Calkins David J, Sterling Peter
Department of Ophthalmology and Visual Sciences, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA.
J Neurosci. 2007 Mar 7;27(10):2646-53. doi: 10.1523/JNEUROSCI.4739-06.2007.
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.
灵长类动物中央凹的突触回路已针对侏儒/小细胞神经节细胞进行了量化。在此，基于连续电子显微镜的部分重建，我们对另外两种类型的神经节细胞的突触回路进行了量化：常见的伞状/大细胞以及一种较小类型的“花环”细胞。兴奋性回路均源自两种类型的OFF弥散型视锥双极细胞，即DB3和DB2，它们从至少6±1个视锥细胞无选择性地收集信息，包括S型视锥细胞。视锥细胞与DB3树突的接触通常位于相邻三联体之间，而与DB2视锥细胞接触的一半与三联体相关。带状突触输出如下：DB3为69±5；DB2为48±4。一个完整的伞状细胞（树突野直径为30微米）将通过大约120个双极细胞和大约85个无长突细胞接触从大约50个视锥细胞收集信息；一个完整的花环细胞（树突野为25微米）将通过大约75个双极细胞和大约145个无长突细胞接触从大约40个视锥细胞收集信息。双极细胞类型的贡献有所不同：伞状细胞大部分接触（60%）来自DB3，而花环细胞大部分接触（67%）来自DB2。我们假设DB3是一种瞬态双极细胞，而DB2是持续性的。这将与其对快速瞬态（伞状）神经节细胞的相对输入相一致。花环细胞具有高比例的DB2输入、高比例的无长突细胞突触（70%）和密集镶嵌，可能对应于非灵长类视网膜中的局部边缘细胞，其在低时间频率下提供更精细的视敏度。S视锥细胞与这两种类型的汇聚可能为初级视皮层和颞中区的皮层区域提供S视锥细胞输入。
