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A.-J. Zhang, S. M. Wu; Center-Surround Antagonistic Receptive Fields of Retinal Bipolar Cells Are Mediated by Heterogeneous Synaptic Circuitry. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3858.
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The objective is to determine synaptic circuitry mediating the center-surround antagonistic receptive fields of various types of retinal bipolar cells.
Bipolar cells (BCs) were impaled with microelectrodes filled with Neurobiotin and Lucifer yellow in superfused flatmount retinas of the tiger salamander, and voltage responses to light spots and annuli of various diameters were recorded. Cell morphology and patterns of dye coupling were examined with a confocal microscope, and the cells’ relative rod/cone inputs were analyzed by the spectral difference method.
We examined center and surround responses of over 250 salamander BCs, and demonstrated that BCs with different rod/cone inputs exhibit different patterns of dye coupling, cell morphology, receptive field center size, surround response strength, and conductance changes associated with center and surround responses. We integrated results obtained with our previous voltage clamp data and proposed four distinct circuitry models for different types of BCs. The receptive field center size was positively correlated with the degree of dye coupling among BCs of the same type. The surround responses of hyperpolarizing bipolar cells (HBCs) are largely mediated by the feedback synapse between horizontal cells (HCs) and cones. The surround responses of a population of cone dominated depolarizing bipolar cells (DBCCS) were mediated by electrical synapses between HCs and DBCs, and the surround responses of other DBCs were mediated by combinations of HC-cone feedback and amacrine cell-BC feedback synapses.
Our results illustrate that different types of retinal BCs form receptive field centers of different sizes and organize surround inputs through different synaptic pathways. Additionally, they suggest that the synaptic circuitry underlying receptive fields in higher-order visual neurons may also be heterogeneous.
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