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Cover picture: The hybrid synaptic surface shown is a reconstruction from serial thin sections of the synaptic terminal of a foveal S cone. Strings of yellow spheres represent the sites at which synaptic ribbons anchor to the presynaptic surface of the terminal. These strings of spheres also mark 24 active zones where glutamate is released. Colored patches represent regions of contact with 31 central elements, provided by the dendrites of four S-cone ON bipolar cells exclusively. Based on numbers of ribbon synapses between the S cone and S-cone ON bipolar cells and between those bipolar cells and blue-yellow (BY) ganglion cells, we conclude that each S cone diverges to approximately six BY ganglion cells, dominating one and contributing more modestly to the others. Conversely, of each pair of BY ganglion cells, one is dominated by a single S cone and one is diffusely driven by several. Related considerations argue that coextensive S-cone ON and "yellow" OFF receptive fields must be present in the synaptic terminal of the S cone, in which case the S-cone terminal itself constitutes the first critical locus for blue-yellow color vision. For details, see the article by Schein et al. in this issue (pages 8366-8378).
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