# Nanoscale dynamics of synaptic vesicle trafficking and fusion at the presynaptic active zone

## TL;DR

This study uses super-resolution imaging to show how synaptic vesicles move and release neurotransmitters at synapses in retinal neurons.

## Contribution

The study reveals the synaptic ribbon's dual role in vesicle transport and fusion, enabling continuous neurotransmitter release.

## Key findings

- The synaptic ribbon acts as a conduit for vesicle diffusion and a platform for compound fusion.
- The ribbon-type CAZ supports both fast and sustained neurotransmitter release in retinal synapses.

## Abstract

The cytomatrix at the active zone (CAZ) is a macromolecular complex that facilitates the supply of release-ready synaptic vesicles to support neurotransmitter release at synapses. To reveal the dynamics of this supply process in living synapses, we used super-resolution imaging to track single vesicles at voltage-clamped presynaptic terminals of retinal bipolar neurons, whose CAZ contains a specialized structure—the synaptic ribbon—that supports both fast, transient and slow, sustained modes of transmission. We find that the synaptic ribbon serves a dual function as a conduit for diffusion of synaptic vesicles and a platform for vesicles to fuse distal to the plasma membrane itself, via compound fusion. The combination of these functions allows the ribbon-type CAZ to achieve the continuous transmitter release required by synapses of neurons that carry tonic, graded visual signals in the retina.