Inner S-cone bipolar cells provide all of the central elements for S cones in macaque retina

J Comp Neurol. 2003 Mar 3;457(2):185-201. doi: 10.1002/cne.10553.


Synaptic terminals of cones (pedicles) are presynaptic to numerous processes that arise from the dendrites of many types of bipolar cell. One kind of process, a central element, reaches deeply into invaginations of the cone pedicle just below an active zone associated with a synaptic ribbon. By reconstruction from serial electron micrographs, we show that L- and M-cone pedicles in macaque fovea are presynaptic to approximately 20 central elements that arise from two types of inner (invaginating) bipolar cell, midget and diffuse. In contrast, S-cone pedicles, with more synaptic ribbons, active zones/ribbon, and central elements/active zone, are presynaptic to approximately 33 central elements. Moreover, all of these arise from one type of bipolar cell, previously described by others, here termed an inner S-cone bipolar cell. Each provides approximately 16 central elements. Thirty-three is twice 16; correspondingly, these bipolar cells are twice as numerous as S cones. (Specifically, each S cone is presynaptic to four inner S-cone bipolar cells; in turn, each bipolar cell provides central elements to two S cones.) These bipolar cells are presynaptic to an equal number of small-field bistratified ganglion cells, giving cell numbers in 2G:2B:1S ratios. Each ganglion cell receives input from two or more inner S-cone bipolar cells and thereby collects signals from three or more S cones. This convergence, along with chromatic aberration of short-wavelength light, suggests that S-cone contributions to this ganglion cell's coextensive blue-ON/yellow-OFF receptive field are larger than opponent L/M-cone contributions via outer diffuse bipolar cells and that opponent L/M-cone signals are conveyed mainly by inner S-cone bipolar cells.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Dendrites / ultrastructure
  • Image Processing, Computer-Assisted
  • Macaca fascicularis / physiology*
  • Male
  • Microscopy, Electron
  • Retina / anatomy & histology*
  • Retinal Cone Photoreceptor Cells / cytology*
  • Retinal Cone Photoreceptor Cells / ultrastructure
  • Synapses / ultrastructure