APP and Alzheimer disease: Notably, in the APP/PS1 mouse model of AD, progenitor neuron proliferation in the DG (as measured by BrdU) begins to be impaired at an age of around 3 months, when oxidative stress and plaque formation start to incline, whilst the total quantities of DCX-positive immature neurons decreased from an age of 10 months (Hamilton and Holscher, 2012).