title: Melanopsin-dependent photoreception provides earliest light detection in the mammalian retina.
abstract: BACKGROUND
  The visual system is now known to be composed of image-forming and non-image-forming pathways. Photoreception for the image-forming pathway begins at the rods and cones, whereas that for the non-image-forming pathway also involves intrinsically photosensitive retinal ganglion cells (ipRGCs), which express the photopigment melanopsin. In the mouse retina, the rod and cone photoreceptors become light responsive from postnatal day 10 (P10); however, the development of photosensitivity of the ipRGCs remains largely unexplored.
  
  
  RESULTS
  Here, we provide direct physiological evidence that the ipRGCs are light responsive from birth (P0) and that this photosensitivity requires melanopsin expression. Interestingly, the number of ipRGCs at P0 is over five times that in the adult retina, reflecting an initial overproduction of melanopsin-expressing cells during development. Even at P0, the ipRGCs form functional connections with the suprachiasmatic nucleus, as assessed by light-induced Fos expression.
  
  
  CONCLUSIONS
  The findings suggest that the non-image-forming pathway is functional long before the mainstream image-forming pathway during development.
authors.affiliation: Department of Visual Neuroscience, Division of Neuroscience and Mental Health, Imperial College London, Charing Cross Hospital Campus, London, W6 8RF, United Kingdom. s.sekaran@imperial.ac.uk
authors.forename: S
authors.initials: S
authors.lastname: Sekaran
authors.forename: D
authors.initials: D
authors.lastname: Lupi
authors.forename: S L
authors.initials: SL
authors.lastname: Jones
authors.forename: C J
authors.initials: CJ
authors.lastname: Sheely
authors.forename: S
authors.initials: S
authors.lastname: Hattar
authors.forename: K-W
authors.initials: KW
authors.lastname: Yau
authors.forename: R J
authors.initials: RJ
authors.lastname: Lucas
authors.forename: R G
authors.initials: RG
authors.lastname: Foster
authors.forename: M W
authors.initials: MW
authors.lastname: Hankins
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002450:Cell Communication / Q000235:genetics; D066298:In Vitro Techniques; D007700:Kinetics; D008027:Light; D055537:Light Signal Transduction / Q000502:physiology; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D016761:Oncogene Proteins v-fos / Q000378:metabolism; D012160:Retina / Q000166:cytology / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000378:metabolism / Q000502:physiology*; D017299:Rod Opsins / Q000235:genetics / Q000378:metabolism*; D013493:Suprachiasmatic Nucleus / Q000254:growth & development / Q000378:metabolism; D000099210:Melanopsin
chemical_list: D016761:Oncogene Proteins v-fos; D017299:Rod Opsins; D000099210:Melanopsin