Uptake of Phaseolus vulgaris leucoagglutinin (PHA-L) by axons of passage.

Iontophoretic injection of Phaseolus vulgaris leucoagglutinin (PHA-L) into the spinal trigeminal tract, the trapezoid body or the inferior cerebellar peduncle produced extensive labelling of axons of passage. Anterograde transport labelled axon terminals more than 13 mm distant and retrograde transport labelled cells more than 3 mm distant. Axons of passage were labelled with both PHA-L and biotinylated PHA-L, and were observed following injection with different micropipette tip sizes, different durations of iontophoresis, and with continuous or pulsed iontophoretic current. The results suggest that while different injection parameters may influence the number of axons that are labelled, the possibility of labelling axons of passage should be considered whenever PHA-L is used.