Optical Approaches to Dissect the Structure and Dynamics of the Synapse at Nanoscale Resolution

The complex nanostructure and spatiotemporal dynamics of central synapses remain among the fundamental mysteries of neurobiology. The resolution of traditional microscopy techniques-constrained by the intrinsic limits of light diffraction-is largely insufficient to study central synapses effectively. Conventional imaging can resolve areas roughly the size of a synapse's active zone, that is, severalfold larger than the size of synaptic vesicles. Recent advances have generated several super-resolution imaging modalities that overcome or bypass the light diffraction limit to support studies of synaptic nanostructure. In this chapter, we present the principles, features, and limitations of the most common super-resolution imaging tools. Though these advancements have greatly improved our understanding of synaptic architecture and dynamics, significant challenges remain. Difficulties of translating the existing tools to in vivo applications, and the inherent trade-off between spatial and temporal resolution, continue to limit studies of the function of central synapses in native tissue.