Effects and Mechanisms of NMDAR-EphB2 on Synapses in Mice by Active Immunization with a GluN1 Peptide

This study investigated the expression of N-methyl-D-aspartate receptor(NMDAR)-EphB2 and associated changes in hippocampal neuronal dendritic spines and synaptic ultrastructure in an anti-NMDAR encephalitis mouse model. Utilizing the GluN1_359-378 antigen, which targets the amino terminal domain of the NMDAR GluN1 subunit, we initially established an anti-NMDAR encephalitis mouse model. Subsequently, pentylenetetrazol (PTZ) was intraperitoneally injected and their seizure susceptibility was observed. Furthermore, Western blot was employed to detect the expression of GluN1, postsynaptic density protein 95 (PSD-95), EphrinB2 and EphB2 in hippocampal tissues. Immunofluorescence was used to detect the expression and co-localization of GluN1 and EphB2 in the hippocampus. Transmission electron microscopy (TEM) was used to observe the synaptic ultrastructure of hippocampal neurons, and Golgi-Cox staining was performed to examine the morphology of dendritic spines. GluN1_359-378 mice exhibited increased seizure susceptibility. Furthermore, GluN1_359-378 mice demonstrated significantly reduced expression of GluN1 membrane protein, as well as EphrinB2 and EphB2 proteins in hippocampal tissues. Additionally, the co-localization coefficient of GluN1 and EphB2 was decreased. Synaptic cleft width, postsynaptic density thickness, active zone length, and dendritic spine density were reduced. In conclusion, the anti-NMDAR encephalitis mouse model, established via active immunization with a GluN1 peptide antigen, exhibits increased seizure susceptibility. This heightened susceptibility may result from the disruption of the NMDAR-EphB2 interaction by NMDAR antibodies, which subsequently reduces NMDAR expression on the cell membrane and leads to alterations in synaptic structure.