title: Adaptation to steady light by intrinsically photosensitive retinal ganglion cells.
abstract: 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.
authors.affiliation: Solomon H. Snyder Department of Neuroscience and Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA. michael.do@childrens.harvard.edu
authors.forename: Michael Tri Hoang
authors.initials: MT
authors.lastname: Do
authors.forename: King-Wai
authors.initials: KW
authors.lastname: Yau
mesh_terms: D000200:Action Potentials / Q000528:radiation effects; D000221:Adaptation, Ocular / Q000528:radiation effects*; D000818:Animals; D001522:Behavior, Animal / Q000528:radiation effects; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000528:radiation effects; D025461:Feedback, Physiological / Q000528:radiation effects; D008027:Light; D055537:Light Signal Transduction / Q000528:radiation effects; D051379:Mice; D008822:Mice, Transgenic; D012165:Retinal Ganglion Cells / Q000502:physiology* / Q000528:radiation effects*; D017299:Rod Opsins / Q000378:metabolism; D000099210:Melanopsin
chemical_list: D002118:Calcium; D017299:Rod Opsins; D000099210:Melanopsin