Impaired learning and memory ability induced by a bilaterally hippocampal injection of streptozotocin in mice: involved with the adaptive changes of synaptic plasticity

Background Alzheimer’s disease (AD) is a neurodegenerative disease characterized by progressive cognitive decline, psychiatric symptoms and behavioral disorders, resulting in disability and loss of self-sufficiency. Objective To establish an AD mice model, investigate the behavioral performance, and explore the potential mechanism. Methods Streptozotocin (STZ, 3 mg/kg) was microinjected bilaterally into the dorsal hippocampus of C57BL /6 mice to establish the AD model. Behavioral changes (anhedonia and despair, balance and motor coordination, locomotion, and learning and memory) were examined and the serum concentrations of insulin and nesfatin-1 were measured by ELISA. The activation of hippocampal microglia was assessed by immunohistochemistry and the protein expression of several molecular associated with the regulation of synaptic plasticity in the hippocampus and the prefrontal cortex (PFC) was detected via western blotting. Results The STZ model mice showed a slower bodyweight gain and higher serum concentration of insulin and nesfatin-1. Although there was no significant difference between groups with regard to the ability of balance and motor coordination, the model mice presented a decline of spontaneous movement and exploratory behavior, together with an impairment of learning and memory ability. Increased activated microglia was aggregated in the hippocampal dentate gyrus of model mice. Moreover, the protein expression of NMDAR2A, NMDAR2B, SynGAP, PSD95, BDNF, and p-β-catenin/β-catenin were remarkably decreased in the hippocampus and the PFC of model mice, and the expression of p-GSK-3β (ser9)/GSK-3β were reduced in the hippocampus. Conclusion A bilateral hippocampal microinjection of STZ could successfully duplicate an AD mice model, as indicated by the impaired learning and memory and the alternated synaptic plasticity, together with the hyperactive inflammatory response in the hippocampus and the imbalanced abundance of serum insulin and nesfatin-1. Apart from these, the mechanism might be associated with the imbalanced expression of the key proteins of Wnt signaling pathway in the hippocampus and the PFC. Graphical abstract