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

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.