title: Melanopsin supports irradiance-driven changes in maintained activity in the superior colliculus of the mouse.
abstract: Melanopsin phototransduction allows intrinsically photosensitive retinal ganglion cells (ipRGCs) to maintain firing under sustained illumination and to encode irradiance. ipRGCs project to different parts of the visual system, including the superficial superior colliculus (sSC), but to date there is no description of melanopsin contributions to the activity of that nucleus. We sought to fill that gap using extracellular recordings to describe light response in the sSC. We failed to observe light responses in the sSC of mice lacking rod and cone function, in which melanopsin provides the only photoreception. Nor did the sSC of intact animals track very gradual ramps in irradiance, a stimulus encoded by melanopsin for other brain regions. However, in visually intact mice we did find maintained responses to extended light steps (30 s) and to an irradiance ramp upon which a high frequency (20 Hz) temporal white noise was superimposed. Both of these responses were deficient when the spectral composition of the stimulus was changed to selectively reduce its effective irradiance for melanopsin. Such maintained activity was also impaired in mice lacking melanopsin, and this effect was specific, as responses of this genotype to higher spatiotemporal frequency stimuli were normal. We conclude that ipRGCs contribute to irradiance-dependent modulations in maintained activity in the sSC, but that this effect is less robust than for other brain regions receiving ipRGC input.
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, M13 9PT, UK.
authors.forename: Miguel
authors.initials: M
authors.lastname: Dasilva
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, M13 9PT, UK.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Storchi
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, M13 9PT, UK.
authors.forename: Katherine E
authors.initials: KE
authors.lastname: Davis
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, M13 9PT, UK.
authors.forename: Kenneth L
authors.initials: KL
authors.lastname: Grieve
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, M13 9PT, UK. robert.lucas@manchester.ac.uk.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Lucas
mesh_terms: D000818:Animals; D008027:Light; D055537:Light Signal Transduction / Q000187:drug effects*; D051379:Mice; D010775:Photic Stimulation / Q000379:methods; D017949:Retinal Cone Photoreceptor Cells / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects; D017299:Rod Opsins / Q000494:pharmacology*; D013477:Superior Colliculi / Q000187:drug effects* / Q000528:radiation effects; D000099210:Melanopsin
chemical_list: D017299:Rod Opsins; D000099210:Melanopsin
keywords: intrinsically photosensitive retinal ganglion cells; melanopsin; superior colliculus; vision