Schwann cell plasma membrane changes induced by nerve crush. A freeze-fracture study

Twenty-four hours after nerve crush, the Schwann cell plasma membrane and subjacent outer layer of Schwann cell cytoplasm were examined by freeze-fracture in myelinated fibres from the rat and rabbit sciatic nerves. The irregular circumferential bands and longitudinal columns of cytoplasm which characterise the surface of the normal Schwann cell were diminished or had disappeared. Concomitantly, the membrane pores (of micropinocytotic vesicles or caveolae) which are normally present on the bands and columns were also lost. The loss of these specialised features is discussed in terms of the onset of cell dedifferentiation in association with cell division. The Schwann cell plasma membrane acquired a new feature: deep impressions of adjacent collagen fibres, present particularly on the cytoplasmic bands and columns and presumed to be related to a transient increase in fibre diameter.