Real electron microscopic images of collagen fibrils in the endoneurium.

Collagen fibrils run in parallel in the endoneurial space, forming fibre bundles. Spaces are evident between these bundles when examined by transmission electron microscopy (TEM). However, the procedures for TEM include chemical fixation, dehydration and embedding, which may cause morphological changes in the specimens. Ultracryo thin sectioning procedures may avoid the artefacts caused by these procedures. An examination of ultrathin frozen sections revealed that the endoneurial space was completely filled with collagen fibrils, with little space between the fibre bundles. These results suggest that the dehydration and/or embedding procedures cause shrinkage of the specimen, resulting in the appearance of a widened space in the endoneurium. Therefore, the widened space between the bundles of collagen fibrils may be a technical artefact.