a positive feedback synapse from retinal horizontal cells to cone photoreceptors一个积极的反馈从视网膜水平细胞突触锥体光感受器.pdfVIP

A Positive Feedback Synapse from Retinal Horizontal Cells to Cone Photoreceptors 1 2 3 2 4 Skyler L. Jackman , Norbert Babai , James J. Chambers , Wallace B. Thoreson , Richard H. Kramer * 1 Department of Physics, University of California, Berkeley, Berkeley, California, United States of America, 2 Department of Ophthalmology, University of Nebraska Medical Center, Omaha, Nebraska, United States of America, 3 Department of Chemistry, University of Massachusetts, Amherst, Amherst, Massachusetts, United States of America, 4 Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California, United States of America Abstract Cone photoreceptors and horizontal cells (HCs) have a reciprocal synapse that underlies lateral inhibition and establishes the antagonistic center-surround organization of the visual system. Cones transmit to HCs through an excitatory synapse and HCs feed back to cones through an inhibitory synapse. Here we report that HCs also transmit to cone terminals a positive feedback signal that elevates intracellular Ca2+ and accelerates neurotransmitter release. Positive and negative feedback are both initiated by AMPA receptors on HCs, but positive feedback appears to be mediated by a change in HC Ca2+, whereas negative feedback is mediated by a change in HC membrane potential. Local uncaging of AMPA receptor agonists suggests that positive feedback is spatially constrained to active HC-cone synapses, whereas the negative feedback signal spreads through HCs to affect release from surrounding cones. By locally offsetting the effects of negative feedback, positive feedback may amplify photoreceptor synaptic release