Fig. 21. Neurobiotin coupling among horizontal cells of the rabbit retina. A. Tracer-coupled A-type horizontal cells in the dark-adapted rabbit retina after injection of Neurobiotin into a single cell. The micrograph shows only a portion of the network, which comprised more than 1,000 cells extending 2,350 μm across the axis parallel to the visual streak. B. Tracer-coupled B-type horizontal cells in the dark-adapted rabbit retina. This network included 227 cells extending 400 μm along the axis parallel to the visual streak. The asterisk indicates the point of injection. Scale bars are 50 μm. (Xin D, Bloomfield SA: Dark- and light-induced changes in coupling between horizontal cells in the rabbit retina. J Comp Neurol 383:512, 1998, with permission of the authors and Wiley-Liss)