Axonal Synapses Utilize Multiple Synaptic Ribbons in the Mammalian Retina
Figure 5
3D reconstruction of calbindin negative ON and OFF cone bipolar cell axons in the IPL.
A: Three different types of calbindin negative OFF cone bipolar cells (green) and seven calbindin negative ON cone bipolar cells (slate blue). The ON bipolar cells can be divided into at least 4 different types according to the branching level of the axon terminals. In these cells, only two different ON cone bipolar cells, which ramified in strata 4 and 5, made axonal synapses (boxes) in stratum 1 of the IPL. The second boxed area is shown in B and C at a higher magnification. B, C: These micrographs were taken from two consecutive ultrathin sections. The unlabeled ON cone bipolar axon (BC) makes axonal inputs onto a monadic amacrine process (A). At this axonal synapse, three ribbons (arrowheads) are engaged.