Fluorescent quantitative PCR results on hippocampal tissue (Figure 3b–d) showed that the mRNA expression levels of postsynaptic density protein 95 (PSD-95), growth-associated protein 43 (GAP-43), and synaptophysin (SYP) were significantly decreased in the T2DM group compared to the CK (p < 0.05, p < 0.01), indicating that diabetes causes synaptic plasticity damage in the hippocampus of mice. The gene discussed is GAP43; the disease is diabetes mellitus.