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Original Article

^a From the Graduate School Neurosciences Amsterdam, The Netherlands Ophthalmic Research Institute, 1105 BA Amsterdam, The Netherlands
^b Department of Visual System Analysis, University of Amsterdam, 1105 BA Amsterdam, The Netherlands
Graduate School Neurosciences Amsterdam; The Netherlands Ophthalmic Research Institute; Meibergdreef 47; 1105 BA Amsterdam, The Netherlands.Fax: +31 20 5666121;

m.kamermans{at}ioi.knaw.nl

Processing of visual stimuli by the retina changes strongly during light/dark adaptation. These changes are due to both local photoreceptor-based processes and to changes in the retinal network. The feedback pathway from horizontal cells to cones is known to be one of the pathways that is modulated strongly during adaptation. Although this phenomenon is well described, the mechanism for this change is poorly characterized. The aim of this paper is to describe the mechanism for the increase in efficiency of the feedback synapse from horizontal cells to cones. We show that a train of flashes can increase the feedback response from the horizontal cells, as measured in the cones, up to threefold. This process has a time constant of 3 s and can be attributed to processes intrinsic to the cones. It does not require dopamine, is not the result of changes in the kinetics of the cone light response and is not due to changes in horizontal cells themselves. During a flash train, cones adapt to the mean light intensity, resulting in a slight (4 mV) depolarization of the cones. The time constant of this depolarization is 3 s. We will show that at this depolarized membrane potential, a light-induced change of the cone membrane potential induces a larger change in the calcium current than in the unadapted condition. Furthermore, we will show that negative feedback from horizontal cells to cones can modulate the calcium current more efficiently at this depolarized cone membrane potential. The change in horizontal cell response properties during the train of flashes can be fully attributed to these changes in the synaptic efficiency. Since feedback has major consequences for the dynamic, spatial, and spectral processing, the described mechanism might be very important to optimize the retina for ambient light conditions.

Key Words: retina • synapse • goldfish • calcium current

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This article has been cited by other articles:

				M. VanLeeuwen, I. Fahrenfort, T. Sjoerdsma, R. Numan, and M. Kamermans Lateral Gain Control in the Outer Retina Leads to Potentiation of Center Responses of Retinal Neurons J. Neurosci., May 13, 2009; 29(19): 6358 - 6366. [Abstract] [Full Text] [PDF]

				M. Kamermans, D. Kraaij, and H. Spekreijse The dynamic characteristics of the feedback signal from horizontal cells to cones in the goldfish retina J. Physiol., July 15, 2001; 534(2): 489 - 500. [Abstract] [Full Text] [PDF]

				D. A. Kraaij, H. Spekreijse, and M. Kamermans The Open- and Closed-Loop Gain-Characteristics of the Cone/Horizontal Cell Synapse in Goldfish Retina J Neurophysiol, September 1, 2000; 84(3): 1256 - 1265. [Abstract] [Full Text] [PDF]

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