycle. In retinas of chicks kept under DD, the content of DA, DOPAC and HVA oscillated in a rhythmic manner for 2 days, with higher values during the subjective light phase than during the subjective dark phase. The amplitudes of the observed oscillations markedly and progressively declined compared with the amplitudes recorded under the LD cycle. In retinas of chicks kept under LL conditions, levels of DA, DOPAC and HVA were similar to those found during the light phase of the LD cycle. Changes in the retinal contents of DA and HVA did not exhibit pronounced daily oscillations, while on the first day of LL the retinal concentrations of DOPAC were significantly higher during the subjective light phase than during the subjective dark phase. Acute exposure of chicks to light during the dark phase of the LD cycle markedly increased DA and DOPAC content in the retina. In contrast, light deprivation during the day decreased the retinal concentrations of DA and DOPAC. It is suggested that of the two regulatory factors controlling the level and metabolism of DA in the retina of chick, i.e. light and biological clock, environmental lighting conditions seem to be of major importance, with light conveying a stimulatory signal for the retinal dopaminergic cells.

Dopamine in the Turkey Retina—An Impact of Environmental Light, Circadian Clock, and Melatonin

“…Under cyclic lighting, the difference between the peak and nadir values was in the range of 2.5-3.3 for DOPAC and 1.5-2 for dopamine. This light/dark ratio is in general agreement with those previously demonstrated for the retina of chicken (Zawilska et al 2003a), duck (Zawilska et al 2003b), rat (Pozdeyev and Lavrikova 2000;Doyle et al 2002b), and mouse (Doyle et al 2002a).…”

“…Thus, although a component of circadian control of dopamine synthesis and metabolism was apparent under constant darkness, it appears that environmental light is the major factor controlling retinal dopamine in the turkey. Similar conclusions were drawn for the retina of chicken in studies where dopamine and DOPAC concentrations in the retina (Zawilska et al 2003a), and DOPAC accumulation in the vitreous body (Megaw et al 2006) were measured by the HPLC technique. In the retina of quail, the rate of rhythmic oscillation in dopamine production (evaluated on the basis of changes in the in vitro activity of tyrosine hydroxylase, a rate-limiting enzyme of dopamine synthesis) progressively dampened along time of constant darkness (Manglapus et al 1999), indicating the importance of light, in addition to circadian pacemaker, in the control of dopamine synthesis.…”

“…Dopamine, the major catecholamine of the vertebrate retina, is localized to a subpopulation of amacrine and/or interplexiform cells, depending on the species (reviewed by Witkovsky 2004). The synthesis and release of dopamine from these inner retinal neurons is stimulated by light (e.g., Iuvone et al 1978;Parkinson and Rando 1983;Boatright et al 1989;Adachi et al 1998;Zawilska et al 2003a, b) and partly controlled by intrinsic circadian clocks (Adachi et al 1998;Manglapus et al 1999;Doyle et al 2002a, b;Zawilska et al 2003a;Ribelayga et al 2004;Megaw et al 2006). Dopamine has been shown to affect several processes in the eye that are under control of environmental lighting conditions and/or the circadian pacemaker, such as for example, photoreceptor disc shedding and phagocytosis, retinomotor movements, rod-cone dominance and visual sensitivity, rod-cone photoreceptor coupling, rod and cone input to horizontal cells, glutamate-gated ionic currents in bipolar and horizontal cells, rhodopsin expression, activity of cGMP-gated channels, and melatonin synthesis (Knapp and Dowling 1987;Besharse et al 1988;Zawilska and Nowak 1994;Maguire and Werblin 1994;Hillman et al 1995;Krizaj et al 1998;Manglapus et al 1999;Li and Dowling 2000;Alfinito and Townes-Anderson 2001;Ribelayga et al 2002;Ko et al 2003;Witkovsky 2004;Iuvone et al 2005;Yu et al 2007).…”

Signaling mediated by the dopamine D2 receptor potentiates circadian regulation by CLOCK:BMAL1

“…The inner plexiform layer exhibits small areas of staining (58) that, interestingly, have been reported to express all of the proteins of the clock machinery (49,59) and to contain a functional oscillator (60). In addition, light has been shown to induce dopamine release in the retina (24,61,62). Our results with the D2R-null mice provide evidence about the identity of the receptor and signaling cascade that dopamine utilizes to impact on the clock molecular mechanism.…”

Somatostatin Peptides Produce Multiple Effects on Gating Properties of Native Cone Photoreceptor cGMP-Gated Channels That Depend on Circadian Phase and Previous Illumination

“…For example, melatonin secreted from photoreceptors produces several effects that appear to be adaptive for dim illumination (Adachi et al, 1998;Anderson and Green, 2000), whereas dopamine secreted from a subpopulation of amacrine cells contributes to a state that is adaptive for high illumination (Manglapus et al, 1999;Ko et al, 2003;Zawilska et al, 2003). Other signals secreted from the inner retina have received less attention as potential modulators of photoreceptors.…”