The correlation between postmortem interval and fourier transform infrared spectra in rat's brain

In the present study, FTIR spectroscopy was applied to observe the process of postmortem degradation in rat's brain and a lot of useful data for the estimation of postmortem interval (PMI) were provided. Sprague-Dawley male rats (weight 240±10 g) were chosen and sacrificed by cervical dislocation. The bodies were kept in a controlled environmental chamber set at (20±2)°C, and their brain cortex as the measuring sample which was extracted at 0, 12, 24, 48, 72, 96, 120, 144 and 168 h from the 8 rats. The tissues were freeze dried in a vacuum at -50 °C overnight in order to dehydrate them. About 2 mg freeze dried tissues were mixed with 200 mg KBr and then ground in an agate mortar for 5 min. The mixture then was pressed into a pellet with a thickness of 0.4 mm and a diameter of 12 mm. The FTIR spectra were quantitatively recorded at room temperature in the range 4000-400 cm^-1 on a Shimadzu 8400S spectrometer (Shimadzu, Japan). IR solution 1.10 software (Shimadzu, Japan) was used for the analysis of the FTIR spectra and for recording the data from the spectra. With the PMI increasing, the peak position of main absorbance bands in the FTIR spectra showed no significant difference, but there was a dramatic variance in the intensity: (1) The relative intensity at 1080 and 1238 cm^-1 (I₁₀₈₀/I₁₃₉₈ and I₁₂₃₈/I₁₃₉₈) related with nucleic acid tended to decrease obviously. (2) The intensity ratio at amide II and I (I₁₅₄₁/I₁₆₄₇) increased with the PMI increasing. The intensity at 1338 and 1313 cm^-1 varied slightly, but their intensity ratio to 1398 cm^-1 decreased. (3) The intensity at 1456 and 1398 cm^-1 showed a trend of decreasing and increasing respectively. (4) Compared with the intensity at 2871 cm^-1, the intensity at 2852, 2871, 2923 and 2958 cm^-1 tended to increase, but the increasing tendency at 2871 cm^-1 was slight. It is concluded that FTIR spectroscopy is going to be an effective method for estimating the PMI in medicolegal practice and the brain tissue may be a suitable marker as a potential sample.