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Dim light adaptation attenuates acute melatonin suppression in humans
Samar A Jasser1, John P Hanifin, Mark D Rollag
1Department of Neurology, Thomas Jefferson University, Philadelphia, PA 19107, USA. samar.jasser@jefferson.edu
Journal of Biological Rhythms
|September 26, 2006
Summary
Dim light adaptation reduces melatonin suppression by blue light in humans, suggesting non-visual photoreceptors are modulated by prior light conditions. This impacts circadian rhythm regulation.
Area of Science:
- Circadian Biology
- Neuroscience
- Ophthalmology
Background:
- Rod and cone photoreceptors are not essential for circadian light responses in rodents.
- Melanopsin knockout mice show residual light responses, indicating alternative pathways to the suprachiasmatic nucleus (SCN).
- Rod and cone photoreceptors may modulate the human retinohypothalamic tract's light sensitivity.
Purpose of the Study:
- To test if dim light adaptation dampens melatonin suppression by monochromatic light in humans.
- To investigate the role of prior light conditions on the human circadian system's light sensitivity.
Main Methods:
- Healthy human subjects (18-30 years) underwent either dim white light or dark adaptation.
- Following adaptation, subjects received a 460-nm monochromatic light exposure.
- Plasma melatonin levels were measured via radioimmunoassay before and after light exposure.
Main Results:
- Dim light adaptation significantly reduced melatonin suppression compared to dark adaptation (p < 0.04 and p < 0.01).
- This indicates a dampening effect of prior light exposure on the circadian system's response.
Conclusions:
- The human circadian photoreceptive system's sensitivity is modulated by preceding light adaptation conditions.
- Subthreshold light exposure can influence the response to subsequent monochromatic light, affecting melatonin suppression.
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