PHA-L can be transported anterogradely through fibers of passage.

Iontophoretic injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) were restricted to the dorsal columns in the spinal cords of 9 rats. In 5 of these, labeling was found in the dorsal column nuclei, indicating that fibers of passage can transport PHA-L. However, labeled fibers were less dense and less intensely stained than those seen following similar injections that involved the dorsal horn.