Abstract
Purpose:
To investigate the synaptic output of S-cones in a mammalian retina.
Methods:
Serial block-face scanning electron microscopy was used to generate high resolution, three dimensional image series from a piece of the ground squirrel retina. IMOD software was used to trace and reconstruct the morphology of cone terminals, bipolar cell dendrites and horizontal cell dendrites from 511 series sections.
Results:
Among 20 cone pedicles reconstructed, two were identified as S-cones. Dendrites of three S-cone bipolar cells were found to make central, invaginating synapses with the two S-cones, which is consistent with their identity of S-cone ON bipolar cells. Other bipolar dendrites connected with S-cones were found to always contact neighboring M-cones, thus are not S-cone selective. In addition to the HI type horizontal cell, which contacts M- and S-cones non-selectively, there appeared to be an HII type horizontal cell that contacts S-cones exclusively.
Conclusions:
1) S-cones provide output predominantly to ON type S-cone bipolar cells in the ground squirrel retina. 2) The S-cone specific horizontal cell may shape the synaptic output of S-cones.