Wheat Germ Agglutinin (WGA) Tracing: A Classic Approach for Unraveling Neural Circuitry

Neuroanatomical tracing is a fundamental technique that has long been considered the primary method for visualizing brain networks in all areas of neuroscience. Although there are many new approaches for tracing neuronal connections, the lectin-based wheat germ agglutinin (WGA) tracing approach is still widely used, and it is firmly regarded as a classic method in the field. WGA has been used extensively to unravel both simple and complex neural networks in the central and peripheral nervous systems. It is reliable and versatile, as projections are labeled in the anterograde and retrograde directions. It is robust enough for tracking fine pathways in small animals, and it is stable enough for long-term tracing of neurons in large species. In some systems, WGA can even travel transynaptically to label the connected neurons. In this chapter, we outline the technical and conceptual details that have made WGA a powerful tool, and we discuss practical considerations for effectively using WGA. We also discuss the recent use of an Alexa conjugated WGA approach for multicolor labeling of different tracts in the same animal.