title: Cone synapses in macaque fovea: I. Two types of non-S cones are distinguished by numbers of contacts with OFF midget bipolar cells.
abstract: L and M cones, divided into two groups by absorption spectra, have not been distinguished by structure. Here, we report what may be such a difference. We reconstructed the synaptic terminals of 16 non-S cones and the dendritic arbors of their ON and OFF midget bipolar cells from high-magnification electron micrographs of serial thin sections of a small region of macaque fovea. Each cone terminal contacted a similar number (~16) of invaginating central elements provided by its ON midget bipolar cell. By contrast, the numbers of connections between a cone terminal and its OFF midget bipolar cell were grouped into two clusters: 30-37 versus 43-50 basal contacts in the triad-associated position and 41-47 versus 61-74 Outer Densities within those basal contacts. The coefficients of variation of these distributions were all in the range of 10% or lower, characteristic of single populations. If these two clusters correspond to M- and L-cone circuits, the results reveal structural differences between M and L cones and between their corresponding OFF midget bipolar cells.
authors.affiliation: Department of Psychology, Franz Hall, University of California, Los Angeles, Los Angeles, California 90095-1563, USA. schein@ucla.edu
authors.forename: Stan
authors.initials: S
authors.lastname: Schein
authors.forename: Ivy Tran
authors.initials: IT
authors.lastname: Ngo
authors.forename: Teresa M
authors.initials: TM
authors.lastname: Huang
authors.forename: Karl
authors.initials: K
authors.lastname: Klug
authors.forename: Peter
authors.initials: P
authors.lastname: Sterling
authors.forename: Steve
authors.initials: S
authors.lastname: Herr
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D005584:Fovea Centralis / Q000502:physiology*; D008252:Macaca fascicularis; D008297:Male; D008855:Microscopy, Electron, Scanning; D017729:Presynaptic Terminals / Q000502:physiology / Q000648:ultrastructure; D051245:Retinal Bipolar Cells / Q000502:physiology* / Q000648:ultrastructure; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology* / Q000648:ultrastructure; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D016707:Tissue Fixation