Abstract: The invention relates to methods and pharmaceutical compositions effective for treating, inhibiting, preventing, slowing, or delaying the onset of a neurodegenerative disease in mammals (e.g., humans) via the co-administration of an effective amount of a compound selected from the group consisting of Formula (I), Formula (II), Formula (III) or Formula (IV) or pharmaceutically acceptable salts thereof and a phosphodiesterase inhibitor (e.g., a PDE 5 inhibitor). In certain embodiments, the mammal is a healthy human, or a human experiencing cognitive dysfunction with or without hypertension.