[Electron microscopic observation of cells ensheathing axons and their association with basal lamina in sciatic-nerve-grafted spinal cords].

In transected and reanastomosed peripheral nerve, cells proliferate in the scar which unites the proximal and distal cut ends of the nerve. Those cells are considered to produce favorable effects on the advancement of naked axons, and ultrastructural studies have revealed that the naked axons are partially or completely ensheathed by cells in the union scar. On the other hand, in a spinal cord model, structure with a histological appearance similar to that of the union scar in the transected peripheral nerve has been produced experimentally by delayed autogenous sciatic nerve grafting into the transected spinal cord gap. In the present study, the same spinal cord model was used and an electron microscopic study of the junctional area between the spinal cord and grafted nerve was carried out in an attempt to answer the following questions: (1) Do cells in the spinal cord-nerve graft junction ensheath axons? And, if so, (2) is it possible to identify these cells? Five adult dogs were used for the experiment. One week after the first spinal cord transection, the wound was opened, necrotic materials in the gap were carefully removed microsurgically, and segments of autogenous sciatic nerve were placed in the gap of the spinal cord. The dogs were killed at 1 and 3 weeks, 3, 9 and 12 months after the delayed nerve grafting and electron microscopic observations were made. The cells which ensheathed axons at the graft junction were classified into five morphologically identifiable cell types: migratory Schwann cells, committed Schwann cells, astrocytes, oligodendrocytes and macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)