and clock genes: regulation by light and endothelin in the zebrafish ZEM-2S cell line," Chronobiology International, vol.
triggers the release of internal calcium stores in response to light.
Section 3 in the new 10th Edition of the IES Lighting Handbook is devoted to "Photobiology and Non-visual Effects of Optical Radiation" and covers the subject of melanopsin
and circadian rhythm.
After all, without light melanopsin
is no longer stimulated, no more calcium accumulates in the cells and the signal cascade is interrupted.
These studies only abolished the genetic expression of melanopsin
, while the functions of ipRGCs as ganglion cells remained unchanged, especially the projection to brain areas and the transduction of photic information.
On the basis of those findings and a few other pieces of evidence, the scientists argue that melanopsin
may be the photoreceptor for the human biological clock.
Hattar, "Mood, the circadian system, and Melanopsin
retinal ganglion cells," Annual Review Neuroscience, vol.
Focusing their efforts on the melanopsin
light sensor, which is responsible for sensing day and night but barely involved - in mammals, at least - in seeing images, Yau's team looked for melanopsin-containing cells in other vertebrates, and found some in the retinal horizontal cells in goldfish and catfish.
uses calcium as a second messenger (Panda et al, 2005; Kumbalasiri et al, 2007) and calcium can entrain circadian rhythms (Love et al, 2004), linkage between this photoreceptor and the circadian regulatory network may be a valuable avenue of future exploration.
The researchers isolated the functions of melanopsin
cells and demonstrated their crucial role in the perception of visual environment.
In the study, detailed in the Proceedings of the National Academy of Sciences, the team used a viral vector to express a light sensitive protein, melanopsin
, in the residual retinal cells in mice which were blind from retinitis pigmentosa.
A protein called melanopsin
in the cells helps them process ambient light.
When these cells are exposed to ongoing light, a protein called melanopsin
continually regenerates within them, signaling levels of ambient light directly to the brain to regulate consciousness, sleep and alertness.
It may be attributed to a phase-resetting effect via melanopsin
and the suprachiasmatic nucleus (Box, (18-24) page 30).