Thin Sections cut at Temperatures of −70° to −90° C

Abstract

IN developing a satisfactory system for high-resolution autoradiography of soluble or unbound compounds¹, we have investigated the possibility of frozen sectioning at low temperatures. At temperatures above −30° C adequate sections can be obtained for certain purposes, but in the temperature range commonly achieved in the standard laboratory cryostat, disruptive crystal formation limits the histological quality, and the thickness of the tissue section limits microscopic and autoradiographic resolution. At −20° C 4µ sections are difficult to prepare and the limit is about 2µ Optimal conditions for avoiding disruptive ice crystal formation obtain in the range of vitreous ice at temperatures below −130° (refs. 2–4). Above −130° C both cubic and vitreous ice may be converted into the stable hexagonal phase during which the individual crystals can grow to 10µ and cause membrane disruption⁵. The transformation occurs rapidly above −70° C and is pronounced at −60° C. In order to utilize the technique of frozen sectioning for dry high-resolution autoradiography, a method is required which will reduce the risk of ice crystal formation and which will provide thin tissue sections in the range of 0.5µ. to 1.0µ or lower.