APP and Alzheimer disease: Interestingly, also other intranasal substances had effects in AD models, as they counteracted Aβ toxicity (Maurice et al., 2013; Kaur and Prakash, 2019), decreased Aβ and inflammation (Lin et al., 2016; Drews et al., 2019), affected APP processing (Guo et al., 2017), prevented memory deficits (Fine et al., 2012; Lou et al., 2016; Rodríguez Cruz et al., 2017), reduced aggregation of Aβ and tau in AD mice (Matsuoka et al., 2007) or decreased tau phosphorylation in alpha-synuclein mice (Magen et al., 2014).