Insoluble Aβ overexpression in an App knock-in mouse model alters microstructure and gamma oscillations in the prefrontal cortex, causing anxiety-related behaviours

We studied two new App knock-in mice models of Alzheimer’s disease ( AppNL-F and AppNL-G-F ), which generate elevated levels of Aβ40 and Aβ42 without the confounds associated with APP overexpression. This enabled us to assess changes in anxiety-related and social behaviours, and neural alterations potentially underlying such changes, driven specifically by Aβ accumulation. AppNL-G-F knock-in mice exhibited subtle deficits in tasks assessing social olfaction, but not in social motivation tasks. In anxiety-assessing tasks, AppNL-G-F knock-in mice exhibited: 1) increased thigmotaxis in the Open Field (OF), yet; 2) reduced closed-arm, and increased open-arm, time in the Elevated Plus Maze (EPM). Their ostensibly-anxiogenic OF profile, yet ostensibly-anxiolytic EPM profile, could hint at altered cortical mechanisms affecting decision-making (e.g. ‘disinhibition’), rather than simple core deficits in emotional motivation. Consistent with this possibility, alterations in microstructure, glutamatergic-dependent gamma oscillations, and glutamatergic gene expression were all observed in the prefrontal cortex, but not the amygdala, of AppNL-G-F knock-in mice. Thus, insoluble Aβ overexpression drives prefrontal cortical alterations, potentially underlying changes in social and anxiety-related behavioural tasks.