Impaired functional connectivity of the hippocampus in murine models of NMDA-receptor antibody associated pathology

Introduction: While decreased hippocampal connectivity and disruption of functional networks are established MRI features in human anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis, the underlying pathophysiology for brain network alterations remains poorly understood. Application of patient-derived monoclonal antibodies against the NR1 subunit of the NMDAR allows for the investigation of potential functional connectivity alterations in experimental murine NMDAR antibody disease models. Objective: To explore functional connectivity changes in NR1 antibody mouse models using resting-state functional MRI (rs-fMRI). Methods: Adult C57BL/6J mice (n=10) were intrathecally injected with a recombinant human NR1 antibody over 14 days and then studied using rs-fMRI at 7 Tesla. In addition, a newly established mouse model with in utero exposure to a human recombinant NR1 antibody characterized by a neurodevelopmental disorder (NR1-offspring) was investigated with rs-fMRI at the age of 8 weeks (n=15) and 10 months (n=14). Mice exposed to isotype-matched control antibodies served as controls. Independent component analysis (ICA) and dual regression analysis were performed to compare functional connectivity between NMDAR antibody mouse models and control mice. Results: Adult NR1-antibody injected mice showed significantly impaired functional connectivity within the dentate gyrus of the left hippocampus in comparison to controls, resembling impaired hippocampal functional connectivity patterns observed in human patients with NMDAR encephalitis. Similarly, analyses showed significantly reduced functional connectivity in the dentate gyrus in NR1-offspring compared after 8 weeks, and impaired connectivity in the dentate gyrus and CA3 hippocampal subregion in NR1-offspring at the age of 10 months. Conclusion: Functional connectivity changes within the hippocampus resulting from both direct application and in utero exposure to NMDAR antibodies can be modeled in experimental murine systems. With this translational approach, we successfully reproduced functional MRI alterations previously observed in human NMDAR encephalitis patients. Future experimental studies will identify the detailed mechanisms that cause functional network alterations and may eventually allow for non-invasive monitoring of disease activity and therapeutic effects in autoimmune encephalitis. ### Competing Interest Statement Acknowledgments: We thank Claudia Sommer for her excellent technical support. JKu and JKr are participants in the BIH-Charite (Junior) Clinician Scientist Program funded by the Charite Universitaetsmedizin Berlin and the Berlin Institute of Health. Funding: Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation; grant numbers FI 2309/1-1 and FI 2309/2-1 to C.F., PR 1274/2-1, PR 1274/3-1, and PR 1274/5-1 to H.P., GE2519/8-1, GE2519/9-1, and GE2519/11-1 to C.G., FOR3004 to H.P. and CG), by the Helmholtz Association (HIL-A03 to H.P.) and the German Ministry of Education and Research (BMBF; grant number s 01EW1901, 01GM1908B to C.G. and 01GM1908D to H.P., CONNECT-GENERATE). Conflicts of interest: JKu received conference registration fees from Biogen, speaker honoraria from Sanofi Genzyme and Bayer Schering and financial research support from Krankheitsbezogenes Kompetenznetzwerk Multiple Sklerose (KKNMS).