Specificity of the horizontal cell-photoreceptor connections in the zebrafish (Danio rerio) retina

J Comp Neurol. 2009 Oct 10;516(5):442-53. doi: 10.1002/cne.22135.


Horizontal cells (HCs) are involved in establishing the center-surround receptive field organization of photoreceptor and bipolar cells. In many species, HCs respond differentially to colors and may play a role in color vision. An earlier study from our laboratory suggested that four types of HCs exist in the zebrafish retina: three cone HCs (H1, H2 and H3) and one rod HC. In this study, we describe their photoreceptor connections. Cones are arranged in a mosaic in which rows of alternating blue (B)- and ultraviolet (UV)-sensitive single cones alternate with rows of red (R)- and green (G)-sensitive double cones; the G cones are adjacent to UV cones and B cones adjacent to R cones. Two small-field (H1 and H2) and two large-field (H3 and rod HC) cells were observed. The cone HC dendritic terminals connected to cones with single boutons, doublets, or rosettes, whereas the rod HCs connected to rods with single boutons. The single boutons/doublets/rosettes of cone HCs were arranged in double rows separated by single rows for H1 cells, in pairs and singles for H2 cells, and in a rectilinear pattern for H3 cells. These connectivity patterns suggest that H1 cells contact R, G, and B cones, H2 cells G, B, and UV cones, and H3 cells B and UV cones. These predictions were confirmed by applying the DiI method to SWS1-GFP retinas whose UV cones express green fluorescent protein. Each rod HC was adjacent to the soma or axon of a DiI-labeled cone HC and connected to 50-200 rods.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Dendrites / physiology
  • Microscopy, Confocal
  • Neural Pathways / physiology*
  • Neural Pathways / ultrastructure
  • Photoreceptor Cells, Vertebrate / physiology*
  • Photoreceptor Cells, Vertebrate / ultrastructure
  • Retinal Cone Photoreceptor Cells / physiology
  • Retinal Cone Photoreceptor Cells / ultrastructure
  • Retinal Horizontal Cells / physiology*
  • Retinal Horizontal Cells / ultrastructure
  • Retinal Rod Photoreceptor Cells / physiology
  • Retinal Rod Photoreceptor Cells / ultrastructure
  • Ultraviolet Rays
  • Zebrafish / physiology*