April 2009
Volume 50, Issue 13
ARVO Annual Meeting Abstract  |   April 2009
The Rod-Mediated Threshold Response of Gnat-2-/- Mice Measured on High Intensity Backgrounds
Author Affiliations & Notes
  • F. Naarendorp
    Psychology, Northeastern University, Boston, Massachusetts
  • T. M. Esdaille
    Psychology, Northeastern University, Boston, Massachusetts
  • C. W. Van Slyck
    Psychology, Northeastern University, Boston, Massachusetts
  • Footnotes
    Commercial Relationships  F. Naarendorp, None; T.M. Esdaille, None; C.W. Van Slyck, None.
  • Footnotes
    Support  None.
Investigative Ophthalmology & Visual Science April 2009, Vol.50, 3055. doi:
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      F. Naarendorp, T. M. Esdaille, C. W. Van Slyck; The Rod-Mediated Threshold Response of Gnat-2-/- Mice Measured on High Intensity Backgrounds. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3055.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose: : To determine the increment sensitivity of Gnat-2-/- mice that lack functional cones. Wild type (WT) rodent rods adapt to unusually high light levels (Sokolov et al., Neuron, 2002). In mice, the spontaneously occurring Gnat-2 mutation leads to cone dysfunction while the rods are spared (Chang et al., IOVS, 2006). Here we study rod vision of Gnat-2-/- mice at high light levels.

Methods: : Adult wheel-running mice were trained to associate the presentation of a light flash with the brief availability of water at a spout in their cage. The light flash stemming from an intensity-controlled LED and mounted above the wheel was randomly triggered as the mouse ran on the wheel. A mouse was deemed to have detected the flash if it immediately ceased running within one revolution after the flash. A brief, 5 deg. test flash ( = 500 nm or 365 nm) was delivered in darkness or in the presence of a white Ganzfeld background light to the ventral retina. ‘Frequency of seeing’ data were collected with the method of constant stimuli. (1 R*s-1 stands for 1 photoisomerization per rod per second).

Results: : (1) In both WT and Gnat-2-/- mice, the flash produced 5-20 photoisomerizations at absolute threshold. (2) On a background that produced about 0.008 R*s-1, the rod threshold was raised to twice the absolute threshold. (3) In WT mice, a 365 nm test flash presented on a moderate background [25 R*s-1] was mediated by cones containing UV-opsin; in Gnat-2-/- mice, the 365 nm flash was mediated by rods. (4) In WT mice, at higher background levels [300 - 400 R*s-1], the 500 nm test flash was mediated by cones that contain M-opsin; in Gnat-2-/- mice, the 500 nm flash was mediated by rods. On backgrounds that produce ~30,000 R* s-1, the rods of Gnat-2-/- mice did not yet show saturation.

Conclusions: : Rod vision of Gnat-2-/- mice is very similar to that of WT mice in low and moderate adapting ranges. Under very bright light, the sensitivity of the rods in Gnat-2-/- mice may be regulated by a light-adaptive mechanism that involves the translocation of transducin, from the rod photoreceptor outer segment to the inner segment as described by Sokolov et al. (Neuron, 2002).

Keywords: photoreceptors: visual performance • detection • transgenics/knock-outs 

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