The distribution of serum albumin in rat peripheral nerve.

To clarify the nature of the blood-nerve barrier (BNB) in excluding serum proteins from peripheral nerve endoneurium, we studied the ultrastructural distribution of albumin in peripheral nerve using light and electron microscopic immunocytochemistry. We found that serum albumin is commonly found within the endoneurium, but that it is not normally found intraaxonally. After subperineurial injection of labeled albumin, the albumin redistributed within intrafascicular clefts towards the perivascular spaces and the perineurium. These results suggest that, contrary to previous evidence, axons are exposed to serum proteins in normal nerves, and implies that they may be subject to interaction with abnormal proteins or altered serum proteins without any disruption of the BNB.