Cryoultramicrotomy--recognition of artifacts.
Frozen thin sections are considered as the ideal specimen for high resolution studies on the morphological and chemical composition of biological material. However, during the preparation of such sections alterations may be induced. Ice crystal formation during freezing may limit the useful area to a superficial layer of the frozen sample. Heating and/or melting whenever occurring during sectioning will not result in detectable redistribution of material within the sections. Freeze-drying within the cold chamber of the microtome occurs at a slower rate (approx. 5 x 10(-3)) than the maximum rate of drying under vacuum. Rehydration of dry sections in a moist atmosphere or by contact with aqueous solutions will result in typical structural alterations probably caused by redistribution of material. Vapor fixation of the freeze-dried sections will prevent these structural alterations whereas aldehyde fixation in aqueous solutions prior to freezing may not always be sufficient to prevent structural alterations. When fully hydrated thin sections are required low temperature sectioning is necessary to prevent freeze-drying. Embedding and resectioning of such sections cut at -105 degrees C revealed that one of the surfaces was distorted by a saw-teeth form of chatter, the other side was flat. Low temperature sectioning and cryotransfer enabled the study of fully hydrated sections at the resolution of a STEM as well as the observation of the freeze-drying process under vacuum.
D000818:Animals; D005612:Freeze Drying; D005615:Freezing; D006652:Histological Techniques; D007668:Kidney / Q000648:ultrastructure*; D008855:Microscopy, Electron, Scanning; D051381:Rats