title: The rat retina has five types of ganglion-cell photoreceptors.
abstract: Intrinsically photosensitive retinal ganglion cells (ipRGCs) are inner retinal photoreceptors that mediate non-image-forming visual functions, e.g. pupillary constriction, regulation of pineal melatonin release, and circadian photoentrainment. Five types of ipRGCs were recently discovered in mouse, but whether they exist in other mammals remained unknown. We report that the rat also has five types of ipRGCs, whose morphologies match those of mouse ipRGCs; this is the first demonstration of all five cell types in a non-mouse species. Through immunostaining and λmax measurements, we showed that melanopsin is likely the photopigment of all rat ipRGCs. The various cell types exhibited diverse spontaneous spike rates, with the M1 type spiking the least and M4 spiking the most, just like we had observed for their mouse counterparts. Also similar to mouse, all ipRGCs in rat generated not only sluggish intrinsic photoresponses but also fast, synaptically driven ones. However, we noticed two significant differences between these species. First, whereas we learned previously that all mouse ipRGCs had equally sustained synaptic light responses, rat M1 cells' synaptic photoresponses were far more transient than those of M2-M5. Since M1 cells provide all input to the circadian clock, this rat-versus-mouse discrepancy could explain the difference in photoentrainment threshold between mouse and other species. Second, rat ipRGCs' melanopsin-based spiking photoresponses could be classified into three varieties, but only two were discerned for mouse ipRGCs. This correlation of spiking photoresponses with cell types will help researchers classify ipRGCs in multielectrode-array (MEA) spike recordings.
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
authors.forename: Aaron N
authors.initials: AN
authors.lastname: Reifler
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Chervenak
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Dolikian
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Benenati
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
authors.forename: Benjamin S
authors.initials: BS
authors.lastname: Meyers
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
authors.forename: Zachary D
authors.initials: ZD
authors.lastname: Demertzis
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Lynch
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
authors.forename: Benjamin Y
authors.initials: BY
authors.lastname: Li
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
authors.forename: Rebecca D
authors.initials: RD
authors.lastname: Wachter
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
authors.forename: Fady S
authors.initials: FS
authors.lastname: Abufarha
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
authors.forename: Eden A
authors.initials: EA
authors.lastname: Dulka
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
authors.forename: Weston
authors.initials: W
authors.lastname: Pack
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
authors.forename: Xiwu
authors.initials: X
authors.lastname: Zhao
authors.affiliation: Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA; Department of Molecular, Cellular & Developmental Biology, University of Michigan, Ann Arbor, MI 48105, USA. Electronic address: kwoon@umich.edu.
authors.forename: Kwoon Y
authors.initials: KY
authors.lastname: Wong
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001369:Axons / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology; D004594:Electrophysiology; D008027:Light; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D010775:Photic Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012025:Reflex, Pupillary / Q000502:physiology; D012165:Retinal Ganglion Cells / Q000166:cytology* / Q000502:physiology / Q000528:radiation effects; D017299:Rod Opsins / Q000378:metabolism; D014785:Vision, Ocular / Q000502:physiology; D000099210:Melanopsin
chemical_list: D017299:Rod Opsins; D000099210:Melanopsin
keywords: Circadian photoentrainment; Intrinsically photosensitive retinal ganglion cell; Light response; Melanopsin; Photoreceptors; Synaptic transmission; Whole-cell recording; ipRGC