title: Photon capture and signalling by melanopsin retinal ganglion cells.
abstract: A subset of retinal ganglion cells has recently been discovered to be intrinsically photosensitive, with melanopsin as the pigment. These cells project primarily to brain centres for non-image-forming visual functions such as the pupillary light reflex and circadian photoentrainment. How well they signal intrinsic light absorption to drive behaviour remains unclear. Here we report fundamental parameters governing their intrinsic light responses and associated spike generation. The membrane density of melanopsin is 10(4)-fold lower than that of rod and cone pigments, resulting in a very low photon catch and a phototransducing role only in relatively bright light. Nonetheless, each captured photon elicits a large and extraordinarily prolonged response, with a unique shape among known photoreceptors. Notably, like rods, these cells are capable of signalling single-photon absorption. A flash causing a few hundred isomerized melanopsin molecules in a retina is sufficient for reaching threshold for the pupillary light reflex.
authors.affiliation: Solomon H. Snyder Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA. mdo@jhmi.edu
authors.forename: Michael Tri H
authors.initials: MT
authors.lastname: Do
authors.forename: Shin H
authors.initials: SH
authors.lastname: Kang
authors.forename: Tian
authors.initials: T
authors.lastname: Xue
authors.forename: Haining
authors.initials: H
authors.lastname: Zhong
authors.forename: Hsi-Wen
authors.initials: HW
authors.lastname: Liao
authors.forename: Dwight E
authors.initials: DE
authors.lastname: Bergles
authors.forename: King-Wai
authors.initials: KW
authors.lastname: Yau
mesh_terms: D000200:Action Potentials / Q000528:radiation effects; D000818:Animals; D001921:Brain / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D017785:Photons; D011680:Pupil / Q000502:physiology / Q000528:radiation effects; D012025:Reflex, Pupillary / Q000528:radiation effects; D012165:Retinal Ganglion Cells / Q000378:metabolism* / Q000528:radiation effects*; D017299:Rod Opsins / Q000378:metabolism*; D000099210:Melanopsin
chemical_list: D017299:Rod Opsins; D000099210:Melanopsin