Vascular permeability and axonal regeneration in tissues autotransplanted into the brain.

Pieces of skin, peripheral nerve, muscle, tendon, thyroid gland, and submandibular gland were autotransplanted into the brains of mice. The animals were killed after 5-week periods. Fluorescently labelled albumin was injected i.v. 1 h prior to death. Silver-impregnated sections were examined under the light microscope for the regeneration of axons from the brains into the implanted tissues. Unstained sections were studied by fluorescence microscopy for the presence of the labelled tracer in the extracellular spaces of the grafts. The muscle and submandibular gland received the fewest regenerating axons, skin and tendon received an intermediate amount of reinnervation, and the thyroid gland and vagus nerve were the most richly innervated. The amount of reinnervation could be roughly correlated with the presence of extravascular protein within the tissues. These data support the hypothesis that regeneration of axons may be dependent upon a source of protein in the extracellular fluid surrounding their growing tips.