Blood-nerve barrier permeability to ions and nonelectrolytes is very low, indicating limited exchange between plasma and nerve endoneurium. The nerve barrier, unlike the blood-brain barrier, does not have a regulatory transport system for calcium. The integrity of the blood-nerve barrier to small nonelectrolytes is maintained with age in the rat. The blood- nerve barrier has regulated carriers for the transfer of manganese , neutral amino acids, and basic amino acids between plasma and nerve. In addition, cationized albumin is taken up into nerve at a greater rate than native albumin, possibly by receptor-mediated transcytosis. Permeabilities of both nerve capillaries and perineurium increase during the first few weeks of Wallerian degeneration. Nerve capillary permeability eventually returns to normal, but perineurial permeability remains elevated, suggesting that nerve fibers are required to maintain perineurial nerve barrier integrity.
