Biotin-dextran is used in tissue staining to prepare neurons for detection by avidin-conjugated detection systems. It is taken up by neuronal processes and transported bi-directionally. It infiltrates axon boutons in the anterograde direction and dendritic processes in the retrograde direction. Staining can be observed in fixed and sectioned tissue from two days to two weeks after biotin-dextran is injected into the brain or spinal cord. It can also be applied to cut nerve tracts. Biotinylated neurons are detected by either light or electron microscopy following incubation with avidin-horseradish peroxidase conjugate and the electron-dense substrate 3,3′-diaminobenzidine (DAB).