APP and Alzheimer disease: To elucidate the depths of pial penetration within cerebral cortices as well as any structural changes of pia mater that may occur with aging, ERTR7-labeled coronal brain sections were next compared between young (2-month-old) wildtype (WT) mice, old (13-month-old) WT mice, and old APP/PS1 mice (13-month-old AD model).