Uptake and retrograde axonal transport of protein tracers in hypoglossal neurons

Summary Protein tracers (albumin labelled with Evan's blue and horseradish peroxidase) accumulate in the cytoplasm of hypoglossal neurons in the brain stem following injection into the tongue of rats and mice resulting apparently from axonal uptake and subsequent retrograde transport from the periphery. The present study was performed to follow the fate of the protein tracers and to find out if they induce any signs of neuronal necrosis.The proteins remained in the nerve cell bodies for about 6–11 days as revealed by fluorescence microscopy and light microscopical enzyme histochemistry after the injection into the tongue. Thereafter the proteins disappeared from the neurons presumably as a result of lysosomal degradation. The incorporation of foreign proteins did not produce as observed by light and electron microscopy any signs of cell degeneration.