Freezing and drying of biological tissues with a toggle‐link helium freezer and an improved freeze‐drying apparatus: Application to neuropeptide immunocytochemistry

Abstract

AbstractA freezing apparatus has been developed for bringing blocks of tissue into contact with a block of sapphire chilled to 17°K. A toggle linkage minimizes rebound by slowing the rate of approach of the tissue to the cold surface to a velocity of zero. A glove box limits condensation on the surface of the sapphire, and a miniature moist chamber protects the specimen from drying and premature freezing. About 50 blocks of tissue can be frozen in an hour and a half by using 5 liters of liquid helium. The tissue is then frozendried at controlled temperature, fixed with OsO4 vapor, and infiltrated with epoxy resin in a simple bench‐top freeze‐drier without breaking vacuum. About two‐thirds of the blocks are useful for electron microscopy. Brain tissue frozen and dried by using these methods retains enough immunoreactivity for enkephalin in plastic sections to permit its detection with immunohistochemistry by using both the light microscope (with immunofluorescence) and the electron microscope (with colloidal gold).