The light‐activated signaling pathway in SCN‐projecting rat retinal ganglion cells

Warren, Erin; Allen, Charles N.; Brown, R. Lane; Robinson, D.

doi:10.1111/j.1460-9568.2006.04777.x

Cited by 106 publications

(136 citation statements)

References 60 publications

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“…The stimulation of melanopsin leads to the activation of a membrane bound signalling cascade involving Gq/11 type G-proteins, activation of PLCβ4 and ultimately the opening of downstream TRP type ion channels, TRPC6 and TRPC7. 49,[68][69][70][71][72][73] However, this model describes only the basic core components of what is likely to be a far more complicated signalling pathway and fails to account for the multiple types of photoresponse observed from individual pRGCs. It is currently unclear to what extent the precise mechanisms of melanopsin phototransduction are conserved between different pRGC subtypes, with the majority of detailed analysis performed to date conducted on M1-type pRGCs.…”

Section: Correlation Of Prgc Subtypes With Response Typesmentioning

confidence: 99%

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Signalling by melanopsin (OPN4) expressing photosensitive retinal ganglion cells

Hughes

Jagannath

Rodgers

et al. 2016

Eye

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Over the past two decades there have been significant advances in our understanding of both the anatomy and function of the melanopsin system. It has become clear that rather than acting as a simple irradiance detector the melanopsin system is in fact far more complicated. The range of behavioural systems known to be influenced by melanopsin activity is increasing with time, and it is now clear that melanopsin contributes not only to multiple non-image forming systems but also has a role in visual pathways. How melanopsin is capable of driving so many different behaviours is unclear, but recent evidence suggests that the answer may lie in the diversity of melanopsin light responses and the functional specialisation of photosensitive retinal ganglion cell (pRGC) subtypes. In this review, we shall overview the current understanding of the melanopsin system, and evaluate the evidence for the hypothesis that individual pRGC subtypes not only perform specific roles, but are functionally specialised to do so. We conclude that while, currently, the available data somewhat support this hypothesis, we currently lack the necessary detail to fully understand how the functional diversity of pRGC subtypes correlates with different behavioural responses, and ultimately why such complexity is required within the melanopsin system. What we are lacking is a cohesive understanding of how light responses differ between the pRGC subtypes (based not only on anatomical classification but also based on their site of innervation); how these diverse light responses are generated, and most importantly how these responses relate to the physiological functions they underpin.

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Section: Correlation Of Prgc Subtypes With Response Typesmentioning

confidence: 99%

“…It is currently unclear to what extent the precise mechanisms of melanopsin phototransduction are conserved between different pRGC subtypes, with the majority of detailed analysis performed to date conducted on M1-type pRGCs. 68,69,71 A role for OPN4L and OPN4S in generating functional diversity?…”

Section: Correlation Of Prgc Subtypes With Response Typesmentioning

confidence: 99%

Signalling by melanopsin (OPN4) expressing photosensitive retinal ganglion cells

Hughes

Jagannath

Rodgers

et al. 2016

Eye

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“…However, the intensity-latency relation is steeply inverse, with latencies ranging from several hundred milliseconds for saturating stimuli to >1 min for near-threshold stimulation. Responses to prolonged light steps generally decay significantly from their initial peak, in part because of light adaptation [63], but the steady-state response is generally remarkably stable. This stability seems likely to be a key functional difference from rods and cones, although a systematic exploration of this difference has not yet been attempted.…”

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confidence: 99%

Phototransduction in ganglion-cell photoreceptors

Berson

2007

Pflugers Arch - Eur J Physiol

145

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A third class of photoreceptors has recently been identified in the mammalian retina. They are a rare cell type within the class of ganglion cells, which are the output cells of the retina. These intrinsically photosensitive retinal ganglion cells support a variety of physiological responses to daylight, including synchronization of circadian rhythms, modulation of melatonin release, and regulation of pupil size. The goal of this review is to summarize what is currently known concerning the cellular and biochemical basis of phototransduction in these cells. I summarize the overwhelming evidence that melanopsin serves as the photopigment in these cells and review the emerging evidence that the downstream signaling cascade, including the light-gated channel, might resemble those found in rhabdomeric invertebrate photoreceptors.Keywords Melanopsin . ipRGC . Photoreceptor . Rhabdomeric . Retina . Ganglion cell . Suprachiasmatic nucleus . TRPC Within the past decade, the existence of a previously unknown class of photoreceptor in the mammalian retina has come to light. These directly photosensitive neurons differ radically in form and function from the well-known rod and cone photoreceptors. They are a rare variety of retinal ganglion cells (RGCs), the class of retinal neurons sending axons through the optic nerve to synapse in the brain. For at least the prior century, it had gone without question that ganglion cells were entirely dependent on polysynaptic influences from rods and cones for their responsiveness to light (indeed, even today there is no reason to doubt this for most ganglion cells). However, as the new millennium dawned, this dogma was being challenged by behavioral studies showing the persistence of certain reflex responses to light in photoreceptor degenerate animals, e.g., [14,15,35,36], and the presence of a possible photopigment, melanopsin, in a rare population of ganglion cells [18,19,21,49,50]. In short order, it became clear that these cells possessed a capacity for autonomous phototransduction [5]. These intrinsically photosensitive RGCs (ipRGCs) are now recognized as playing key roles in synchronizing circadian rhythms to the day-night cycle, mediating the pupillary response to light, and modulation of melatonin release by the pineal gland. Many aspects of this rapidly developing story have been thoroughly summarized elsewhere [4,6,14,16,31,44,54,61]. The reader is referred to these reviews for background on the intellectual origins of the discovery of melanopsin and the ipRGCs, on their structure and physiology, and on their contribution to circadian photoentrainment and other nonimage-forming visual functions. The goal of the present review is to summarize the current state of knowledge concerning the nature of the transduction process in ipRGCs. Structural and functional properties of ipRGCs relevant to the phototransduction processThe ipRGCs represent a tiny minority of the RGCs of mammalian retinas (<1-2%) [9,21,51]. Like other ganglion cells, ipRGCs extend dendritic processes...

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“…The amphioxus photocurrent is seemingly mediated by TRPclass channels (20), like in PLC-using visual receptors of invertebrates (9), and in ipRGCs (10)(11)(12)(13). Interestingly, TRP channels gated by intracellular Ca have been described in various systems (46)(47)(48).…”

Section: Discussionmentioning

confidence: 99%

“…Some reports argue against both calcium and DAG as critical signaling elements, hinting instead at a potential role for PIP 2 in channel gating (8), but firm evidence has yet to be garnered. As for the nature of the light-sensitive conductance, ion channels of the TRP superfamily have been implicated (10)(11)(12)(13).…”

mentioning

confidence: 99%

Calcium activates the light-dependent conductance in melanopsin-expressing photoreceptors of amphioxus

Peinado

Osorno

Gómez

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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Melanopsin, the photopigment of the "circadian" receptors that regulate the biological clock and the pupillary reflex in mammals, is homologous to invertebrate rhodopsins. Evidence supporting the involvement of phosphoinositides in light-signaling has been garnered, but the downstream effectors that control the lightdependent conductance remain unknown. Microvillar photoreceptors of the primitive chordate amphioxus also express melanopsin and transduce light via phospholipase-C, apparently not acting through diacylglycerol. We therefore examined the role of calcium in activating the photoconductance, using simultaneous, high timeresolution measurements of membrane current and Ca 2+ fluorescence. The light-induced calcium rise precedes the onset of the photocurrent, making it a candidate in the activation chain. Moreover, photolysis of caged Ca elicits an inward current of similar size, time course and pharmacology as the physiological photoresponse, but with a much shorter latency. Internally released calcium thus emerges as a key messenger to trigger the opening of lightdependent channels in melanopsin-expressing microvillar photoreceptors of early chordates.melanopsin | calcium | photoreceptor | amphioxus

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The light‐activated signaling pathway in SCN‐projecting rat retinal ganglion cells

Cited by 106 publications

References 60 publications

Signalling by melanopsin (OPN4) expressing photosensitive retinal ganglion cells

Signalling by melanopsin (OPN4) expressing photosensitive retinal ganglion cells

Phototransduction in ganglion-cell photoreceptors

Calcium activates the light-dependent conductance in melanopsin-expressing photoreceptors of amphioxus

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