Fig. 10: Connectomic reconstruction identifies midget and DB4/5 cone bipolar types as presynaptic to the starburst amacrine.

a Reconstructed starburst amacrine cell (teal; see Fig. 9) showing 3 cone bipolar cells with large axon terminals (blue) and three cone bipolars with small axon terminals (gold). The three large blue bipolar terminals are all presynaptic to the starburst. The two most proximal small gold bipolar terminals are also presynaptic to the starburst cell; the distal small bipolar overlaps but does not synapse with the starburst. Hairpin turn in starburst dendrite denoted by black arrowhead (see Fig. 9a, g also). b Complete reconstruction of a midget ganglion cell within the starburst dendritic field (midget cell identified by its uniquely small dendritic field size at this retinal eccentricity). The small gold bipolar-cell axon terminals are enmeshed by the ganglion cell dendrite and provide profuse synaptic input to this midget ganglion cell (25, 34, 27 ribbons synapses each from the three midget bipolar cells shown; this midget ganglion cell received a total of 405 ribbon synaptic inputs; the vast majority, ~90% were derived from midget bipolar cells) identifying them as midget bipolar cells. c Zoomed view of boxed area in b illustrates the close association of midget bipolar and midget ganglion cell for the two bipolars that also contact the starburst amacrine. d, e Two examples of ribbon synapses from midget bipolar (gold) to midget ganglion cell dendrites (purple). f partial reconstruction of an inner (ON center) parasol ganglion cell (orange; identified by uniquely large soma diameter) receives synaptic input from the 3 large (blue) bipolar terminals (~5 synapses/bipolar, 16 ribbon synapses total). Since inner parasol cells receive their major synaptic input from diffuse bipolar (DB) cell types 4 and 5 we identify this bipolar type as DB4/5 (these two types are not easily distinguishable (see main text). Hairpin loop in starburst amacrine (teal, black arrowhead) is created by wrapping around the primary dendrite of this parasol cell. g, h Two examples of ribbon synapses from the DB4/5 bipolars onto the dendrites of the parasol cell shown in (f).