Effect of serum hyperosmolality on morphometry of healthy human sural nerve

Fascicles of human sural nerve, fixed by immersion in isosmolar 2.5% glutaraldehyde solution and in isosmolar osmium tetroxide and embedded in epoxy, undergo a 10% shrinkage in area when compared with cryostat sections. By contrast, fascicles fixed in hyperosmolar solutions (whether 5.6% glutaraldehyde solution or 2.5% glutaraldehyde raised to the same level of hyperosmolality with sucrose) undergo a 43% shrinkage in area. Axis cylinders of myelinated fibers undergo a selective and severe shrinkage and assume noncircular shapes, the shapes allowing the transverse area to decrease when the perimeter remains unchanged. These studies raise the intriguing question of whether interstitial hyperosmolality in metabolic diseases, such as diabetes mellitus, or in uremia may cause osmotic axonal shrinkage, altered transverse fiber shape, and abnormality of function and structure of nerve.