Permeability barriers to cytochrome-c in nerves of adult and immature rats.

Nerves in the tongues of adult and immature rats were examined with respect to their permeability to exogenous cytochrome-c (mol wt 12,000) injected into the tongue. The distribution of cytochrome-c was determined in cryostat sections on the basis of the peroxidase activity of this protein. Nerves of 14-day-old rats were permeable to injected cytochrome-c. The larger nerves of older animals showed only localized accumulations of cytochrome-c reaction product both between and within axons adjacent to endoneurial blood vessels. Reaction product was not found, however, in association with blood vessels penetrating nerves of the tongue that were not within the limits of tracer spread. In the smallest nerve brances, thin linear strands of reaction product filled the interstices between the nerve fibers.