Relationship between the Degeneration and Regeneration of Neuromuscular Junction and Wound Age during the Repair of Mouse Skeletal Muscle Contusion / 法医学杂志

Objective To investigate the morphological changes in the degeneration and regeneration of neuromuscular junctions （NMJ） during the repair of mouse skeletal muscle contusion and discuss the correlation between the degeneration and regeneration of NMJ and wound age. Methods A total of 50 healthy adult male mice were randomly divided into 10 groups, including 9 experimental groups and 1 control group. Immunofluorescent staining was applied, and neurofilament was marked with neurofilament protein-H （NF-H）, presynaptic membrane was marked with synaptophysin （Syn）, presynaptic membrane was marked with acetylcholine receptor （AChR）. Morphological changes of NMJ regeneration at different time points after mouse skeletal muscle contusion were detected. Results The neurofilament and presynaptic membrane of NMJ at the junction of contusion zones began to degrade after contusion, and completed degradation at about 3 d post-injury. Then they gradually regenerated, roughly completing the regeneration at about 21 d and basically reaching the control group level. The ratio of presynaptic membrane quantity to presynaptic membrane quantity showed a trend of decreasing then rising and finally reaching the control level. Conclusion During the repair of mouse skeletal muscle contusion, the morphological changes and wound age of the NMJ at the junction of contusion zones have a close correlation, which is expected to be one of the biological indicators for forensic skeletal muscle wound age estimation.

Relationship between Changes of Pericyte Number and Wound Age during Repair of Skeletal Muscle Contusion in Mice / 法医学杂志

Objective To observe the change pattern of pericyte number at different time periods after mice skeletal muscle contusion and discuss its role in wound age estimation. Methods A mice gastrocnemius muscle contusion model was established. The form and number changes of pericytes at 1, 3, 5, 7, 9, 14, and 28 d post-injury were detected by multiple immunofluorescence staining. Results Compared with the slender shape of pericytes in normal skeletal muscles, pericytes in the contusion area had increased volume, rounder form and a round nuclei. Part of pericytes were found to express satellite cell markers paired-box transcription factor （Pax7） or myoblast determination 1 （MyoD1）. The changes of pericyte number in skeletal muscles after contusion were time-dependant, and showed unimodal distribution with the extension of wound age. In the central contusion area, the number of pericytes peaked at 5 d post-injury while in the peripheral contusion area, the number of pericytes peaked at 5 d and 7 d post-injury. Conclusion The number of pericytes in contusion area varies time-dependently after skeletal muscle contusion in mice and might be a reference index for muscle wound age estimation, and is involved in the repair and regeneration of skeletal muscle injury.

Relationship between Expression Changes of CB2R and Wound Age of Brain Contusion in Mice / 法医学杂志

Objective To investigate the expression of cannabinoid type 2 receptor （CB2R） at different time points after brain contusion and its relationship with wound age of mice. Methods A mouse brain contusion model was established with PCI3000 Precision Cortical Impactor. Expression changes of CB2R around the injured area were detected with immunohistochemical staining, immunofluorescent staining and Western blotting at different time points. Results Immunohistochemical staining results showed that only a few cells in the cerebral cortex of the sham operated group had CB2R positive expression. The ratio of CB2R positive cells gradually increased after injury and reached the peak twice at 12 h and 7 d post-injury, followed by a decrease to the normal level 28 d post-injury. The results of Western blotting were consistent with the immunohistochemical staining results. Immunofluorescent staining demonstrated that the changes of the ratio of CB2R positive cells in neurons, CB2R positive cells in monocytes and CB2R positive cells in astrocytes to the total cell number showed a single peak pattern, which peaked at 12 h, 1 d and 7 d post-injury, respectively. Conclusion The expression of CB2R after brain contusion in neurons, monocytes and astrocytes in mice suggests that it is likely to be involved in the regulation of the biological functions of those cells. The changes in CB2R are time-dependent, which suggests its potential applicability as a biological indicator for wound age estimation of brain contusion in forensic practice.

Time-dependent Protein Expressions of MMP-2 and MMP-9 in Liver Contusion Rats after Impact / 法医学杂志

Objective To observe the protein expression patterns of matrix metalloproteinase (MMP)-2 and MMP-9 in the liver tissue of liver contusion rats at different time after impact. Methods Fifty healthy adult male SD rats were randomly and evenly divided into control group and experimental groups (1 h, 3 h, 6 h, 12 h, 18 h, 24 h, 3 d, 5 d, 7 d after liver contusion). A rat liver contusion model was established by a free-falling device. The rats were killed at corresponding time, and the contused hepatic lobes were extracted. The protein expressions of MMP-2 and MMP-9 in contused liver tissue of the rats in each group were observed by immunohistochemical staining (SP method) and Western blotting. Results After the liver contusion, the expression of positive cell and the protein semiquantitative result showed that the protein expression of MMP-2 enhanced at 6 h and peaked at 24 h, then decreased gradually at 3-5 d, and returned to normal levels at 7 d. The difference of expression between group and its previous adjacent group after 6 h (except 18 h) had statistical significance (P<0.05). The protein expression of MMP-9 rose obviously at 1 h after liver contusion and peaked at 18 h, then decreased gradually at 3-7 d which still higher than control group. The expression difference between group and its previous adjacent group (except 12 h and 24 h) had statistical significance (P<0.05). Conclusion The protein expressions of MMP-2 and MMP-9 in contused liver tissue after impact show good time-dependent patterns, which may provide important reference indicators for the time estimation of liver contusion.