Endoneurial fibrosis following nerve transection. An immunohistological study of collagen types and fibronectin in the rat.

Indirect immunofluorescent techniques with antibodies to type I, III, and V collagens and fibronectin were used to study rat sciatic nerve tributaries after transection with intact contralateral nerves as controls. Codistribution of type I and III collagens characterized the epineurium of normal nerve. In the perineurium, however, type I collagen was absent, but type III and V collagens and fibronectin were detected. Type I and III collagens were codistributed in the endoneurial stroma where a homogeneous staining by antibodies to fibronectin was also observed. During the 4-week observation period after transection the perineurium reacted by slight thickening which was most clearly demonstrated by staining with antibodies to fibronectin and to type V collagen. A widening of the type I-negative cleft also occurred. Endoneurial, type V collagen-positive cuffs around the nerve fibers became disorganized, and a concomitant increase of the stroma containing type I and III collagens and fibronectin was observed. The codistribution of the fibrous collagen types appeared similar in normal epineurium and endoneurium. Type V collagen was located in the perineurium and in endoneurial cuffs surrounding the nerve fibers. The present data indicate that collagen accumulation takes place in the perineurium and endoneurium of transected nerve. The cell type responsible for the synthesis of the connective tissue material is discussed.