Related Experiment Videos
Spectral sensitivity of melatonin synthesis suppression in Xenopus eyecups
G M Cahill1, S E Parsons, J C Besharse
1Department of Biology, University of Houston, TX 77204-5513, USA.
Abstract:
Melatonin synthesis in retinal photoreceptors is stimulated at night by a circadian oscillator and suppressed acutely by light. To identify photoreceptor mechanisms involved in the acute suppression of melatonin synthesis, an action spectrum was measured for dark-adapted Xenopus laevis eyecups at night. Intensity-response curves at six wavelengths from 400 to 650 nm were parallel, suggesting that a single photopigment predominates in melatonin suppression. Half-saturating intensities at 400, 440, 480, and 533 nm were not significantly different from one another, at 1-2 x 10(8) quanta cm(-2) s(-1). Significantly higher intensities of 580- and 650-nm light were required for melatonin suppression. These results indicate a predominant role for the principal green-absorbing rods in acute regulation of retinal melatonin synthesis in response to light, and argue against an important role for the red-absorbing cones. Higher than expected sensitivity at short wavelengths suggests that photoreceptors sensitive to blue and/or violet light may also contribute to melatonin suppression.
Insights
Light acutely suppresses retinal melatonin synthesis. This study in Xenopus laevis eyecups reveals that green-absorbing rods play a primary role in this process, with possible contributions from blue/violet light photoreceptors.
Area of Science:
- Ophthalmology
- Neuroscience
- Chronobiology
Background:
- Melatonin synthesis in retinal photoreceptors is regulated by circadian rhythms and light.
- Acute light exposure suppresses melatonin production, but the specific photoreceptor mechanisms are not fully understood.
Purpose of the Study:
- To identify the photoreceptor mechanisms responsible for the acute suppression of melatonin synthesis by light in the retina.
Main Methods:
- An action spectrum was measured for dark-adapted Xenopus laevis eyecups at night.
- Intensity-response curves were generated at wavelengths ranging from 400 to 650 nm.
Main Results:
- Parallel intensity-response curves suggested a predominant photopigment in melatonin suppression.
- Half-saturating intensities were similar for wavelengths 400-533 nm, but higher intensities were needed at 580-650 nm.
- Green-absorbing rods appear to be the primary mediators of light-induced melatonin suppression.
Conclusions:
- The principal green-absorbing rods play a dominant role in the acute light-mediated regulation of retinal melatonin synthesis.
- Red-absorbing cones are unlikely to be significantly involved.
- Photoreceptors sensitive to shorter wavelengths (blue/violet) may also contribute to melatonin suppression.