Endogenous dopamine and cyclic events in the fish retina, I: HPLC assay of total content, release, and metabolic turnover during different light/dark cycles

Abstract

In this study, we investigated the potency of dopamine for being an intrinsic signal for cyclic events in the fish retina. Dopaminergic activity was measured during different light/dark cycles, during continuous darkness, and during short-term light and dark adaptation within 1 h. During a 12-h light/12-h dark cycle, the total content of endogenous dopamine was high during the dark phase and low during the light phase. The potassium-induced release of endogenous dopamine followed a parallel time course. The concentration of the dopamine breakdown product 3,4-dihydroxyphenylacetic acid (DOPAC), which reflects the endogenous dopaminergic activity, was high during the light phase and low during the dark phase. Similar alterations occurred in accelerated 6-h light/6-h dark cycles, again indicating a strong coupling of dopaminergic activity with light. The cyclic alterations in the total endogenous dopamine content persisted during continuous darkness after an entrainment of the fish to a 12-h light/12-h dark cycle. Although the magnitude of the change was weaker, changes in dopamine content, potassium-induced dopamine release, and DOPAC were also measured during 1 h of light or dark adaptation. During a 1-h period of dark adaptation, the total content of dopamine and the potassium-induced release of endogenous dopamine increased, while DOPAC values decreased. These values changed in the opposite direction during 1 h of light adaptation.Our findings strongly suggest that dopamine is the intrinsic signal for light during both the light and dark phases and during short-term adaptation. Light seems to be the major trigger for dopaminergic activity within the fish retina. An endogenous clock might participate in the control of the dopaminergic activity. This has to be, however, confirmed by further investigations.

Protein kinase C mediates transient spinule-type neurite outgrowth in the retina during light adaptation.

“…2c), ruling out the involvement of this system. The depletion was controlled by measuring the total dopamine content of the retina using HPLC-EC techniques (21) and only data from retinas where the dopamine level was less than 10o of an untreated retina were included.…”

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.…”

A circadian clock regulates rod and cone input to fish retinal cone horizontal cells.

“…1, bottom right) (12)(13)(14)37), influences the light responses of cone, but not rod, horizontal cells (22,38).…”

“…In addition, a circadian clock can be entrained by cyclic environmental stimuli, such as light (10). In vertebrate retinas, a variety of cellular phenomena are regulated by circadian rhythms, including melatonin production and release (11,12), tyrosine hydroxylase activity (13), dopamine content and release (14), retinomotor movements (15), horizontal cell spinule formation (16), and opsin synthesis (17). In addition, circadian and diurnal rhythms of visual sensitivity and responsivity, as measured by psychophysical detectability and by the electroretinogram, have been found in many vertebrates, including humans (2,(18)(19)(20)(21) Intact, isolated retinas were superfused at 0.5 ml/min with a Ringer's solution that contained 130 mM NaCl, 2.5 mM KCl, 20 mM NaHCO3, 0.7 mM CaCl2, 1.0 mM MgCl2, and 20 mM glucose, as described (22,23 …”