Relationship between hippocampal structure and high incidence of depression after spinal cord injury in mice

AIM: To explore whether the high risk of depression caused by spinal cord injury is related to structural changes of hippocampus. METHODS: Mouse spinal cord injury model was established. The Basso Mouse Scale (BMS) was used to evaluate the postoperative motor function of mice at different periods after injury. The depression of mice was evaluated by behavior experiment. The morphological changes of cells in hippocampal tissue were observed by HE staining. The structural changes of hippocampal subcellular synapses were observed by electron microscopy. RT-qPCR was used to detect the changes of synaptic protein markers synaptophysin (SYP) and postsynaptic density protein 95 (PSD-95) at the mRNA level. RESULTS: The mice had significant depressive behaviors in model group, and the depression degree was the most serious on the 7th day (P<0.01). Compared with control group, the arrangement of hippocampal cells was disordered, the cell number was decreased, and the shape was irregular in model group. Compared with control group, the observation results of electron microscopy showed that the number of synapses in the hippocampal ultrastructure was decreased, the length of synaptic activity zone was shortened, the thickness of postsynaptic density was thinned, the width of synaptic gap was increased, and the curvature of synaptic interface was decreased in the model group (P<0.05). The mRNA expression levels of SYP and PSD-95 in model group were lower than those in control group (P<0.05). CONCLUSION: The change of hippocampal structure is one of the important reasons leading to high risk of depression caused by spinal cord injury.