Age and sex dependent hippocampal neuronal hyperactivity in Alzheimer model mice

Both seizures and epileptiform discharges have been reported in various amyloid plaque- forming mouse models of Alzheimer's disease (AD). These mice also show premature mortality possibly related to epileptic seizures. Yet, the relationship between epileptic manifestations and amyloid pathology remains elusive. We utilized deltaFosB as a marker for sustained neuronal hyperactivity to localize the epileptic focus and compared it with age and sex differences in premature mortality between APP/PS1, 5xFAD and wildtype littermate mice and epileptiform discharges (EDs) during sleep in cortex and hippocampus. APP/PS1 mice showed elevated FosB/deltaFosB (shortly FosB) staining in the dentate granule (DG) cells and CA1-CA3 pyramidal cells. These were also the origins of identified epileptiform discharges (EDs) in LFP recordings. APP/PS1 mice showed much higher premature mortality than 5xFAD mice, females more than males. FosB staining intensity in APP/PS1 mice was robustly elevated compared to wildtype mice and peaked at 3 months of age. In contrast, FosB intensity in 5xFAD was lower than in wildtype mice at 1 and 3 months of age, showing a modest elevation at 10 months. In APP/PS1 mice between 1.5 and 3 months of age, the DG amyloid load correlated positively with FosB intensity. Furthermore, the DG FosB intensity showed a positive correlation with the frequency of EDs during sleep. These findings suggest that FosB staining intensity can be used as a proxy for local epileptiform activity in AD model mice and help unveil cellular and molecular basis of AD related neuronal hyperactivity and epilepsy.