A simple method of in vitro electroporation allows visualization, recording, and calcium imaging of local neuronal circuits.

Since Cajal's early drawings, the characterization of neuronal architecture has been paramount in understanding neuronal function. With the development of electrophysiological techniques that provide unprecedented access to the physiology of these cells, experimental questions of neuronal function have also become more tractable. Fluorescent tracers that can label the anatomy of individual or populations of neurons have opened the door to linking anatomy with physiology. Experimentally however, current techniques for bulk labeling of cells in vitro often affect neuronal function creating a barrier for exploring structure-function questions. Here we describe a new technique for highly localized electroporation within a cell or cell population that enables the introduction of membrane impermeable charged dyes including dextran-conjugated fluorophores, hydrazide tracers, and calcium indicator dyes in vitro. We demonstrate that this technique is highly versatile, allowing for labeling of large or small areas of tissue, allowing for the investigation of both cellular morphology and physiological activity in identified neuronal circuits in acute brain slices. Furthermore, this approach allows subsequent targeted whole-cell patch recording based on well-defined connectivity as well as assessment of physiological activity in targeted circuits on a fast time scale.