Morphological study of erythrocyte shapes in red pulp of mouse spleens revealed by an in vivo cryotechnique

The purpose of this study was to clarify erythrocyte shapes in splenic cords of living mouse spleens, using our in vivo cryotechnique followed by scanning (SEM) or transmission (TEM) electron microscopy. Some spleens of mice were quickly frozen by the in vivo cryotechnique while their hearts were beating under anesthesia. In contrast, other spleens were prepared by an in vitro freezing method after they were taken out from the abdominal cavity. They were routinely freeze-substituted, and prepared for SEM and TEM. A few mouse spleens were also routinely fixed and embedded in Quetol-812 to obtain conventional morphology. Erythrocytes in living mouse spleens showed a variety of shapes with narrow spaces between them, trapped among reticular fiber tissues. Similar various shapes of erythrocytes were kept in the red pulp even after blocking normal blood circulation, as prepared by the in vitro freezing method. In comparison to the above-mentioned findings, some erythrocytes were changed to biconcave discoid shapes by the conventional immersion fixation with chemical fixatives. They also showed wide spaces between each other among reticular fiber tissues. Such conventional morphological studies could hardly reveal the in vivo shapes of erythrocytes in functioning spleens with normal blood circulation. In contrast, the various shapes of erythrocytes in the functioning spleens were demonstrated by our in vivo cryotechnique. It is suggested that most erythrocytes congesting in spleens keep their original configuration in spite of microenviromental alteration in splenic blood circulation.