REGENERATING AXONS IN BASAL LAMINA TUBES OF NONNEURAL TISSUE

In order to examine the behavior of regenerating axons in the basal lamina tube of non-neural tissue, tissue blocks of renal medulla and skeletal muscle were grafted to the sciatic nerve of the host mouse after the blocks had been treated by repeated freezing and thawing, and the growth of the regenerating axons in the graft was examined 2, 4 and 7 days after grafting. The manner in which regenerating axons grew out through basal lamina tubes were compared with the case of nerve graft. The basal laminae of the grafted tissues were left almost intact in the form of tubes after cellular elements had been degraded. Regenerating axons were observed almost exclusively inside the basal lamina tubes derived from renal tubules, skeletal muscle fibers and capillaries. Growth cones of regenerating axons were usually attached to the inner surface of the tubes, whereas axon shafts were rarely in contact with the basal lamina. Growth cones attached to the basal lamina by filopodium-like short processes and/or by their main body. These findings suggest that the basal lamina of non-neural cells differs in components on its inner surface from Schwann cells and that, unlike the case of Schwann cell basal lamina, regenerating axons (except their growth cones) cannot effectively attach themselves to the basal lamina of non-neural cells.