Reliable detection of RNA in hippocampus sections of mice by FISH up to a post-mortem delay of 24 h.

Proteins can be successfully localized in post-mortem (PM) brain tissue sections if the time until PM tissue sampling is not too long. In this study, we show that this also applies to the localization of RNA and in particular to the RNA of microglia-specific receptor proteins using the probes and the RNAscope Multiplex Fluorescent Detection Kit v2 from Advanced Cell Diagnostics. Brains were removed from killed mice after different PM delays and processed into paraffin sections. In sections of brains from animals whose cadavers had been kept at room temperature (21 °C) before tissue removal, ubiquitously expressed RNAs of genes with low to high expression levels (Polr2a, PPIB, and UBC) were reliably detected in the brain sections even if tissue removal was delayed by up to 48 h. In addition, microglia-specific G protein-coupled receptor RNA (Gpr34, P2ry12) could be reliably assigned to microglia by simultaneous labeling of the microglia with microglia-specific antibodies (Iba1 or P2ry12). Only after a delay of 48 h until tissue removal were the receptor RNA signals significantly lower. The reduction in receptor RNA signals could be delayed if the animal cadavers were stored at 4 °C until the brains were removed. Tissue sections of PM brain samples allow the spatial and cellular localization of specific RNA, at least if the sampling takes place within the first 24 h of PM.