Role of melanopsin in circadian responses to light.
Level 5 - mechanism / opinion, no new human data
Preclinical animal knockout study without human data.
PubMed 12481140 · doi:10.1126/science.1076701
What was done
Melanopsin knockout mice and wild-type controls were evaluated for circadian photic responses. Assessed outcomes included entrainment to a light/dark cycle, phase shifts following a light pulse, changes in circadian period under varying light intensities, and induction of the immediate-early gene c-fos after a nighttime light pulse.
What was found
Melanopsin knockout mice were capable of entraining to light/dark cycles, phase-shifting in response to light pulses, lengthening circadian period with increasing light intensity, and inducing c-fos expression after nighttime light exposure. However, the magnitude of these behavioral responses in knockout mice was 40% lower than in wild-type controls.
Why it matters
This study shows that melanopsin is not solely responsible or strictly essential for transmitting photic information to the mammalian circadian clock, but it contributes significantly to the overall magnitude of photic responses.
Limits
The study was conducted entirely in a rodent model, limiting direct translation to human circadian physiology. Specific sample sizes, exact light intensities, and statistical variance measures are not reported in the abstract.
Cited by
- supports Melanopsin was discovered as a circadian photopigment in 2001 by three independent research groups.