Abstract: Objective To study the change of DNA degradation in nucleolus of mice organs and its relationship with the postmortem interval,and to investigate a new accurate method to estimate the postmortem interval.Methods Eight parameters of cell nuclei were chosen,including the head DNA level,the tail DNA level,the head radius,the tail length,the tail moment,the Olive moment,the head area and the tail area.The changes of DNA degradation were analyzed in skeletal muscle,myocardium,liver,kidney and brain in mice at different intervals(0-72 h postmortem) by using single-cell gel electrophoresis and fluorescent microscope connected with auto-analysis-image system.Results The tail DNA level,the tail length,the tail moment,the Olive moment and the tail area showed an increasing tendency.The head DNA level,the head radius and the head area showed a decreasing tendency within 72 h postmortem in mice.A quadratic regression equation(P<0.001) and multiple regression equation of DNA degradation tendency were established(P<0.000 1).Conclusion The regression equations established can be used as a new method for estimating postmortem interval in forensic practice.

Key words: forensic pathology, cell nucleus, DNA degradation, postmortem interval estimation, mice