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Daniel Y. Tso, Yevgeniy Freyvert, Ronald Miller, Bret Martell, Theresa Blatchford; Noninvasive Functional Retinal Imaging in the Mouse is Spatially-specific and Dependent on the Electrical Activity of Photoreceptors. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4989.
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Intrinsic signal optical imaging studies have shown the existence of stimulus-evoked signals in the retinal tissues that are likely to be of outer retinal origin. The wide range of knockout mouse models of retinal dysfunction provides an opportunity for further dissection of the origins of these signals. This study aims to elucidate the baseline characteristics of activity dependent intrinsic signals in the retina of the mouse, and to begin dissection of the signal origins using KO mouse models.
Animals and Preparation. Mice were sedated and anesthetized using ketamine/xylazine. Atropine and phenylephrine were administered to dilate the pupil and inhibit accommodation. Hypromellose was applied to lubricate the eye and prevent corneal drying. Mice were imaged in a stereotaxic frame and physiologically monitored throughout the experiment.Imaging. A custom built imaging device was used to stimulate with visual light patterns and simultaneously illuminate the retina with near infrared light (750-780nm). A CCD camera recorded the reflectance change of the retina in 8-16 blocks of trials, with each trial consisting of several stimulus and blank conditions. Images were acquired at a rate of one frame per second, and for a period of 20-40 seconds. Stimuli were generated either using single or arrays of LEDs, or a DLP-based pico-projector. A region of interest (ROI) was selected and the data was analyzed for fractional changes in reflectance. These imaged functional signals were examined both for their spatial distribution and for their time course.
The observed functional signals are spatially-specific across the mouse retina but are generally several times smaller in amplitude than in the larger species tested, having a typical peak amplitude of about 0.1%. Our previous studies have indicated that the anatomical source of these functional signals originates from the outer retina. Preliminary studies using the Gnat1 -/- rod transducin knockout mouse (courtesy of Janis Lem, Tufts) suggests that these functional retinal signals are absent in this KO. This preliminary finding implies that the signals are dependent on a functional transducin and may be driven by the electrical activity of photoreceptors.
This novel functional imaging technique of mouse retina has demonstrated stimulus-driven reflectance change signals similar to those observed in the macaque monkey, cat and human retina. Studies using the transducin KO mouse narrow down considerably the retinal origins of these signals. It is anticipated that studies using other knockout mice models may yield important results relevant to human diseases of the retina.
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