Cryo-electron microscopy of vitrified nerve myelin.
The ultrastructure of rat optic and trigeminal nerve myelin was studied using different cryotechniques. Replicas of rapid cryofixed and deep-etched material were compared with cryosections of chemically unfixed specimens and also of glutaraldehyde-fixed specimens. Hydrated cryosections were analysed in a cryotransfer device. The data reported here show discrepancies with the current descriptions of myelin structure based on osmium-fixed and resin-embedded material. The structures called the major line (as a fusion of the cytoplasmic surfaces of the glial cells) in conventional electron microscopy and the intraperiod line (as a fusion of the outer surfaces) are seen in the present material to represent actually aqueous spaces. The extracellular space (E-space) is most sensitive to chemical fixation and other preparation procedures, and probably also expands under pathological conditions. The virtual C-space (cytoplasmic space = major line) is more stable. The cytoplasmic surfaces are most probably joined by globular proteins (myelin basic protein). The most compact organization of myelin is seen in fresh, unfixed nerves. A continuous bilayer could not be observed and the bilayer membrane showed particulate subunits.
Meller
K
K
Abteilung für Cytologie, Ruhr-Universität Bochum, Federal Republic of Germany.
D000818:Animals; D015925:Cryopreservation / Q000379:methods*; D005404:Fixatives; D005613:Freeze Etching; D008854:Microscopy, Electron / Q000379:methods*; D009186:Myelin Sheath / Q000648:ultrastructure*; D009992:Osmium; D051381:Rats
D005404:Fixatives; D009992:Osmium