Abstract: Objective To investigate the degradation changes of β-actin mRNA and 18S rRNA in different time points and temperature after death, and to explore the relationship between the changes and postmortem interval（PMI） in the brain of mice. Methods Twenty-four health adult C57BL/6 mice were randomly divided into two groups（12 each group）. They were sacrificed by cervical dislocation and placed in chamber with two different temperature（4 ℃ and 37 ℃, humidity was 80%）. The mice brains were sampled at 6 different time points（immediately, 0.5 h, 2 h, 6 h, 24 h, 48 h）, and total brain RNA were extracted. Ct value of each sample was obtained using RT-PCR and real-time PCR technology, and β-actin mRNA and 18S rRNA content ratio was calculated. The correlation between the content ratio and PMI was expressed using statistical regression analysis. Results At 37 ℃, RNA degradation rate was faster than 4 ℃, which showed that there was correlation between temperature and RNA degradation. Comparing with the stability of β-actin mRNA, 18S rRNA was more stable. Conclusion The study on degradation of β-actin mRNA and 18S rRNA in mice brain using real time PCR technology could provide a new theoretical basis for estimation of PMI and would be supplementary to the traditional methods.

Key words: forensic pathology, polymerase chain reaction, RNA, ribosomal, 18S, β-actin, brain, postmortem interval, mice