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J Verweij, EP Hornstein, JL Schnapf; Feedback from Horizontal Cells to Cones in the Primate Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2921.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: A feedback signal from horizontal cells to cones is believed to be involved in color processing and spatial antagonism in the retina. Can horizontal cell feedback be measured directly in cones in primate retina? What are the ionic and pharmacological mechanisms that generate the signal? What are its spatial and spectral properties? Methods: Whole-cell recordings were made from single red and green cones in isolated retina of macaque monkey. Cones were stimulated with spots of light (40-700 µm diameter) and annuli (150 -700 µm outer diameter). Results: When intracellular chloride was set to 41 mM (ECl = -30 mV) and the membrane potential held at -40 mV, an annulus of light evoked an inward current, opposite in polarity to the center response. The surround response was reversibly blocked by 100 µM cobalt and 25 µM CNQX. In contrast, GABA (1 mM) and GABA antagonist picrotoxin (200 µM) had no effect, although in some cells the signal was inhibited after prolonged GABA exposure (≷ 10 min). The surround signal had fast and slow components. The slow component reversed at ECl and was blocked by BAPTA, consistent with a calcium dependent chloride conductance. Surround receptive fields were large (diameter ≷ 500 µm) and of mixed spectral cone type. Conclusion: Primate cones have antagonistic center/surround receptive fields. Surround illumination increases calcium influx which in turn activates calcium dependent chloride currents. At physiological intracellular chloride concentrations (18 mM) the feedback signal is difficult to detect because calcium and chloride fluxes counteract each other electrically. Nonetheless, the calcium flux is expected to create pronounced antagonistic surrounds in bipolar cells.
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