Tracing axons.

For more than a century, neuroscientists have gained insight into brain function by examining its complex patterns of connectivity. To achieve this, a wide variety of axon-tracing techniques have been employed to chart the projections of neurons. New, experimentally flexible, reporter-based tracers, many of which are fusion proteins designed to target axons and dendrites, are being developed and are assisting the molecular characterization of the nervous system.