ADCYAP1 and Alzheimer disease: Reduced PACAP levels were observed in the brain of different transgenic AD mouse models (Wu et al., 2006; Han et al., 2014b, 2017) and in cortical brain samples from AD patients, where PACAP levels were inversely related to the amount of amyloid plaques and neurofibrillary tangle, as well as to dementia rating scores (Han et al., 2014a).