Schwann cell multiplication after crush injury of unmyelinated fibers.

The intensity and duration of Schwann cell multiplication in unmyelinated fibers after crush injury of cervical sympathetic trunks (CSTs) in adult mice was studied using radioautography and electron microscopy. At the level of crush, labeling indexes rose to 22.5% on the second day after injury, but distal to this level, labeling reached a peak of only 2.5%. By the ninth day labeling declined to 1% or less at both sites. Electron microscopy confirmed that the increase in nuclei at the crush was mainly an increase in Schwann cells. Thus, the intensity of Schwann cell multiplication differed between crush and distal sites along the same unmyelinated nerve. The Schwann cell proliferation in the distal CSTs was less intense than that reported in previous studies on myelinated nerves.