MULTIPOTENTIALITY OF SCHWANN-CELLS IN CROSS-ANASTOMOSED AND GRAFTED MYELINATED AND UNMYELINATED NERVES - QUANTITATIVE MICROSCOPY AND AUTORADIOGRAPHY

Cross-anastomoses and autogenous grafts of unmyelinated and myelinated nerves were examined by electron microscopy and radioautography to determine if Schwann cells were multipotential with regard to their capacity to produce myelin or to assume the configuration seen in unmyelinated fibers. Two groups of adult white mice were studied. In 1 group the myelinated phrenic nerve and the unmyelinated cervical sympathetic trunk (CST) were cross-anastomosed in the neck. From 2-6 mo. after anastomosis, previously unmyelinated distal stumps contained many myelinated fibers, while phrenic nerves joined to proximal CST became largely unmyelinated. Radioautography of distal stumps indicated that proliferation of Schwann cells occurred mainly in the first few days after anastomosis but was also present to a similar extent in isolated stumps. In other mice CST were grafted to the myelinated sural nerves in the leg. One month later, the unmyelinated CST became myelinated, and there was no radioautographic indication of Schwann cell migration from the sural nerve stump to the CST grafts. Schwann cell proliferation in distal stumps is apparently an early local response independent of axonal influence. At later stages axons from the proximal stumps caused indigenous Schwann cells in distal stumps from the previously unmyelinated nerves to produce myelin while Schwann cells from the previously myelinated nerves became associated with unmyelinated fibers. Consequently, the regenerated distal nerve resembled the proximal stump. This change may be possible because Schwann cells which divide after nerve injury reacquire the developmental multipotentiality which permits them to respond to axonal influences.