Preservation of ultrastructure and immunoreactivity in cryosections of brain tissue stored in a sucrose‐gelatin solution at freezing temperatures

Summary We evaluated the preservation of ultra‐structure and immunoreactivity in cryosections of central nervous system tissue mounted with and stored in a sucrose–gelatin solution for one month at −20°C or −80°C. The ultra‐structure of synaptic structure in these sections was well preserved and comparable to that of freshly cut cryosections. Quantitative analysis of mitochondrial ultra‐structure demonstrated gradually lower degrees of preservation in sections stored at −20°C and −80°C compared with that in freshly cut sections. We observed distinct metabotropic glutamate receptor 1 (mGluR1)‐immunogold labelling at peri‐synaptic sites in freshly cut sections and also in those stored at −20°C and −80°C. Quantitative analysis of mGluR1 immunoreactivity revealed that the total number of immunogold particles per synapse and the number of non‐specifically bound particles were similar under all three conditions. However, the percentage of gold particles bound to a specific synaptic region was greatest in freshly cut sections (79.0%) and progressively lower in sections stored at −20°C (76.1%), in which sections were not frozen, and in sections stored at −80°C (68.0%). These data indicate that ultra‐thin cryosections may be conveniently stored in a sucrose–gelatin solution at −20°C for cryoultramicrotomy‐immunolabelling.