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DA Burkhardt, PK Fahey; Receptive Field Organizaton of Bipolar Cells: Center/Surround Symmetry . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3778.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the properties of the center-surround receptive field organization of bipolar cells. Methods: Intracellular recordings were obtained from cone-driven bipolar cells in the light-adapted retina of the tiger salamander (Ambystoma tigrinum). Responses to flashes of negative and positive contrast for centered spots and concentric annuli of optimum spatial dimensions were analyzed as a function of contrast magnitude. Results: For both depolarizing and hyperpolarizing bipolar cells, it was found that remarkably similar responses were observed for the center and surround when comparisons were made between responses of the same response polarity and thus, responses to opposite contrast polarity. In many cells, the form of the contrast/response curves for center and surround approximated mirror images of each other. Contrast gain and C50 (the contrast required for half maximal response) were quantitatively similar for center and surround when comparisons were made for responses of the same response polarity. The contrast gain of the surround was 3-5x higher than that measured for horizontal cells. The effects of APB (100uM) on center-surround symmetry were investigated in 22 depolarizing bipolar cells. In about 60% of the cells, the responses of center and surround were eliminated or attenuated to a similar degree. In the other 40%, APB eliminated the center response without greatly affecting the surround. Conclusions: The tendency of bipolar cells to show "symmetry" between center and surround responses has apparently not been observed to date since past work has been restricted to flashes of positive contrast. The symmetry and gain of the contrast response of the bipolar cell surround differs markedly from that expected for a linear feedforward pathway mediated by horizontal cells. However, center-surround symmetry might be simply explained if the surround response were largely due to feedback from horizontal cells to cones. Our results with APB provide some support for this view.
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