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Rose Pasquale, Yumiko Umino, Eduardo C Solessio; Cx36-independent rod pathways mediate visual contrast sensitivity to high temporal frequencies. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2219.
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© ARVO (1962-2015); The Authors (2016-present)
In the retina, rod signals are transmitted along multiple pathways, each connecting to underlying cone circuitry. Rod signals spread to cone pathways via Cx36 gap junction electrical synapses (Cx36-dependent rod pathways) as well as by direct chemical synapses from rods to cone bipolar cells (Cx36-independent rod pathways), with the contribution of the latter to visual function still unclear. Our goal is to dissect the contributions of Cx36-dependent and independent rod pathways to temporal contrast sensitivity (TCS).
We utilized transgenic mouse lines (3-6 months) to separate retinal pathways and used a novel operant behavior assay developed in our lab to measure the TCS of mice in response to full-field flicker applied over a wide range of temporal frequencies and background intensities. Immunohistochemical and electroretinogram (ERG) analyses were performed to assess retinal integrity. Statistical significance was tested by two-way ANOVA.
Operant behavior results show that mice with non-functional cones (GNAT2cpfl3) have normal TCS at low mesopic backgrounds (100R*/rod/s). At higher mesopic backgrounds (2000R*/rod/s), GNAT2cpfl3 mice exhibited a significant reduction in sensitivity to low temporal frequencies (1.5-12 Hz) (n=5+/-SEM) while their sensitivity to high temporal frequencies (15-42 Hz) remained normal. TCS to high frequencies also remained normal in Cx36-/-::GNAT2cpfl3 double mutant mice with isolated Cx36-independent rod pathways (n=4+/-SEM) suggesting that Cx36-independent rod pathways function to relay fast temporal information at 2000R*/rod/s. Control studies show that TCS to high frequency flicker is negligible (n=5+/-SEM) when presented in high (8000R*/rod/s) background levels suggesting that the observed responses are driven largely by rods and not by remaining cone function in GNAT2cpfl3 mice. ERG recordings indicate that the mouse lines used for these studies did not exhibit overt remodeling (n=9+/-SEM).
Our results suggest that, at high mesopic light levels (2000R*/rod/s): 1) Cone pathways contribute to the detection of low temporal frequency flicker; and 2) the poorly understood Cx36-independent rod pathways relay high temporal frequencies. Together, these data are consistent with the concept that rod pathways play a dynamic role in mammalian visual function.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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