title: Development of melanopsin-based irradiance detecting circuitry.
abstract: BACKGROUND
  Most retinal ganglion cells (RGCs) convey contrast and motion information to visual brain centers. Approximately 2% of RGCs are intrinsically photosensitive (ipRGCs), express melanopsin and are necessary for light to modulate specific physiological processes in mice. The ipRGCs directly target the suprachiasmatic nucleus (SCN) to photoentrain circadian rhythms, and the olivary pretectal nucleus (OPN) to mediate the pupillary light response. How and when this ipRGC circuitry develops is unknown.
  
  
  RESULTS
  Here, we show that some ipRGCs follow a delayed developmental time course relative to other image-forming RGCs. Specifically, ipRGC neurogenesis extends beyond that of other RGCs, and ipRGCs begin innervating the SCN at postnatal ages, unlike most RGCs, which innervate their image-forming targets embryonically. Moreover, the appearance of ipRGC axons in the OPN coincides precisely with the onset of the pupillary light response.
  
  
  CONCLUSIONS
  Some ipRGCs differ not only functionally but also developmentally from RGCs that mediate pattern-forming vision.
authors.affiliation: Department of Biology, Johns Hopkins University, Baltimore, MD 21218, USA.
authors.forename: David S
authors.initials: DS
authors.lastname: McNeill
authors.forename: Catherine J
authors.initials: CJ
authors.lastname: Sheely
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Ecker
authors.forename: Tudor C
authors.initials: TC
authors.lastname: Badea
authors.forename: Duncan
authors.initials: D
authors.lastname: Morhardt
authors.forename: William
authors.initials: W
authors.lastname: Guido
authors.forename: Samer
authors.initials: S
authors.lastname: Hattar
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001369:Axons / Q000502:physiology; D005260:Female; D007150:Immunohistochemistry; D058449:Intravitreal Injections; D008027:Light; D051379:Mice; D008810:Mice, Inbred C57BL; D055495:Neurogenesis / Q000502:physiology; D020419:Photoreceptor Cells, Vertebrate; D011247:Pregnancy; D011680:Pupil / Q000502:physiology; D012025:Reflex, Pupillary / Q000502:physiology; D012160:Retina / Q000254:growth & development; D012165:Retinal Ganglion Cells / Q000378:metabolism / Q000502:physiology*; D017299:Rod Opsins / Q000096:biosynthesis / Q000502:physiology*; D013493:Suprachiasmatic Nucleus / Q000254:growth & development / Q000502:physiology; D014795:Visual Pathways / Q000254:growth & development* / Q000502:physiology*; D000099210:Melanopsin
chemical_list: D000469:Alkaline Phosphatase; D017299:Rod Opsins; D000099210:Melanopsin