RETENTION OF GLYCOGEN IN CRYOSUBSTITUTED MOUSE-LIVER

A periodic acid-Schiff (PAS)-type reaction in which osmium-ammmine was used as the reagent was carried out on ultrathin sections of mouse li ver in order to study the extent to which glycogen is preserved. Compa risons were made between tissues that were, on the one hand, conventio nally fixed and dehydrated and, on the other, those that were high-pre ssure frozen and cryosubstituted in acetone. A control was carried out for both groups using a routine uranyl acetate-lead citrate staining procedure. In the latter case, glycogen could be identified as electro n-clear patches in the cytoplasm whereas after a PAS-type reaction, gl ycogen became darkly contrasted. In the case of conventionally fixed s amples, glycogen appeared to display a certain amount of clumping sepa rated by gaps whereas in cryosubstituted specimens it was denser and o ften showed elongated interconnecting structures. These results sugges t that cryofixation and cryosubstitution provide better preservation o f glycogen in mouse liver tissue compared with chemically fixed specim ens. In addition, the fine structure of glycogen appears more homogene ous, showing less aggregation in cryo-treated liver samples.