Cryoultramicrotomy: electrostatic transfer of dry ultrathin frozen sections on grids applied to the central nervous system.

Due to the extreme fragility of ultrathin frozen sections of brain tissue, the cryoultramicrotomy of non-embedded tissue has not been sufficiently used for immunocytochemical studies of the central nervous system. Sections are easily disrupted by the liquid surface tension when a droplet of sucrose is used (method by Tokuyasu, 1973) for their transfer on the grids. Use of silicotungstic acid (Tsuji, 1986) in place of sucrose improved the preservation of the ultrastructure but still could not resolve the difficulty. This report describes a new procedure for transferring dry ultrathin frozen sections by means of electrostatic attraction induced on the membrane covering the grids. Once attached electrostatically to the membrane, the sections were retained by van der Waals' forces. The dry ultrathin frozen sections obtained from both fresh and fixed brains displayed good preservation of their ultrastructures over a large surface. This new method which electrostatically transfers dry ultrathin frozen sections, avoiding the use of any liquid, is expected to serve for the immunocytochemical identification of neuronal cell bodies and terminals as well as their neurotransmitters and enzymes in both fresh and fixed brains.