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C. Gias, M. Semo, A. A. Vugler, P. J. Coffey; Melanopsin Cortical Response in the Rodless Coneless Mouse to Light Stimulation Revealed Using Optical Imaging of Intrinsic Signals. Invest. Ophthalmol. Vis. Sci. 2010;51(13):673.
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Non-cortical visual functions mediated by melanopsin-expressing ganglions cells have been previous identified. These retinal cells have been shown to project to the dorsal lateral geniculate nucleus in the primate suggesting a possible role in the thalamo-cortical visual pathway. The aim of this work is to examine the contribution of melanopsin to cortical activity in the rodless coneless (rd/rd cl) mouse using optical imaging of intrinsic signals.
Adult (80-160 days) male rd/rd cl and appropriate wildtype control mice were anaesthetised with urethane. The pupil of the left eye was dilated by topical application of 1% atropine sulphate. A midline incision was made and the skin above the skull retracted to expose the surface of the skull. Images overlying the visual cortex were taken with a 12 bit digital camera under near-infrared illumination. A blue light stimulus was delivered for 20 seconds following 30 minutes dark adaptation. Maps of activity were produced by highlighting the spatial changes in the optical imaging signal following stimulus presentation.
In wildtype mice, a cortical response appeared within 5 sec of stimulus onset in a region of the cortex corresponding to V1. Subsequently, the response extended to surrounding cortical areas spanning the posterior aspect of V2M and retrosplenial dysgranular cortex (RSD). The amplitude of the response increased monotonically peaking approximately ~20-25 sec after stimulus onset in each region before returning slowly to baseline. A strong cortical response was preserved in rd/rd cl mice. Kinetically, the cortical rd/rd cl response was deficient at the earliest timepoints (<5s). However, at later timepoints the rd/rd cl and wildtype responses were remarkably similar in terms of both spatial extent and magnitude.
Strong activation throughout the rd/rd cl visual cortex to light stimulation demonstrates that melanopsin impacts cortical activity with distinct spatiotemporal domains and suggests a potential role in conscious visual perception.
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