Evidence for vesicular transport of horseradish peroxidase across endoneurial vessels of the sciatic nerve in normal mice.

The permeability of the endoneurial blood vessels of the sciatic nerve to horseradish peroxidase (HRP) was investigated in mice. The animals were killed 2,5, or 30 min after an i.v. injection of the protein, and the distribution of HRP in the sciatic nerve was studied by light and electron microscopy. HRP was frequently found in endothelial vesicles that were located near both the luminal and the abluminal side of the endothelium. The intercellular junctions appeared to be closed to HRP. The perivascular and interstitial macrophages in the endoneurium accumulated HRP by endocytosis. The results are interpreted as evidence for vesicular transport of HRP across endoneurial vessels to interstitial and perivascular macrophages.