Retrograde transport of radioactivity along axons of ascending cerebellar pathways after injection of N-[3H]acetyl-D-mannosamine into the mesencephalon of the rat.

Either the sialic acid precursor N-[3H]acetyl-D-mannosamine ([3H]ManNAc) or horseradish peroxidase (HRP) or both were injected into the mesencephalon of 15 rats. Localisation of radioactivity was performed by light microscopic autoradiography and HRP was histochemically localised with 3,3'-diaminobenzidine. After injection of either [3H]ManNAc or HRP, cell bodies in the central cerebellar nuclei were filled with radioactivity or HRP respectively. The distribution over contra- and ipsilateral interposed, dentate and fastigial nuclei of [3H]ManNAc-labelled and HRP-labelled cells is similar for both types of labelling. Since HRP is known to be transported retrogradely, a similar localisation of radioactivity-accumulating cells and HRP-filled cell bodies in the central cerebellar nuclei, lead us to the conclusion that radioactively-labelled ManNAc or its derivatives are also retrogradely transported in this system. There seem to be two possibilities for label uptake in afferents axons: (1) the uptake into axons which are disrupted by the injection needle and (2) the uptake by intact nerve endings or axons. After injection of [3H]ManNAc, the neuropil of central cerebellar nuclei shows a higher concentration of silver grains than the labelled cell bodies. This could be due to labelled dendrites caused by retrograde transport.