Retrograde axonal transport of horseradish peroxidase for determining motor projection patterns to the developing limb in Xenopus.

Horseradish peroxidase (HRP) injected into developing limb buds of Xenopus laevis tadpoles is carried by retrograde axonal transport to the somata of motoneurones in the ventral horn. Small injection of 10% HRP were found to remain well localised to specified sites in the limb bud. Two types of labelled cells were found: diffusely labelled and granular labelled. Diffusely labelled cells result from axonal damage in the presence of HRP. Granular labelled cells result only from uptake of HRP from the region of the axon endings. No gradular uptake was found from axon shafts. It is concluded that the distribution of granular labelled cells accurately reflects the region of the ventral horn projecting to the site of injection in the limb.