Marking of olfactory axons of fishes by intravital staining with Procion brilliant yellow.

Olfactory axons of fishes can be traced after vital staining of the olfactory surface with the fluorescent dye Procion brilliant yellow M 4-RAN. Following selective accumulation by the receptor dendrites and perikarya the dye migrates intra-axonally over distances of more than 200 micrometer. Fluorescence microscope observation of formaldehyde fixed and paraffin sectioned preparations of the olfactory organ demonstrate clearly the system of intraepithelial axons and their first order bundles running toward the olfactory nerve.