الفهرس 
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Abstract
The time of death is still the most complex and important element to be calculated and assessed in the investigations of death, even after multiple studies and researches have been identified.
Following death, a sequence of complicated biochemical and histopathological processes result in evident changes in the structure of the human organs and tissues. The majority of these changes chronologically take place, enabling the calculation of the post-mortem time.
A variety of postmortem interval researches have been performed in recent decades concerning histological, histochemical, biochemical, and ultrastructural changes in tissues and organs. These studies can provide valuable information about the postmortem interval.
The present study was aimed to estimate postmortem interval through immunohistochemical markers and histological examination of different organs of rats (liver, kidney, heart, and skeletal muscle) at different time intervals. Also, it was performed to assess the role of these methods in the evaluation of postmortem interval.
This study was done at the Forensic medicine and toxicology department, Faculty of Medicine, Minia University, from the first of January 2020 up to December 2020. The study included fifty adult male albino rats weighing about 150-200 gm (not exceeds 8 weeks old). After one week of accommodation, they were divided into 5 groups (10 rats in each group). They were sacrificed by cervical dislocation; the sacrificed rats were kept at room temperature (22 ± 2 ºC daytime/ 9 ± 2 ºC nighttime).
Organs (liver, kidney, heart, and skeletal muscle) were obtained by dissection at 0, 24, 48, 72, 96h after death. Then the organs were processed for histological and immunohistochemical examination. This experimental study was performed in agreement with the guidelines for laboratory animal care and use and the Ethical Committee of Faculty of medicine of Minia University.
The results of this study regarding postmortem histological changes by using H&E stained sections of rats’ organs (liver, kidney, heart, and skeletal muscle) revealed gradual deterioration in the tissue structure of these organs with increasing the time of death.
The liver tissues showed normal structure at the time of death, then swollen hepatocytes with pyknotic nuclei at 24 h, then partial hepatocytes degradation started at 48 h and continued hepatocytes breakdown at 72 h up to the loss of architecture at 96 h.
While the kidney tissues showed normal histology at the time of death, then pyknosis of nuclei and cytoplasmic vacuolization in the renal tubular epithelium at 24 h, then degradation of the cell membrane, cytoplasm, and nuclei were seen in the glomerular epithelium and the renal tubules at 48 h and progression of these changes with some empty renal tubules and cytoplasmic debris and pre-tubular casts up to the loss of architecture at 96 h.
The heart showed normal histological morphology at the time of death, then wavy and displaced myocardial fibers with pyknotic nuclei at 24 h, then partial loss of myocardial fibers, nuclei irregularities, and widely spaces myocardial fibers seen at 48 h then at 72 hrs, multiple focal areas of myocardial fibers degenerations with an irregular shaped nucleus these changes continued to show extensive autolysis of myocardial fibers with lost cellular architecture at 96 hrs.
While the skeletal muscle showed normal histological morphology at 0 h after death, then swollen skeletal muscle myofibers with an eccentric nucleus and partial loss of striations at 24 h interval, the loss of cross striations with nuclear changes continued at 48 hrs with also segmented muscle fibers at 72 hrs, then ended with extensive areas of tissue loss with replacement by thin collagenous connective tissue at 96 hrs.
Caspase-3 immunohistochemical study revealed a significant difference in its expression between different groups and showed a significantly strong negative correlation with PMI in all organs of this study. Immunoreactivity of caspase-3 showed a gradual decrease with increasing PMI and ranged from high expression at 0 h interval to weak expression at 96 h interval.
The p53 immunohistochemical analysis showed a significant difference in expression between different groups and revealed a significantly strong negative correlation with PMI in all studied organs. Immunoreactivity of p53 displayed a gradual decrease with increasing PMI and varying from strong expression at 0 h interval to weak expression at 96 h interval.
Simple and multiple linear regression analyses for predicting PMI for both p53 and caspase-3 in the studied organs were conducted, and also equations for PMI determination were done. Simple linear regression analysis was significant for both p53 and caspase-3 in all organs. The results of using multiple linear regression analysis were better than the simple one, with high adjusted R2 and less SEE in all studied organs, which revealed good reliability of the equations.
These equations were extracted for PMI determination by; simple linear regression analysis {PMI = constant + (B * independent variable)}, where the independent variable is p53 or caspase-3 and by multiple linear regression analysis {PMI = constant + (B1 * independent variable1) + (B2 * independent variable2)}, where the independent variable is p53 and caspase-3.
It is concluded from this study results that the postmortem histological changes and also the expression of immunohistochemical markers (caspase-3 and p53) in all studied organs occur in a time-dependent manner. So, they can be used as good predictors to estimate the PMI.
Further studies are recommended about the immunohistochemical markers (caspase-3 and p53) and histological changes in other organs after death and also their role in estimating the postmortem interval in humans.