Synapses of the inner plexiform layer in the retina of cyprinid fish.

Two types of synapses are known to occur in the inner plexiform layer of the vertebrate retina. The typical ribbon synapse has two postsynaptic elements, whereas the conventional synapse displays only one. Ribbon synapses are characteristic of bipolar cells, and the conventional synapses are seen in amacrine and interplexiform cells. Two varieties of conventional synapses with one postsynaptic element are described in the present study. One has the well-known presynaptic cluster of synaptic vesicles, whereas the other has several clusters surrounding dense globules. Furthermore, there are conventional synapses with two postsynaptic elements, called branched conventional synapses. They are most numerous in the middle of the inner plexiform layer and are characterized by a presynaptic aggregation of synaptic vesicles usually clustering around a dense globule. The neuronal processes with branched conventional synapses also have conventional synapses with one postsynaptic element and are therefore thought to be amacrine cell processes.