title: Microcircuitry for two types of achromatic ganglion cell in primate fovea.
abstract: Synaptic circuits in primate fovea have been quantified for midget/parvocellular ganglion cells. Here, based on partial reconstructions from serial electron micrographs, we quantify synaptic circuits for two other types of ganglion cell: the familiar parasol/magnocellular cell and a smaller type, termed "garland." The excitatory circuits both derive from two types of OFF diffuse cone bipolar cell, DB3 and DB2, which collected unselectively from at least 6 +/- 1 cones, including the S type. Cone contacts to DB3 dendrites were usually located between neighboring triads, whereas half of the cone contacts to DB2 were triad associated. Ribbon outputs were as follows: DB3, 69 +/- 5; DB2, 48 +/- 4. A complete parasol cell (30 microm dendritic field diameter) would collect from approximately 50 cones via approximately 120 bipolar and approximately 85 amacrine contacts; a complete garland cell (25 microm dendritic field) would collect from approximately 40 cones via approximately 75 bipolar and approximately 145 amacrine contacts. The bipolar types contributed differently: the parasol cell received most contacts (60%) from DB3, whereas the garland cell received most contacts (67%) from DB2. We hypothesize that DB3 is a transient bipolar cell and that DB2 is sustained. This would be consistent with their relative inputs to the brisk-transient (parasol) ganglion cell. The garland cell, with its high proportion of DB2 inputs plus its high proportion of amacrine synapses (70%) and dense mosaic, might correspond to the local-edge cell in nonprimate retinas, which serves finer acuity at low temporal frequencies. The convergence of S cones onto both types could contribute S-cone input for cortical areas primary visual cortex and the middle temporal area.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA. david.j.calkins@vanderbilt.edu
authors.forename: David J
authors.initials: DJ
authors.lastname: Calkins
authors.forename: Peter
authors.initials: P
authors.lastname: Sterling
mesh_terms: D025042:Amacrine Cells / Q000502:physiology; D000818:Animals; D002450:Cell Communication; D003712:Dendrites / Q000502:physiology / Q000648:ultrastructure; D005584:Fovea Centralis / Q000166:cytology* / Q000502:physiology* / Q000648:ultrastructure; D007091:Image Processing, Computer-Assisted; D008252:Macaca fascicularis; D008297:Male; D008854:Microscopy, Electron; D009434:Neural Pathways / Q000502:physiology; D051245:Retinal Bipolar Cells / Q000145:classification / Q000502:physiology* / Q000648:ultrastructure; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology; D013569:Synapses / Q000502:physiology*