Behavior of axons, Schwann cells and perineurial cells in nerve regeneration within transplanted nerve grafts: effects of anti-laminin and anti-fibronectin antisera.

Wistar rats (close cloned strain) were used to investigate the effect of endogenous laminin and fibronectin on axons, Schwann cells and perineurial cells in the regenerating peripheral nervous system (PNS). Sciatic nerve grafts obtained from donor rats were frozen, thawed and treated with rabbit anti-rat laminin or anti-fibronectin antiserum. Control grafts were treated with normal rabbit serum alone. One cm long portions of the sciatic nerve of the recipient rats were replaced with grafts. At 15 days after transplantation the number of regenerated axons in the laminin- and fibronectin-depleted grafts was half of that in the control. The growing axons in the laminin-depleted grafts did not recognize the basal lamina scaffolds (BLS) remaining in the basal lamina tubes, while in the control and fibronectin-depleted grafts 90% or more of axons grew inside the BLS. Elongation of axons always preceded migration of Schwann cells with the latter subsequently adhering to and wrapping around the former. Perineurium-forming fibroblastic cells recognized the combination of axons and Schwann cells and formed perineurial fasciculi around them. These fibroblastic cells did not recognize empty BLS but responded to them only when fibronectin was depleted. Macrophages sometimes closely faced the naked axons which elongated outside the BLS. These results suggest that in the early stages of nerve regeneration endogenous laminin and fibronectin not only regulate the growth of regenerating nerve fibers, but also exert a positive influence on perineurial cells and macrophages, both of which play important roles in nerve tissue injury and repair.