Analysis of Neuro-Neuronal Synapses Using Embryonic Chick Ciliary Ganglion via Single-Axon Tracing, Electrophysiology, and Optogenetic Techniques

The calyx-type synapse is a giant synaptic structure in which a presynaptic terminal wraps around a postsynaptic neuron in a one-to-one manner. It has been used for decades as an experimental model system of the synapse due to its simplicity and high accessibility in physiological recording methods. In particular, the calyx of the embryonic chick ciliary ganglion (CG) has enormous potential for synapse science because more flexible genetic manipulations are available compared with other synapses. Here, we describe methods to study presynaptic morphology, physiology, and development using CGs and cutting-edge molecular tools. We outline step-by-step protocols for presynaptic gene manipulation using in ovo electroporation, preparation of isolated CGs, 3-D imaging for single-axon tracing in transparent CGs, electrophysiology of the presynaptic terminal, and an all-optical approach using optogenetic molecular reagents. These methods will facilitate studies of the synapse and neuronal circuits in the future. © 2019 by John Wiley & Sons, Inc.