Melanopsin-dependent persistence and photopotentiation of murine pupillary light responses

Yanli Zhu, Daniel C. Tu, Darcy Denner, Thomas Shane, Christine M. Fitzgerald, Russell N. Van Gelder

Research output: Contribution to journalArticle

39 Scopus citations

Abstract

PURPOSE. To determine the relative contributions of inner and outer retinal photoreception to the pupillary light response. METHODS. Wild-type, retinal degenerate (rd/rd), and melanopsin mutant (opn4-/-) mice were tested for pupillary light responsiveness by video pupillometry before, during, and after exposure to supersaturating light intensities. Similar lighting protocols were used to probe responses of intrinsically photosensitive retinal ganglion cells (ipRGCs) recorded with multielectrode arrays ex vivo. RESULTS. Both outer retinal photoreceptors (rods and cones) and inner retinal photoreceptors (intrinsically photosensitive retinal ganglion cells [ipRGCs]) are sufficient to drive the pupillary light response in mice. After supersaturating light exposure, rather than bleaching or adapting, rd/rd mice showed paradoxical potentiation of responses to subsaturating light exposure. opn4-/- mice, in contrast, could not sustain pupillary constriction under continuous bright illumination, and showed desensitization after bright-light exposure. Both the intensity of light necessary to induce potentiation and the spectral sensitivity for sustained and potentiated responses differed from that necessary to trigger pupillary constriction, suggesting that photopotentiation is dependent on a pigment-state distinct from that triggering the pupillary light response itself. Multielectrode array recordings of ipRGCs from rd/rd retinas demonstrated persistent cell firing under continuous light exposure but did not show potentiation. CONCLUSIONS. Unique photoreceptive properties of intrinsically photosensitive RGCs confer resistance to bleaching and/or adaptation under continuous bright illumination to the pupillary light response and suggest the presence of a photopigment with multiple absorption states.

Original languageEnglish (US)
Pages (from-to)1268-1275
Number of pages8
JournalInvestigative Ophthalmology and Visual Science
Volume48
Issue number3
DOIs
StatePublished - Mar 1 2007

ASJC Scopus subject areas

  • Ophthalmology
  • Sensory Systems
  • Cellular and Molecular Neuroscience

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