Objective:To investigate the expression regulation of Substance P(SP) during incised rat skin healing processs and its significance in forensic medicine.Methods:Using immunohistochemistry technique and image analysis system to study the dynamic expression and the postmortem stability of SP at different time during incised rat skin healing processs.Counting each slide for SP-positive cell rate from 5 different zones randomly choosed under 400×microscope

then calculating a mean value.Performing LSD-t test.Results:Positive stain of SP was detected in the neutrophil cells 1h after injury and the SP-positive rate reached maximum on the 4th day

then it began to decrease.The expression of SP in the damage zone and the surrounding skin tissues was significantly higher than the normal control group for 8 days after injury(P <0.05);Weak SP-expressions

which have no obviously changes

in the epidermic cells

sweat gland cells and endothelial cells were detected in the postmortem injury groups and normal control groups.No significant differences of SP-expressions were found among each subgroups of postmortem stability group under the environment of-20℃

4℃ and 30℃ degree

compare to the time immediately after death(P>0.05).Conclusion:The SP-expression during incised rat skin healing processs is time-dependent

and the SP is quite stable after death.So SP may be used as a useful reference marker to estimate the time since injury.