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A.J. Zhang, J. Zhang, Z. Yang, X.L. Yang, S.M. Wu; Patterns of electrical coupling and receptive field properties of horizontal cells in the tiger salamander retina . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1322.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The objective is to correlate the patterns of electrical coupling with receptive field properties of various types of horizontal cells (HCs), and to understand how HCs mediate lateral spread of light–evoked signals in the outer retina. Methods: HCs were impaled with microelectrodes filled with Neurobiotin and Lucifer yellow in the superfused flatmount retinas of the tiger salamander, and voltage responses to light spots or annuli of various diameters were recorded. After each experiment, neurobiotin and Lucifer yellow were ejected with positive and negative current pulses for 4–8 minutes, and the retina was superfused for 30 minutes for dye diffusion. Then the retina was fixed, washed, and reacted overnight with 1:100 streptavidin conjugated with CY–3. The HC images were viewed with a confocal microscope. Results:Lucifer yellow revealed the morphology of the recorded HCs, but it did not pass through gap junction channels in the salamander retina. There are two patterns of neurobiotin tracer coupling in HCs: (1) In a subpopulation of axon–bearing HCs, dye coupling were not observed near the soma, but an array of neurobiotin–positive HCs somas were observed near the axon terminals of the injected cell. (2) Near the soma of a subpopulation of axonless HCs, neurobiotin–positive HC somas were found. There are at least two physiological types of HCs: the narrow field cells exhibit responses that increase as the diameter of the spot increases to about 500 µm and decrease when the spot becomes larger, and the broad field cells exhibit responses that increase with increasing spot diameter beyond 1,500 µm (Skrzypet and Werblin 1983). Application of 500 µM 1–octanol, a gap junction blocker, decreased the amplitude of the HC responses to large light spots (>2,000µm), but exerted little actions on responses to smaller light spots. Relationships between HC receptive field properties and patterns of electrical coupling are under investigation. Conclusions: Similar to the mammalian retinas, there are two morphological types of HCs in the tiger salamander retina, one bears axon with elaborated axon terminals and the other is axonless. Axon terminals of a subpopulation of axon–bearing HCs are dye coupled with other HCs, and somas of a subpopulation of axonless HCs are dye coupled with other HCs. The light response of broad field HCs is mediated by coupled HC network and blockade of gap junction channels reduces the receptive field size of these cells.
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