Fixation of the central nervous system for electron microscopy by aldehyde perfusion: I. Preservation with aldehyde perfusates versus direct perfusion with osmium tetroxide with special reference to membranes and the extracellular space

Abstract

Glutaraldehyde, formaldehyde, and osmium tetroxide perfusion fixation of the central nervous system of rats were compared and evaluated. Aldehyde fixation was considered superior to the direct osmium tetroxide fixation with respect to methodological considerations and at least equal with respect to fixation criteria. Use of gas mixture, prewash, vasodilator drugs, and low temperature perfusate were not found necessary with aldehyde perfusion. A very close cell-to-cell membrane relationship is universally found, restricting the extracellular space to considerably less than that previously reported. The possible significance of the general absence of extracellular space is discussed. Certain ultrastructural differences of osmium tetroxide and aldehyde perfusion fixation are described. An attempt also has been made to visualize the first signs of perfusion fixation through a hole in the skull during perfusion.