Skip to main content
. 2019 Oct 2;39(40):7893–7909. doi: 10.1523/JNEUROSCI.0778-19.2019

Figure 4.

Figure 4.

Summary of the morphological and synaptic asymmetry for ON and OFF S-cone pathways in macaque fovea. A, Zoomed view looking down through an S-cone pedicle (not shown) at invaginating blue cone (S ON) bipolar (blue) and flat S-OFF midget bipolar (yellow) contacts, with the synaptic ribbon array (red). The blue cone (S ON) bipolar cells give rise to very large terminations that occupy all central element positions in the pedicle, while the remaining fraction of the pedicle face is occupied by the flat contacts of a single OFF midget bipolar cell. B, Another view looking down at a single S-cone ribbon array innervated by two branching and converging blue cone (S ON) bipolar dendritic trees (blue). In contrast, a single private-line connection of an OFF midget bipolar cell is present, in which a single stout dendrite forms a spray of terminal branches at the base of the pedicle (Fig. 1F). C, Two L/M OFF midget bipolar axon terminals (orange) and a single neighboring S-OFF midget bipolar terminal (yellow), with synaptic ribbons shown in red. S-OFF midget bipolar cell axon terminals show the typical midget morphology but exhibit fewer synaptic ribbons relative to their L/M cone counterparts (see Results). D, E, Fundamental differences in ON and OFF circuitry originating from S cones and L/M cones in foveal retina. D, On average, each S-cone pedicle synapses with 1.5 blue cone (S ON) bipolar cells (blue) and 1 OFF midget bipolar cell (yellow). The blue cone (S ON) bipolar projects an axon terminal to the inner border of the IPL where it synapses with the blue ON small bistratified ganglion-cell type (purple shades), while the OFF midget bipolar forms a private-line synapse with an OFF midget ganglion cell (yellow shades). E, Reconstruction of a complete L/M cone midget circuit. The L/M cone pedicle (yellow) synapses with a single ON (green) and OFF (orange) midget bipolar cell; these in turn form private-line synaptic complexes with an inner-stratifying ON (red) and outer-stratifying OFF (magenta) midget ganglion cell, respectively. The entire circuit is entwined in close physical proximity throughout its length (inset).