Melanopsin Is Highly Resistant to Light and Chemical Bleaching in Vivo

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The molecular circadian clocks in the mammalian retina are locally synchronized by environmental light cycles independent of the suprachiasmatic nuclei (SCN) in the brain. Unexpectedly, this entrainment does not require rods, cones, or melanopsin (OPN4), possibly suggesting the involvement of another retinal photopigment. Here, we show that the ex vivo mouse retinal rhythm is most sensitive to short-wavelength light but that this photoentrainment requires neither the short-wavelength-sensitive cone pigment [S-pigment or cone opsin (OPN1SW)] nor encephalopsin (OPN3). However, retinas lacking neuropsin (OPN5) fail to photoentrain, even though other visual functions appear largely normal. Initial evidence suggests that OPN5 is expressed in select retinal ganglion cells. Remarkably, the mouse corneal circadian rhythm is also photoentrainable ex vivo, and this photoentrainment likewise requires OPN5. Our findings reveal a light-sensing function for mammalian OPN5, until now an orphan opsin.

Section: Discussionmentioning

confidence: 99%

Neuropsin (OPN5)-mediated photoentrainment of local circadian oscillators in mammalian retina and cornea

Buhr

Yue

Ren

et al. 2015

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“…At least for the brightest stimuli, part of the Ca 2+ -independent adaptation may reflect the very low level of melanopsin in ipRGCs such that the depletion of signaling melanopsin becomes significant. Although melanopsin is reported to be bistable (4,6,(55)(56)(57), whether this bistability is absolute and how quickly melanopsin returns to the signaling state are still unclear at present.…”

Section: +mentioning

confidence: 99%

Adaptation to steady light by intrinsically photosensitive retinal ganglion cells

Yau

2013

Intrinsically photosensitive retinal ganglion cells (ipRGCs) are recently discovered photoreceptors in the mammalian eye. These photoreceptors mediate primarily nonimage visual functions, such as pupillary light reflex and circadian photoentrainment, which are generally expected to respond to the absolute light intensity. The classical rod and cone photoreceptors, on the other hand, mediate image vision by signaling contrast, accomplished by adaptation to light. Experiments by others have indicated that the ipRGCs do, in fact, light-adapt. We found the same but, in addition, have now quantified this light adaptation for the M1 ipRGC subtype. Interestingly, in incremental-flash-on-background experiments, the ipRGC's receptor current showed a flash sensitivity that adapted in background light according to the Weber-Fechner relation, well known to describe the adaptation behavior of rods and cones. Part of this light adaptation by ipRGCs appeared to be triggered by a Ca 2+ influx, in that the flash response elicited in the absence of extracellular Ca 2+ showed a normal rising phase but a slower decay phase, resulting in longer time to peak and higher sensitivity. There is, additionally, a prominent Ca 2+ -independent component of light adaptation not typically seen in rods and cones or in invertebrate rhabdomeric photoreceptors.

“…Photon capture by rod and cone photopigments converts the chromophore from a photosensitive to a photoinsensitive state, triggering phototransduction (10). To regain light sensitivity, the enzymatic retinoid cycle within the retinal pigment epithelium is required for regeneration of the chromophore back to the lightsensitive state.…”

mentioning

confidence: 99%

“…To regain light sensitivity, the enzymatic retinoid cycle within the retinal pigment epithelium is required for regeneration of the chromophore back to the lightsensitive state. In contrast, melanopsin is a dual-state photopigment, in which photons drive both processes of phototransduction and part of chromophore regeneration (10)(11)(12). Recent rodent and human data suggest that exposure to longer wavelength light (590-620 nm; orange-red) triggers melanopsin chromophore regeneration and increases overall subsequent intrinsic photosensitivity of ipRGCs (13,14).…”

mentioning

confidence: 99%

Photic memory for executive brain responses

Chellappa

Meyer

et al. 2014

Light is a powerful stimulant for human alertness and cognition, presumably acting through a photoreception system that heavily relies on the photopigment melanopsin. In humans, evidence for melanopsin involvement in light-driven cognitive stimulation remains indirect, due to the difficulty to selectively isolate its contribution. Therefore, a role for melanopsin in human cognitive regulation remains to be established. Here, sixteen participants underwent consecutive and identical functional MRI recordings, during which they performed a simple auditory detection task and a more difficult auditory working memory task, while continuously exposed to the same test light (515 nm). We show that the impact of test light on executive brain responses depends on the wavelength of the light to which individuals were exposed prior to each recording. Test-light impact on executive responses in widespread prefrontal areas and in the pulvinar increased when the participants had been exposed to longer (589 nm), but not shorter (461 nm), wavelength light, more than 1 h before. This wavelength-dependent impact of prior light exposure is consistent with recent theories of the light-driven melanopsin dual states. Our results emphasize the critical role of light for cognitive brain responses and are, to date, the strongest evidence in favor of a cognitive role for melanopsin, which may confer a form of "photic memory" to human cognitive brain function.fMRI | non-image-forming