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Michael L Risner, David Sprinzen, Douglas McMahon; The influence of dopamine on contrast sensitivity in physiologically defined retinal ganglion cells. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2643.
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© ARVO (1962-2015); The Authors (2016-present)
Previously, our lab has found that light-mediated vision is altered in mice that lack retinal dopamine. Specifically, we found that the light-adapted ERG b-wave is blunted and behavioral contrast sensitivity is reduced in retinal tyrosine hydroxylase knockout mice (rThKO). The purpose of the present study was to further investigate the retinal mechanism(s) that control light-adapted vision using the rThKO mouse model. Here we examined light-adapted contrast sensitivity of retinal ganglion cells (RGCs) in control and rThKO mice using multi-electrode array (MEA) electrophysiology.
Retinas were harvested and flat mounted on 6 x 10 or 8 x 8 MEAs. To measure contrast sensitivity, drifting sinusoidal gratings were projected onto the retinal surface using a small light-emitting diode (LED) monitor that was attached to the epifluorescent port of an upright microscope. The image was focused onto the photoreceptor layer of the retina using a 10X objective. The mean luminance of the gratings was 0.12 µW/cm2. Contrast ranged from 3 to 30%. Sinusoidal gratings from 1.0 to 28.5 cycles/mm were used to measure contrast sensitivity. Gratings were presented at four different angles: 0, 90, 180, and 270 degrees. Stimuli were presented in random order and each contrast-spatial frequency combination was presented at least 16 times. Contrast-response functions were obtained for each spatial frequency by measuring the average number of spikes. Contrast threshold was defined as just above overall mean spike rate of all stimuli.
To initially assess contrast sensitivity we combined all RGC types. Thus far we have obtained recordings from 21 RGCs from control animals and 9 RGCs from rThKO animals. Our preliminary results indicate reduced contrast sensitivity in rThKO RGCs. Contrast sensitivity is reduced at low, middle, and high spatial frequencies.
These results corroborate our previous psychophysical findings. We will further investigate the influence of dopamine on contrast sensitivity in physiologically defined RGCs and rescue contrast sensitivity using dopamine agonists.
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