Phototransduction by Retinal Ganglion Cells That Set the Circadian Clock

  title={Phototransduction by Retinal Ganglion Cells That Set the Circadian Clock},
  author={David M. Berson and Felice A. Dunn and M. Takao},
  pages={1070 - 1073}
Light synchronizes mammalian circadian rhythms with environmental time by modulating retinal input to the circadian pacemaker—the suprachiasmatic nucleus (SCN) of the hypothalamus. Such photic entrainment requires neither rods nor cones, the only known retinal photoreceptors. Here, we show that retinal ganglion cells innervating the SCN are intrinsically photosensitive. Unlike other ganglion cells, they depolarized in response to light even when all synaptic input from rods and cones was… 
Melanopsin in the circadian timing system
It appears that of the known photoreceptor systems, none, in and of itself, is necessary for circadian photoreception, and it appears that within the photoreceptive systems there is some degree of redundancy, each contributing in some way to photic entrainment.
Rod photoreceptors drive circadian photoentrainment across a wide range of light intensities
Using mice that lack functional rods or in which rods are the only functional photoreceptors, it is found that rods were solely responsible for photoentrainment at scotopic light intensities and rods use two distinct retinal circuits to drive ipRGC function to support circadian photoentrainedment across a wide range of light intensITIES.
Strange vision: ganglion cells as circadian photoreceptors
Melanopsin—Shedding Light on the Elusive Circadian Photopigment
Although melanopsin is clearly the leading candidate for the elusive photopigment of the circadian system, further research is needed to resolve the mystery posed by its absorbance spectrum and to fully elucidate its role in circadian photoentrainment.
Ocular Photoreception for Circadian Rhythm Entrainment in Mammals.
The circadian clock of the mammalian cornea is also light entrainable and is also neuropsin-dependent for this effect, and the retina thus utilizes a surprisingly broad array of opsins for mediation of different light-detection tasks.
Architecture of retinal projections to the central circadian pacemaker
The results suggest that the retina provides multifaceted synaptic inputs to the brain to mediate proper photic inputs to coordinately influence non-image–forming visual functions, and provides a better understanding of how retinal neurons connect to the central circadian pacemaker to synchronize endogenous circadian clocks with the solar day.
Intrinsic light responses of retinal ganglion cells projecting to the circadian system
The intrinsic light‐activated current observed in SCN‐projecting RGCs resembles currents carried by ion channels of the transient receptor potential (trp) family, which are known to mediate the light response of invertebrate photoreceptors.
Retinal pathways influence temporal niche
A switch from nocturnal to diurnal entrainment of circadian activity rhythms in double-knockout mice lacking the inner-retinal photopigment melanopsin (OPN4) and RPE65, a key protein used in retinal chromophore recycling, is reported, revealing a novel mechanism by which changes inretinal input can mediate acute temporal-niche switching.
Phototransduction in ganglion-cell photoreceptors
  • D. Berson
  • Biology
    Pflügers Archiv - European Journal of Physiology
  • 2007
The overwhelming evidence that melanopsin serves as the photopigment in these cells is summarized and the emerging evidence that the downstream signaling cascade, including the light-gated channel, might resemble those found in rhabdomeric invertebrate photoreceptors is reviewed.


Melanopsin in cells of origin of the retinohypothalamic tract
It is shown that most retinal ganglion cells that project to the SCN express the photopigment melanopsin, which mediates circadian entrainment in mice.
Melanopsin-Containing Retinal Ganglion Cells: Architecture, Projections, and Intrinsic Photosensitivity
It is shown that melanopsin is present in cell bodies, dendrites, and proximal axonal segments of a subset of rat RGCs, most likely the visual pigment of phototransducing R GCs that set the circadian clock and initiate other non–image-forming visual functions.
Spectral sensitivity of a novel photoreceptive system mediating entrainment of mammalian circadian rhythms
The results suggest that the photoreceptive system mediating entrainment is markedly different from that involved in visual image formation, and the reciprocal relationship between intensity and duration holds for extremely long durations.
Recent developments in circadian photoreception: more than meets the eye.
In this short article, some of the recent experimental findings that show that the absence of rod and cone photoreceptors does not block the effects of light on the circadian system are outlined and the progress to date in identifying the photopigments that may mediate the effects on the mammalian biological clock is reviewed.
Functional redundancy of cryptochromes and classical photoreceptors for nonvisual ocular photoreception in mice.
Data indicate that classical opsins and cryptochromes serve functionally redundant roles in the transduction of light information to behavioral modulation and suggest a pleomorphic role for cryptochrome in both photoreception and central clock mechanism.
Sensitivity and integration in a visual pathway for circadian entrainment in the hamster (Mesocricetus auratus).
The results suggest that the visual pathways that convey light information to the mammalian circadian pacemaker possess several unique characteristics that may make this visual system unresponsive to environmental ‘noise’ that would interfere with the entrainment of circadian rhythms to light‐dark cycles.
Light Responsiveness of the Suprachiasmatic Nucleus: Long-Term Multiunit and Single-Unit Recordings in Freely Moving Rats
The results show that the basic light response characteristics that were observed at the multiunit level result from an integrated response of similarly behaving single units, and research at the single-unit level is a useful approach for investigating the basic principles of photic entrainment.
Melanopsin: An opsin in melanophores, brain, and eye.
Melanopsin mRNA is expressed in hypothalamic sites thought to contain deep brain photoreceptors and in the iris, a structure known to be directly photosensitive in amphibians, and expression in retinal and nonretinal tissues suggests a role in vision and nonvisual photoreceptive tasks.
Effects of Irradiance and Stimulus Duration on Early Gene Expression (Fos) in the Suprachiasmatic Nucleus: Temporal Summation and Reciprocity
This report provides the first demonstration that the mechanism of photon integration by the circadian system is expressed at a cellular level in the SCN, and that integration occurs over a range of 5 log units of photon number.