title: Melanopsin Phototransduction Contributes to Light-Evoked Choroidal Expansion and Rod L-Type Calcium Channel Function In Vivo.
abstract: OBJECTIVE
  In humans, rodents, and pigeons, the dark → light transition signals nonretinal brain tissue to increase choroidal thickness, a major control element of choroidal blood flow, and thus of photoreceptor and retinal pigment epithelium function. However, it is unclear which photopigments in the retina relay the light signal to the brain. Here, we test the hypothesis that melanopsin (Opn4)-regulated phototransduction modulates light-evoked choroidal thickness expansion in mice.
  
  
  METHODS
  Two-month-old C57Bl/6 wild-type (B6), 4- to 5-month-old C57Bl/6/129S6 wild-type (B6 + S6), and 2-month-old melanopsin knockout (Opn4-/-) on a B6 + S6 background were studied. Retinal anatomy was evaluated in vivo by optical coherence tomography and MRI. Choroidal thickness in dark and light were measured by diffusion-weighted MRI. Rod cell L-type calcium channel (LTCC) function in dark and light (manganese-enhanced MRI [MEMRI]) was also measured.
  
  
  RESULTS
  Opn4-/- mice did not show the light-evoked expansion of choroidal thickness observed in B6 and B6 + S6 controls. Additionally, Opn4-/- mice had lower than normal rod cell and inner retinal LTCC function in the dark but not in the light. These deficits were not due to structural abnormalities because retinal laminar architecture and thickness, and choroidal thickness in the Opn4-/- mice were similar to controls.
  
  
  CONCLUSIONS
  First time evidence is provided that melanopsin phototransduction contributes to dark → light control of murine choroidal thickness. The data also highlight a contribution in vivo of melanopsin phototransduction to rod cell and inner retinal depolarization in the dark.
authors.affiliation: Department of Anatomy and Cell Biology, Wayne State University, Detroit, Michigan, United States 2Department of Ophthalmology, Wayne State University, Detroit, Michigan, United States.
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Berkowitz
authors.affiliation: Department of Neurobiology, Northwestern University, Evanston, Illinois, United States.
authors.forename: Tiffany
authors.initials: T
authors.lastname: Schmidt
authors.affiliation: Department of Family Medicine and Public Health Sciences, Wayne State University, Detroit, Michigan, United States.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Podolsky
authors.affiliation: Department of Anatomy and Cell Biology, Wayne State University, Detroit, Michigan, United States.
authors.forename: Robin
authors.initials: R
authors.lastname: Roberts
mesh_terms: D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002829:Choroid / Q000166:cytology / Q000378:metabolism*; D008027:Light; D055537:Light Signal Transduction; D008279:Magnetic Resonance Imaging; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017948:Retinal Rod Photoreceptor Cells / Q000166:cytology / Q000378:metabolism* / Q000528:radiation effects; D017299:Rod Opsins / Q000378:metabolism*; D041623:Tomography, Optical Coherence; D000099210:Melanopsin
chemical_list: D020746:Calcium Channels, L-Type; D017299:Rod Opsins; D000099210:Melanopsin