Functional and structural changes in the rabbit vagus nerve in vivo following exposure to various hypoosmotic solutions.

Hypoosmolar solutions were recently shown to produce a reversible conduction block of rabbit vagus nerve and to potentiate local anesthetic agents. The object of the present study was to determine the ability of neural tissue to recover structurally and functionally following exposure to hypoosmotic solutions. Cervical vagus nerves of rabbits were bathed in situ for 2 hours in a control solution or in 0.4, 0.5, and 0.6 aqueous dilutions of physiologic salt solution. Nerves excised immediately after exposure, or 1 to 4 weeks later, were subjected to light and electron microscopic examination. Following exposure to control and 0.6 dilution, nerves were normal in all respects at 8 days. However, nerves exposed to 0.4 and 0.5 dilutions, although apparently functionally intact as tested by conduction of C fiber action potentials, showed evidence of axonal damage characterized by accumulation of macrophages and proliferation of Schwann cell processes. It may be inferred that the osmotic fragility of axons is similar to that of erythrocytes and that immersion in 0.6 N osmotic solution is probably harmless to the nerve.