Phenotyping of Gap-Junctional Coupling in the Mouse Retina

In the mammalian retina, gap junctions, made of connexin proteins, are found in all neuronal cell types and are important for the transmission of rod photoreceptor signals, spike synchronization, noise reduction, and signal averaging. There are several methods available to assess gap junctional coupling in the retina: simultaneous electrical recordings from two adjacent cells, cut-loading, and intracellular injection of gap junction-permeable tracers. Here, we focus on the latter as it allows precise targeting of the cell of interest and is suitable to assess tracer coupling in a wide variety of retinal cell types, e.g., horizontal cells, amacrine cells, and ganglion cells. Tracer coupling experiments are usually performed in the intact retina and can provide information on the extent of coupling, the identity of synaptic partners, and (when combined with immunohistochemistry or pharmacology) the underlying connexin or the regulation of gap junctions.