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C. Gias, A. Vugler, P. J. Coffey; Spatial Cortical Vision in the RCS Rat Using Optical Imaging of Intrinsic Signals. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3307.
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The purpose of this work is to study cortical spatial vision in the Royal College of Surgeons (RCS) rat at various stages of retinal degeneration using optical imaging of intrinsic signals.
Dystrophic RCS rats at 4 weeks, 7 weeks and 14 weeks of age were compared to age-matched non-dystrophic rats. The visual stimuli consisted of sinusoidal gratings with spatial frequencies between 0.05 c/d to 0.7c/d at 99% contrast and contrast levels between 99% to 20% at 0.1 c/d. In addition, bright light flashes were also used to stimulate the retina. The skull overlying primary visual cortex was thinned to translucency and illuminated using narrow-band light peaking at 570nm wavelength. Changes in the reflected light during visual stimulation were recorded using a 12-bit CCD camera. A 16-channel electrode was subsequently inserted in the location of maximum optical imaging responses to measure multiunit and local field potentials responses through the cortical layers in response to visual stimulation.
The results of this study show a reduction in the amplitude of the reflected light responses at increasing spatial frequencies and decreasing contrast in the non-dystrophic rats across the different age groups in line with previous electrophysiological experiments. This is also the case in the dystrophic RCS rat in those cases where responses to grating stimulation could be elicited. No response to gratings was elicited in the 14 weeks old RCS dystrophic group although bright light flashes could still evoke a cortical response. Multiunit and evoked field potential responses to visual stimulation across layers were confirmed at the cortical location where optical imaging responses were maximal.
These results show that optical imaging of intrinsic signals can be used as a non-invasive screening method to study the progress of cortical spatial vision degeneration in a rat retinal degenerative model. These results also confirm previous electrophysiological and behavioural studies on the pattern of cortical functional degeneration in the RCS rat.
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