Extracellular space and membrane changes in brain owing to different alkali metal buffers

Summary

Various alkali metal buffers were used in combination with glutaraldehyde, formaldehyde and acrolein to fix rat visual cerebral cortex by perfusion. Standard procedures of post-fixation, dehydration, and embedding were followed so that the buffer became the experimental variable. The cacodylate buffer system proved most versatile, and caesium, rubidium, potassium, sodium, and lithium cacodylate were used. An unusual amount of extracellular space averaging 300 nm was present with caesium cacodylate which contrasted with the apposed plasma membranes prevalent when lithium or sodium cacodylate was used. Rubidium and potassium cacodylate produced similar results with variable and irregular extracellular space. The effects of the addition of dimethyl sulphoxide, magnesium chloride and calcium chloride to the various cacodylate buffers were explored. In the case of caesium cacodylate, these additives caused less extracellular space and the retention of more material in this space in an irregular manner; with potassium cacodylate there was no noticeable difference, but with sodium and lithium cacodylate extracellular space increased. We suggest that the observed differences in extracellular space are explanable in terms of changes occurring in the polysaccharide cell coat which are caused by the buffers and additives.