Effects of circadian rhythm and cAMP on retinomotor movements in the green sunfish, Lepomis cyanellus.

The photoreceptors and retinal pigmented epithelium (RPE) of teleosts undergo diurnal changes in position in response to day/night changes in light conditions. These position changes, called retinomotor movements, may also persist under conditions of constant darkness. In this study, the authors have compared the retinomotor movements of rods, cones, and RPE under conditions of constant darkness and constant temperature in the green sunfish, Lepomis cyanellus . In this species, cones undergo circadian cycles of retinomotor movements in constant darkness but rods and RPE do not. Also cone contraction commences in early morning before the expected time of light onset, thus suggesting that circadian rhythms may play an important regulatory role in these cells even under cyclic light conditions. Since treatments that elevate cAMP previously have been shown to induce dark-adaptive retinomotor positions, the authors also have compared the effects of exogenous cAMP analogs on retinomotor positions of rods, cones, and RPE pigment in cultured green sunfish retinas. The authors found that concentrations of cAMP analogs required to produce extreme dark-adaptive retinomotor positions were at least fivefold higher for cones than for rods and RPE.