Intrinsically Photosensitive Retinal Ganglion Cells (IPRGCs)
Intrinsically photosensitive retinal ganglion cell (ipRGC)
m1sw (M1s) bw3ro, bw2rf (M3s?)
Other Classifications ON melanopsin (M2): Cdh3 (Sumbul et al., 2014)
6 (Coombs et al., 2006) C3 (Sun et al., 2002)
ON-OFF melanopsin (M3): G12 (Volgyi et al., 2009)
Genetic Marker/Gene Expression Opn4 (melanopsin) Brn3b transcription factor (Brn3b- : SCN, Brn3b+ : OPN shell) (M1) Cdh6 http://www.ncbi.nlm.nih.gov/pubmed/21867880
Description Rods and cones, the two traditional photoreceptors in the retina that allow us to see, were long considered to be the only cells in the mammalian eye that possessed direct photosensitivity. However, a novel type of photoreceptor that differs greatly from these two in both form and function was discovered just over a decade ago. These cells express the photopigment melanopsin (as opposed to rhodopsin of rods and cone opsins of cones). Interestingly, these cells are retinal ganglion cells (RGCs), allowing them to have direct communication with visually sensitive areas of the brain. Intrinsically photosensitive retinal ganglion cells (ipRGCs) encode ambient light levels (irradiance) rather than image-related information, and are best known for their roles in synchronizing circadian rhythms with night and day, and light-mediated pupil constriction. They provide input not only to circadian and pupillary centers, but also to a number of other retinorecipient regions of the brain. Making up <5% of the total number of RGCs in the reitna, ipRGCs are a remarkably rare subpopulation of RGCs. Although they were initially thought to be composed of only one type, recent morphological and functional studies indicate that there are in fact several distinct subtypes of ipRGCs, termed M1 through M5.