A Role for Melanopsin in Alpha Retinal Ganglion Cells and Contrast Detection

Abstract

SUMMARY Distinct subclasses of retinal ganglion cells (RGCs) mediate vision and non-image forming functions such as circadian photoentrainment. This distinction stems from studies that ablated melanopsin-expressing intrinsically photosensitive (ip)RGCs and showed deficits in non-image forming behaviors, but not image vision. However, we show that the ON alpha RGC, a conventional RGC type, is intrinsically photosensitive in mammals. In addition to their classical response to fast changes in contrast through rod/cone signaling, melanopsin expression allows ON alpha RGCs to signal prior light exposure and environmental luminance over long periods of time. Consistent with the high contrast sensitivity of ON alpha RGCs, mice lacking either melanopsin or ON alpha RGCs have behavioral deficits in contrast sensitivity. These findings indicate a surprising role for melanopsin and ipRGCs in vision.

Signalling by melanopsin (OPN4) expressing photosensitive retinal ganglion cells

“…In keeping with this hypothesis, M4-type pRGCs have now been identified as a subset of alpha ON ganglion cells, 21,39 a type of retinal ganglion cell known to be involved in the processing of visual information and contrast sensitivity. 21 However, the dLGN also receives input from other non-M1-type pRGCs, 39 and thus, it has been difficult to determine the specific contribution of each pRGC subtype to these responses.…”

“…17 More recently it has become clear that melanopsin contributes not only to a range of NIF pathways but also performs multiple roles in image forming visual pathways. Melanopsin provides visual centres with information regarding overall levels of environmental light, and performs roles in irradiance coding and brightness discrimination, [18][19][20] contrast detection, 21 and adaptation of visual responses. 22 Melanopsin also acts as an irradiance detector for the retina, 22,23 providing measures of overall illuminance and facilitating the adaptation of cone photoresponses under bright-light conditions.…”

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

“…melanopsin | calcium | photoreceptor | amphioxus T he discovery of melanopsin-using photosensitive ganglion cells in the vertebrate retina (ipRGCs) (1, 2) not only clarified how various nonvisual light-dependent processes are controlled, but also incorporated novel contributions to visual function by nonconventional light sensors (3)(4)(5). In addition, the unexpected molecular kinship between melanopsin and the opsins of invertebrate microvillar photoreceptors (6, 7) questioned the longheld belief that this lineage of receptors was excluded from vertebrate phyla.…”

Estudo da resposta da melanopsina na neuropatia óptica e no distúrbio de sono através do reflexo pupilar à luz

“…Neste estudo, a medida psicofísica da sensibilidade a contrastes espaciais de luminância através de estímulos de grades senoidais, indicou perdas nas faixas baixas e altas de frequência espacial dos pacientes com glaucoma moderado e avançado, apontando um prejuízo tanto na via parvocelular, especializada no processamento de cores e frequências espaciais altas, quanto na via magnocelular, especializada no processamento de movimento e frequências espaciais baixas (Berninger et al, 1989;Hubel & Livingstone, apresentaram um déficit nas frequências espaciais baixas e um aumento na sensibilidade ao contraste para as frequências espaciais altas, relativo aos controles (Schmidt et al, 2014 possível explicação para isso, poderia ser um mecanismo compensatório das vias ou células não afetadas no estágio inicial do glaucoma. Em um modelo de glaucoma de pressão normal, foi observado aumento da arborização dendrítica na camada plexiforme interna em estágios iniciais da doença, no entanto, na fase mais avançada este achado não foi mais observado coincidindo com a perda de células ganglionares (Vidal, 2013).…”

“…Nos mamíferos a via NFI é mediada por cones, bastonetes e ipRGCs. As ipRGCs além de ser diretamente fotossensíveis, também recebem entradas de cones e bastonetes (Provencio et al, 1998;Berson et al, 2002;Hattar, Liao, Takao, Berson, & Yau, 2002); essas células desempenham vários papéis, que poderiam até mesmo incluir envolvimento na formação de imagens (Dacey, et al, 2005;Zaidi, et al, 2007;Brown et al, 2010;Ecker, et al, 2010;Schmidt et al, 2014).…”